Construction Technology Flashcards
(125 cards)
1
Q
What are the differences between cohesive soils and non-cohesive soils?
A
Cohesive soils (clay, silt) have smaller/smoother particles, attract positive water charge due to a small negative electrical charge, are easily moulded under load due to water present giving them plasticity, are affected by seasonal changes in water content causing them to swell in winter/shrink in the summer, are subject to frost heave and are affected by tree roots drawing up water from the soil.
Non-cohesive soils (sands/gravels) are coarse grained, irregular in shape, exhibit high frictional resistance when compressed under load, high load bearing capacity, do not bond together if not consolidated, which leads to low loadbearing capacity in saturated state caused by high groundwater levels separating particles. Excavation sites need a lot support.
2
Q
What is the difference between displacement piles and replacement piles?
A
- Displacement piles (driven) are driven or jacked into the ground, displacing the soil around the pile shaft outwards and downwards. Used in offshore applications.
- Replacement piles (bored auger) remove the soil to form a hole and concrete is poured in situ. Popular in urban areas as there is minimal vibration.
3
Q
In a congested urban building site, what type of pile would you recommend using and why?
A
Replacement or bored auger piles, as there is minimal vibration. These piles are also quick to construct, no prefabricated elements are required except steel reinforcement and they can be used where there is limited headroom.
4
Q
How are piles/pile caps linked together?
A
A reinforced concrete beam supports the loadbearing wall over the piles and links them all together.
5
Q
What effect would removing a large tree have on foundations?
A
Large trees can affect soils and foundations to a depth of 4m. When trees are removed, moisture in cohesive soils builds up and the soil expands, causing heave. Large broad -leaved trees of high water demand are notorious for causing damage. Ground displacement is likely to only be 150mm or less, but foundations can move and basement walls and floors crack and lift, potentially causing serious structural damage.
6
Q
How would a crack taper following the removal of a large tree? (What effect would removing a large tree have on foundations? How would the subsequent crack taper?)
A
Generally cracking to brickwork and windows. The cracking is more likely to be vertical (subsidence more likely to be diagonal). The crack would be wider at a lower level, tapering as it rises. Cracks generally occur at right angles to the diagonal and upward movement.
7
Q
How deep should a foundation be to avoid frost heave?
A
In frost susceptible soils like chalk the depth to the underside of the foundation should be at least 450mm, but in clay soils subject to volume change, strip foundations should be taken to a depth of 750mm on low clay shrinkage soils, 900mm on medium clay shrinkage soils and 1m on high shrinkage soils according to Approved Doc A.
8
Q
Name 2 types of underpinning.
A
- Mass concrete underpinning – one of the most common methods. It is conducted in successive sections, leaving the greater proportion of the existing foundations supported throughout. Each section is generally between 900mm and 1.5 m.
- Beam and pier underpinning – comprises a reinforced concrete beam, inserted either directly above or below the existing foundation, supported by mass concrete piers constructed at 2.5-3m centres.
- Pile and needle underpinning – comprises reinforced concrete needles inserted horizontally through the existing wall above foundation level and supported at each end by small-diameter piles that transmit the building’s loads to a deeper, firmer stratum. The needles are inserted at approximately 1.5m centres along the length of the wall being underpinned. The piles are taken down to a suitable loadbearing strata.
- Cantilever ring beam underpinning – comprises horizontal steel I-section cantilever needles inserted into the wall and supported on a reinforced concrete ring beam and mini piles. The needles transmit the loads from the wall to the beam and thence piles to a deeper bearing stratum.
- Double angle mini-pile underpinning involves the installation of small-diameter piles in pairs formed at an angle through the existing foundation at between 1-1.5m intervals.
9
Q
Under what conditions would you expect a raft foundation to be used?
A
Raft foundations are used for lightly loaded buildings on poor soils where the top 450-600mm of soil is overlaying a poor quality strata. It is normally the same size or larger than the plan area of the building and it effectively floats on the ground by spreading the load over a larger area.
There are 3 types –
- Nominally reinforced rafts (lightly loaded low-rise instances) – poor soils, light loads
- Designed reinforced concrete slab rafts (heavily loaded or point loaded situations)
- Reinforced concrete beam and slab rafts
10
Q
What is the purpose of a foundation?
A
- To safely sustain and transmit to the ground combined dead, imposed and wind loads to prevent movement which would impair the stability of the building. The safe transmission of the load to the ground should take place without differential settlement or any settlement that could adversely affect the neighbouring or surrounding buildings and structures.
- Foundations are designed to sustain and transfer dead and live loads
- Resist the movement of soils so that swelling, shrinkage of cohesive soils or expansion due to freezing of water in clays does not affect the stability of the building.
- Remain durable, resisting attacks from salts and chemicals in the ground.
- Can be designed to resist the passage of heat transfer.
11
Q
What is the difference between live, dead and imposed loads?
A
- Dead loads refer to the structure’s self-weight and generally remains constant throughout the structure’s life.
- Live loads are also known as imposed loads, and consist of all loads temporarily placed on the structure, like loads of people, furniture, machines, traffic, etc. This keeps changing and depends on the use of the building.
12
Q
Define subsidence.
A
Subsidence occurs when the soil beneath a building is unstable and sinks downward, usually associated with volumetric changes of subsoil. It is caused by a change in ground conditions caused by prolonged dry spells, especially when coupled with shrinkable clay soils. Leaking drains (washing away soil around foundations), broken culverts, effects of trees and shrubs can all absorb significant volumes of water from the soil, collapsed mine workings or decomposing organic fill. Differential subsidence is problematic.
13
Q
What factors would you consider in determining the foundation type?
A
- Loads from the building
- Types of soils
- Soil bearing capacity
- Ease of construction
- Water table level
- Adjoining structures, water bodies, slopes
- History of natural disasters or extreme weather
- Economics if a number of options available
14
Q
Why would you use a piled foundation?
A
- They are typically used to transfer the load from superstructures through weak, compressible strata or water onto stronger, more compact, less compressible and stiffer soil or rock at depth, increasing the effective size of a foundation and resisting horizontal loads.
- They are typically used for large structures and in situations where soil is not suitable to prevent excessive settlement.
15
Q
What is the disadvantage of a raft foundation?
A
- advantages:
o constructed for shallow depth and requires less excavation
o suitable in soils of low bearing capacity
o loads coming from the superstructure are distributed over a larger area
o differential settlement of soil can be reduced - disadvantages
o In some cases a large amount of reinforcement is required, which increases the cost of the project
o Special attention is required in the case of concentrated loads
o If they are not treated properly, there is a chance of edge erosion
o Skilled workers are required to construct the raft foundations.
16
Q
What is settlement?
A
- Settlement is the downward foundation movement as a result of soil being compressed by the weight of a building within ten years of construction or poorly compacted made ground.
- Occurs shortly after construction
- Usually small movements and non-recurring
- Differential settlement can cause serious problems
17
Q
How would you investigate whether a building was subsiding?
A
- Inspect the cracking (diagonal cracks at 45° subject close to windows and doors) with tapered cracks becoming larger with height. Crack displacement both vertically and horizontally, extend below the DPC and ground level, are at least 3mm wide and both internal and external.
- Inspect the surrounding areas for the presence of trees, bushes or hedges
- Consider if there are any drainage issues to the area.
- Consider the weather conditions – drought?
- Check the soil type for the area and if there is any history of mining in the area.
- Recommend that a structural engineer inspects, and monitor the cracking.
18
Q
Name four different types of foundation solutions normally found in construction?
A
- Pad foundations
- Raft foundations
- Strip foundations
- Piles
19
Q
What is CBR?
A
- California Bearing Ratio - a test performed on construction materials laboratories to evaluate the strength of soil subgrades and base course materials.
20
Q
How are earthworks supported and why?
A
- They are supported by shuttering to stop movement and the collapse of the earth.
21
Q
Under what conditions would you expect a raft foundation to be used for a substructure?
A
- Used on soft or loose soils, such as sand where the load needs to be spread.
22
Q
What are the different types of piling and when would you expect each of them to be used?
A
- Friction piles – develop most of the pile bearing capacity by shear stresses along the sides of the pile and are suitable where harder layers are too deep to reach economically. The pile transmits the load to the surrounding soil by adhesion or friction between the surface of the pile and the soil.
- Continuous flight auger piles (CFA) – a cast in situ method of piling first used in the 1960s in the UK and is now one of the most common. Due to its low level of vibration and sound it is particularly suited to environmentally sensitive sites and soft/water-bearing strata where deep casings would otherwise be necessary. The auger screws into the ground and when reaching the design depth, concrete is pumped through the hollow stem of the auger, whilst it is slowly extracted, removing the ground material. Advantages – low sound/vibration, installed quickly and economically, high load bearing, sheer and movement capacities and can be adapted to operate in conditions with low headroom/confined spaces.
- Impact driven piles – (also known as displacement piles) are commonly used to provide support for structures, transferring their load to layers of soil or rock that have sufficient load bearing capacity and suitable settlement characteristics. Can be the most cost effective. It is a long slender column made of pre-formed material and is installed by impact hammering, vibrating or pushing it into the ground to a design depth/resistance. Can be installed to accommodate compression, tension and lateral loads. Can be steel, precast concrete, timber or composite. Advantages – pre-fabricated off site, displace and compact the soil, increasing the load bearing capacity of the pile and no soil and little spoil needs to be removed, cost effective, superior structural strength. Disadvantages – planning required as well as heavy equipment, adequate reinforcement needed for pre-cast/pre-stressed concrete piles, length may not be exact and splicing may be required, may not be suitable for ground with poor drainage or compact sites where vibrations may impact neighbouring properties, noisy to install.
23
Q
Describe the component of a piled substructure and what their function is.
A
- Pile foundations are deep foundations that are formed by long, slender columnar elements typically made of steel or reinforced concrete and sometimes timber. It is defined as piled when its depth is more than three times its breadth.
- Principally used to transfer loads from superstructures through weak, compressible strata or water onto stronger, more compact, less compressible and stiffer soil or rock at depth, increasing the effective size of a foundation and resisting horizontal loads. Typically used for large structures and in situations where soil is not suitable to prevent excessive settlement.
24
Q
Describe three different ways of waterproofing a new build basement area.
A
- Type A (Barrier) system – Tanking – objective is to provide a continuous waterproof membrane which is applied to the base of the slab and walls – it can be applied internally or externally according to site circumstances. Alternatives to mastic asphalt or polythene sheeting are bituminous compounds – epoxy resin compounds and bitumen laminates. External mastic asphalt tanking preferred as it prevents the ingress of water and protects the structure from aggressive sulphates in the soil and ground water. Internal mastic asphalt tanking should only be adopted if external tanking is not possible as it will not protect the main structure and may be forced away from the walls/floor by hydrostatic pressure. To be effective the horizontal and vertical mastic must be continuous.
- Type B (Structurally Integral) system – Dense monolithic concrete – forms a watertight basement using dense, high quality or prestressed concrete by a combination of good materials, workmanship, detailing and construction methods. Not always vapour proof and may also need a coating/tanking. Watertightness depends on the water/cement ratio and degree of compaction.
- Type C (Drained) system – drained cavity system – accepts a small amount of water seepage through a monolithic concrete wall and collects moisture and drains it away. Achieved by building an inner non-load bearing wall to form a cavity, which is joined to a floor composed of triangular tiles laid to falls, which enables the water to drain away to a sump. The inner wall should be vapour tight or the cavity should be ventilated.
25
Name 3 types of materials for rooflights.
- Glasses reinforced plastic (GRP)
- Polycarbonate
- Georgian wired glazing
26
What are the two common finishes for roof sheets?
- PVC Plastisol
| - Polyester paint coated
27
How do you distinguish between Plastisol and Polyester Coated Finish roof sheets?
- Plastisol has an embossed leather grain texture with good corrosion resistance and excellent abrasion resistance.
- Polyester coated finish is cheaper and offers a smooth finish, but does not have such a long lifespan.
28
What are the three types of portal frame?
- Pitched roof symmetric portal frame.
- Tied portal frame
- Mono pitch portal frame
- Propped portal frame
- Mansard portal frame
29
What are composite panels?
- Typically used in the external cladding of buildings.
- Can be bent, curved and joined together in an almost unlimited range of configurations
- First emerged in the 1960s.
- Two metal skins are bonded to an insulating core, forming a composite sandwich panel.
- The metal component can be aluminium, zinc, stainless steel etc.
- Available in a wide variety of colours, finishes and profiles
- It can be manufactured from an insulating material such as polyethylene, or from a fire retardant material.
- Advantages: Weather resistance, lightweight, acoustic insulation, thermal insulation, a consistency of finish that requires little maintenance, they do not wrinkle as the external skins are bonded to the core under tension.
- They can be more cost effective and can be installed faster than precast panels and have reduced structural support requirements because of their lighter weight.
30
What are the issues surrounding composite panels?
- Flammable cores that are difficult to extinguish and can result in a total loss situation.
- The fire can spread rapidly within the panels and it is shielded from extinguishing water. Sprinkler protection, gas extinguishing systems and water mist systems would be unable to control or extinguish the fire.
31
From a technology perspective, what is the difference between steel and concrete frames? (i.e. fire resistance, light weight, etc.)
- Steel – flexibility (endless design applications), lightweight (60% lighter and may allow for a less expensive foundation system), building design may be easier to modify, high lead in time, fast erection on site, inherently non-combustible, but strength reduces when heated to extreme heat so needs fire protection (thin intumescent coatings can be applied offsite), reduced labour costs through dryness of form, fluctuating prices of steel, structurally strong, stiff, tough and ductile, long life span and can be reused or adapted, it may corrode if it comes into contact with water.
- Concrete – waste materials can be included within the mix (ground granulated blast-furnace slag and pulverised fuel ash), inherent fire protection, precast concrete can reduce build time, heavier, ongoing maintenance and repairs required, consistent pricing, high strength in compression, but lacks tensile strength and must be reinforced by steel rebar to increase tensile capacity, ductile strength and elasticity, can be moulded into many different shapes, but there are limitations for floor-to-floor construction heights and long open spans, reinforced concrete is water resistant and will not corrode with proper construction and care.
- Both have high embodied energy in their manufacture. Steel is nearly 100% recyclable (90% used today created from recycled steel). Concrete contains natural products – can be crushed and reused in future admixtures.
32
What would you consider in the design of a concrete floor in a warehouse?
- Floor loadings
- Subsoil types – subgrade soils could be a problem when they are highly expansive or compressible (silts, clays) and do not provide uniform support.
- Structural design of the concrete floor slab – ground bearing slab or a pile supported suspended slab. If a consolidation of plastic soils is determined to be a potential problem a suspended slab may be the only effective solution in which the floor slab is built on piles or between ground beams.
- Joint design requirements – proper design of the concrete mix, use of concrete reinforcement, satisfactory curing and appropriate joint spacing contribute to crack prevention. A specialised joint system must be specified that will accommodate the movement and support the traffic without creating a discontinuity in the surface level.
- Surface characteristics – ability to resist wear and dusting – depends on the composition of the concrete ad hardness and toughness of the topping material, including finish coatings. Chemical resistance (floor should be protected with chemically resistant material and coating that resists any aggressive substances)
- Whether to decorate/apply an epoxy resin.
33
How would you remove redundant racking bolts from a concrete floor slab?
- Core drill out the redundant fixing bolts, clean the hole to remove all dust and lose material and inject an epoxy resin into the hole.
34
How often are movement joints required in a brickwork wall?
- Clay brickwork – 10-12m
- Lightweight concrete block/brick with lightweight aggregates – 6m
- Dense concrete block and brick (dense aggregate) – 7.5-9m
- Calcium silicate brick – 7.5-9m
- Masonry in a parapet wall – half the above spacings and 1.5m from corners
- Movement joint widths for clay bricks not less than 1.3mm/m and not less than 10mm/m for other masonry.
35
How often are wall ties required in cavity wall construction?
- Every 450mm vertically and every 900mm horizontally
36
What are ACMs?
- Aluminium composite material
- Commonly used for cladding buildings, typically as a form of rainscreen (drained and ventilated or pressure equalised facade) is part of a double wall construction.
- Rainscreen simply prevents significant amounts of water from penetrating into the wall construction. Thermal insulation, airtightness and structural stability are provided by the second, inner part of the wall construction.
- Consists of 2 skins of aluminium bonded to either side of a lightweight core of materials such as polyethylene (PE), polyurethane (PUR) or a mineral core.
- Popular due to its flatness, variety of surface finishes and colours, lightweight and formability.
- During a fire, the panels can delaminate, exposing the core material.
- Grenfell – with a polyethylene core (PE) contributed to the fire. Reynobond PE ACM cladding used was a cheaper, more flammable version of the Reynobond FR, which had a fire retardant core, or Reynobond A2 which has a non-combustible core.
- Types – Non-combustible mineral fibre (fibreglass/mineral wool)
- Polyisocyanurate foam (PIR)
- Phenolic foam (PF)
- Polyurethane foam (PUR)
- Expanded (XPS) or extruded polystyrene (EPS)
37
What is the purpose of the Building Regulations?
- Establish requirements for specific aspects of building design and construction.
- Approved Documents then provide guidance for satisfying those requirements in common building situations.
38
What is the LPCB?
- Loss Prevention Certification Board
- Part of BRE Global – sets the standards needed to ensure that fire and security products and services perform effectively.
- Offer 3rd party certification
39
What is the Fire Resistance standard: Euroclass system?
- One of the main standards used in Europe to classify the fire reaction of construction and partition products. There are 7 levels of categorisation from A1 to F (A1 best) The additional categorisation for smoke is S1 to S3, with S1 the best. For flaming droplets they range from d0 to d2, with d0 the best.
- A1 – Non-combustible
- A2 – Limited combustible (No flashover)
- B – Combustible (No flashover)
- C – Combustible (flashover after 10 minutes)
- D – Combustible (flashover before 10 minutes)
- E – Combustible (flashover before 2 minutes)
- F – Combustible (No performance determined)
(flashover is a near simultaneous ignition of most of the directly exposed combustible materials in an enclosed area).
- A1 or A2 with an S1 sub-rating are equivalent to non-combustible. A ratings are only likely to apply to mineral fibre insulated panels
- Best for expanded plastic insulated panels is category B. Panels with s1 or s2 sub-rating and d0 sub-rating are considered as a construction with limited combustibility, but not fully equivalent to non-combustible.
40
If a client requested replacement of a natural roof slate covering with cement tiles, what would you advise and what would be the considerations?
- I would try and understand their motivations for this alteration.
- If cost is the key driver, I would advise that although natural roof slate is more expensive, cement tiles would weigh considerably more than the slates, and a structural engineer would need to be involved to ensure that sufficient structural support is installed to accommodate this, bringing up the cost.
- Aesthetically, I would also highlight that these may affect the appearance of the property if this is out of keeping with the type of property, and they tend to weather poorly.
- There is also a greater environmental cost to the production of cement.
41
Name three different types of pitched roof truss.
- King post
- Queen post
- Hammerbeam
42
What is the difference between a hipped and pitched roof?
- A hipped roof is a type of roof where all sides slope downwards to the walls, usually with a fairly gentle slope. It has no gables or other vertical sides to the roof. It is self-bracing, requiring less diagonal bracing than a gable roof. Gable roofs only have 2 triangle-shaped slopes that extend from the bottom of the roof’s eaves to the peak of its ridge.
- A pitched roof is a roof that slopes downwards, typically in 2 parts at an angle from the central ridge.
43
What are the advantages of constructing a warm flat roof over a cold flat roof?
The cold roof has a vapour control layer beneath the insulation to reduce the risk of condensation to the underside of the weatherproof layer, but the difficulty of ensuring the integrity of the VCL leads to the need to ventilate the roof space and reduce condensation risk. The warm flat roof is a simpler construction as ventilation is not required, is cheaper and has a reduced probability of thermal bridging and condensation through the roof joists and hangers, as the insulation is continuous, rather than placed between the joists in cold roofs. It is the best option for the UK climate due to high levels of humidity, as there is likely to be insufficient ventilation to the cold roof.
44
Name four different types of covering for a flat roof.
- Mastic asphalt
- Bitumen felt
- Singly ply membranes
- EDPM (Ethylene Propylene Diene Monomer) rubber roofing
- Glass reinforced plastic
- Liquid applied coating.
45
Name two ways by which a single ply membrane can be fixed.
- Mechanical fastenings. These secure the single ply membrane over the top of the insulation and vapour control later, and are fastened in place to the roof deck.
- Adhesive bonding. In the past it was necessary to secure roof membranes with hot melt adhesive, but now it can be fully adhered by applying cold adhesive.
- Full and partial bonding.
46
How are slates fixed to a pitched roof?
They are normally fixed with 2 nails per slate, centre nailed, and a further fixing is used to secure the bottom edge of each slate to prevent it lifting in high winds or due to thermal expansion.
47
What is a counter-batten and when it is used?
They are wooden strips that are installed vertically over pitched roofs to which horizontal tiling battens are attached. They are used to allow rainwater to pass off the tiles and away from the roof.
48
How would you repair a leaking parapet gutter on an industrial unit? Brand/manufactures/cost:
- HD Sharmans’ Plygene gutterline system - £86/lm.
| - Apply a new silicone coating - £55/lm (HD Sharmans’ seamsil)
49
Where does the vapour control layer sit in a warm roof construction?
Beneath the insulation, but above the decking.
50
What is the disadvantage of single ply membranes?
- Over time single ply membranes can shrink, become brittle and lose elasticity, resulting in seam failure.
- They are subject to damage from wind uplift, which can tear off sections of the membrane.
- Blisters can result from localised loss of adhesion with water getting trapped.
- It shrinks over time, placing stress on flashings and resulting in tears/cracking.
- It is easily punctured, and the thin layers are not very durable, so gravel/loose screws can rip through them.
- It is vulnerable to leaks, although they are generally sealed pretty tightly with adhesives, tape or mechanical fasteners.
- It is sensitive to UV degradation and can degrade quickly, opening the roof up to damage, tears and leaks.
51
Why are collars installed between rafters?
- A collar tie is a tension tie in the upper third of opposing gable rafters that is intended to resist rafter separation from the ridge beam during periods of unbalanced loads, such as that caused by wind uplift or unbalanced roof loads from snow.
52
What is the purpose of a wall plate?
- A wall plate is a load bearing structural member used horizontally.
- It is a length of timber bedded on mortar on top of the internal leaf of an external cavity wall.
- It provides a fixing point for the feet of rafters and distributes the load exterted by the roof structure down through the walls without creating pressure points where each rafter meets the wall, and also acts to prevent windlift.
53
What is the difference between a rafter and a truss?
- Rafters are long timber boards used for the frame of a roof, also known as stick framing. They are made in situ by the roofers and they are outer beams which slope down from the peak of the roof. Ceiling joists then secure the rafters and the exterior walls. The ridge beam or board is placed at the centre of the roof, which helps to support the roof rafters at the top.
- Trusses consist of multiple beams that provide additional support to the roof structure. They are manufactured in a factory within a controlled environment reducing wastage. It is a structural framework of timbers that are designed to provide support for a roof.
54
If stripped back to the roof covering, what might you need to consider prior to replacement?
- The weight of the different replacement options
- The durability
- The cost
- The condition of the roof structure
- Insulation/sustainability measures.
55
What are the main components of a hipped end pitched timber roof structure?
- Ridge board, rafters (principal and common), purlins, tie beam, struts, posts.
56
What is an RCA?
- An appraisal of establishing the hypothetical cost to reconstruct a building from scratch to modern building regulations, but keeping the visible exterior and standard fit out in the interior more or less the same. The purpose is to ensure that the property has the appropriate level of insurance.
57
How is the reinstatement cost calculated?
- The building is measured, following IPMS 2
- The surveyor reviews plans for the building
- The surveyor examines the building components externally and internally and make reasonable assumptions based on their knowledge and experience of buildings regarding superstructure, frame and hidden structural composition of the building.
- The surveyor carries out an elemental take-off, calculating what the different parts of the building would cost in a fair market to form the basis of a raw calculation.
- These figures are updated from the year/financial quarter the data originated to the current quarter using the tender price index.
- Demolition costs, planning and statutory fees are then included, along with any considerations, such as whether the building is listed, proximity to underground lines, etc.
- Reach the ‘day one reinstatement’ figure known as the declared value (equivalent of fixed price, lump sum, competitive tender submitted by a suitable/competent contractor).
58
How often should an RCA be done?
- RICS advises that a major review should be undertaken every 3 years or earlier should significant alterations be made, with annual adjustments made to reflect inflationary effects. Desktop reviews could be undertaken yearly.
59
What is purpose of undertaking an RCA?
- Ensure buildings/estates are adequately insured in the event of a claim
- To avoid over insurance e.g. based on capital value
- To avoid distortion through index linking
- To comply with the lease and best practice.
60
What information is needed for an RCA to be completed?
- An accurate address
- Access to all areas of the property
- Scalable plans
- Health and safety files
- Previous RCAs, SoCs, schedules of areas
61
If the value of the RCA is found to be inaccurate, what are the potential implications?
- The client is paying too much for insurance premiums and could result in a claim against the landlord/freeholder
- If it is undervalued, this would severely affect a pay out from the insurer in the event of a claim.
- Important to ensure that the surveyor is suitably qualified.
62
Do RCAs include all plant and equipment, such as a communal boiler system or a lift?
- Yes – if it is fixed to the building, then it is included.
- Chattels and anything that could conceivably be considered to be part of the contents of a building are excluded. Sometimes all commercial fit outs are excluded apart from a Cat A fit out.
63
Regarding RCAs, do listed buildings require a different approach?
- They cannot be valued using the generic functional unit rate method as specialist period construction is not readily available in pricing books or databases.
- Specialist firms may have in-house data or the general figures could be uplifted to increase the provision on a percentage basis.
64
Does the RICS provide guidance on RCAs?
- Guidance note – provides recommendations/approach for accepted good practice
- Reinstatement cost assessment of buildings 3rd edition Feb 2018.
65
What information is required to accept an RCA instruction?
- Clarify that an RCA for insurance purposes is required and not a valuation or survey
- Establish extent of what is to be insured, esp. with respect to fixtures and fittings and external areas - the extent should be confirmed in writing in case there is a dispute later.
- Clarity on the date of the forthcoming renewal
- Other background information – original construction drawings, photos etc.
66
How do you undertake an RCA inspection?
- Make a general inspection of the property to confirm the extent of the property conforms to the description provided by the client.
- Assess the age of the building or make an assumption
- Consider if there are any restrictions to demolition /rebuilding – buildings in occupation, party wall issues, temporary protection, proximity to public transport infrastructure and city congestion zones.
- Likelihood of deleterious materials
- Take sufficient notes, photos, measurements and sketches to record the layout of the building, measurements (IPMS 2/GIFA), schedule of accommodational use, summary of the building’s construction, ceiling heights , services, external areas, boundaries, specialist features, topography.
67
What are the different types of RCA reports?
- Day one reinstatement – most are insured on what is commonly known as day one reinstatement basis – insurance settled on a new for old basis. It involves a declared value and an inflation provision.
o Declared value – the cost of rebuilding and associated on costs at the level of costs applying at the commencement of the insurance period without any provision for inflation.
o Inflation provision – a percentage uplift selected by the insured to cover inflation during the insurance year and during the subsequent period required for designing, planning, tendering and actual reconstruction, however long that may take. Can only be estimated based on anticipated building costs in the future and worst case scenarios. Commonly percentage uplifts vary between 15 and 50%
- Reinstatement including inflation provision
o Same basis of an RCA, but the sum insured does not have two constituent parts recognised separately in the policy. There will be one sum insured inclusive of an allowance for inflation and it is this sum that is insured, rather than the declared value under day one reinstatement basis, that will be used for premium calculation and average purposes. Recognising the difficulty in predicting the rate of inflation, insurers have often accepted a margin of error of 15% at the time of a loss so the claims will be paid in full providing the sum insured is at least 85% of the true value at the time of the loss.
- Reinstatement less wear and tear (indemnity basis)
o Few buildings insured on this basis. May be used where a building is very old or not in a good state of repair, the insurer may be unwilling to grant full reinstatement cover or the insured may wish to save money on the premium, while accepting the inevitable betterment contribution to be made in the event of repairs being necessary.
o Role to value on an RCA basis, but to depreciate elements to reflect their current condition. If services are obsolete and decorations poor, there may be no value attached.
- Obsolete buildings
o Make an assessment on an RCA basis but depreciate elements to reflect their current condition.
o Could be suitable if a building would be demolished and rebuilt in different and cheaper form if it was destroyed/damaged. Partial damage would be repaired up to an agreed amount but beyond that amount the building would be knocked down and replaced by a modern building providing the same function.
o The premium would be calculated on the full cost of reinstatement of the existing building with a reduction to reflect the insurer’s limit of liability is a lesser amount based on the demolition of what remains of the original building and the cost of the modern replacement. The saving of premium is quite small as most losses are partial.
- Site clearance, debris removal and ‘making safe’ costs only
o If a building is due for demolition no material cover may be necessary if, when damage occurs, the date of demolition can be brought forward.
o Cost of demolition may be higher as a consequence of the damage and additional expense may be incurred in making the building safe in the meantime. Such extra costs arisings as a result of damage may be assessed and insured on their own. Compliance with stringent waste control regulation and professional fees associated with supervision will need to be reflected in such an assessment.
- Second hand value of building materials
o Rarely requested – a building may be due for demolition/redevelopment and may have no value except that arising from items that have a second hand value, such as fireplaces, architectural features and roofing tiles. If the second hand value could be lost as a result of damage, then the value can be assessed.
68
How do you ensure the costs are accurate on an RCA?
- Determine IPMS 2 measurements of the building and the net rebuilding cost is calculated by multiplying the gross internal area of the building by a suitable rate for its reconstruction.
- Use BCIS, SPONS and other in-house tendered price data to establish costs.
- Location of the property should be considered
- Listing has an impact on costs
- Conservation area restrictions will also have an impact on cost levels and timescales.
- Access restrictions should also be considered.
- Professional fees – party wall surveyors and fees for undertaking the reconstruction.
69
What considerations should you take into account when compiling an RCA?
- Whether the building is listed/in a conservation area
- Is in close proximity to infrastructure, e.g. tube lines
- Proximity to neighbours, congestion, difficult of access
- Location
- Deleterious materials
70
How is an RCA calculated?
- Day one reinstatement (declared value)
- Calculate GIA (IPMS 2) and apply a suitable BCIS re-building rate
- Apply location adjustment
- Make adjustments based on site specific factors
- Select a demolition rate
- Make allowance for fees
- VAT excluded
71
What is a portal frame and when is it used?
- A type of frame where the beams and columns act as one, reducing beam thicknesses and allowing for larger spans. The joints between the beam and columns are rigid so that the bending movement in the beam is transferred to the columns.
- Became popular in the 1960s
- Used to create wide-span enclosures such as warehouses, agricultural buildings, hangars, sports venues, large retail units, etc.
72
What are the advantages of portal frames?
- Quick and easy to build
- Cost-effective
- Can be used for multiple purposes
- Low maintenance
- Aesthetically pleasing
- Structural efficiency – large spaces enclosed with little use of materials and for a low cost.
73
How is composite metal cladding fixed to a steel frame?
- It is fixed to the secondary steelwork consisting of side rails and purlins for the walls and roof respectively.
- Proprietary fasteners (self-tapping or self-drilling) can be used to connect sheeting to supporting steelwork and connect adjacent sheets. They are either plated carbon steel or stainless steel covered with plastic cappings.
74
What are portal frames typically constructed of?
- Steel
- Reinforced precast concrete
- Laminated timber (glulam)
75
What are some types of portal frame?
- Pitched roof symmetric portal frame
- Portal frame with mezzanine floor
- Tied portal frame
- Mono-pitch portal frame
- Mansard portal frame
- Propped portal frame
76
What span does a portal frame offer?
- Between 15 and 50m
- Clear height to the underside of the haunch of 5 and 12m
- Roof pitch of 5-10°
- Light gauge purlins and side rails
77
What fire resistance is required in a portal frame construction?
- In the UK a structural steel single storey building does not normally require fire resistance.
- Most common situation it is required it where prevention of fire spread to adjacent buildings is required.
- Also where the portal frame is close to the boundary, fire resistant cladding, fire protection to the steel up to the underside of the haunch.
78
What is the purpose of bracing to a warehouse?
- Bracing is required to resist longitudinal actions due to wind and cranes, and to provide constraint to members.
- Vertical bracing in the side walls of the frame
o Transmit horizontal loads to the ground
o Provide a rigid framework to which side rails and cladding may be attached so that rails can provide stability to the columns.
o Provide temporary stability during construction.
o May be located at one or both ends of the building, within the length of the building or in each portion between expansion joints.
79
When was the Georgian period?
1714-1837
80
When was the Victorian period?
1837-1901
81
When was the Edwardian period?
1901-1914
82
Describe Georgian construction type.
- Slate mansard or butterfly roofs hidden behind raised parapet walls. Kings/queen posts with rafters and joists built into the walls.
- Timber sash windows with 6-12 smaller panes of glass, that get smaller as you rise up the building.
- Timber doors
- Chimneys at either end
- Symmetrical, classical, Greek revival.
- Lath and plaster finishes
- Herringbone strutting adds resistance to floors
- Suspended timber joists built into the walls on a wall plate for upper floors.
- Basements constructed on stone flags.
- Flemish brick bond (alternative headers and stretchers)
- Thicker walls at ground level.
- Clay red or yellow London stock bricks
- Rubble walls with facing stonework
- Lime mortar allows movement
- Shallow brick footings or none at all with solid brick walls – 225mm thick.
83
Describe Victorian construction type.
- Pitched roof with bargeboards.
- Ostentatious ornamentation
- Larger timber windows with less glazing panes and cast iron casements (sheet glass from 1848)
- Gothic revival, Italianate, arts and crafts
- DPCS introduced in 1875 (Public Health Act – lead, slate, bitumen)
- Concrete foundations shallow, however reinforcement was not unknown
- Solid walls in the early Victorian times
- Lime mortar typically used
- Some cavities used towards the late Victorian times with iron wall tiles used.
- Timber suspended floors built into walls on iron brackets
- Sleeper walls introduced to reduce spans
- Air bricks installed for ventilation
- Filler joisted clinker or coke breeze used in public buildings – caused corrosion and pit cracking of the concrete
- King or queen post roofs held together with iron plates
- Clay and slate roof tiles
- Sash windows with larger/single panes
- Bay windows
84
Describe Edwardian construction type.
- Use of steel or reinforced concrete frames allowing architects to free walls from structural constraints and classical forms.
- Fabricated walls could be clad in brick/stone or cased in concrete. Concrete floors could remain visible as bands across the brick faced façade.
- Edwardian French, baroque.
85
What is the purpose of the approved documents?
- They provide guidance for how the building regulations can be satisfied in common building situations. There is no obligation to adopt the solutions presented in the approved documents - the building regulations can be satisfied in other ways.
86
What impact do building regulations/approved documents have on design?
- They ensure the requisite standard and quality of building construction is maintained, and ensure that design work considers fire safety, detailing and accessibility and sustainability.
87
What are the main approved documents?
- A – Structure – requires buildings to be designed to be structurally robust and not impair the structural stability of other buildings. It stipulates design standards for use on all buildings and gives simple design rules for most masonry and timber elements for traditional domestic buildings – includes roof frames, brick walls and tables of material strengths.
- B – Fire Safety – covers precautionary methods necessary to provide safety from fires for building occupants, persons in the vicinity of buildings and firefighters. Requirements and guidance covers means of escape, fire detection and warning systems, the fire resistance of structural elements, fire separation, protection, compartmentation and isolation to prevent fire spread, control of flammable materials and access and facilities for firefighting.
- C – Site preparation and resistance to contaminants and moisture – weathertightness, watertightness of buildings, subsoil drainage, site preparation and measures to deal with contaminated land, radon, methane and all other site related hazardous and dangerous substances.
- D – Toxic substances – controls hazards from the toxic chemicals used in cavity fill insulation systems.
- E – Resistance to the passage of sound – requirements for sound insulation between buildings, including new dwellings, conversion of buildings to form dwellings.
- F – Ventilation – includes standards for ventilation, air quality for all buildings and requirements for the prevention of condensation.
- G – Sanitation, hot water safety and water efficiency – standards for the provision of sanitary and washing facilities, bathrooms and hot water provision. Requirements in respect to unvented hot water systems.
- H – Drainage and waste disposal – guidance on adequate drainage and also deals with pollution prevention and sewage infrastructure and maintenance. Technical design standards cover sanitary pipework, foul drainage, rainwater drainage and disposal wastewater treatment and discharges and cesspools.
- J – Heat producing appliances and fuel storage system – construction, installation and use of boilers, chimneys, flues, hearths and fuel storage installations. Requirements to control fire sources, prevent burning, pollution, carbon monoxide poisoning, etc.
- K – Protection from falling, collision and impact – standards for the safety of stairways, ramps and ladders, together with requirements for balustrading, windows and vehicle barriers to prevent falling. Also, guarding against and warning of hazards from the use and position of doors and windows.
- L – Conservation of fuel and power – Insulation values of buildings elements, the allowable areas of windows, doors and other openings, the air permeability of the structure, heating efficiency of boilers, hot water storage and lighting. Controls mechanical ventilation and air conditioning systems, space heating controls, airtightness tests of larger buildings, solar emission. Certification, testing and commissioning of heating and ventilation systems and requirements for energy meters. Carbon index ratings.
- M – Access to and use of buildings – requires the inclusive provision of ease of access to, and circulation within, all buildings, together with requirements for facilities for disabled people.
- N – Glazing – safety glazing to avoid impact hazard and for the suitable awareness and definition of glazed areas. Also included are safety requirements relating to the use and cleaning of windows.
- O – Overheating – overheating mitigation requirements for new residential buildings.
- P – Electrical safety – design, installation, inspection and testing of electrical installations in order to prevent injuries from electrical shocks and burns, and to prevent injuries arising from fires due to electrical components overheating or arcing.
- Q – Security – dwellings - reasonable provision to resist unauthorised access to any dwelling.
- R – High speed electronic communications networks – new requirement for in-building physical infrastructure which enables connections to broadband networks.
- 7 – Materials and workmanship – requirement to carry out building work using the proper materials and in a workmanlike manner.
88
What did the December 2021 revision to Approved Document L change?
- Requirement for new homes to produce 30% less CO2 than current standard and a 27% reduction of emissions from other new buildings, including offices and shops.
- Comes into effect 15 June 2022
- Paves the way for Future Homes and Building Standards in 2025, which means all future homes are net zero ready and will not need retrofitting.
89
When were the building regulations introduced?
- 1965
90
What do the buildings regulations set out?
- what qualifies as building work and so falls under the control of the regulations
- what types of buildings are exempt (temporary buildings).
- The notification procedures that must be followed when starting, carrying out and completing building work.
- Requirements for specific aspects of building design and construction.
91
What are the different types of cores in composite cladding?
- PE (polyethylene)
- PIR (polyisocyanurate)
- PUR (polyurethane)
92
What is the typical construction of a 1970s commercial/industrial building?
- Single skin asbestos roof
- Pre-cast concrete frame
- Single skin masonry or cavity with single skin asbestos sheets
- Cast in situ concrete slabs
- Asbestos rainwater goods
- Single glazed aluminium windows.
93
What is the typical construction of a 1980s commercial/industrial building?
- Built up insulated roof with metal profiled sheets and PVC-u or PVF2 finish – issues with corrosion etc.
- PVC-u rooflights – solar degradation
- Steel frame
- Cavity and built up metal profiled cladding sheets.
- Cast in situ concrete floor
- Double glazed windows
- Siphonic rainwater systems – issues being undersized
- Issues with corrosion/movement with metal used.
94
What is the typical construction of a 1970s office building?
- Flat roof, cold deck, no insulation – lack of insulation which causes interstitial condensation.
- Concrete frame – HAC, carbonation, ASR, chloride attack, sulphate attack
- Pre-cast concrete or cast in-situ floors
- Infill cladding panels – movement between different materials i.e. cladding and frame
- Single glazed aluminium framed windows – heat loss
- Deleterious materials
95
What is the typical construction of a 1980s office building?
- Insulated flat roof with no vapour barriers – interstitial condensation
- Steel frame – susceptible to corrosion/lack of fire protection
- Double glazed windows – gaskets and units fail
- Curtain walling – issues with water ingress and gasket/mastic failure (glass lasts 60-70 years , but gaskets fail in 20)
- Some deleterious materials remain – lead/asbestos
96
What is a portal frame and when is it used?
- A type of frame where the beams and columns act as one, reducing beam thicknesses and allowing for larger spans.
- Typically used in industrial, storage, retail and agricultural units as they are efficient at enclosing large areas in single storey or low rise buildings.
97
How is composite metal cladding fixed to a steel frame?
- It is fixed to the secondary steelwork consisting of side rails and purlins for the walls and roof respectively.
- Proprietary fasteners (self-tapping or self-drilling) can be used to connect sheeting to supporting steelwork and connect adjacent sheets. They are either plated carbon steel or stainless steel covered with plastic cappings.
98
How does a diaphragm wall work?
- It is a continuous reinforced structural concrete wall constructed in a deep trench excavation to act as a retaining wall, support for the underground structure as a foundation or facilitate cut off provision in order to support deep excavation. It is either cast in situ or using precast concrete components and is usually used as permanent works on a project.
- Often used on congested sites, close to existing structures where there is restricted headroom or where the excavation is of a depth that would otherwise require the removal of much greater volumes of soil to provide battered slopes.
- Suitable for most subsoils and their installation only generates a small amount of vibration and noise. Floor slab connections and recessed formwork can be incorporated into the walls.
- Range in thickness from 500-1500mm and can be excavated to a depth of 50m
- It is constructed panel by panel, each interlocked to ensure structural stability and water tightness.
- 1. Construction of the guide wall (two temporary parallel beams constructed along the side of the all to give the excavation tool and stabilise the top portion (avoids soil collapse, helps mark the panel positions and support the steel reinforcement cages). It is constructed above ground level in case water table is too high.
- 2. Soil removal and stabilisation with adequate excavation support to prevent the trench collapsing. To protect the sides, bentonite slurry is used to produce lateral pressure that is sufficient to retain the vertical soil.
- 3. Wall concreting – reinforcement cage is inserted into the trench (lapping if more than one required), the poured concrete replaces the bentonite clay in the trench (densite of bentonite low compared to concrete and bentonite clay that is displaced is collected and reused.
99
Where would you expect to find the main reinforcement in a Beam and why? (structural concrete component)
- Beam – The lower portion with at least 50mm of cover, as this area is likely to be subject to tension.
100
Where would you expect to find the main reinforcement in a Column and why? (structural concrete component)
- Column – Around the edge - all bars in compression should be tied by a link passing around the bar in such a way that it tends to move the bar towards the centre of the column. This is to prevent caused by load/slenderness of the column, reaction to beams upon the columns and reaction to wind loadings.
101
Where would you expect to find the main reinforcement in a Staircase and why? (structural concrete component)
- Staircase – Concrete steps to be reinforced with concrete bars so it carried the loads coming upon the staircase and transfers them to the ground.
102
Where would you expect to find the main reinforcement in a Suspended Slab and why? (structural concrete component)
- Suspended Slab – The reinforcement will be fabricated to form a continuous mesh mat to prevent deflection at the bottom as compression occurs at the top and tension at the bottom.
103
Where would you expect to find the main reinforcement in a Cantilevered Slab and why? (structural concrete component)
- Cantilevered Slab – In the cantilevered slab, the top fibres are subject to tensile stresses so the main reinforcement is provided above the neutral axis.
104
Where would you expect to find the main reinforcement in a Pad Foundation and why? (structural concrete component)
- Pad foundation – bottom. In order for pad foundations to spread the load into the soil the pad must be either sufficiently deep (allowing the force of the load to spread out at a pre-defined angle) or be constructed with adequate reinforcement. Reinforced concrete pads should be designed so that the depth is sufficient to resist a shear force (punching shear). This can develop around the perimeter of the column, wall or other vertical component that the pad is supporting. To resist bending movements, the pad footing should be designed so that the force applied is to the middle third of the base.
105
Where would you expect to find the main reinforcement in a Raft Foundation and why? (structural concrete component)
- Raft foundation – one layer at the top and one layer at the bottom and around columns to spread the load across the entire area of the building.
106
What size is a brick or block?
- 102.5 x 215 x 65mm – standard brick
| - 440 x 100 x 215 – standard block
107
What does C40 mean in relation to concrete and what does the 40 relate to?
- Concrete with a compressive strength of 40n/mm2
108
Explain the purpose of using a plasticiser in a mortar mix?
- It increases the workability of the concrete when wet.
109
What is GRC?
- Glass fibre reinforced concrete
- Lightweight external cladding panels and can imitate stone.
- Easy installation and cost effective (80% lighter than pre-cast steel reinforced concrete cladding) Enhanced energy efficiency.
- High strength, alkali resistant glass fibres embedded in a concrete matrix
- Fibres act as the principal load bearing component while the surrounding matrix keeps them in position and transfers the load between the fibres.
- Typically manufactured in sections by machine spraying OPC and aggregate mix with glass fibres dispersed throughout.
- Moulds to create complex profiles. Generally ribbed or sandwich form offering good durability, fire resistance, weather resistance and sound insulation.
110
What is the difference between a common, facing and engineering brick?
- Common – no lowest quality, no attempt to make colour uniform, etc.
- Engineering – Low compressability and is stronger, low absorption rate.
- Facing – used for aesthetic reasons.
111
What is pointing?
- The mortar between bricks and used to bed the bricks
| - It can have several types of joint.
112
How does English Bond differ from Flemish bond?
- Flemish – brick construction pattern that consists of alternative stretchers and headers for each course.
- English – alternate courses of brick laid as stretchers and headers.
113
Explain the term corbeling.
- An architectural member that projects out from a wall and acts as a type of bracket to carry weight – traditionally made of stone, timber or metal.
114
What is rainscreen cladding and how does it work?
- Part of a double wall construction that can be used to form the exterior walls of buildngs.
- Used from 50’s to 60’s
- ‘A wall comprising an outer skin of panels and an airtight insulated backing wall separated by a ventilated cavity. Some water may penetrate the cavity but the rainscreen is intended to provide protection from direct rain.
- Typically formed of relatively thin pre-fabricated panels that prevent significant amounts of water penetrating into the wall construction. Thermal insulation, airtightness and structural stability are provided by the second inner part of the wall construction.
- 2 types – drained and ventilated – allow any penetrating moisture to drain/evaporate and vent to the outside – ensure any penetrating moisture cannot cross the gap between the rainscreen and the internal wall construction.
- Pressure equalised (PE) – allows movement of air between the inside and outside of the rainscreen – it equalises the pressure across the rainscreen so that water is not driven or sucked through the joints.
115
What is curtain walling?
- Non-structural cladding systems for the external walls of buildings – generally associated with large, multi-storey buildings.
- Curtain walls separate the interior from the exterior, but only support their own weight with the loads imposed on them (wind, seismic loads) which they transfer back to the main structure of the building.
- Typicall comprise a lightweight aluminium frame onto which glazed/opaque infill panels can be fixed.
- Common from the 1930s.
- Can adopt a stick system (installed piece by piece on site) or be unitised (prefabricated).
- Infill panels – vision glass, spandrel (non-vision) glass, aluminium, stone/brick veneer, terracotta, fibre reinforced plastic, louvres/vents.
- Systems used to prevent the passage of water through joints include face sealed, water-managed and pressure-equalised systems.
116
What alternative materials are available for window frame construction?
- PVC
- Timber
- Stone
- Aluminium
- Steel
- Composite
117
What is a mullion?
- A vertical member within a window frame (transom is a horizontal member)
118
Name 4 different types of glass used in glazing systems.
- Annealed glass – basic product - base product for more advances glass types.
- Heat strengthened glass – semi-tempered/toughened increasing the mechanical and thermal strength of annealed glas. When it breaks the fragments are similar in size to annealed glass but with a greater likelihood of staying together. Limited strength.
- Tempered/Toughened glass – Most commonly used in structural applications – process makes the glass four to five times stronger and safer than annealed or untreated glass. When it does break, it produces small, regular, typically square fragments.
- Laminated glass – Any of the above glass types can be laminated with PVB. Offers safety and security as rather than shattering on impact, it is held together by the interlayer, reducing the safety hazard.
119
What materials are typically used for internal partitioning?
- Brickwork, blockwork, or timber, steel or aluminium framed, with boarding, such as plasterboard, timber, metal or fibreboard.
120
What different types of plaster and render are there?
- Cement plaster (mixture of sand and cement may be plastic and requires experienced and skilled labour – plasticiser and lime is added to ease spreading over the surface)
- Gypsum plaster (widely used as an undercoat, finish coat and replaced lime and cement broadly – small expansion prevents shrinkage and cracks)
- Lime plaster (common with lath and plaster)
- Heat resistant plaster – for coating chimney breasts and used for a fire barrier in ceilings.
- External rendering – similar to plastering and uses a mixture of cement and sand, or cement, lime and sand applied to the face of a building in several coats.
- Roughcast – wet plaster mix with cement, lime, shingle and sand.
- Pebbledash or dry dash – aggregate such as pea shingle dashed or thrown onto a rendering background before it has set and is tamped on to the surface with a wooden float to obtain a good bond.
- Spattered finish – applied by a machine, guns or sprays using special mixes.
121
What different types of retaining walls or structures are common in the industry?
- Sheet piling (sections of sheet materials (often steel) with interlocking edges that are driven into the ground to provide earth retention and excavation support)
- Gabions (made out of wire mesh formed into boxes/baskets and then filled with rock or stone – helps prevent erosion and stabilises any steep slopes)
- Piled retaining wall (a secant piled wall formed by constructing alternating primary (female) and secondary (male) piles where the secondary piles partially cut into either side of the primary piles to form a continuous impervious structure)
- Reinforced wall ( constructed by gradually increasing the tensile force applied to the soil on the backside of the wall – wall reinforced by using high tensile strength reinforcing materials)
122
What is the difference between suspended and a solid ground floor construction?
- Solid – Tend to require little maintenance and are less prone to movement.
o Sub base – well-compacted building rubble/loose stone material
o Hardcore – filling material to make the required level and create a solid base
o DPM – an impervious layer such as a heavy duty polythene sheet.
o Concrete bed – provides a solid surface level
o Insulation – to limit heat transfer with the ground
o Screed – usually a sand/cement mix laid to prepare for the installation of floor finish.
o Finish – carpet, tiles, etc.
- Suspended – usually constructed using timber joists suspended from bearing walls, which are then covered with floorboards/boarding. The joists are typically laid across the shortest span. Ventilation may be provided to the void by placing air vents/bricks within the exterior walls allowing air to travel from one side of the building to another. Can cause draughts which can be avoided by installing an airtight breather membrane which will help maintain an airtight seal.
123
What is the function of a floor screed?
- To provide a level and flat surface for the floor coverings.
124
What is granolithic paving?
- A type of construction material composed of cement and fine aggregate, such as granite or other hard wearing rock – generally used as flooring or paving.
- Similar appearance to concrete – used to provide a high strength, durable surface where texture and appearance are not important. Commonly laid as a screed.
125
Describe the different ways of dealing with ground water in excavations.
- Groundwater pumping – also known as dewatering – involves pumping groundwater from an array of wells/sumps around the excavation. The objective is to lower groundwater levels to below working levels in the excavation.
- Low permeability cut off walls – low permeability barriers are installed to the ground around the perimeter of the excavation – these act as barriers to the groundwater flow and effectively exclude groundwater from the excavation.
- Grout barriers – injection into the ground of fluid grouts that set solidly in the soil pores and rock fissures blocking the pathway for groundwater to flow.
- Artificial ground freezing – a very low temperature refrigerant is circulated through a series of closely spaced boreholes drilled into the ground. The ground around the boreholes is chilled and eventually frozen. This has a very low permeability and will significantly reduce groundwater inflow into any excavation.
