Building Pathology (Level 3)

Question 1

What are the causes and remedies for some of the defects associated with flat roofs?

Answer 1

Ponding - a minimum gradient of 1 to 40 is required for a flat roof to shed water effectively, where the appropriate floor has not been built in or has been altered by structural movement, ponding is likely to occur. Where water is allowed to sit on the surface of a felt roof for an extended period, its lifespan will be drastically reduced. An increase in the gradient of the roof will need to be achieved through structural alteration and recovering.

Blistering - blisters can be caused by vapour barrier pressure occurring below the roof covering. The blister should be cut and then rebounded to the underlay, allowing for any trapped moisture to escape first. The source of the moisture should also be traced and rectified.

Crazing - surface crazing is caused where there is a lack of adequate protection from the harmful effects of exposure to the sun or, in rare cases, chemical attack. If this is only in small localised patches, no treatment is necessary, but should be regularly rechecked. If the crazing is more widespread, the areas will have to be reroofed and a specialist protection introduced.

Thermal Movement - cracks and splits can occur where there is thermal or moisture movement between the roof substrate and the membrane. It is likely that localised reroofing will be necessary to address this issue using a high performance felt.

Flashings and falls around openings defects - poor workmanship or deterioration of the flashing details around openings can lead to water ingress. Also, poor detailing or construction of the structure can lead to structural movement around roof lights.

People - punctures and rips are most often caused by impact damage by personal or loose debris. They should be repaired using localised patch repairs.

Question 2

Tell us the methods of assessing flat roof defects you have learned about?

Answer 2

Electronic leak detection is possible through a weak electrical fuel directed on the dampened surface and any current that earths into the building changes the nature of the field locally.

This should pinpoint the penetration or just as importantly, show where water penetration is not caused by a roof leak.

Also a thermographic examination should be carried out to identify the areas of the leaks.

Thermographic image will highlight areas of moisture retained within the roof in order to pinpoint the location of the leak.

Question 3

What are the common defects associated with flat roofs?

Answer 3

The common defects associated with flat roofs include:

1. Blistering.
2. Splitting of coverings.
3. Sagging due to failure of the decking between joists.
4. Ponding due to insufficient falls.
5. Damages to flashings.

Question 4

What should you take into account when deciding whether to repair or replace a flat roof?

Answer 4

Its age, life expectancy and overall condition.

Are the defects are localised or affecting the whole of the roof and if the defect is affecting the surface layer or the roof structure.

A client’s intentions for the building also need to be established, including their budget, the building’s use, any disruption caused through repair and possible phasing requirements.

Question 5

You are asked to inspect a flat roof, take us through the inspection process?

Answer 5

Firstly, I would gather historical building information and details of any current or previous issues with the roof.

I would then make arrangements for access and prepare necessary RAMS to establish the roofs;

• Age.
• Previous repairs undertaken.
• When and where the roof leaks.
• Ponding issues.
• Use of the rooms below.
• Whether the roof is used as a balcony or terrace.
• Access arrangements.

Question 6

What is damp?

Answer 6

A building is only considered to be damp if the moisture becomes visible through discoloration and staining of finishes or causes mould growth, sulphate attack , frost damage, or even drips and puddles.

Question 7

How can you test for damp?

Answer 7

The use of a protometer can establish the prevalence of damp in buildings.

Moisture metres or a speedy carbide metre can also be used to determine the moisture content of walls, and the level of damp.

Question 8

What is a protometer/moisture metre?

Answer 8

A protometer works by measuring the electrical resistance between two applied electrodes.

Protometres are generally used to monitor the moisture content in wood, when used on other materials, the actual readings may be misleading, however, this approach does give a sense of moisture content.

Question 9

What is a speedy carbide meter?

Answer 9

A speedy carbide meter is a device to measure moisture in masonry.

By drilling into masonry and putting the dust generated into a sealed container with a known measurement of calcium carbide allows the moisture content to be determined.

This works as the dust and calcium carbide releases a gas in proportion to the amount of moisture present.

Question 10

Describe three issues and remedies for rising damp.

Answer 10

1. Rising damp is caused either by lack of a damp proof course, a defective damp proof course or external features bridging the damp proof course.
2. The remedy therefore involves removing the external feature causing bridging, the injection of water repellent chemicals into the brickwork or the fitting of new physical dump proof membrane.
3. Where a damp proof course is not suitable, lime plaster and wash can be used to minimise damage caused by the internal finishes.

Question 11

How would you identify penetrating damp? What are the causes and how would you remedy it?

Answer 11

Penetration damp can be identified through the appearance of damp patches on walls, ceilings or floors.

These patches tend to grow or darken after periods of heavy or prolonged rain.

Causation can be due to rain driving through exposed masonry walls and have insufficient thickness, problems with cavity trays, cracked or detached rendering, defects to window sills and blocked cavity ties.

Remedies for penetrating damp include the repointing of defective mortar joints, application of masonry water repellent, making good defective joint details, inspection of cavity trays, and cavity ties to address any blockages and the inspection of areas of roofs such as chimneys, parapets and thresholds to address any defects in these elements.

Question 12

What is a cold bridge?

Answer 12

A cold bridge is created when materials that are poor thermal insulators come into contact, allowing heat to flow through the path created.

Insulation around a bridge is of little help in preventing heat loss or gain due to thermal bridging.

The bridging has to be eliminated, rebuilt with reduced cross section or with materials that have better insulating properties, or with an additional insulating component, called a thermal break.

Question 13

What are the causes of condensation and how would you remedy it?

Answer 13

Hot air is able to carry moisture and when this hot air hits a cold surface, it loses some moisture as condensation.

This water comes from breathing, domestic activities such as cooking and bathing.

It can lead to staining at cold bridges, peeling wallpaper and mould growth.

Causes of condensation include a lack of insulation, lack of ventilation, and unheated areas of the building.

Remedies of condensation include a reduction in moisture generation, providing adequate ventilation, provide adequate heating and improving the building insulation.

How long would you leave the brick and plaster to dry out before commencing work?

You need to allow time for the brick to dry out before commencing works.

A dehumidifier can speed up the process, however, a minimum of three to four months is recommended.

Question 14

What ways could moisture enter the building and how would you differentiate between the types?

Answer 14

Penetrating damp - moisture gets into the building because there is a porous bridge transferring moisture by capillary action from the external face of the walls to the internal face of the walls. This could be due to a single skin of masonry, water trap behind render and mortar snots on cavity ties. There may also be a hole in the roof which allows moisture in and gets into the ceiling due to the force of gravity.

Rising damp - moisture rises up the wall from the ground due to capillary action, normally up to a maximum of 1 metre high tide marks. This is identified through a visual inspection of its location and extent, and also use of a moisture meter. If there is a DPC, this may be failing with something bridging the DPC. However, one would need to ensure that there are no other possible causes.

Condensation - hot moist air hits a cold surface and condenses, causing the surface to absorb the moisture, which encourages staining and mildew growth. This is identified through the distinctive mildew, the location of poorly ventilated areas with high humidity, kitchens, bathrooms, bedrooms and rooms used for drying clothes.

Question 15

You are inspecting a building and identify a number of cracks in the external wall, take me through your thought process?

Answer 15

I would firstly note the material the wall is constructed from and what form of construction the building is. I would also consider any local factors which could be causing the cracking, such as:-

• Trees.
• Stumps.
• Alterations to building.
• Drains in the vicinity of the crack.
• If there have been any alterations to the building such as extensions, rooms in the roof or internal layout alterations.

Question 16

What other sorts of cracks would you expect to see on a brick building, and what might have caused them?

Answer 16

Subsidence - a movement down in the ground level. In clay soil, the growth of large trees which remove water from the ground can cause this. This can lead to vertical cracking if in the centre of the building or diagonal cracking if at the corner of the property. The cracks will be larger at the top and thinner at the bottom.

Heave - a movement upwards in the ground level. In clay soil, the removal of a tree will lead to an increase in the moisture content of the soil, which will cause the soil to swell. This leads to vertical cracking if in the centre of the building or diagonal cracking if at the corner of a property. The cracks will be larger at the bottom and thinner at the top.

Settlement - a movement down due to the increased load. Buildings will settle when first constructed or if there is a change in the load as the new load settles to the bearing capacity of the soil.

Differential settlement - if two sections of the building are constructed of different foundations or the ground is made-up of different soil types or strata then one may settle more than another, causing cracking between the two sections of the building. The issue is most common with extensions.

Lintel failure - lintel failure allows a triangular section of brickwork above the window to drop down, creating a triangular crack from the corner of the window towards the centre.

Corroded steel lintel - where a steel lintel has been used above an opening and the edge is exposed or close to the surface, this can corrode overtime and expand causing cracking.

Question 17

What size cracks are of concern?

Answer 17

Up to 2mm - very slight concern.

2mm - 5mm - slight or aesthetic concern.

5mm - 15mm - moderate concern.

15mm - 25mm - severe.

Over 25mm - very severe with stability concerns.

Question 18

If there was stepped cracking on the corner of a building, what might have caused it?

Answer 18

1. Settlement.
2. Subsidence.
3. Heave.

Question 19

What if the cracks were present on concrete?

Answer 19

I would consider the common concrete defects such as carbonation, chloride attack and silica reaction, as well as issues relating to structural movement and poor design and construction.

Question 20

What type of soil is susceptible to heave and what are the possible causes?

Answer 20

I would consider the common concrete defects such as carbonation, chloride attack and silica reaction, as well as issues relating to structural movement and poor design and construction.

Question 21

What type of soil is susceptible to heave and what are the possible causes?

Answer 21

Cohesive soils such as clay.

Possible causes include removal of trees and changes in the water table.

Leaking drains or inadequate foundations that are built within the movement zones.

Question 22

What types of timber defects are there?

Answer 22

The main timber defects are:-

• Dry rot.
• Wet rot.
• Insect attack.

Question 23

Describe the different types of rots and how you would recognise them?

Answer 23

• Dry rot - wood shrinks and splits into large cuboidal cracking. The wood is light in weight, crumbles under touch and has a dull brown colour with a cotton wool type texture. Mycelium is often visible and greyish in colour when wet and yellow or purple when dry.
• Wet rot - wood shrinks and splits on a smaller scale, with the wood becoming darkened. Mycelium can be white, brown, amber, green or black with strands that are flexible when dry. The floating bodies can be a number of different colours and can occur both inside and outside.

Question 24

What are the medical measures to dry and wet rot?

Answer 24

To locate and eliminate the sources of moisture and promote rapid drying whilst removing the rotten wood.

There can also be a surface application of fungicidal fluid and introduction of support measures if required.

Question 25

The ends of the joists in a timber floor built in an external wall have been seriously affected by dry rot. How will you recognise this type of rot and what action would you take to resolve the problem?

Answer 25

Typical indications of dry rot include:- - Wood shrinkage and dark cracks of a cubicle manner. - A silky grey to mushroom coloured skin, frequently tinged with patches of lilac and yellow, which often develops under less humid conditions. - This “skin” can be peeled like a mushroom. - White, fluffy cotton wool mycelium develops under humid conditions. Any affected timbers should be removed and replaced with pre-treated timber. Any remaining timbers at risk of being affected by the dry rot should be treated with an effective fungicide. Where the dry rot has passed through the masonry, it should be isolated using physical containment and/or masonry sterilisation.

Question 26

The ends of the joists in a timber floor built in an external wall have been seriously affected by wet rot. How will you recognise this type of rot and what action would you take to resolve the problem?

Answer 26

Wet rot results in a high moisture content of around 50 - 60% to propagate and spread. It is usually found in areas where there may be a water leak, or building failure, such as along window sills and in roof voids. Indications of wet rot outbreak include:- - Surface cracking where cracks follow the timber grain. - Hyphae strands which are light brown and yellow (a key difference from dry rot). - Infected timber turns dark brown in colour. The first step to remedy wet rot is to find and eliminate the source of dampness to prevent the timbers becoming damp. All infected and/or damaged timber should be removed, as this may be structurally impaired due to the decaying action of the wet rot and the remaining timber treated with a suitable preservative. If the wet rot is in a confined space, such as a cupboard or loft space, it may be necessary to consider methods to improve the ventilation.

Question 27

What are the remedial measures for dry rot?

Answer 27

- The medial action for dry rot is far more intrusive. - The first step is to establish the full extent of the outbreak, many parts of which may be initially concealed from view, underneath floorboards, behind furniture and panels. - Affected timber, similar to wet rot needs to be cut out and replaced, including those within approximately 300mm to 450mm beyond, to allow for possible further contamination. - All surrounding timbers should be treated with a chemical biocide, to ensure all strands and spores are killed off. - Affected plaster that has come into contact with dry rot needs to be removed, and all surfaces treated with a steriliser or biocide. Lastly, the area should be kept dry and heated, to ensure all timbers are fully dried out to prevent or reduce the likelihood of further outbreaks.

Question 28

Explain the life cycle of dry rot?

Answer 28

The four main dry rot life cycle stages are as follows:- 1. Spore - spores are omnipresent and in very large numbers. Dry rot spores appear as a fine orange brown dust. The spores are activated when combined with timber and moisture. 2. Hyphae - where timber and moisture are present the spore will produce very fine white strands called hyphae, which allow the dry rot fungus to grow by feeding on the timber. Thereby breaking down the structure of the timber while it grows to form a mycelium. 3. Mycelium - the resulting hyphae mass is known as mycelium. Mycelium has the ability to grow over a significant distance and a variety of materials, which allows an outbreak to progressively destroy the structural timbers of an entire building if left undetected. 4. Fruiting body - to perpetuate itself, the fungus will create a fruiting body (sorrowful). This mushroom like form, is a function to pump out spores into the atmosphere that can be transferred by air currents to other susceptible areas within the building, allowing them to germinate and create a new attack of dry rot, thus bringing us back to the beginning of the dry rot life cycle.

Question 29

Name some common insects that are known to attack timber and explain what remedial methods are available?

Answer 29

Category A - where insecticidal treatment is required for the common furniture beetle, death-watch beetle and house longhorn beetle. Category B - where treatment is only necessary for associated rot due to wood boring weevils. Category C - where no treatment is needed for bark borers. The medial measures for these insects include:- - Studying the flight holes to identify the type of beetle and determine if the infestation is still active or dormant. - Apply two coats of boron based treatment to all affected areas overlapping at least 300mm into the sound timber. - In the case of a severe attack, replacement timber with pre-treated wood is required.

Question 30

How do you identify the presence of woodworm?

Answer 30

Holes in the wood members in question are present with live infestations showing powder (faeces) around the holes. The size of the holes varies, but are typically 1mm to 1.5mm in diameter for the most common household species. Adult beetles which emerge from the wood may also be found in the summer months.

Question 31

How do woodworms affect timber in buildings?

Answer 31

Typically, the adult beetles lay eggs on, or just under the surface of the wood members in question. The resulting grubs then feed on the timbers, causing both structural and cosmetic damage before hatching as beetles, which then breed, lay eggs, and then repeat the process causing further damage.

Question 32

What is a woodworm infestation likely to indicate?

Answer 32

Most species of woodworm acquire that the wooden item contain a higher moisture content than is normally found in a typical home. A building with a woodworm problem in the structure or furniture probably also has a problem with excess damp.

Question 33

How is a woodworm infestation treated?

Answer 33

Woodworm infestation is generally controlled with chemical insecticides. However, it is also advisable to investigate and solve possible damp issues as dry wood is not usually affected and wood that remains damp may be reinfected at a later date.

Question 34

You are surveying a defected timber floor in an early 19th century building. What are the causes and methods available to deal with this, if the client requires a level floor?

Answer 34

Confirm the cause of the deflection, whether this is due to:- - Notching. - Rot. - Insufficiently sized joints. - Insufficient centres. - Overloading. - Deterioration of sleeper walls. Confirm if the issue can be remedied and whether the timber floor can be retained. There may be a potential to:- - Supplement the timber joists. - To overboard. - Remove and replace the suspended timber floor. - Install an alternative solid floor.

Question 35

A newly cast reinforced concrete slab is exhibiting crazing and cracking on its surface, what are the possible causes?

Answer 35

- Poor or adequate curing, which is caused by environmental conditions being conductive to high evaporation rates and a lack of adequate protection. - Too wet of a mix, excessive floating or use of a jitterbug that will depress the coarse aggregate may have been undertaken, resulting in an excessive concentration of cement paste and fines at the surface. - Finishing operations performed while bleed water remains at the surface and other finishing procedures that produce a high water cement ratio at the surface. - Sprinkling cement on the surface to dry up the bleed water.

Question 36

What are nickel sulphide inclusions?

Answer 36

They are inherent in the glass production process and are microscopic imperfections in the glass, known as inclusions. Most of these are completely harmless, but nickel sulphide inclusions have been shown to cause disastrous failure of tempered glass. When glass is rapidly cooled to achieve the properties of tempered glass, the nickel sulphide inclusions remain in a high temperature form. Over several years, the nickel sulphide will return to its low temperature state, and in the process will increase in volume. This can cause cracking and additional tensile stresses which, in tempered glass, can lead to spectacular failures with no visible cause. This phenomenon has also been referred to as spontaneous glass failure.

Question 37

What else may have caused glazing to crack if it wasn't nickel sulphide inclusions?

Answer 37

Structural movement around the window opening could have put pressure on the glazing and caused a crack.

Question 38

You find a leak at a high level on the first floor of a two storey building constructed with a traditional cavity wall construction. Please outline the process which you would go through in assessing the cause for the defect. Also, what are the potential causes of such a defect?

Answer 38

I would review any existing building information available before inspecting the property. I would look at the building as a whole to get an understanding of its construction and the materials used to assess whether there have been any alterations to the building. It is also prudent to speak to the building owner or occupier to enquire whether they can advise the location of the source of the leak and when it is most prevalent. My first thought would be to suspect a roof leak, so I would assess the roof both externally and internally for signs of defective or missing roof coverings and defective or missing flashings around roof penetrations. When in the roof space, I would also look for evidence of leaking pipes.

Question 39

How does cavity wall tie failure present itself and how would you fix it?

Answer 39

Cavity wall tie failure can be identified when horizontal cracking appears in every five or so brick courses or in render. It is due to the corrosion of old steel ties, such as large fishtail ties. To remediate this issue, I would firstly use a borescope to confirm the defect is wall tie failure. I would then look to locate wall ties and isolate or remove them to ensure no further damage is caused. Installing replacement stainless steel mechanically fixed ties secured with an epoxy resin can be utilised to remedy this issue.

Question 40

What is nail fatigue?

Answer 40

This is a common problem for pitched roofs with slates or tiles. The nails have rusted through, allowing the slates or tiles to fall. If one nail corrodes, this could be a sign that large sections are at risk. The remedial measure would be to strip the roof and secure the tiles or slates with new nails. Some roofers advocate a foam spray solution, but as it sets hard, it prevents the roof from moving and also impedes the ventilation.

Question 41

What is Japanese knotweed and what does it look like?

Answer 41

Japanese knotweed is a large, herbaceous perennial plant. Japanese knotweed has hollow stems with distinct raised nodes that give it the appearance of bamboo. While stems may reach a maximum height of three to four metres each growing season, it's typical to see much smaller plants in places where they sprout through cracks in the pavement or are repeatedly cut down. The leaves are broad and oval. The flowers are small, cream or white.