Roofs Flashcards
(108 cards)
1
Q
What components and materials are typically used within a pitched roof?
A
- Purlin
- Rafters
- Ridgeboards
- Roof Joist
- Flashing
- Fascia board
- Downspout
- Gutters
- Tiles
- Underlayer
- Valley
- Sheathing
- Truss
- Struts
- Wall Plate
- Blinder
- Roof Tie
- Purlin strut
2
Q
What is the difference between a truss roof and cut roof?
A
Truss roofs are factory made trusses which are delivered to site complete and then installed on site
Cut roof is the traditional method of cutting the timber on site and building up the roof using rafters,ridgeboards, joists and purlins etc – the exact details being determined by the size of roof, size of timbers etc.
3
Q
What is a chimney?
A
A vertical channel or pipe which conducts smoke and combustion gases up from a fire or furnace and typically through the roof of a building.
4
Q
What is a ridge?
A
The ridge of a sloped roof system is the horizontal top area where two sloped roof areas meet
5
Q
What is a flashing?
A
- Required when any part of a roof meets a vertical surface or abutment
- Used commonly on roof window, chimney or a dividing wall between two terraced properties
- The joint between the vertical surface and the roof covering needs to be sealed against leaks
6
Q
What is a fascia?
A
- A board that runs along the roofline and acts as a finishing edge or trim that connects to the ends of the rafters and trusses
- The fascia is to protect the roof and the interior of the home from moisture by blocking its entrance
7
Q
What is a gutter?
A
A rain gutter’s main purpose is to funnel water off the roof and away from the home. Too much water falling too close to your home can erode the soil around it
8
Q
What is a valley?
A
Valleys are created when two sloping roof areas intersect and are one of the critical detail points on a steep-slope roof system
They occur on primary roof areas and where projections, such as dormers, break the plane of the main roof
A valley’s main function is to create runoff pathways to direct water flow from the roof planes into a valley trough
The volume of water varies with the valley’s length and slope.
9
Q
What is a sheathing?
A
Roof sheathing is a layer of plywood, wafer board or wood planks which is nailed on the rafters and stands between them and the shingles that finish the roofing.
10
Q
What is roof underlaying?
A
- A roofing underlay is placed under the exterior roof
- its primary function protects the thermal insulation material and the building structure from the effects of the weather.
- The roofing underlay works as a secondary roof underneath the primary roof.
- The roofing underlay acts as a condensation barrier, which leads condensed water away from the underlay, and thereby also the insulation material.
11
Q
What is a ceiling joist?
A
Ceiling joists support the ceiling and act as a tie to the rafters to stop the rafter feet from spreading
12
Q
What are common rafters?
A
A sloped roof member that is smaller than the principal rafter, which spans from the top plate of the exterior wall to the roof ridge rafter.
13
Q
What is a roof tie?
A
Rafter ties resist the outward thrust that rafters exert on the exterior walls. They help keep walls from spreading due to the weight of the roof.
14
Q
What is a purlin?
A
A purlin is added which prevents the rafters from
sagging mid span
The purlin is supported by the gableend walls (party walls in mid-terraced houses) and is sometimes strutted
from an internal loadbearing wall (and sometimes the gable walls) to provide additional support
15
Q
What is a wall plate?
A
The purpose of the wall plate is to accommodate the wooden beams of a framing, to ensure a uniform bearing height and to better distribute the bearing force over the bearing.
16
Q
What 3 types of trusses
A
Kingpost
Queen Post
Fink
17
Q
What is roof flashing made of?
A
- Lead is commonly used for flashings, however;
- zinc
- aluminium
- slate
- and cement mortar are often found in the UK
18
Q
What is a common result of roof flash deterioration and what would the Building Surveyor encounter with roof flashing ?
A
- Leaks commonly occur as a result of deterioration of flashings or poor workmanship
- the Building Surveyor will often encounter situations where temporary felt or ‘flashband’ repairs have been made
19
Q
Name the common defects of a roof
A
There are many defects however these defects are common. • Moss Growth on Roof Surface • Roof Flashings • Roof Spread • Sagging Roof Surface • Nail Sickness • Turnerising
20
Q
Why is moss growth a problem and what are the remedial works?
A
• A common problem to many roof coverings and often exacerbated where there are trees nearby.
• The moss builds up on the roof surface which then allows water to sit on the roof, which in turn can
allow damage to occur to the surface of the tiles
• Moss should be cleared on a regular basis before it has the opportunity to build up. Care must be taken during removal to ensure that it does not fall into gutters causing blockage
21
Q
What is roof spread?
A
- Roof spread occurs when a roof frame is not adequately tied
- Resulting in horizontal movement which can push fascia boards out sideways, and often leaves a visible gap between the soffit board and brickwork
- In extreme cases,brickwork can be pushed out at the top and the wall develops an outward curve
22
Q
How does roof spread usually occur?
A
Roof spread mainly occurs in ‘cut’ roofs (made from sawn timber) and is usually a result of poor design
23
Q
Is a truss roof likely to be affected by roof spread?
A
Roof Spread is much less likely to occur in trussed roofs, which are designed and manufactured in a
factory and brought to site for final erection
24
Q
Is a truss roof likely to be affected by roof spread?
A
Roof Spread is much less likely to occur in trussed roofs, which are designed and manufactured in a
factory and brought to site for final erection
25
Why does roof spread occur?
Roof spread often occurs, particularly in older buildings where a new heavier roof covering (such as concrete tiles) is installed on a roof that was
designed for a lighter roof covering (such as slate)
26
What are the remedial works for roof spread?
Depending on the severity of the roof spread, the usually remedy is to introduce bracing (usually metal), to tie the walls back to the structure
27
How expensive can roof spread be?
Roof spread is not generally covered by standard house insurance policies, therefore the expense of remedying will normally be the responsibility of the owner
28
How does roof sagging occur?
Sagging to the surface of a roof can occur for a number of reasons, which are unlikely to be visible from the
outside of a building.
A sagging roof may be a result of a damaged or broken roof rafter.
29
What should the Building Surveyor inspect when investigating Roof Sagging
* Broken or damaged rafters
* Moisture ingress causing Wet Rot
* Dry Rot
* Deflection to Purlins
* Poor Ventilation (Possible Condensation)
* Bearing points of structural members
In older properties, deflection of the purlins may occur over many years as result of progressive loadings (such as snow), and also weakening on the purlins
30
Does roof sag mean there's a problem?
In older properties, deflection of the purlins may occur over many years as result of progressive loadings (such as snow), and also weakening on the purlins.
31
What is nail sickness on pitched roofs?
• Loose roof slates are more often the result of the fixing nails failing as they rust away (a problem known as 'nail sickness')
• 'Nail sickness' can typically be first seen by the lower edges of a
row of slates being out of line - one fixing will fail on a number of
slates and these will then begin to twist
32
Why might the slate tiles get loose?
The slates themselves may disintegrate around the nail holes due to the roof settling, frost or wind damage, or things falling onto them
33
What does nail sickness indicate?
When slate roofs begin to suffer from 'nail sickness' or breakdown of the actual slates, it usually indicates that the roof is approaching an age when complete re-roofing will be required
It is likely that the fixing nails and all the slates will probably have
originally installed at the same time so they should be suffering
the same degree of ageing
34
How would you investigate nail sickness?
'Nail sickness' can typically be first seen by the lower edges of a row of slates being out of line - one fixing will fail on a number of slates and these will then begin to twist
35
What is turnerising?
‘Turnerising’ is a process usually applied when roofs have started to deteriorate or leak
Turnerising involves the covering of a roof with a mesh and coating it in bitumen
36
Is turnerising beneficial?
Good for temporary repair however, it is almost impossible to economically save or re-use materials which have been treated in this manner
37
Name the defects of roof voids
There are many potential defects that can occur within a roof void and the Building Surveyor should pay due regard to:
* Wet Rot
* Dry Rot
* Ventilation
* Insulation
* Vermin
* Fire Separation
* Water Storage
* Woodworm
* Structural Timbers
* Services
38
What is the cause of wet rot?
Wet rot is caused by high moisture content (typically will start to occur at 30% with optimum decay rate at 50% to 60%) in timbers, coupled with poor ventilation
39
What does wet rot physically affect?
The attack with affect the timber that will be limited to those areas that contain sufficiently high moisture content
40
What does wet rot cause?
Wet rots are a common cause of structural defects and there are number of species which attack timbers in buildings
41
What are the physical features of wet rot timber?
Attacked timber is either darkened or bleached depending on species and is left in cuboidal or longitudinal cracks
42
What are the physical features of wet rot timber?
Attacked timber is either darkened or bleached depending on species and is left in cuboidal or longitudinal cracks
43
What is the remedial action of wet rot?
• Finding out where the water is coming from and
stop it (Eradicate the source)
• Removing all rotted timber and replacing it with
pressure-treated wood or wood that has been
painted with a preservative
• Treat any remaining wood within the affected
area with a wood preservative
• Monitor for further signs and treat as soon as
possible
• Ensure good levels of ventilation, including
ensuring that air bricks are not blocked
44
What is the cause of wet rot?
• All causes are related to a constant source of moisture ingress, within an environment that does not allow the affected timber to dry out. (i.e poorly ventilation, poorly heated areas etc.)
```
Examples of sources:
• Leaking Rainwater Goods
• Leaking Plumbing, i.e Bath, WC, Heating
• Vegetation Growing on Wall
• Damp Environment, i.e Basements
• Poorly Maintained Joinery
• Leaking Roof
• Rising Damp (Possibly)
• Excessive Condensation
• Joists Built into Walls
• Exposed Lintels
• Poor Quality Untreated Timber
• Poor Workmanship, i.e Poor Weather sealing
```
45
What is dry rot?
* Named ‘Dry Rot’ because of its ability to grow into dry areas.
* Dry rot is a living and growing fungus, which feeds off and destroys timber in order to live
46
What can dry rot not grow on?
• Dry Rot cannot feed on masonry itself, but carries the
| moisture with it in the strands to allow it to spread
47
How does dry rot work?
The ‘intelligent’ fungus has developed the ability to soak up moisture from timber, totally drying it out, and then develop strands which can travel across and through bricks and mortar to other timbers in unventilated conditions
48
What are the four main stages in the dry rot lifecycle and explain them.
1. Spores
2. Hyphae
3. Mycelium
4. Fruiting Body
49
What are the ideal conditions for dry rot?
```
• Timber with a moisture content of
22% - 30% (Circa)
• Prefers temperatures of between
240 and 300
• Poorly ventilated areas
• Dark areas such as concealed spaces
```
50
How would you identity dry rot?
```
• Identification of spores, hyphae,
mycelium or fruiting body
• Cuboidal cracking
• Always undertake a thorough inspection
and consider all factors
```
51
What is the remedial action for dry rot ?
• Eradicate the moisture source
• Brush down exposed masonry to remove surface fungal growth.
• Deep-drill masonry at pre-determined centres and irrigate with Fungicidal Wall Solution introduced under pressure.
• Sterilise all exposed masonry surfaces with Fungicidal
• Remove all dry rot affected timber including a minimum of 1m past
the last identifiable location and dispose from site.
• Provide new treated and primed timber to location where previously removed.
• Provide new treated and primed timber to location where previously removed.
• Spray all new and adjacent timbers including cut ends with fungicidal spray.
• Re-plaster as necessary using a cement and sand render mix.
• Ensure adequate ventilation is available
52
What is the remedial action for dry rot ?
• Eradicate the moisture source
• Brush down exposed masonry to remove surface fungal growth.
• Deep-drill masonry at pre-determined centres and irrigate with Fungicidal Wall Solution introduced under pressure.
• Sterilise all exposed masonry surfaces with Fungicidal
• Remove all dry rot affected timber including a minimum of 1m past
the last identifiable location and dispose from site.
• Provide new treated and primed timber to location where previously removed.
• Provide new treated and primed timber to location where previously removed.
• Spray all new and adjacent timbers including cut ends with fungicidal spray.
• Re-plaster as necessary using a cement and sand render mix.
• Ensure adequate ventilation is available
53
What is infestation decay?
•There are a number of small beetles that attack wood
54
What do beetles attack?
• Most beetles attack wood that is alive (i.e., trees) or green lumber,) but a few will attack seasoned wood, like furniture, flooring, panelling etc.
55
How do beetles damage timber?
• Damage occurs to timber as a result of the larva boring through the wood and the eventual appearance of the adult insect
56
What are the four common beetles in the UK and how do they differ?
• Different insects will exhibit varying life spans, different flight hole sizes and will be active at different times of the year
57
What other animals can affect services in the roof void?
Rat can damage electrical cables
| Birds may die in the water tank
58
What is considered a flat roof?
A roof is designated as flat if it has a slope of less than 10 degrees
59
How long do flat roofs last?
A well constructed and properly maintained flat roof should remain in in serviceable use for approximately
15 – 20 years
60
What are the 3 common types of flat roof construction?
Built-Up Felt Roofing
Asphalt Roofing
Single Ply Membranes
61
What are advantages of a flat roof?
Flat roofs are very convenient, easier to construct, and cost less than pitched roofs
62
Where are flat roofs generally used?
Flat roofs have traditionally been used in hot climates where water accumulation is not a problem, however they are commonly found in wet climates’, and in particular in the UK
63
What is water ponding?
Water ponding occurs when a roof is constructed without adequate falls to allow water to discharge efficiently
64
What can water ponding result in?
```
• Water ponding can result in:
• Degradation of the felt
• Stress and failure of joints
• Increased risk of condensation
due to cool roof surface
• Moss and lichen build up
```
65
How do flat roofs discharge rainwater?
Gutters and downspouts.
Internal drains.
Scuppers
66
What are the common faults with built-up felting roof?
De-bonding at Upstands
Blistering of Felt
Cracks and Tears
67
What is a built-up felt roofing?
Built up felt roofing involves layers of tar impregnated roofing felt rolled out onto a roof.
Each layer overlaps the previous layer and in between the deck material and each layer of felt a layer of hot tar is mopped over the surface
68
What is an asphalt roof?
Asphalt - ‘A composition of bitumen, pitch, lime, and gravel, used for forming pavements, and as a water-proof cement for bridges, roofs, etc.’
Asphalt is commonly used at upstands around rooflights, plinths, roof access hatches.
69
How do flat roofs discharge rainwater?
Gutters and downspouts.
Internal drains.
Scuppers
70
Which type of construction is considered the best?
```
Single ply membrane . The benefits includes its;
it's durability
appearance and ease of
installation on a variety of roof types
modern
light weight
much quicker to install
suitable for weaker structures
life expectancy in excess of 50 years
```
71
What are the common problems with Asphalt roofs?
Blistering
Crazing
Cracking and tears
Slump
72
What signs would you look for in a flat roof in the summer?
The water will evaporate leaving the leaves and dirt in a collected area
73
How does poor workmanship and materials affect flat roofs?
Poor workmanship affects flat roofs.
In many cases it will be found that rainwater penetration has occurred behind the asphalt skirting, either because the skirting has not been adequately turned into the brickwork joint or the cover flashing has
been omitted
Similarly if materials are not carefully selected or wrong materials are put together
such as in the instance of zinc and lead abutting (both of which are common roofing materials) then corrosion or other defects can occur.
74
How do people affect flat roofs?
During a warm summer flat roofs become illegal terraces and their asphalt or felt coverings are subjected to point loads just when they are most vulnerable. The result is a series of pot marks which allow moisture to ingress and cause the covering to fail the following winter.
75
How do you prevent asphalt and felt roofs from bubbling?
A good quality solar reflective paint or a layer of light coloured chippings will reduce thermal movement and associated stresses to asphalt and felt roofs. Where the surface is not adequately protected creasing will occur and eventually lead to splits.
76
How does moss growth affect roofs?
Flat roofs that remain wet for long periods provide the ideal conditions for moss growth. Moss can attack the surface of the felt and the moss itself acts as a sponge soaking up water and leading to further problems as it freezes and thaws in winter.
77
How does condensation occur on roofs?
Modern flat roof construction should have a vapour check barrier
Where there is no vapour control, high moisture levels can occur in the voids within a roof and if this is formed of timber, it can allow rot to occur.
78
What is a vapour barrier
a membrane to stop warm moist air reaching the colder portions of a flat roof and condensing
79
How does blistering occur?
Blistering is normally caused by the expansion of small amounts of moisture and air trapped beneath the covering
As the temperature of the roof increases, so does the pressure inside the blister and the adhesion of the asphalt weakens
The felt may expand permanently where the blister occurs and if damaged or left for prolonged periods of time can cause splitting and therefore water ingress.
Rainwater may also become trapped under the asphalt during wet weather which may give rise to blistering
80
What is blistering?
They look like little bubbles or pimples in your roofing material and are often moisture related.
81
What are remedial works for blistering?
* Blisters may be found in many sizes up to about 150mm and if not split they may be left. Those which have split should be cut out and patched
* The source of the moisture should also be traced and rectified
82
What happens if blisters are not treated?
With time and natural weathering these popped blister areas can in fact lead to leaks and roof damage
Like all blisters there comes a time that they will surely pop. When blisters pop on shingle roofs the granules become dislodged leaving the asphalt unprotected from the UV rays of the sun.
83
What are the uses of mastic asphalt
* Mastic asphalt is suitable for use with concrete, block and beam, wood wool slabs and suitably constructed timber roofs
* The asphalt is often protected from ultra violet degradation and heat build-up by applying a solar reflective paint finish
84
How is asphalt applied?
* As it is applied in molten form, it can be dressed around rooflights, pipes etc without any difficulty
* Asphalt is usually laid in 2 coats on an isolating membrane of black sheathing felt
* On completion mastic asphalt forms a seamless membrane
85
What is crazing and what type of roof does it affect?
Crazing is solely a surface phenomenon which occurs periodically on mastic asphalt surfaces exposed to direct sunlight
86
How does crazing begin?
Crazing usually begins as a network of fine vein like lines and these in extreme cases, develop into shallow fissures as much as 6mm in width and 5mm deep
87
How does crazing occur?
Crazing only occurs on material directly exposed to the rays of the sun. Asphalt which is effectively shaded or screened rarely contains any traces of this defect
88
How can the possibility of crazing be reduced?
The possibility of crazing can be significantly reduced with the application of a solar reflective paint covering
89
How does cracking occur on asphalt roofs?
• Cracking can also be related to thermal
stressing where movement is locally
restricted
• Cracks in asphalt may also relate to
brittleness induced by solar radiation;
or differential thermal or moisture movement
90
What should the Building Surveyor look for when investigation an asphalt roof?
• Asphalt is relatively easily damaged by impact.
• Therefore the Building Surveyor should look also for;
signs of heavy plant
materials
or evidence of human damage
91
What is slump and how does it occur?
A common defect with asphalt is slump, which occurs when the material becomes ‘mobile’ at high
temperatures
92
How can you reduce the possibility of slumping?
Wire mesh secured to the upstand and sufficient time (4-6 hours) between coats to allow for cooling, will significantly reduce the likelihood of slump occurring
93
What are the reasons of asphalt failure?
• Many failures in asphalt roofing are a result of differential movement taking place at the joints between the horizontal surfaces and the vertical abutments of parapet walls, particularly where a timber
substrate has been installed
Building movement will apply tensions to the waterproofing layer of the roof and if the material is not pliable or stretchable enough, then this will eventually cause the sheeting to tear and break. .
94
How does thermal movement occur on roofs?
Repeated cycles of heating and cooling cause flat roof materials to expand and contract.
Materials must be equipped to deal with these movements without cracking under the pressure to avoid water penetration.
95
What are angle fillets?
Angle fillets should be provided at the base of all skirtings to avoid sharp angles which have a tendency
to crack
96
What are the consequences of no angle fillets?
In older asphalt roofs a crack may may be formed at the junction between the skirting and the asphalt
roof due to the absence of an angle fillet
97
What components and materials are used for Flat roofs? (felt)
```
Scupper
Roofing felt
Hot mopped tar between layers
Gravel top coat
Sheathing
Curb
Flashing
Drip Cap
```
98
What are angle fillets?
High density mineral wool angle fillet for flat roofing.
Angle Fillets are designed to reduce the corner angle from 90° to 45°.
Angle fillets should be provided at the base of all skirtings to avoid sharp angles which have a tendency
to crack
99
What components and materials are used for Flat roofs? (felt)
```
Scupper
Roofing felt
Hot mopped tar between layers
Gravel top coat
Sheathing
Curb
Flashing
Drip Edge
```
100
What is the function of a drip edge?
The lower edge of a roof should extend beyond the fascia board by about 3/4 inch so that runoff drains into the gutters.
101
What are the consequences of short or no drip edge?
If this slight overhang is too short, water will drip behind the gutters, leading to rotted roof sheathing and fascia, stained siding, and even soil erosion and a flooded basement.
102
What is the reason of a gravel top coat?
The weight provided by the gravel is used to anchor down the roof materials,therefore using far fewer fasteners to hold the materials to the decking.
The ballast is used to keep the roofing system cool and of out of the sun’s harmful rays, thus keeping energy costs down.
The gravel top coat is also extremely resilient to heavy foot traffic and high-wind scenarios.
103
Gutters and downspouts
Gutters and downspouts carry water from the roof away from the building, protecting the cladding system and the foundation.
104
Internal drains
Internal drains are typically connected to pipes that go down through the house and discharge into a storm sewer.
105
Scuppers
Scuppers are simply openings through parapet walls or perimeter curbs that allow water to drain into a downspout running down the exterior of the building.
Scuppers are essentially a continuation of the roof membrane. The scupper itself is usually surrounded with a metal box that acts as a flashing and allows water to run through the wall.
106
Can water flow from one roof to another?
Flat Roofs That Drain Onto Steep Roofs Below
| Steep Roofs That Drain Onto Flat Roofs Below
107
How does Steep Roofs That Drain Onto Flat Roofs Below work?
Where there is a steep roof discharging onto a flat roof, the flat roof membrane should extend about 3 feet up under the steep roofing shingles or tiles.
Depending on the material, the shingles may extend down to the flat membrane
If rigid tiles are used, they should not contact the membrane for fear of piercing it during differential building movement
108
How does Flat Roofs That Drain Onto Steep Roofs Below
Where a built-up flat roof is located above a steep roof.
The proper detail is to provide a gravel stop at the top and a counter flashing that extends down over the steep roof for several inches.
If the slope of the steep roof is relatively low and wind-driven rain, it is a risk
