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What are the primary functions of roof sheathing?
- Strengthen the roof system by providing rigidity and
- Preventing rocking of the rafters and
- Provide a nailing base for the roof finish
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What is the most commonly used sheathing material?
OSB
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In Canada, is it permissible to use roof sheathing that is identified by US markings only?
NO
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What grade and minimum thickness of plywood and OSB could be applied to trusses 600mm on centre?
- 3/8" (9.5 mm) plywood or OSB 0-2 graded can be used if H clips or horizontal blocking is installed.
- If neither measure is employed, the minimum sheathing thickness allowed is 1/2" (12.5 mm)
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Describe what each number and letter in the following grade marking means: 2R24
- 2 - horizontal edges must be supported
- R - suitable for roofs
- 24 - max span
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Do all of the edges of 18 mm fibreboard roof sheathing required support?
Yes
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Describe a vented roof panel.
- OSB
- Rigid insulation
- 12-19 mm space for ventilation
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Describe what conditions must exist in order for ice damming to occur.
- Hot roof melts snow
- Cold overhang refreezes causes damming
- Water can creep up shingles and into house
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What materials are used for asphalt shingles?
- Heavy felt or fibreglass impregnated with hot ashpalt
- The upper surface is covered with a finely crushed slate
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What materials are used for roll roofing?
The same but in a roll.
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Describe the appearance of a wood hand-split shake.
A rough slit face and sawn back and varying thickness
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Describe the appearance of a wood shingle.
Smooth sawn on both surfaces and uniform.
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Does a standing seam metal roof have exposed fasteners?
No fasteners are exposed, resulting in a weather tight roof.
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What types of screws or nails are used to fasten corrugated galvanized roofing?
- Resilient washer screws or nails.
- The fastener heads are exposed and special care must be taken in locating and tightening the fasteners to prevent water penetration.
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What is the most important factor to consider when applying tile to an existing roof surface?
That the roof has adequate structural support.
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List 2 reasons to use PVC roofing materials.
- 1. excellent durability
- 2. corrosion resistance
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What is the primary application of plastic roofing materials?
Greenhouse construction
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List 3 applications of fibreglass roofing?
- Greenhouses
- Carports
- Agricultural barns
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Describe the traditional built-up roofing system.
- Several layers of hot application and asphalt bitumen and alternate plies of asphalt saturated roofing felt.
- The built-up roofing membrane is applied over rigid insulation board and followed with a flood coat of bitumen and a protective layer of light-coloured gravel.
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Describe the purpose of each component of the roof membranes: asphalt bitumen, roofing felts, gravel cover
- Asphalt bitumen: main waterproofing
- Roofing felts: reinforce the membrane
- Gravel cover: protects the asphalt from the sun's harmful effects
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What must be done to open valleys to protect them from moisture penetration?
Application of valley flashing with a minimum of 600 mm wide sheet metal or 2 layers of roll roofing, as per code, centred on the valley.
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How far should the step flashing extend up the wall behind the sheathing membrane?
75 mm
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What is the maximum size a chimney can be before a cricket or saddle is required?
750 mm
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How far must eave protection extend up the roof slope?
A minimum of 900 mm not less than 300 mm up the inner face of the exterior wall.
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What are the lowest slopes to which normal and low slope asphalt shingles can be applied
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Where is flashing required on a roof surface?
All roof penetrations and intersections
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When underlayment is used, how should it be laid and how much should it overlap?
- Parallel to eaves and
- should overlap the eave protection by 100 mm
- Each row should be top or end lapped a minimum of 50 mm
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What is the purpose of the starter strip used when asphalt roofing?
Prevent water from getting through to roof at gaps between shingles
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Where should asphalt shingles be nailed?
- 25-40 mm from the sides
- not less than 12 mm over each cut-out
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How do you determine the proper exposure when applying asphalt shingles?
Manufacturers recommendations, usually 140mm maximum
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List 3 options for securing asphalt shingle tabs.
- 1. Self-sealing strips
- 2. Interlocking features
- 3. A dab of roofing cement no larger than 25 mm in diameter under each tab
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What is the benefit of applying spaced decking beneath wood shingles or shakes?
- Allows the underside to breath dissipating moisture.
- Wood shingles decay begins on the underside when moisture is trapped.
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What type of underlayment must be used beneath wood shakes?
- Breathable type underlayment not less than 450 mm (18") wide interlaid between each course of shakes.
- The bottom edge is positioned above the butt line (bottom edge of shingle), equal to a distance of double the length of the exposure.
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How far apart should individual wood shingles and shakes be applied?
- Individual shingles: 6 mm
- Shakes: 6-9 mm (to allow for expansion of the wood)
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Roll roofing is typically applied to what type of roof surface?
Lower sloped roofs
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