Shingles are one layer of a roof system
A reliable roof combines sound framing and decking, compatible underlayment, eave and valley protection, flashing, correct fasteners and ventilation. The visible shingle cannot compensate for a weak layer below.
Measure each sloped plane plus eaves, ridges, valleys, chimneys and penetrations. Use the current instructions for the exact product rather than the building footprint alone.
1. Confirm slope and product limits
Not every shingle is approved for every pitch. IKO, for example, prohibits one referenced asphalt product below 2:12 and specifies special underlayment from 2:12 to below 4:12. Treat this as product-specific guidance, not a universal value.
Measure rise over run and check low- and steep-slope requirements, local rules and the project design.
2. Inspect OSB or timber decking
The deck must be smooth, firm, clean, dry and securely fixed. Replace swollen, loose or deflected areas and correct proud fasteners before covering.
Select panel grade, thickness, direction, support and expansion gaps from the structural design and panel manufacturer's guidance. Store bundles flat, dry and without concentrating roof loads.
3. Detail underlayment and water paths
Match underlayment and laps to slope, climate and system. Eaves, valleys, chimneys, roof windows, pipes and wall junctions require deliberate secondary-water and flashing details.
Sealant alone is not durable flashing. Layer membranes, drip edges and metal flashings so water always drains onto the course below.
4. Preserve starter, offset and nail pattern
Use the specified starter and course offset so joints do not align. Keep courses straight and follow the exposure marked for the product.
Drive approved nails square and flush, never proud or through the surface. Nail quantity and location vary by product, pitch and wind zone; follow the wrapper diagram and any hand-sealing requirement.
5. Balance intake and exhaust ventilation
Provide a clear air path from low-level intake to high-level exhaust where the roof design requires ventilation. Keep insulation out of the air channel and coordinate vapour control.
Calculate net free vent area for the design and local rules. Do not discharge bathroom or kitchen air into the roof void.
6. Respect weather and fall risk
Cold shingles may be brittle and seal strips may need special handling; extreme heat can mark the surface. Work only within manufacturer weather guidance.
Roofing requires suitable access, anchors and fall protection. Stop for rain, ice or unsafe wind.
Ordering checklist
Prepare:
- Sloped area and measured pitch
- Deck type, thickness and condition
- Shingle series, colour and lot
- Underlayment, eave, valley and flashing details
- Eave, ridge, valley and penetration lengths
- Approved nails, starter, ridge pieces and adhesive
- Intake/exhaust net free area
- Controlled allowance for cuts and repairs