A decision you can check
- 01
Start with the roof covering
Use an underlayment approved for the selected shingles, metal, tile or other system and compatible with the deck.
- 02
Map vulnerable zones
Identify eaves, valleys, low slopes and penetrations that may require self-adhered or enhanced water protection.
- 03
Plan exposure and fastening
Check maximum exposure duration, cap or fastener requirements, lap dimensions and wind conditions during construction.
- 04
Coordinate ventilation and flashing
Underlayment is one drainage layer; complete the eave, ridge, wall and penetration details as a coordinated roof system.
Write a specification someone else can check
Temporary dried-in status is not the same as a finished weatherproof roof.
Some high-temperature metal-roof applications need specifically rated membranes.
- Start with the roof covering
- Map vulnerable zones
- Plan exposure and fastening
- Coordinate ventilation and flashing
Convert the decision into quantities
Enter the measured geometry in the Roofing Calculator, replace defaults with the selected product coverage and round only at the final purchasable unit. List accessories and preparation materials separately so a coverage change does not silently scale unrelated items.
Roof work has serious fall risk and should use compliant professional protection and access.
Verify at order and delivery
Check the exact local designation or product code, performance class, size, colour or batch where relevant, stated coverage, yield, density or capacity, ordered quantity and accessory compatibility on the written order. Inspect delivered roof covering before installation and isolate damaged or mismatched material while return and replacement options remain open.
What usually throws the order off
- Comparing warranty years without system scope
- Reusing incompatible flashing
- Treating underlayment as finished roofing
- Accessing the roof for DIY measurement
Frequently asked questions
What must the roof covering specification identify?
Make the scope checkable against these decisions: start with the roof covering; map vulnerable zones; plan exposure and fastening; coordinate ventilation and flashing. Record the exact local designation or product, performance class, dimensions, finish where relevant, accessories and controlling technical document.
Which calculator default changes after product selection?
Replace whichever default the exact roof covering controls—coverage, yield, density, dimensions, package quantity or capacity—while keeping the verified project geometry unchanged.
Who should approve a substitution?
The owner and responsible designer or installer should confirm in writing that the substituted roof covering preserves required performance, appearance, compatibility, installation method and documented supplier or project acceptance criteria.
Technical references
These references support the measurement and planning method. Product instructions, the site and applicable local requirements control the final installation.