2024 Ontario Building Code Guide: Built-up Roofing Requirements (OBC 9.26.11)
Sarah's Expert Insight
OBC Compliance Specialist
"In the variable climates of London, Oakville, and Muskoka, the integrity of a built-up roof depends entirely on the precision of the bitumen mopping and cant strip detailing. As empcontracting.ca Inc. your construction contractor in London, Ontario, we prioritize the three-layer minimum and proper aggregate surfacing to ensure your flat roof withstands heavy snow loads and freeze-thaw cycles common to our region."
Understanding the intricacies of the 2024 Building Code Compendium is essential for high-quality flat roof installations. If you are looking for compliance and durability, empcontracting.ca Inc. your construction contractor in London, Ontario, provides expert guidance on these standards.
Material Standards and Aggregate Surfacing (9.26.11.3 - 9.26.11.4)
According to OBC 9.26.11.3, bitumen roofing felts must be at least No.15 felt. For surfacing, clean and dry aggregate like gravel, crushed stone, or slag is required, sized between 6 mm and 15 mm.
Minimum Weight Requirements
- Gravel/Crushed Stone: 15 kg per square metre.
- Crushed Slag: 10 kg per square metre.
Installation and Layering Protocols (9.26.11.6 - 9.26.11.7)
Built-up roofing must consist of at least three mopped-down layers of roofing felt flood coated with bitumen. During hot process applications, each layer must overlap the previous one, ensuring no felt-to-felt contact. Layers must be laid free of wrinkles and broomed to ensure complete adhesion.
Roofing Over Wood-Based Sheathing (9.26.11.8)
When applying roofing over wood, plywood, or OSB, an additional base layer of felt must be laid dry with a 50 mm headlap. However, this dry layer can be omitted if the sheathing joints are taped and the deck is primed with asphalt.
Attachment and Cant Strips (9.26.11.9 - 9.26.11.10)
Secure attachment to the decking or insulation is mandatory. At roof edges, cant strips must be installed, with at least two plies of the membrane carried over the top. Flashing must extend over the cant strip and be shaped to form a proper drip edge.
Disclaimer: This content is generated from the Ontario Building Code for educational purposes. Always consult with a licensed professional engineer or your local building department before starting any construction project in London, Ontario.