OBC 9.26.4: Essential Roof Flashing and Valley Standards for Ontario Construction
Sarah's Expert Insight
OBC Compliance Specialist
"In regions like London and Muskoka, the freeze-thaw cycle makes strict adherence to OBC flashing standards non-negotiable. At empcontracting.ca Inc., we often see that improper valley membranes and inadequate masonry counter-flashing are the leading causes of premature roof failure and interior water damage. My professional advice is to always prioritize the specified metal thicknesses and lap dimensions to protect your investment against Ontario's heavy snow loads and driving rains."
Understanding the Ontario Building Code (OBC) is vital for ensuring the longevity and weather-resistance of residential structures. Section 9.26.4 outlines the specific requirements for roof flashing, particularly at valleys and wall intersections, to prevent water ingress. For expert implementation, trust empcontracting.ca Inc. your construction contractor in London, Ontario.
9.26.4.3. Valley Flashing Requirements
Proper valley installation is critical for directing water flow. The OBC requires valley flashing to be installed over continuous sheathing. Key standards include:
Closed Valleys
Closed valleys are restricted on shallow slopes (less than 1 in 1.2) when using rigid shingles. They must consist of sheet metal, self-sealing composite membranes (polyethylene and bituminous material), or specific roll roofing at least 600 mm wide.
Open Valleys
Open valleys must be flashed with either a layer of sheet metal (min. 600 mm wide) or two layers of roll roofing. The code specifies precise nailing patterns and overlap widths to maintain a watertight seal.
9.26.4.4. Intersection of Shingle Roofs and Masonry
Where roofs meet masonry walls or chimneys, flashing and counter-flashing are mandatory. The counter-flashing must be embedded at least 25 mm into the masonry and extend 150 mm down, lapping the lower flashing by at least 100 mm. For sloped roofs, these must be stepped to maintain a 75 mm head lap.
9.26.4.5. Intersections with Siding and Other Wall Cladding
For walls clad in materials other than masonry (such as vinyl or wood siding), flashing must extend at least 75 mm up the wall behind the sheathing paper and 75 mm horizontally onto the roof surface. Along slopes, this flashing must also be stepped with a 75 mm head lap to ensure moisture is shed effectively.
For professional roofing and structural work that meets or exceeds these codes, contact empcontracting.ca Inc. your construction contractor in London, Ontario today.
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.