Understand the existing ventilation layout
Identify the vents already present at the gables, soffits, ridge and roof. Gable openings can admit or exhaust air as wind and pressure change; describing them as exhaust-only vents is too simple. Adding another opening does not necessarily improve the intended airflow.
Before changing vents, check whether the roof is designed as a vented or unvented assembly. Roof shape and separated attic spaces matter. Document condensation or leaks so ventilation changes address an observed problem.
Use net free area, not grille dimensions
A vent’s gross outside dimensions include its frame, louvers and insect screening. Net free area describes the unobstructed area available for airflow and should come from the product data. Two vents of the same outside size can provide different ventilation.
Do not use a generic ventilation ratio as a complete Ontario specification. Have the applicable roof design and code requirements checked, including the location and distribution of openings and any separate attic spaces.
Plan the opening, flashing and access
Check existing openings for blockage, painted louvers, damaged screening and water staining. If the opening must be enlarged, confirm the framing implications before cutting. A replacement should fit the wall drainage detail as well as the siding appearance.
Record the product, net free area and flashing approach in the scope. Coordinate any change to ridge or soffit vents, and obtain photos of concealed work. Air sealing below the attic and resolving roof leaks remain necessary when they are the source of moisture; a new gable grille is not a universal remedy.
Technical references for this guide
- Natural Resources Canada: Keeping the Heat In — roofs and attics — Gable ventilation can suit different attic configurations; moisture control includes air sealing.
Sources & References
- Ontario Building Code — Relevant Standards & Guidelines
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Discuss your exterior project
Select the exterior work and note the current material and repair or replacement needs.
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