MarkhamBuilding InspectionsInspections

Supply and Return Air Ducts in Exterior Walls

Published by City of Markham

This is the City of Markham’s document, as published on its website on 18 October 2026. The municipality may have changed it since: check the current version at the source. Legal notice

Type: Guide
Published by: City of Markham
Date: January 1, 2025
For: builder
Building types: All building types
Pages: 3

Overview

Markham's three-page Builder Tip Issue No. 19, dated January 1, 2025 and updated to the 2024 Ontario Building Code, on heating ducts and return-air chases built into exterior walls or walls next to an attached garage; one of the City's housing tips. It quotes Articles 9.25.2.1., 9.25.2.3., 9.25.3.1., 9.25.3.3. and 9.25.4.1. on insulation, its protection, air barriers and vapour barriers. The Objective cites the 22 °C indoor temperature and illustrates two ways to keep the wall insulated: a 2x6 stud cavity, or 2x4 studs with exterior rigid insulation.

What it covers

9.25.2.1. Required Insulation
9.25.2.3. Installation of Thermal Insulation
9.25.3.1. Required Barrier to Air Leakage
9.25.3.3. Continuity of the Air Barrier System
9.25.4.1. Required Barrier to Vapour Diffusion
Objective

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