Ducts in attics/crawlspaces: sealing and insulation

Avoid losses, condensation and poor comfort when heating/cooling ducts pass through cold or unconditioned spaces.

VERT / GREEN

Map routing, joints, returns and sections outside conditioned space.

JAUNE / YELLOW

Leaky or poorly insulated ductwork can hurt comfort and efficiency even when equipment operates correctly.

ROUGE / RED

Active condensation, wet insulation, crushed/disconnected duct or contaminated crawlspace air drawn into return: correct the cause before simply adding insulation.

Quick triage

Ducts run through unheated attic/crawlspaceCondensation/wet duct insulationReturn air open to dirty/unconditioned areaDucts sealed/insulated/documented

What the professional checks

The HVAC professional checks leakage, insulation, jacket vapour control, pressure, airflow, returns, condensation and envelope interaction.

Official sources

RNCan — conduits scellés et isolés

Checked 2026-08-23

Related path

Continue with the right tools

These links connect this page to the next useful checks and decisions without repeating the full content.

Connect symptoms to the enclosureStart from condensation, staining, odours or movement before choosing a repair.Open →Adapt the enclosure to climateConnect heat, cold, water, wind and wildfire to building priorities.Open →Assess overall resilienceReview water, climate, safety, autonomy and records with a local score.Open →Screen hazardous materialsIdentify situations where work should stop and testing is needed before disturbance.Open →Open climate guidanceReview climate constraints relevant to assemblies and materials.Open →

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Systems to check before closing the work

This section connects envelope, air, fire, structure, water and code instead of treating each project in isolation.

Renovation dependenciesEnvelope and condensationCode versions

Explore: Remaining system checks not to miss

Remaining system checks not to miss

This section covers issues that can block a project, cause a loss or become expensive once concealed.

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Explore: Specialized systems to cross-check

Specialized systems to cross-check

This section completes gas, soil, water, fire, climate and structural interfaces.

Crawl space

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This section connects systems that become costly or regulated when a primary project triggers them.

Hot tub structure + electrical

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This section covers interfaces that become important when multiple home systems interact.

Skylight/tubular daylightingSIP/ICF

Explore: Often-overlooked service interfaces

Often-overlooked service interfaces

This section connects systems that cross utility, plumbing, HVAC, envelope and metering boundaries.

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Explore: Finish and service details to verify

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This section connects small details that become costly once finishes are closed.

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