Insulating Existing Walls in Ontario: Options, Costs and Moisture Risks
A practical guide to insulating existing walls in Ontario homes: dense-pack, interior and exterior options, typical costs, moisture risks and when it pays.
, 6 min read
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Last reviewed November 2, 2026
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A practical guide to insulating existing walls in Ontario homes: dense-pack, interior and exterior options, typical costs, moisture risks and when it pays.
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Weatherstrip and insulate the attic hatch
An unsealed attic hatch is a major air leak in many homes. Weatherstripping plus a piece of rigid foam on top costs under $50.
Air seal and insulate basement rim joists
Rim joists are often leaky and uninsulated. Sealing them with foam and adding rigid insulation can noticeably reduce drafts and heat loss.
Replace worn door weatherstripping and sweeps
If you can see daylight or feel a draft around an exterior door, the seals need work. New weatherstripping costs roughly $20–$50 per door.
Caulk gaps around pipes, wires and vents
Small holes where services pass through walls and ceilings add up to a large leak. Use fire-rated sealant around chimneys and flues.
Use window insulation film on drafty windows
Shrink-film kits cost a few dollars per window and reduce drafts and heat loss through old single-pane glass for the winter.
Top up attic insulation to R-50 or more
Many older Ontario homes have only R-12 to R-20 in the attic. Upgrading toward R-50 to R-60 often cuts heating and cooling losses noticeably, and HRS has offered up to $1,250 for standalone attic insulation.