Rules
Natural insulation vapour barriers: what Canada's code requires
Natural insulation vapour barriers in Canada follow provincial codes, not the US IRC. Here is who enforces them and what a permit file needs before approval.
What to take away
- The National Building Code of Canada caps natural insulation vapour barrier permeance at 15 ng/(Pa s m2), about 0.26 US perms, in houses and small buildings.
- Provinces adopt that model with amendments. Ontario, British Columbia, Alberta and Quebec each publish their own edition, and no two read alike.
- Natural insulations are not exempt. Hemp batts from NatureFibres, cellulose from Greenfiber, and wood fiber boards from Steico or Gutex still need a compliant assembly or an accepted alternative solution.
- Municipal officials enforce the rule at permit stage. Insurers, provincial new home warranty programs and some lenders add conditions the code does not.
- Skipping the paperwork can mean an order to expose finished walls before occupancy is granted.
- Permeance figures belong on a data sheet in ng/(Pa s m2). A marketing claim about breathability is not evidence.
The natural insulation vapour barrier question in Canada starts with a model document that becomes law only when a province adopts it. Most search results quote the US International Residential Code instead, which uses perms and climate zones and follows a state-by-state adoption path. The two are not interchangeable.
The permeance number in Part 9
Part 9 of the National Building Code covers houses and small buildings up to 600 m2 in building area. Section 9.25 covers heat transfer, air leakage and condensation control.
Article 9.25.1.1 requires a vapour barrier in residential occupancies. The performance bar is a permeance of not more than 15 ng/(Pa s m2), which equals roughly 0.26 US perms.
The code says vapour barrier. Building science prefers vapour retarder, because the job is to slow diffusion rather than stop it. A 6-mil polyethylene sheet meets the number easily, and so does a foil facing on some rigid boards.
Variable permeance membranes also pass. CertainTeed MemBrain, Siga Majrex and Pro Clima Intello Plus tighten in winter and open in summer, which suits a wall that has to dry.
Hygroscopic insulations do not meet those numbers on their own, and that is where the friction starts. Hemp batts from NatureFibres in Quebec, cellulose from Greenfiber or Applegate, and wood fiber boards from Steico or Gutex all depend on the assembly around them.
The Wikipedia entry on vapour barriers covers the Canadian requirement and how natural materials sit around it.
Who has jurisdiction over a vapour barrier in Canada
The Canadian Commission on Building and Fire Codes develops the model code. The commission sits inside the National Research Council of Canada in Ottawa and publishes the National Building Code, the National Plumbing Code and the National Fire Code. Ottawa does not inspect your basement.
Provinces and territories adopt their own editions. Ontario enforces the Ontario Building Code, British Columbia the BC Building Code, Alberta the Alberta Building Code, and Quebec the Code de construction du Quebec. Each starts from the national model and then amends it, so the text differs across the country.
Municipalities enforce through permits and site inspection, and the local official is the authority having jurisdiction. Insurers, provincial new home warranty programs such as Tarion in Ontario and BC Housing's Homeowner Protection Office, and some lenders add private conditions.
The NRC codes centre publishes the model documents and the adoption picture by province.
Who decides what
- Federal: writes model code, no inspection
- Province: adopts and amends the code
- Municipality: permits and site inspection
- Private: insurers, warranty, lenders
| Decision | Who decides | Form it takes |
|---|---|---|
| Minimum vapour retarder permeance of 15 ng/(Pa s m2) | Province, through its adopted code | Code article, such as NBC 9.25.1.1 |
| Acceptance of an unusual assembly | Municipal authority having jurisdiction | Stamped drawings or a designer report |
| Insurance and warranty conditions | Private bodies such as Tarion and BC Housing | Policy wording and warranty terms |
| Vapour retarder products that clear the limit | Manufacturer data sheets | 6-mil polyethylene, CertainTeed MemBrain, Siga Majrex, Pro Clima Intello Plus |
| Higher energy tiers | Province, by code edition | BC Energy Step Code, Ontario SB-12, NBC 2020 Tiers 1 to 5 |
What a permit application has to contain
- Scaled wall sections marking the vapour retarder position in each assembly
- Product data sheets stating permeance in ng/(Pa s m2), not just a marketing claim
- Ventilation and humidity notes for bathrooms, kitchens and laundry
- An alternative solution report where the assembly departs from Part 9
- Foundation and basement details, signed where a designer is involved
Reviewers read those documents against the adopted code, not against brochures. A designer-stamped alternative solution report in Ontario typically costs a few hundred dollars for one wall section and low four figures for a whole house package.
Where a declared number drives the decision, How to read an EPD is worth doing before you accept a manufacturer summary.
Permit file contents
- Scaled wall sections marking vapour retarder
- Product data sheets with permeance figures
- Ventilation and humidity notes
- Alternative solution report if departing Part 9
- Signed foundation and basement details
Where the Ontario, BC, Alberta and Quebec codes diverge
Ontario, British Columbia, Quebec and Alberta each publish a code that begins with the national model and then adds energy and airtightness provisions. Ontario's Supplementary Standard SB-12 sets energy targets for houses. British Columbia runs the BC Energy Step Code, and Step 5 is the top rung.
Alberta adopted the Alberta Building Code 2019, based on the 2015 national model. Quebec works under its own regulation on the energy efficiency of buildings. The 2020 National Building Code adds five energy tiers that provinces can adopt in stages.
Hygroscopic insulations are treated the same way in principle: prescriptive compliance, or an accepted alternative. In practice the paperwork differs, and the province decides which evidence a reviewer will accept.
Newer products face a further hurdle, because a material with no long track record has no prescriptive path to cite. Mycelium insulation panels are the clearest live example, and reviewers still treat them as research rather than code.
Example: an alternative solution refused in Guelph, Ontario
A homeowner outside Guelph, Ontario submits drawings for a hemp-insulated addition with no polyethylene layer, arguing that the wall dries outward. The package includes a product brochure and a link to a blog post. The municipal reviewer declines the assembly, because equivalent performance was not demonstrated under the alternative solution route in Article 1.2.1.1.
The permit stays open, the designer starts again, and the insulation itself was never the problem. The hemp insulation R-value per inch figure on that brochure was never in dispute either.
What non-compliance actually triggers
Most breaches do not end in a fine. A building official can order the interior finish removed so the assembly can be inspected, and occupancy withheld until the work complies.
An insurer can also refuse a moisture or mold claim where the built wall departs from the drawings on file. That risk is quiet and lasts for the life of the policy.
Basements are where this bites hardest, partly because moisture and soil gas overlap. Radon-resistant building materials covers the details provincial codes leave to the builder.
Compliance is checked after the walls are closed, not before.
