The 2020 Model Codes: What Changed

A new edition of the model codes lands every few years, and the reaction is usually either that nothing has changed or that everything has. Both are wrong. Most of the document carries forward, and the changes concentrate in a few areas where the technical committees have been working.

For the 2020 edition those areas were energy, accessibility, radon and mass timber. Those are the parts most likely to change what you can build.

Where the changes landed#

The energy change is the one with the longest tail. Moving from a single compliance threshold to tiers set up a structure where jurisdictions could require higher performance over time without rewriting the code each time. That structure is what later step codes and tier requirements build on.

What it meant for a house#

For a typical single-family build the practical effects came through the envelope and the radon rough-in. Higher effective insulation values pushed exterior insulation and better airtightness detailing into ordinary construction rather than leaving them to high-performance builders.

The radon provisions were modest in cost and significant in intent: put the pipework and the sealed sub-slab layer in during construction so that a system can be completed later if testing shows it is needed. Doing that at the framing stage is inexpensive. Retrofitting it is not.

The accessibility changes were felt mainly outside housing. Barrier-free provisions in the model codes largely address buildings the public enters, so a single-family house sees little of it. Multi-unit residential is where the effect shows up, in entrances, corridors, door widths and washrooms.

Taken together, the edition is a good illustration of how these documents evolve. Nothing in it reinvents house construction. It tightens the envelope, adds a cheap provision against a known health risk, opens a path for a structural material, and cleans up wording in a hundred places nobody notices.

Mass timber had little effect on houses and a large effect on what became possible in mid-rise construction, opening a path for wood buildings at heights that previously required concrete or steel.

How to read a new edition without reading all of it#

Nobody reads a code cover to cover. The efficient approach is to work from the change documentation rather than the code itself. Publishers issue lists of technical changes between editions, and provinces publish their own summaries when they adopt.

Those documents tell you which clauses moved and why, which is far more useful than comparing two books. They also flag the changes that were contentious, which tends to correlate with the ones that will affect your work. Industry associations publish their own summaries too, usually aimed at a particular trade, and those are often the fastest way to see what a change means on site rather than on paper.

The other habit that helps is watching for provincial bulletins after adoption. A new edition always generates interpretation questions, and the answers arrive as bulletins over the following year rather than as amendments to the code.

Common questions#

Does an older permit stay under the old edition?

Generally yes. The edition in force when the application was made normally governs the project through to completion, even if a new one takes effect during construction.

Do the model codes cover renovations?

They cover new work, and provinces set rules for how much of an existing building comes into scope when you alter it. That part varies more between provinces than the technical requirements do.

Do the tiers mean I have to build to the highest one?

No. Tiers give jurisdictions a ladder to require higher performance over time. What applies to you is whichever tier your province or municipality has set, and that can differ by building type.

Does a new edition apply to my existing house?

No. Buildings are assessed against the code in force when they were built. New editions govern new work.

How do I know which edition applies to my project?

Ask the building department. During a transition the usual rule is that the edition in force when the permit application is made governs the project.

Why do provinces not adopt at the same time?

Adoption requires a regulatory process, and often consultation, training and industry lead time. Provinces set their own priorities and schedules.

Where do I find what changed?

Start with the published list of technical changes for the edition, then your province’s adoption summary. Comparing the two books directly is slower and less useful.

Are the changes always more restrictive?

Not always. Editions also relax provisions where evidence supports it, and mass timber is a good example of a change that permitted more rather than less.