Basement Stairs When You Finish a Basement: What the Alberta Code Asks For
Rise, run, headroom, width, handrails, guards and the 3-way switch for a basement stair under the Alberta code, and what happens to an old stair at permit.
By David Hutten, Owner, Green Ladder Contractors
Under the Alberta code a basement stair can have a rise of no more than 200 mm (about 7 7/8") and a run of at least 255 mm (about 10"), with 1950 mm (about 6' 5") of headroom and a width of at least 860 mm (about 33 7/8"). Finishing the basement also ends 2 exemptions an unfinished one has, so the stair needs a light switch at the bottom and finished treads.
The basement stair is the one part of a basement development that was already there before anybody drew a plan. In a lot of older Red Deer homes it was built when the basement was a furnace room and a place to keep the canning. So it tends to be steeper, narrower and darker than the stairs between the main floors, with a beam or a duct across the top where your head goes.
Here is what the Alberta code asks of that stair, which rules switch on when the basement is finished, and what happens to an older stair at permit.
The numbers for a basement stair in Alberta
The National Building Code 2023 Alberta Edition, in force here since May 2024, treats a stair inside a house as a private stair. Table 9.8.4.1 sets the rise, measured nosing to nosing, at no more than 200 mm (about 7 7/8") and no less than 125 mm (about 4 7/8"). Table 9.8.4.2 sets the run at no less than 255 mm (about 10") and no more than 355 mm (about 14"). The tread itself can be up to 25 mm (about 1") deeper than the run, which is where the nosing lives.
The City of Red Deer puts the rise on its own list of design considerations for every basement development - consistent through the flight, with no rise over 7 7/8".
Consistent is the word that catches people. Risers can vary by no more than 5 mm (about 3/16") between neighbours and 10 mm (about 3/8") across the whole flight, and the same goes for the runs. A subfloor and new flooring at the bottom of the stair raise the floor, and every bit of that comes off the bottom riser. So the flooring thickness and the bottom step get worked out together, early in the plan.
How much headroom does a basement stair need?
1950 mm (about 6' 5") for a stair serving a single house, measured straight up from a line touching the tread nosings to the lowest thing above it. In an older basement the lowest thing is usually the floor framing at the top of the stair, a beam, or a duct someone ran across the opening years later.
Where the basement is a secondary suite, the code allows 1850 mm (about 6' 1") under beams and ducting (the rest of the suite rules are in our basement suite post).
How wide does it have to be?
At least one stair between each floor level in a house has to be 860 mm wide (about 33 7/8"). A handrail and its brackets can project up to 100 mm (about 4") into that width.
Handrails
Inside a house, a stair narrower than 1100 mm (about 43") needs a handrail on at least one side. An interior stair with 2 risers or fewer does not need one at all, and a basement stair is always longer than that. The City of Red Deer lists continuous handrails on all flights as a design consideration for basement developments.
The rail goes 865 mm to 1070 mm high (about 34" to 42"), measured from the line of the nosings. It has to be graspable from the bottom riser to the top riser, it can start from a newel on the bottom tread, and it needs 50 mm (about 2") of clearance from the wall behind it.
The attachment is spelled out too. Screwed into studs or blocking, the code deems a handrail strong enough where the fastening points are no more than 1.2 m (about 4') apart, the first one at each end is within 300 mm (about 12") of the end, and each point has 2 No. 8 wood screws going at least 32 mm (about 1 1/4") into solid wood. On a stair with drywall going up beside it, that blocking goes in while the wall is still open.
Guards on an open side
Plenty of basement stairs are open on one side for part of their length. Any side not protected by a wall needs a guard wherever the walking surface is more than 600 mm (about 24") above the floor beside it. On a typical stair that leaves the bottom 3 treads or so without one.
Inside a house a guard has to be at least 900 mm high (about 35 1/2"), measured on a stair from the line of the nosings. Openings in it can't pass a 100 mm ball (about 4"), and the triangle formed by the tread, the riser and the bottom rail can't pass a 150 mm ball (about 6"). An open side at the top, where the stair drops into the basement beside a hallway, needs one too.
Lighting and the second switch
Every stairway has to be lit. For a stair with 4 or more risers in a house, Article 9.34.2.3 calls for 3-way switches at the head and the foot of the stair controlling at least one light.
There is an exception, and it is the one most unfinished basements are using. A basement with no finished space (and no outside entrance or built-in garage off it) can have its stair light on a single switch at the top. Finish the basement and that exception is gone, so the electrician needs a switch at the bottom. The electrician roughs it in while the wall at the foot of the stair is still open.
The treads themselves
One more rule that switches on with the finishing. Article 9.8.9.6 asks for treads and landings on interior stairs in a house to be finished in hardwood, vertical grain softwood, resilient flooring or something equivalent, and it makes an exception for stairs to unfinished basements. The rough construction treads a lot of basement stairs still have were fine while the basement was unfinished.
Does an old stair have to be brought up to code?
The Alberta code does not set out to make existing houses comply retroactively. Article 1.1.1.2 of Division A says the authority having jurisdiction shall accept construction that lawfully exists in Alberta, that renovation must not decrease the level of life safety, and that the authority may accept existing construction that does not fully comply and may place conditions on it. The note under that article says the code is not intended to be applied retroactively to existing buildings, and also that parts being reconstructed or modified are built to the current code.
So a stair that is left alone is in the inspector's hands, and a stair that gets rebuilt is built to today's numbers. In Red Deer that means the Safety Codes Officer on your building permit. The City's own basement page already lists handrails and a maximum rise for every basement development, so it is sensible to expect those 2 to be looked at, and a missing guard on an open side is likely to be in the same conversation. How far the officer goes beyond that on a particular stair is their call. We would find that out at permit, before any framing goes up.
Rebuilding is where the arithmetic matters. Take a basement with 13 risers at the 200 mm maximum. That is 12 treads, and at the 255 mm minimum run they need about 3060 mm of horizontal run (about 10'). If the existing stair fits in less than that, a replacement needs more floor at the top or the bottom, or a landing and a turn, and that changes the basement layout.
The American figures you will read online
A lot of stair advice online is written to the American residential code, and several of its numbers differ from Alberta's.
Headroom there is 6' 8", where Alberta asks for 1950 mm (about 6' 5"). That 3" comes up on a lot of older Red Deer stairs.
Maximum rise there is 7 3/4", where Alberta allows 200 mm (about 7 7/8"). The minimum run is 10" in both.
Width there is 36", where Alberta asks for 860 mm (about 33 7/8").
Handrails there go 34" to 38" high and are required at 4 risers. Here the range runs to 1070 mm (about 42"), and inside a house they are required on anything over 2 risers.
Guards there start at 30" above the floor below. Here the trigger is 600 mm (about 24").
Before the framing goes up
It helps to measure the stair first - rise, run, headroom and width - and look at what the finished floor will do to the bottom step. From there you can decide whether the stair stays, gets a handrail and a guard, or gets rebuilt (a rebuild can move a wall, so this one goes early). The blocking for the rail and the switch at the bottom then get roughed in while the walls are open.
We are happy to measure an existing basement stair and set it against these numbers before the plan is drawn, and on an older house it is usually worth doing first.
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David Hutten
Owner, Green Ladder Contractors
David Hutten started building at age 10 and has more than 30 years of hands-on construction experience. Green Ladder Contractors renovates kitchens, bathrooms and basements and builds home additions, garages and decks across Red Deer and Central Alberta.
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