What is the maximum stair riser height for a deck in New Brunswick?

The maximum stair riser height for a deck in New Brunswick is 200mm (approximately 7-7/8 inches), as specified by the NB Building Code. This limit applies to all exterior deck stairs serving residential properties, regardless of whether the deck is attached or freestanding, and regardless of the total height of the staircase.

The 200mm maximum riser height works in conjunction with the minimum tread run of 235mm (approximately 9-1/4 inches). These two dimensions are directly related and exist as a pair because stair safety depends on the ratio between how high you step and how deep the tread is. A riser at the full 200mm with a tread at the minimum 235mm creates a fairly steep staircase, which is technically compliant but not always comfortable, particularly for taller deck heights where you are climbing many steps. Many experienced builders in New Brunswick target a riser height between 175mm and 190mm with treads of 250mm to 270mm, which produces a more natural walking rhythm.

Equally important is the uniformity requirement. The NB Building Code mandates that all risers within a single flight of stairs must be within 6mm of each other. This is a tight tolerance and one of the most common reasons deck stairs fail inspection. If your top riser is 185mm and your bottom riser is 195mm, you are technically within the 6mm range. But if one riser drifts to 178mm while another sits at 198mm, that 20mm difference exceeds the 6mm tolerance and will not pass.

The practical implication of the 6mm uniformity rule is that you must calculate your stair layout carefully before cutting any stringers. Measure the total rise from the finished deck surface to the finished ground level at the stair landing. Divide that total by your target riser height to determine the number of steps. Adjust until you get a riser height that divides evenly into the total rise while staying at or below 200mm.

For example, if your deck surface is 1,400mm above grade, dividing by 200mm gives you exactly 7 risers. That works perfectly. But if your deck is 1,450mm above grade, dividing by 200mm gives 7.25 risers, which is not a whole number. You would need 8 risers at 181.25mm each, which is well within the 200mm maximum and gives you uniform risers. The mistake many DIY builders make is forcing 7 risers into that 1,450mm height, which would require risers of approximately 207mm, exceeding the code maximum.

New Brunswick's climate adds a practical layer to riser height decisions. Lower risers with deeper treads provide better footing on icy mornings because your foot has more surface contact on each step. During winter months, snow accumulation effectively raises treads and shortens the apparent riser height, which can make steep stairs feel even steeper. Building at the lower end of the permissible riser range, around 175mm to 185mm, gives a more comfortable and safer staircase year-round.

The minimum tread run of 235mm is measured horizontally from the face of one riser to the face of the next, not including any nosing overhang. If you add a nosing, it projects beyond the tread face and does not count toward the 235mm minimum. Nosings are not required by NB code on exterior deck stairs, but they improve footing and are generally recommended.

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