Expert: Richard Taylor, AIA - 8/3/2011

Question
I have to replace treads for my house which has about 26 treads going up 2 floors; half of them winding.  The township building inspector won't tell me what he wants.  I have tried to find specks on iccsafe website but it is overwhelming.

Can you put it in laymans terms for me?  Or point me to some specks which will make sense.

nose must pass the riser by 1.5 " no tread less than 26" wide........

the way they write it about the winders is hard to understand

Answer
Good morning Joseph - thanks for your question.

Stairs are a fairly complex exercise in geometry, and the constantly-changing building codes don't make that any easier!

For starters, you need to know what your local jurisdiction has adopted; not all adopt all parts of the model codes.  So while the IRC code might specify a particular stair geometry, your local area may not adhere to that.

The model code specifies the maximum height of a riser (the vertical part); the minimum depth of the tread (the horizontal part); the minimum width of the stair; handrails, nosings, winders etc.  All of these factors work together to create a code "safe" stair.

The 2009 IRC requirements include:

Max riser height: 7 3/4"
Min tread depth: 10"
Nosing projection: 3/4" to 1 1/4"
Min stair width: 36"
Min headroom above any part of stair: 80"

In addition, riser heights and tread depths may not vary more than 3/8" on any one run of stairs.

"Winders" are a bit tricky - at 12" from the "inside" of the stair, the tread depth must be at least 10"; the narrowest point of any tread may not be less than 6".  That effectively negates the winders you find in many older homes, but that requirement has been in place for quite a few years now.

In your case, if you are just replacing the tread surface - not the whole stair - then in my opinion you only need to meet the nosing requirement.  That might be the question you should ask the inspector.

Hope this helps!

Richard Taylor, AIA
www.rtastudio.com
www.rtastudio.blogspot.com