Expert: Ted Barnhill (Principal, Design45 LLC) - 8/13/2008

Question
We are building a 2 story garage, with a bonus room above. It will be 24'wide, with a 8/12 pitch. Our intention is to have a 4' kneewall on the 2nd floor eave ends to raise the ceiling height. Our town requires us to follow IRC 2006, and wants a 55 lb snow loading on the roof. My question is how do I brace the kneewalls so that they don't "spread" under the often heavy snows we have here in NH?

Answer
Kim,

That's a lot of snow load - even more than we design for here in Minnesota!  There are several structural solutions to your issue.  You may use one or more of them in combination; which ones depend on your design goals.

1. Use a ridge beam.  This may be a rather large beam unless you use a midspan column, which is a nuisance in your garage.

2. Use collar ties, sometimes called collar beams, in conjunction with large rafters (as rafter bending may be an issue).

3. Balloon frame walls with continuous studs, or provide perpendicular cross walls to resist lateral thrust.

I recommend that you consult with a structural engineer to help identify the best solution for your project.  Good luck.  -Ted.