Warping of joists in a two way pitched roof? 1

[Loki]

We are designing a building with structural steel framing, open web joists and metal deck at the roof. The architect wants to pitch steel in two directions to achieve a 1/4" per foot slope. Does anyone have a feel for how much warping can be tolerated in the joists before it becomes a problem?

Because of the geometry of the footprint, there are a couple of areas where the pitch would be as much as 3" in 12' in two directions, which seems too much to me. I know this type of warping happens frequently and would appreciate hearing any thoughts or experiences that anyone could pass on.

Thanks!

 

[JAE]

I've done exactly what you are describing. We had a 50 foot bay where two orthogonal sides of the square bay were level and the other two were sloping down at 1/4" / ft. No problems...worked very well and made it easy to drain the roof. There also were no difficulties in laying down the deck. The slope is fairly subtle.