Expert: Mark Sundberg - 7/27/2009

Question
I live in the northeast and my roof slope is 3/12.  I need the snow to slide off.  I would like a slope of 7/12. Is it possible to  build a new roof over the existing one one ?  Is this an option without tearing old roof  and rafters completely off.

Answer
Hi Michael,

Yes, it's certainly possible, but may depend on how your building is constructed. But my guess is it would be. As to having to tear off the existing, probably not, though you'd probably want to cut off the existing eave overhangs at the wall line to allow the new roofing to extend out and down. Being it's at a steeper slope, it would have to go through the existing eaves.

Otherwise, you could leave the rest in place except for any other interferences.

Just build up a plate on your existing ridge line, then build a short stud wall up to the new ridge line. At the wall lines, lay another plate to take the new rafters. If the spans are more than 10' to 12', you will probably want to add additional purlin lines, again, just a plate on the existing roof (maybe cut away the roofing at where these plates are to get a good seating and connection) midway or so between the wall and the ridge and again, build up a small cripple stud wall to support the new rafters mid-span.

That's about it though I would suggest you have somebody knowledgeable about such things take a look at the existing structure to make sure it can take the additional load. Most likely it can, as the additonal load will be only the weight of the new structure which will be fairly light, plus you will get a 4 pounds per square foot credit off the live load. My guess is this would end up adding maybe 3 to 5 psf to the total load. Hopefully the structure is adequate for that.