flatroof to pitched. Insulating above old roof - Contractor Talk - Professional Construction and Remodeling Forum

Red Adobe · 07-10-2009, 09:46 PM

Insulation is not my trade so I'd likw to pick ya'lls brain

Southern New mexico so heating isnt near as much of an issue as cooling

I'm bidding to put a pitched metal roof over an existing built up flat roof. There is no isulation in the ceiling at all and from 6" to 9" cavity from top of plaster to bottom of deck sheathing. Thru the hallway I can blow cellulose into the whole ceiling. (foam would be better but with veggas and plaster it would be a nightmare for myself and the HO ) There is no pipes,duct work or reccessed lighting. I am rewiring it all but its all in flex conduit

I'm using metal and a radiant barrier under that for the pitch but I am wondering if blowing say 10-12 inches on the top of the old roof is worth doing? I have called cacoon insulation and another co and they have no idea saying they have no case studies on such a application over a roof.

being a tar and gravel I plan on shoveling off about 4 inches of peagravel
to compenstae for the weight of the new pitched roof I'm wondering about any possile reaction of cellulose and the old roof tar????

Thank for any thoughts on this

SLSTech · 07-10-2009, 09:59 PM

Why not stick with a flat roof - foam with a white reflective coating - that is mainly what is used in AZ

Red Adobe · 07-14-2009, 10:30 AM

Way too many nightmare leaks are found on older flat roofs in this part of the country. I used to patch roofs for people and got away from it many years ago. The only way i will step foot on a flat roof is if its getting replaced ......

The other reason for pitched is overhangs. 17" on southside, its just right to shade the entire wall in summer and let the passive solar work in winter. I'm going out 10' on west side for a patio Outdoor kitchen and hot-tub area.

Since I'll have the machine there to do the interior ceiling anyway, Im going to blow the top as well it will only be $200 for the extra cellulose. The only thing I have heard from anyone is it wont hurt anything
They did suggest that if I took the rock off that I put a permiable housewrap over the "tar" just as a precuation to seperate the tar from the cellulose