Commercial roof experts weigh in please
I am on the board of a local nonprofit organization. The building complex it has is an arrangement of flat-roofed boxes, all with parapets, and the roofing is in need of replacement.
Furthermore, a recent energy audit has shown there are considerable gains possible by adding insulation to the roofs or ceilings below.
Roofs are all hot mop type.
What range of cost might be needed, per square of replacement roof, to strip the roof to its deck, then screw down prefab panels in ridgid foam, and do a membrane roof atop? Let’s say we want to average two inches thickness of foam insulation.
Replies
r.s.mean construction estimator is a good place to start.
Gene
I did this with National Craftsman Estimator.
Since you are in NY I did labor at $60 hour.
Insulation is EPS. Most roofers use ISO board.
You can also get insulation that is tapered to improve the drainage of your roof.
I am not familar with that membrane. Most guys around here use PVC that is mechanically fastened and the seams are heat welded.
Rich
You don't have to strip the roof down to the deck. There might be some reason too, but it's not absolutely necessary.
Bob's next test date: 12/10/07
You're right, Jim.
I have since discussed this with a commercial roofer, and we've a plan to look at things in detail, once the snow melts.
Ideally, a way can be found to not only avoid stripping, but to realize what little gain there can be in insulation value by leaving the existing boardstock in place.
There are limits, however, to what can be done in doing a new roof over an existing, and there may be spots where at least one layer of modified torchdown might have to be cleaved away.
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"A stripe is just as real as a goddamn flower."
Gene Davis 1920-1985
There is a system called dura last (http://www.duro-last.com/) that will strip the stones, then lay the insulation, then install their custom made membrane system. The issue I would have is leaving a layer of flammable material (the old ashphalt) in there. If it won't affect your fire insurance rates, then I'd go for it. Bob's next test date: 12/10/07
not a roofer,but just had a job done. 2000sf 40 wide by 50 long ,parapet walls on 3 sides about 2' high,tore off a old rubber roof,and fiberboard to a metal deck. then install a sloped foam system to get some slope.seems it went from 8" to 2". they then put down a layer of fiberboard .then laid a .60 rubber roof. these guys did a really nice job. roof came in at 8500. [not including once it was tore off the metal deck was bad and had to be replaced,one of those things you don't know till your there,another 6000 for that] larry
if a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
Just finished that for a new building. 5000 sf, 4 ft parapet all the way around. 2 or 3" rigid foam (I forget what thickness, I'll check when I get to the office) then a layer of denshield, then the membrane. The denshield was primarily to provide stiffness so it could be walked on. Two layers of foam glued together with ribbons of great stuff (or whatever the generic term is) then the denshield was bedded in ribbons of great stuff, and 14 screws with washers per 4x8 sheet screwed to the metal deck. membrane was adhered to the denshield with water based adhesive on the flat, and solvent based adhesive on the parapet walls (solvent based because it sets quicker).
So how much? I forget. :) I'll check in a couple of days. The specs require that the mfgr send a factory rep to the site and inspect the roof before the job is accepted and the warranty begins.
"Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt