Experience 27 years licensed architect, work in 12 states. Currently working in Hawaii. Over 1000 buildings designed or worked on in a significant role
3 years quality control officer for Navy construction projects.
Education/Credentials Bachelor of Architecture, Cal Poly, San Luis Obispo, CA. 1977.
Question I have a low slope tar & gravel roof that is approx 3,000 sq ft. I live in Edmonton, Alberta so we get weather from 40 deg below 0 to 38 deg above. It is so busy in this area that you cannot even get a reputable roofer to come out to look at the problem and estimate the repair. I do not want to have to do this again in a few years so I was thinking of doing the following.
Scrape off as much of the gravel that I can to reduce the weight on the rool.
Screw 2" x 4"'s running down the slope on two foot centers with 9" roofing screws. (The roof consists of a pine decking that shows up as our ceiling. It then must have some sort of vapour barrier, then six inches of styrofoam insulation, I assume a couple layers of that paper type board and then the tar and gravel.) Then screw 5/8" plywood onto the 2 x 4's, cover with the recommended felt and finish off with a metal roof.
Does this seem like a good solution? I have talked to so many "roofing specialists" in the area and each one has no clue or they just want to install the type of roof that they sell. None of them seem to know what they are talking about. The one estimate for a rubber roof was $36,000.
Answer Aloha Michael,
Welcome to modern home repairs.
Well, you seem to have a relatively good plan, but a little light on the details. Not sure what the roofers in Edmonton are like.
Scrapping off the existing gravel would be a good first step. It would probably be a good idea to simply remove the existing roofing as much as possible, mostly to save weight. Changing roofing on flat roofs, especially in snow country is a serious issue. Any change in weights can have serious results. You should have the existing roof structure analyzed for its strength and how much more weight it can bear, assuming the standard snow loads for where you live.
I am assuming you want to get some insulation in this roof, both to save energy and the subsequent costs and perhaps to make the space itself a bit more comfortable. If so, adding some insulation is a very good idea. Given you have next to nothing now, any improvement will be good, but with Styrofoam having an R-Factor of about 5 to 6 per inch, you'd really want about 7" to 8" of the stuff to achieve the R42 ceiling recommended for an area like Edmonton. In fact, I'd recommend higher, more like 10" to 12" as energy costs are not going to go down. It's a one time cost now versus an ever increasing cost forever.
Anyway, you will need to have stringers that are as deep as the insulation, plus maybe an inch of air space.
So, first would be a vapor barrier, then the stringers and insulation, then 1/2" to 5/8" plywood, then roofing paper/felt and then the roofing itself.
Most any competent roofer should get that. However, I imagine due to the short building season there, they are all very busy during the summer.
