If you framing is solid and there is only one coarse of shingles in fair shape currently on the roof I would agree with Codeman, install the steel right over the shingles. But to take it one step further I'd suggest running 2/3 purlins 2' apart and in length with the ridgeline and placing 1.5" foam board in between the purlins. I did this on the shell of my entire 24 x 40barn when I built it and then Tyvek'd outside that and even before adding any additional insulation it could be heated easily with a woodstove and stayed cool in the summer as well. My neighbors across the street re-roofed their cottage home a few years back, which had about a 6/12 pitch shingled roof, and at my suggestion did the 2x3 (or 4 if they're cheaper) purlins with 1.5" right over their shingles and are thrilled with it. Less rain noise and with the increas in the R value the home is a lot more temperate.
The key to this on a low pitch roof is how well and sturdily your framing was done and if you aren't well qualified to judge this for yourself be sure to have an engineering study done. We have to do thisby law on every solar roof installation and a basicstudy on a moderate;y sized house usually comes in under a $1,000. Money well spent both for piece of mind ...and probably still less than it might cost to have the old shingles removed and properly deposed of
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06-27-2025, 06:25 PM
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