Retrofitting a Roof with Raised-Heel Trusses
We will need a new roof soon and I am wondering if it would be cost prohibitive to retrofit our house with raised heel trusses.
We live in Michigan, zone 5 and we do have problems with ice damning sometimes and I would love to add more insulation over the ceiling near the exterior walls.
Our roof currently has asphalt shingles and the roofer said the plywood used for the roof was too thin so we have some sagging between the supports and he would need to replace it with thicker plywood.
I like the idea of a metal roof because I would like to get solar panels, but I do worry that it might make the roof too slippery to clean the gutters safely.
Can anyone tell me if it is even possible to do a retrofit with raised heel trusses? Would it be too expensive?
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I would balk at the cost to retrofit your house with raised heel trusses. Might as well move. You could install a metal roof over purlins nailed to your current framing, making the issue of inadequate decking moot. Of course, you would have to use a metal roof product that can span the purlins. You can insulate with cellulose at the attic floor level, using baffles to maintain ventilation of the attic, or insulate at the roof, probably spray foam.
You could condition the attic using 4" R20 rigid foam on top of the roof decking, then purlins screwed to rafters, and then install your metal roof on top. Under the roof decking, you need 8.25" R29 min. ocSPF. Make sure you seal the attic perimeter really well. I would think that's a lot less expensive than a total reroof with heel trusses.
Where are all the roofers and builders that know how to put rigid foam on top of the roof? I haven’t found any in Nashville...
You won't find it.
The closes you can get is have somebody that does framing come in and install nailbase panels over the existing roof than have the roofer come out and install the metal.
Generally with older houses, the lowest cost option is spray foam. Not green, but it works.
Usually ice dam issues are more to do with air leaks than insulation. I would do a bit of blower directed air sealing before looking at increasing the insulation, there is a good chance this will fix your issues. There generally is no ROI on insulation upgrades outside of blowing in some extra loose fill into the atti.
Unlike the others, I don't think it's completely crazy, in general, to replace the whole roof system. Installing trusses can go quickly compared to fussy detail work. But given your large overhangs, you don't actually have that much of a thermal weak point at the perimeter--the insulation depth above the exterior walls isn't so bad. Given that and the high prices for lumber right now, I'd focus on excellent air sealing of your attic floor, a good bafffle system, and then plenty of cellulose on the attic floor. While the roof decking is off is a great time to seal the tops of the exterior walls without crawling around an attic.
I agree with Charlie. And check how much attic venting you have currently. That could be the problem.
If you need a new roof and supposedly the plywood is too thin and will be changed anyway, then the only thing left is trusses. Trusses are "cheap". BUT, if you install raised heel trusses on your style of roof/building, you will dramatically change the architectural look of your house. For that reason alone I'm not sure I would do it in your situation.
As for metal roofing, I don't think it would compliment your style of house. And too many slopes over doors and walkways, so you would need a bunch of commercial style ice brakes, which in my opinion are ugly as sin, especially for an urban residence.
I'm still trying to think through the implications, but i agree with the rest of the posters who have responded. Unless it was somehow possible to leave the old trusses in place, and sister raised-heel trusses in between, don't you end up having to replace:
- All the ceilings in the house.
- re-route any wiring that is run in the attic.
- Extend the siding to cover the heels.
- New soffits.
- all new insulation
When you could just put down another layer sheathing and make up for the lack of insulation at the exterior walls with more in the centre of the attic.
Thank you so much to everyone who replied! I learned a lot from your responses. I also appreciate the feedback about metal roofing not being consistent with the style of the house as I have a hard time picturing what it would look like.
I was partly thinking to get a metal roof because I would like solar panels soon and it seems like the metal roof would be easier to attach the panels to with less likelihood of leaking later.
I agree with your thoughts about solar on a metal roof instead of shingles. But I've come to the conclusion that in areas with significant snow it's better to have the solar ground mounted. Otherwise clearing the snow all winter can be a pain. Either that, or plan on only using your roof mounted solar for 2/3 of the year, and don't bother with it at all during the winter (assuming you're also grid tied).
Interesting. I have a ground mount and spent much of this winter clearing snow off of my panels. Unfortunately, the ground mount is very tall so I had to make a long handled squeegy that is difficult to use. If I planned it better, I would have had them mount them in longer rows, closer to the ground. Be careful clearing snow as you don't want to scratch the surface too much....
Let's assume grid tied like almost all homes are, so solar isn't your sole power source. Winter days are shorter to begin with and the sun is less intense, so you're already getting less solar power than the other three seasons. Snow typically falls on cloudy days (who knew?!) and so you're not losing much energy generation while it's actually snowing. Once the sun does come back out it has a tendency to melt off snow from the roof in all but the absolute coldest climates (again, where the sun is lower and days shorter) so in the end you're not really losing as much generation opportunity as you might think.
A bracket can be attached to the rib of a true standing seam roofing with a vertical, mechanically seamed rib. Supports on other metal roofing products are usually just an L bracket with a gasket or sealant between the bracket and the roof. The brackets I've seen on shingled roofs slip under the shingles so that water sheds over the bracket, which is probably better than relying on sealant.