Heat reflective roofing materials
mpls1921
| Posted in Energy Efficiency and Durability on
So, since I need a new roof this year for my 1.5 story Minneapolis Bungalow, I would like to consider materials that would reduce the heat gain on my upstairs during the day. I am going to be looking into adding 2″ of polyiso over the roof deck, but that may or may not happen based on cost.
However, I understand that some materials are energy star rated for reducing the cooling load. Steel, which may be too expensive, and some shingles.
Based on the manufacture web sites, these special shingles do not appear to be normally available in MN (usually AZ, CA, etc). Is there any reason NOT to use these shingles in MN?
Thanks,
Erik
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Replies
Erik,
Energy Star roofing products are unlikely to provide any energy savings in a cold climate like yours.
They are intended for homes in hot climates with ductwork in an unconditioned attic.
Needless to say -- I hope I'm right -- no one in Minnesota installs ductwork in an unconditioned attic. Right?
If you have ductwork in an unconditioned attic, you've got a big problem. There are a few things you can do to improve the situation -- but none of them include installing Energy Star roofing.
Martin,
Why would low gain roofing not help? It gets hot here in the summer (over 90F), despite our cold winters.
I looked into Certainteed's low SRI shingles this summer when my roof was damaged by hail. They aren't cheap, IIRC about $180/sq. But when you factor in that its a lifetime shingle, high end construction, its pretty competitive to other high end shingles. The bigger problem, at least in my area in Michigan, was that I needed to buy a truckload at a time, slightly more than my 23sq roof needed. The word on the street that I've heard is that they are very popular in Chicago, part because of tax credits, as it helps reduce the heat island effect, as well as you noted, reducing the cooling load. So no, i don't see any reason you couldn't use them. They're called the solaris line, heres a link
http://www.certainteed.com/products/roofing/residential/premium-designer
I do believe more companies are offering low SRI shingles as well. HTH
Martin, when I purchased the house (1921 bungalow), it had been retrofitted with forced air heat and cooling. And yes, parts of the runs were in unconditioned attic space. However, I have since brought those spaces into the envelope by spraying the roof deck with open cell foam. However, as it is a 1.5 story that was far from the whole roof deck and as another poster indicated, it is often 90F+ here in the summer, and my roof gets very little shade from the south or west. Cold climate does not apply June-September. Additionally, the HVAC runs to my second floor are fairly long with many turns, so my AC has a hard time keeping the upstairs cool. Anything to reduce the solar heat gain would be nice…Is there any reason NOT to use the energy star products here?
Erik,
There's no reason not to use Energy Star roofing, if that's what you want.
But your real problem has nothing to do with roofing specifications. Here's your problem: "The HVAC runs to my second floor are fairly long with many turns, so my AC has a hard time keeping the upstairs cool."
You problems may include an undersized air conditioner, a cooling system that needs to be zoned, undersized ductwork, leaky ductwork, convoluted ductwork, poorly insulated ductwork, or windows with the wrong SHGC. You need to find a smart HVAC expert who can diagnose your problems and suggest solutions.
I agree that the ducting could have been better and that it should have been zoned. I have achieved some degree of sucess resolving the problem by re-balancing both the outlets and return ducts.
I will re-visit the possibility of having the HVAC system modified.
That said, if the Energy Star roofing has a positive effect in southern CA, why would it not be worth having in Minneapolis in summer (given that I already need a new roof)?
Erik,
For people like you, with ductwork in an unconditioned attic, Energy Star roofing might make a small difference in your energy bill. But don't expect your savings to be very large.
Well, as I mentioned, the ducts are no longer in an unconditioned space. However, much of my upstairs ceiling is serperated from the roof deck by only 3.5" (roof framing) with some loose fill celulouse in the space between the rafters. I can feel that the ceiling is quite warm during the day. I'm actually just as interested in comfort as the energy savings (if it didn't warm up so much during the day, I could avoid using the AC) As I indicated earlier, I should put at least 2" of foam above the roof deck, but that may be too expensive (will get quotes on it).
Erik,
You've established in an earlier thread that proper venting is not an option.
If you have to replace your roofing anyway, yes in principle more insulation and a lighter color roofing material will help reduce the heat transmitted into the upstairs rooms during the summer.
Light colored metal roofing should reflect more of the sun's heat than light colored asphalt shingles. You can verify this by the products Solar Reflective Index (SRI).
Light colored asphalt shingles purportedly last longer than there darker colored counterparts.
Roofing contractors will offer you free bids on different options. This will quickly put your options into a cost perspective. Are you familiar with the Roof Depot near the Green Institute? Your most cost effective choices will be what is stocked locally. The Roof Depot has a showroom where you can get a sense of what the local contractors are picking from (don't know if they stock metal siding.)
Firestone is a local rep for the higher grade of standing seam metal profile roofing which can look quite nice on bungalows.
Thanks for all the input. I will use it as I seek bids from the pro's.
Erik
How thick is the foam insulation