Planning for solar
SouthGeorgianBay
| Posted in General Questions on
The house I’m building will have a pretty good roof for solar. It’s a simple 8/12 gable, with the south side facing a little east of south. The only real shading will be birds and clouds.
I’d like to install a metal roof, for a variety of reasons. Any suggestions for making sure the roof will work well with solar? Extra fasteners? Heavier gauge?
I’m leaning towards standing seam, but they aren’t cheap, especially the galvalume variety. I’m open to other types of metal roofs.
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Replies
Graham,
These days, manufacturers have developed PV racks for every known kind of roofing -- so don't worry.
When preparing for solar, most metal roof manufacturers recommend an altered fastening installation routine, i.e. more fasteners.
Graham, I'm doing just what you describe. I've just put on a metal roof and will have solar panels. Since my metal roof will not have any penetrations (plumbing vent and radon vent will both go up the insulated chimey), I wasn't keen on putting hundreds of little holes in it to hold on the PV panels.
My solution was PV on a pole:
http://gmisolar.com/solar-panel-tracking-systems-pole-mounted-solar/
It doesn't put holes in your nice metal roof and gets better output by rotating with the sun.
Standing seam roofs accommodate pv panels without all those penetration.
From an installers perspective, almost any roof can be installed on in a waterproof and durable manner. Some are harder/ more $$$ than others.
In general standing seam is one of the best roofs you can buy ( durable, and is probably the least likely to leak over its very long life) it is more expensive for sure, but it allows for the least expensive type of solar racking. In the end the premium for standing seam is more than the savings in solar racking, the racking savings just help soften the blow.
My advise: standing seam, tell your roofer to use more clips/fasteners (not the expensive parts of a roof), tell your solar installer you want zero penetrations ( so they take the conduit off the side of the roof and penetrate the side wall under your roof overhang) and enjoy the bonus fact that your roof and solar array have a very well matched life expectancy, so you won't likely have to re-roof while your solar array still has life in it. Removing/re-installing an array on a roof currently costs about 30- 40% of a new system. So we never install arrays on shingle or exposed fastener metal roofs more than a few years old without STRONGLY advising the client on the future cost implications.
Unless you have a BIG roof, asphalt shingles and PV on a pole will likely cost more than nice standing seam with a roof mounted array with zero roof penetrations (there are exceptions to this, sure, but if you're the average home filling most of you southern roof it will likely hold true). And doubly true with tracking pole mounts. Tracking is fine in the right climate, in the right conditions (utility time of use rates for example), but as PV prices have fallen, those right conditions are fewer and farther between. Hopefully I didn't just de-rail the thread.
If you want what I think is the ideal underlayment for a metal roof, see:
http://www.cosella-dorken.com/bvf-ca-en/products/roof/underlayments_meta...
which you can buy here:
http://www.spycor.com/DELTA_TRELA_Roofing_Membrane_by_Cosella_Dorken_p/d...
It costs more, but boy does it seem perfect.
Thanks for the helpful replies. If I do go with standing seam, I would likely go with your advice Daniel re. extra fasteners, such as every 12" instead of every 24". The added time and cost would be minimal, I'd imagine.
Any thoughts on snap lock vs. mechanically fastened panels?
Not sure. I'd tell you roofer that you will be putting S-5! clamps on at a later date and see if they say one vs. the other is better. They'll also be able to tell you which S-5! clamp will be the one to use when you do put the array up there. (S-5! is the leading brand for standing seam clamps, and they have a solar module mounting solution that is rated for the purpose, but there are others, don't feel tied to S-5!, they're just a good industry standard reference.)