dhanson865
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Redoing roof before solar

Thu Jun 19, 2014 7:02 pm

I'm about to get quotes on replacing the asphalt shingles on my roof and I'm wondering about prepping the roof for solar PV down the road.

While they have the shingles off should I put thicker boards in place to handle the load of the solar panels/racks/etc or is it likely a non issue?

I'm thinking energy star shingles and in my state that comes in a whopping 1 color choice (white, white, or white). Any thoughts on white roof and how that interacts with solar PV?

OK so the general questions are there, let me know if there is anything else you would check or ask for as I'm getting quotes from contractors in the coming days.


As to details 35.934,-84.0749 is pretty close to me if you like to punch it into a solar calculator. Kwh per month for the last few years are roughly Min 600, Max 1700, Avg 1000 but that is with no charging of hybrids or EVs and I'm likely to change that in the near future. House built in early 1970s most likely with the cheapest possible materials but nothing truly substandard (it is in a good neighborhood but obvious the developers built to a cheap spec).

TN doesn't play nice with solar PV in general even though we get good insolation see http://www.simpleenergyworks.com/tva-ki ... steps.html" onclick="window.open(this.href);return false; for an installers rant on PV in TN.

But I figure it'll be cost effective to grab some solar PV and put it on my roof well before the end of the roof I'm about to put up so I'm looking ahead.
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thimel
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Re: Redoing roof before solar

Thu Jun 19, 2014 7:43 pm

Solar panels are light and get screwed to the rafters. Any structural worry is making sure they don't blow off in a strong wind.
It is a good idea to do the roof before the solar. That way you don't have to later remove and reinstall the solar when the roof needs replacing.
I don't think the roof color should bother the solar.
I had the solar company come out to see if they wanted to install supports while the roof was off. One company would have done that, but the one I went with didn't want to. You might want to check.

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Re: Redoing roof before solar

Thu Jun 19, 2014 9:44 pm

Previous poster covered it well. The mounts I prefer quick mount PVs QMC are best installed after the roof is redone as then there is virtually no cutting of the shingles.

Only real concern might be if you are in a high wind area and the roofing contractor would use additional tar/etc to seal the shingles down. Thst might make installing the flashing a pain but otherwise should be no worries.

dhanson865
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Re: Redoing roof before solar

Fri Jun 20, 2014 8:40 pm

well I've gotten one quote back, waiting on the other but its looking like the cost to replace the roof is way less than I feared.

I guess I can start wondering how many solar panels to put on the roof some day.
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mikeEmike
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Re: Redoing roof before solar

Sat Jun 21, 2014 7:55 am

I have heard that if you're doing your roof beforehand, you should ask the roofers to mark the location of the rafters to make it easier for the solar installers to find them when installing the roof jacks. Otherwise, locating them is something of an inexact science, involving knocking on the roof until you hear a solid sound, drilling and hoping you hit the center of the rafter, and using measuring tape to locate the next rafter, hoping that they are the correct distance over, which they aren't sometimes. Regardless, the flashing should cover up any "misses", but the fewer holes in a new roof, the better. Anyways, that's how I had to do it (keep in mind, I'm not a professional solar installer). The real professional solar installers might have some fancy rafter-finding scanner, so maybe it doesn't matter, but it case they don't, having the rafters marked would be nice. I wish I did.

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Re: Redoing roof before solar

Sat Jun 21, 2014 8:51 am

Make sure you discuss solar with the roofer and roofing with the solar installer. They will guide you.
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garygid
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Re: Redoing roof before solar

Sat Jun 21, 2014 9:16 am

Check that the roof support structure will hold the extra load (weight and wind)
of the intended solar installation. Some structures need to be reinforced,
sometimes just due to building code changes over the years.

Some install the panels close to the roof, but I had mine installed higher to have better
(hopefully cooling) airflow underneath the panels. However, an almost closed space
under the panels, being shaded by the panels, might be similar in temperature.
It might depend upon exactly how the panels are constructed. Mine were fairly
thin, and the goal is to have the panels cool in operation, if possible.

The panels usually produce less output when they are hot, so a circulating water preheat
or pool water heater attached to the back if the panels would seem to be a good idea,
to cool the panels a bit, but I have not seen that done anywhere.
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Re: Redoing roof before solar

Sat Jun 21, 2014 12:08 pm

garygid wrote:Check that the roof support structure will hold the extra load (weight and wind)
of the intended solar installation. Some structures need to be reinforced,
sometimes just due to building code changes over the years.

Some install the panels close to the roof, but I had mine installed higher to have better
(hopefully cooling) airflow underneath the panels. However, an almost closed space
under the panels, being shaded by the panels, might be similar in temperature.
It might depend upon exactly how the panels are constructed. Mine were fairly
thin, and the goal is to have the panels cool in operation, if possible.

The panels usually produce less output when they are hot, so a circulating water preheat
or pool water heater attached to the back if the panels would seem to be a good idea,
to cool the panels a bit, but I have not seen that done anywhere.
The weight of a PV system ends up being about the same pounds per sqft of an additional layer of shingles. That is to say if instead of removing the old layer of roofing you just reroofed over it that's about how much weight is being added. I'd be curious to see what structures are not able to handle that and I would suspect they probably deficient for the current roof.

I'd be wary of any installers that are installing the panels close to the roof as that likely means they are installing them directly on the roof and are using questionable flashings, etc. Industry standard is a mount lagged to the truss with a full flashing, L foot to a rail, panels attached to the rails which ends up being significantly off the roof.

I suspect it's not commonly done because it would be difficult to cool the panels enough to make a big enough difference in their temperature to do that over just using the standard solar thermal systems and it would greatly reduce the effectiveness of the thermal system.

WisJim
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Re: Redoing roof before solar

Sun Jun 29, 2014 4:15 pm

Good PV panels will have a 20 to 25 year warranty and should last twice that long, so ideally your roof should last 40 plus years, too, which means some kind of metal roof would be the best bet. It will save you money in the long run on the roof, too, assuming you stay in the house that long.

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JimSouCal
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Re: Redoing roof before solar

Sun Jun 29, 2014 4:46 pm

WisJim wrote:Good PV panels will have a 20 to 25 year warranty and should last twice that long, so ideally your roof should last 40 plus years, too, which means some kind of metal roof would be the best bet. It will save you money in the long run on the roof, too, assuming you stay in the house that long.
Yes, I am doing a re-rrof during renovation and plan on using standing seam metal roof for a clean clip on install...

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