Redoing roof before solar

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dhanson865

Well-known member
Joined
May 25, 2011
Messages
1,523
Location
Tennessee
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-killing-solar-with-3-easy-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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
garygid said:
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.
 
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.
 
WisJim said:
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...
 
Standing seam metal roof would be my roof of choice, too. We did that on our recent re-roof of our barn, wish we had found the contractor for a metal roof when we did the house--but our PVs are mostly ground and pole mount.
 
WisJim said:
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.

I'm currently looking at laminated asphalt shingles Energy Star rated that have a prorated warranty out to 50 years, with the expectation I'd have to redo the roof in 30 or so.

Energy Star rated shingles are good for keeping the AC costs reduced in the summer and presumably keeping the solar panels cooler and more efficient plus there is that 30% tax rebate/refund (doesn't matter either way I have the tax liability to cover it on the asphalt shingles).

If I went Metal roof the cost would be much higher, I'm not sure how the heat rejection compares or if I get the energy star rebate/refund (or if the cost of install * 30% would exceed my tax liability).
 
You can get the same benefits of lighter colored shingles without the cost and the name. The tax benefits in our state do not match the difference in price.

dhanson865 said:
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-killing-solar-with-3-easy-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.
 
dhanson865 said:
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?

I have no experience with a white roof but a homeowner nearby was unhappy with his because the bird droppings were very obvious on his roof and they looked awful. There must be many birds, trees and wires near or over the house for this to happen. My problem with the cedar shake roof on my house is the birds or other animals pecking holes or storing nuts in the structure. Had to replace a small part of the roof for this reason. We will be re-roofing soon and will switch to asphalt shingles.
 
They are also not put up the same way. I do not like gaps in my roof coverage. I like solid sheets of plywood with waterproofing.
Also when they are not treated properly every few years they curl which is bad news for you and good news for water and critters.

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wood-shingle-distortion.jpg


linkim said:
My problem with the cedar shake roof on my house is the birds or other animals pecking holes or storing nuts in the structure. Had to replace a small part of the roof for this reason. We will be re-roofing soon and will switch to asphalt shingles.
 
kieranmullen said:
They are also not put up the same way. I do not like gaps in my roof coverage. I like solid sheets of plywood with waterproofing.
Also when they are not treated properly every few years they curl which is bad news for you and good news for water and critters.

The photo in your post looks like my cedar roof, except mine is not as bad. Here in Silicon Valley, we don't receive much rain and the temp goes up to about 90F in the summer on occasion. My roof is 28 years old so its time for a re-roof.

Just talked to a solar company and am strongly considering installing PV once we decide on the new roof.
 
I would get a white roof. The energy star credits are not enough to pay for the energy star shingles but you can just get white pretty cheap and keep your house attic a bit cooler. On the backside of the roof not facing south I would put some solar powered attic fans and make sure the exchanger is in a shaded area.

linkim said:
kieranmullen said:
They are also not put up the same way. I do not like gaps in my roof coverage. I like solid sheets of plywood with waterproofing.
Also when they are not treated properly every few years they curl which is bad news for you and good news for water and critters.

The photo in your post looks like my cedar roof, except mine is not as bad. Here in Silicon Valley, we don't receive much rain and the temp goes up to about 90F in the summer on occasion. My roof is 28 years old so its time for a re-roof.

Just talked to a solar company and am strongly considering installing PV once we decide on the new roof.
 
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