24" on center trusses, gambrel roof garage. Support a PV system?

[Quercus]

Obviously an engineer would need to do calculations, but does anyone have a system installed on something constructed like that?



The gables face east/west. My house's gables face north/south.

(PO did the siding, BTW!)

[alpinebound]

alpinebound

just installed 8 21 kg panels on a roof with 24" trusses and flimsy 3/8 sheathing. it so happens are house is oriented the same we put 2 in the front east for the morning sun and six in the back.
we arent going to be here for ever so we made 8 pentrations in the roof layed 2 boards perpindicular to the trusses lagged and silconed with 4" x1/4" lags into the truss rafters got some aluminium angle iron from the scrap yard and made mounts
i would rate the mounteing moderatly shotty but i feel good about them not blowing off or caving in the roof

[Cal Dan]

I don't do solar installs (other than my own hillbilly style) but I am a contractor and have been a framer for 34yrs.

Trusses are calculated to take a "dead load" (what is there now) and a "live load" (stacked up materials, men working, tools, etc.). What I am trying to say is you are good to go as far as weight is concerned. Your issue will be roof penetration (don't let your roof leak!). Proper lagging (as Alpinebound did) would be best. Blocking between trusses would be OK if necessary. Do a good job of connecting but pay special attention to, I'll say it again, don't let your roof leak.

Good Luck, Dan

[Quercus]

I don't do solar installs (other than my own hillbilly style) but I am a contractor and have been a framer for 34yrs.

Trusses are calculated to take a "dead load" (what is there now) and a "live load" (stacked up materials, men working, tools, etc.). What I am trying to say is you are good to go as far as weight is concerned. Your issue will be roof penetration (don't let your roof leak!). Proper lagging (as Alpinebound did) would be best. Blocking between trusses would be OK if necessary. Do a good job of connecting but pay special attention to, I'll say it again, don't let your roof leak.

Good Luck, Dan

I did roll roofing on a flatt-ish section of our home's roof and it's held up well. I'd probably look at doing a tear-off and re-roof of the garage in order to ensure that there are no leaks-- the shingles up there are not leaking, but look to be pretty much at the end of their lifespan.

Will have to do some research on the best way to do the roof and the panels at the same time.

[Cal Dan]

I did roll roofing on a flatt-ish section of our home's roof and it's held up well. I'd probably look at doing a tear-off and re-roof of the garage in order to ensure that there are no leaks-- the shingles up there are not leaking, but look to be pretty much at the end of their lifespan.

Will have to do some research on the best way to do the roof and the panels at the same time.

Good timing. You shouldn't have to do much research as most panel installs are done on an roof that is already there. But it doesn't hurt to put some thought into it. Now would be the time to add anything (structurally) that you think might help.

[Cal Dan]

One other note...

My experience is here in Ca where we have earthquakes and we tend to overbuild. I am assuming that your trusses are OK. You know what happens when we "ass u me". Maybe double check with someone you trust there locally, but I think you should be OK.

[Quercus]

One other note...

My experience is here in Ca where we have earthquakes and we tend to overbuild. I am assuming that your trusses are OK. You know what happens when we "ass u me". Maybe double check with someone you trust there locally, but I think you should be OK.

DEFINITELY.

I wanted to know whether it was in the realm of possibility before investing time and money in evaluation.

[inetdog]

Trusses are calculated to take a "dead load" (what is there now) and a "live load" (stacked up materials, men working, tools, etc.). What I am trying to say is you are good to go as far as weight is concerned. Your issue will be roof penetration (don't let your roof leak!). Proper lagging (as Alpinebound did) would be best. Blocking between trusses would be OK if necessary. Do a good job of connecting but pay special attention to, I'll say it again, don't let your roof leak.

Thanks Dan,
Very comprehensive. One more issue for consideration is that panels can also present an uplift load in some wind conditions. The attachment to the trusses needs to be able to handle upward force too. But drilling a vertical hole all the way through the member might cause weakness in some cases of old structural design, and particularly mobile homes with thin lumber. Sistering another member to the side of the trusses involved may be the best way to handle these cases.
If you do not have easy access to the under-roof space, do not make assumptions about what the members look like!
We had one member discover that because of poor ventilation his whole roof structure was failing. If he had not opened up the space to repair some roofing he would not have discovered the structural problems. Just attaching the panel mounts blind would have made the problem even worse.

[Cal Dan]

Thanks Dan,
Very comprehensive. One more issue for consideration is that panels can also present an uplift load in some wind conditions. The attachment to the trusses needs to be able to handle upward force too. But drilling a vertical hole all the way through the member might cause weakness in some cases of old structural design, and particularly mobile homes with thin lumber. Sistering another member to the side of the trusses involved may be the best way to handle these cases.
If you do not have easy access to the under-roof space, do not make assumptions about what the members look like!
We had one member discover that because of poor ventilation his whole roof structure was failing. If he had not opened up the space to repair some roofing he would not have discovered the structural problems. Just attaching the panel mounts blind would have made the problem even worse.

This is all very true.
There are a thousand different situations and possibillities and at least a few ways to deal with any potential problem.
It's still early here on the left coast. Thanks for finishing my narrow thoughts Building doesn't look too old. Probably not too much to worry about. Just use your head

[Quercus]

I drywalled a ceiling up under those trusses about 7 years ago, and things looked good then. I actually pulled all the insulation off the underside of the roof and re used it to insulate the horizontal /ceiling area when I re-did the space, and so got a really good look at things. The trusses were in good shape, and are about 35 years old.

At any rate, it sounds like it's worth taking next steps and having a pro evaluate it for solar.

We're taking a tax credit for a 100% electric car this year, so next year would make sense to do a PV system, unless we went with Solar City as some are doing around here.