foundation for solar on a older roof.

packnrat

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hills of ca,
thinking about solar on my roof, but house was build back in 1952.
does anybody here know the general framing codes for how a roof support should be. to handle the weight of the panels up there.
as i am not sure if the number of rafter or age will be enough support.
but in doing all this i would also be redoing the shingles. there age is ? a lot of the “sand” is coming off them.
looking to replace with a full metal roof.
but do not want to dump a zillion dollars here as i might be out of ca in ten years.
 

Hedges

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Our local codes don't require a structural permit for rooftop PV array if it is no more than 18" high and 40 lbs per attach point. So I divide the weight of panels, rails, etc. by 40 and that's how many standoffs & lag screws required.

Perhaps they figure with that many attachment points, it doesn't matter if screws go into rafters or just sheathing. I would make sure they hit rafters (which is difficult.) If you are re-roofing, maybe make marks on the eaves and ridge to indicate where they are.

Most panels aren't particularly heavy per square foot, but some are about 50% heavier than others. Wind loading could be the greater issue. I've read that keeping panels a few feed back from edge of roof reduces this.

I don't like the idea of just using lag screws through roofing and applying goop. With shingles, I want flashing. So instead of L-feet, would consider standoffs that flashing fits over. Some are one-piece standoffs, makes it difficult to place flashing after screwing down. Others are 2-piece: Screw down base, slip in flashing, insert round upright of standoff and thread on.

For metal roof, there are feet that have waterproof adhesive to seal from the top. For standing-seam metal roof, there are clamps which grip the seam.
 

Hedges

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If grid-tie in California, rates are lowest until 3:00 PM and 3x higher 4:00 PM to 9:00 PM.
Most cost-effective way to address that is to deliver 3 times as many kWh to the grid as you will consume during the high-rate period.
If you have multiple roof angles to work with, more kW of panels can be used with fewer kW of inverter without clipping production at its maximum.

There have been restrictions on roof area covered by panels, but more recent codes less restrictive than before. Probably need one 3' walkway from eave to ridge on street side of house. Panels not within 18" of ridge so long as another 18" available on other side of ridge.

Probably rapid shutdown boxes required on panels (unless using microinverters).

If you might want to add battery backup later, select inverters for compatibility what that.
 

MarkSolar

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If you need a roof anyway, I'd look at solar shingles.
The problem with homes of that era was the lack of hold downs for the rafters. They typically toe nailed the rafter/joist into the top plate because there were no products made for that back then. So I wouldn't worry about over loading the roof, but keep the panels low and away from the edges if you use them. If you live in an unusually windy area like coastal, you might take a look in the attic and see if you can see how the rafters were fastened.
 

packnrat

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hills of ca,
no not on the coast, but up in the foothills better than 100 miles inland. about 1000 ft elv.
in a valley in the past number of years no real wind. have lived in areas that got Wind. some snow ( none this past year) but below the snow line. and yes i have been up in the atic and no metal on the rafters. and they look to be a good two + feet apart.

i have read the shingles are lousy when put up to even the flexible panels.

i can use one side of the roof. it is a good 30 ft by 15 ft. only a couple vent pipes.( bathroom).

thanks to this lock down, i can not go to the government center to even find out what the local codes are. so-far unable to find them online,
but if redo the roof i would add in as needed for supports, insulation, etc.
and if possible/needed have room in the back yard for ground mounted. no trees for most of the day till dusk. back yard looks south west. and can easy fit in three times as many as the roof.
i now live in town so no need to be completely off grid. but have the room to even have a battery shack. back yard is a good 1/2 acre.
even if i could get paid by pge i still would pay for water in / out and garbage pick up ( for me just a small can that does not always get full).

ca has a electrical power shortage. and the state cuts power to the rural areas. so a good solar power back up can be worth it.
 

MarkSolar

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I'm ground mounting right now, we have a farm and it's next to the barn, so not shortage of space. If you have the space, I'd consider ground mount. Downside is ground mounting adds at least a few grand over cost of roof mounting, but on the positive side you never have to worry about fixing a roof leak, putting on a new roof, or crawling under panels to find wiring problems. The modern mounts they use on the roof are much better than the early ones, they appear to be flashed well. But there's still the complication of future repairs and reroofing.

A 30x15' roof is not really a lot of space, especially if you have a few vent stacks. Not sure what your power expectation is but that's probably 25ish panels, even with 425W panels that's only 10kW, which is about what you'd want for a 7.5kW inverter.

If you're worried about power outages, you're going to have to add batteries and a transfer switch to keep your solar running when the grid goes off. That adds a whole bunch of cost. We already had an automatic backup generator, so I'm set if the grid goes down. I just wanted to save money on the power bill, and our state has net metering so it's a pretty good deal.
 

packnrat

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May 16, 2021
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Location
hills of ca,
i live alone, work nights. only big draw is the ice box. window ac only, most everything else is off most of the week. in 4 days i put in over 50 hrs. sleep one day away ( monday- my saturday). i get home at 5:30 am so the bed room ac is a mandatory item. most days of the year are sunny.

i figure a good bank of say six-eight 24 volt lipos with just the roof solar can get me through most days. as another way i do have a honda eu3000. set up to plug into the house. but not auto power. so far the governor has not cut power more than 24 hrs here.
 

MarkSolar

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So sounds like you can get plenty of output with your available space. We've got totally different setup, lots of power to heat livestock water in winter and run barn fans in summer. We're here 24x7 making electric meter spin.
 

packnrat

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May 16, 2021
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Location
hills of ca,
very true. i live in a old house in town. no livestock allowed. used to have a much larger place up on a hill with a view forever and it sat on over 5 acres. even had my own privet shooting range there. was looking at doing a full acre in solar. but everything dropped out on me. i lost most everything.
this place may be old. a good 3/4 acre. front window i see the hills to the east. out my back windows the hills to the west. no snow. but still get the valley heat. and miles of back country roads and mt passes to ride my fz1.
 
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