Solar Roof exceeding roof weight limit?

[slcasner]

I have just placed an order for Solar Roof + 2x Powerwall to replace an existing 4kW solar panel system installed in 2000, but I'm concerned that we might not get approved for a building permit. My city Sunnyvale (Santa Clara County, N. Cal) Building Division re-roof requirements includes:

Roofs Exceeding 7.5 lbs./Square Foot

New roofs that exceed a total weight of 7.5 lbs/SF (including sheathing and roofing material) may require additional roof framing and support. Information about the existing roof framing will need to be provided to Building Division staff at the One-Stop Permit Center for specific direction on a particular project.
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Has anyone here had a problem with this in Sunnyvale or similar requirements in other jurisdictions due to the weight of the Solar Roof tiles?

When we were planning our PV system installation in 2000 we initially wanted to install Atlantis Energy SUNSLATES which was a system somewhat like the Solar Roof but using Eternit cement/fiber imitation slate tiles as the substrate with a glass-covered PV module applied to the tiles in the active area. The weight of the plain Eternit tiles was 5 lb/sq.ft. and 7.2 lb/sq.ft. for the SUNSLATE tiles, not including the weight of the plywood sheathing. We contracted for an engineering analysis of our roof framing that found the framing to be adequate for the static load, but the City of Sunnyvale wanted a lateral load analysis including a shear wall analysis because of all of the added weight on the roof. The structural engineer said that based on the date of construction of our house (1980) it would likely not have adequate shear wall design and the load analysis would not pass. So at that time we simply renewed the wood shake roof at the same time as we installed 4kW of solar panels. Now our insurance company is requiring us to replace the wood roof and the existing solar system has degraded so I'd like to replace both with the Solar Roof but I'm concerned about the weight.

I have not found any Tesla document with technical specifications for the Solar Roof tiles, but what I've found on the web is that the PV tiles weigh 7.34 lb/sq.ft. and the inactive tiles weigh 4.15 lb/sq.ft. That's comparable to the SUNSLATES. With plywood roof sheathing and membrane the total weights would be about 9.3 and 6.0 lb/sq.ft. Has anyone here encountered a problem with the roof weight?

 

[jboy210]

I had no issues up in Alameda county.

FWIW a 45" X 14" Tesla Solar Roof tile weighs about 7 pounds ( I weighed the signed one I have). With overlapping that tile will cover 45" X 9" = 2.8 sq feet of exposed roof. 7lbs/2.8 sq. ft. = 2.5 lbs/sq. ft. for the SolarRoof tile. So even with underlayment material and plywood, I think you are safe. FWIW, a typical California approved ceramic roof tile weighs much more than a Tesla Solar Tile per sq. foot.

 

[wjgjr]

To add to what @jboy210 said, the spec sheet I received for the shingles, which Tesla submitted to our utility/county, says:

Installed System Weight Textured Glass: 16.4 kg/m² or 3.4 psf
Installed weights include all components of system above roof sheathing

I assume this means it includes the underlayment (which was firestone for me, so newer roofs might have a slightly different number,) but, in any case, this certainly would come in at under 7.5 unless the sheathing was something unusual.

 

[trautmane2]

In case it helps, here is the spec sheet:

 

[slcasner]

Thanks, all. The real spec is less than half of the number I got from a YouTube video. That person was starting with the weight per "square", that is 10 x 10 feet, and calculating from there. There was no mention of how he got the starting value, so maybe he was just confused. (He did divide by 10 rather than 100 to get the weight per square foot, which could be overlooked as a "thinking while recording video" error, but maybe he's just not a reliable source.)

I poked around the Tesla Energy web pages but did not find that spec sheet. Is it published somewhere? If not, it should be -- there's no reason to suppress that information. Please attach as a PDF if you can so I can save a copy for future use.

I also didn't see any specifications for the inverter used in the Solar Roof system, but I saw a post here about Delta Solivia. Is that correct?

 

[trautmane2]

I poked around the Tesla Energy web pages but did not find that spec sheet. Is it published somewhere? If not, it should be -- there's no reason to suppress that information. Please attach as a PDF if you can so I can save a copy for future use.

I got it from my site plan document which Tesla gives you after they draft a layout and you sign the purchase agreement. I'm happy to post as a PDF, but am worried now that maybe I should not have shared the spec. What do others think? Naively, I assumed this was public information and just shared it here as a convenience. But when I just looked for it publicly, I see you are right - it's not posted anywhere.

 

[trautmane2]

I also didn't see any specifications for the inverter used in the Solar Roof system, but I saw a post here about Delta Solivia. Is that correct?

My inverter is a Delta M8-TL-US (for a 9.9 kW system).

 

[jboy210]

My inverter is a Delta M8-TL-US (for a 9.9 kW system).

I think the Delta M series are the ones they use with a SolarRoof system. We have an M8 and an M4. 12.75 kW system.

 

[gern]

My Solar roof (installed last January) uses 2 Solivia 5.2 TL inverters and 1 M4-TL-US inverter.

 

[wjgjr]

I think the Delta M series are the ones they use with a SolarRoof system. We have an M8 and an M4. 12.75 kW system.

I think you are correct that they are using that these days. I have a Solivia, but it seems like the Delta M is what they are installing now.

 

[jjrandorin]

I got it from my site plan document which Tesla gives you after they draft a layout and you sign the purchase agreement. I'm happy to post as a PDF, but am worried now that maybe I should not have shared the spec. What do others think? Naively, I assumed this was public information and just shared it here as a convenience. But when I just looked for it publicly, I see you are right - it's not posted anywhere.

Unless there is some specific verbiage not to share that info, it seems like its ok to me.

I might suggest, however, if you want to share the PDF with the OP, maybe you email it to him or something rather than post it on the forum, if you are concerned.

 

[slcasner]

Unless there is some specific verbiage not to share that info, it seems like its ok to me.

I might suggest, however, if you want to share the PDF with the OP, maybe you email it to him or something rather than post it on the forum, if you are concerned.

I agree. And an attachment to a PM would be great, or I can send email address.

 

[trautmane2]

Unless there is some specific verbiage not to share that info, it seems like its ok to me.

Ok - thanks. I went back and looked at my document. The actual site plan has this confidentiality statement:



but the data sheet does not and really looks like public info, so I separated that into a new PDF and posted it here for you:

 

[wjgjr]

but the data sheet does not and really looks like public info, so I separated that into a new PDF and posted it here for you:

Thanks for posting that - that is the same datasheet I received. It is odd that they don't have it available on their website since it doesn't really have any secret information (and they do post datasheets for the powerwalls, for example.) And, all the information is available somewhere, so nothing wrong with posting.

I am guessing that the disclaimer that we all see on the drawings is because Tesla doesn't want you to take that work (which they often do for just the deposit, which is sometimes refundable) and have another installer try to use it.

 

[slcasner]

...but the data sheet does not and really looks like public info, so I separated that into a new PDF and posted it here for you:

Thanks!