TPO Roof Install

Fred: Welcome to the neighborhood.

Quick questions:

1.) Is your flat roof mostly horizontal ?
2.) If it is mostly horizontal (say, <10 % off horizontal or so), are the planned arrays parallel to the roof ?
3.) if the answers to #'s 1 & 2 are yes, do you have the room/unshaded area for a ground mount ?

Short comment on penetrations:

IMO only, your concerns are well thought out. I had my concrete tile roof repapered by good roofers before my array was installed. They did the penetrations and set the posts per the design drawings with the PV vendor's knowledge and approval. The posts are double flashed. 10+ years and no leaks (knock on wood ?!?!).

Thank You J.P.M. for your reply. Our roof is mostly horizontal but sloped slightly (with the use of parapet walls and crickets) for water drainage. The planned panels will be tilted (~10%) facing south. Our yard unfortunately is pretty small and ground mount won't be an option. I guess getting a good roofer is paramount for any type of flashing work.

By going with heavier rail you can increase the spans and have less penetraions if the framing members are adequate. . Many of the rail manufacturors have online planning tools that you can access.
Four years ago in Southern California my HOA redid my roof with a TPO membrane. I had to remove and reinstall the panels and reimburse the roofer for flashing which he quoted per standoff. He then warranted the roof and the penefrations. The charge for flashing 34 standoffs was $50 per standoff or $1700.

In that same town there was a lot of new onstrution and to mazimize lot coverage and heght limits there were a lot of flat roofs eig constructed, One solar installer I know would place the standoffs on the roof and the roofer would install the flashing and warranty the roof, that reduced the risk to the installer since he was not on the hook for any roof leaks. If you have control over the timing of roof installation and solar that might be an approach to drive some cost out of the equarion. If the TPO is already installed you might consider a ballast mount if you roof would support the load.

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Thank you Ampster for your comments. Flashing cost at $50 each 4 years ago sounds reasonable. This install is going on our existing roof and the original roofer quoted a cost much higher than that and would only offer a 5-year warranty. I am checking with the solar installer on possibility of switching to use rail racking since I am afraid the roof wouldn't withstand the weight of ballasts. Keeping my fingers crossed.

We used a ground mounted rail system from IronRidge to plant our 40 panel array out behind our house. We have been totally satisfied with the quality and design of their products. During the planning process and also during the installation, I had several conversations with the engineering dept at their headquarters in Hayward, CA. I was very impressed with the responsiveness of the techs and their willingness to answer my questions and address my concerns. Looking at their website I see they have some products applicable to a flat roof installation. You might take a look:

I have seen some standoffs designed to use a pourable sealant and other ones with a mastic base that are designed for membrane roofs. They still need to be lagged into framing members.

Fred: Does your EE/CE designation mean you are a civil engineer as well as an electrical engineer ? or does CE mean computer engineer ? Are you a P.E. ?
The reason I ask is in relation to your mention of ballasted systems.
A lot of problems can come with ballasted systems. Besides the weight, which, depending on location can or may be considerable depending on wind loading external loads, they can cause local deformation of foam and membrane systems and form depressions and pockets due to the weight of the ballast that can collect water. Such places can also be sites where cracks in such membranes can form. So, potential for water and cracks in the same place.
They also may be an opportunity for roofing vendors to void warranties.
Ballast systems without some fixation can also move over time and creep.
It all just gets to be a PITA, starting with building codes and inspectors who might get porky about things like generated stresses from wind loadings and dead weights vs. allowable roof loads.
If you are a civil engineer, see ASCE 7-10 for particulars (Minium Design Loads for Buildings and Other Sturtures) for design considerations including design for wind loading.

Thank You SolTex, IronRidge racking system for flat roof does look very promising. Pourable sealant in place of membrane flashing also sound very interesting. I will check with the installer to see if they could make either work.

I have both electrical and computer engineering degrees, but not a civil engineer to have good understanding of the structural aspect of things unfortunately.

Never considered the potential damages to the membrane from the ballasts, just the worry of added weight alone is enough for me to rule it out. Thanks again J.P.M.

Understood.
You're most welcome.
Anyway, ballasting is usually not the best way to go.

J.P.M.

You can try solar stack pedestals which are attached with roofing adhesive. They have been approved for use in California, but some districts may need convincing. The company will support you in helping the local AHJ walk through their California approvals. But no roof penetrations. They offer a 10deg tilt option. I'm using them with a 10 degree east/west tilt to maximize roof space utilization. If you don't need to do that, you can set them all tilted toward the south. The difference in production between 10 degrees south and 30-35degrees, the optimum tilt, is less than 10%, so an easy tradeoff for no roof penetrations. Unirac RMDT is an 8% East/west tilt ballast option. If you have a parapet, that will work also, and with the east/west tilt, you don't have to worry as much about the lift factor from wind. If you are looking to minimize the costs, you should do with larger panels (like 530w or higher, instead of the 400w in your quote) and optimizers along with a string inverter. For a 5.4kw system, you can get a 6kw inverter for $750, 10 540w panels for $3k plus maybe $500 in delivery charges and 10 optimizers for $450, the solar stack racking and glue would cost about $2000 because it has to be shipped freight. You need some additional hardware and components, but they are less expensive than these major components. Should be less than $8k all in for equipment, assuming you don't need to upgrade your electric panel.

I'd check with the local AHJ before I committed to that and even then I'd be skeptical.

So I'm not connected to the company in any way, I'm just passing on info I found. I've seen their CA certification, so they are approved for use in CA and adhere to CA building code, but some AHJ's may not be aware of the current codes (I've found that to be the case). They are approved for hurricane force wind zones in south Florida, so there should be no reason they wouldn't be fine in CA. Honestly, I think it is too expensive, but without roof penetrations, it makes it much easier to install, even DIYers could do it.

I don't doubt your varsity for one hot second, but I've seen a lot of official and austere looking claims in adverts that later turned out to be, shall we say,..."optimistic".

But one of my other reasons for caution is indeed, as you write, that as a practical reality, and like a U.S. Marine, the AHJ can be your best friend or worst enemy.
As you state, some AHJs don't get the word, or for some reason(s) - valid or otherwise - don't agree with what the code says or more likely to my experience, takes issue with the particular interpretation of the code for a particular application, especially when or if some homeowner defiantly waves a likely specious sales pitch under the AHJ's nose.

With advance apologies to any DIYers to whom this may not apply, and probably a bit off topic, but another red flag to me that you mentioned is that of adhesive attachment being easier for DIY which, to my experience can easily, but not necessarily mean expedient, cheap and usually skunked in work without a knowledgeable set of eyes looking at that work and so of questionable safety.

Thank you fraser for your comments.

I am guessing many home owners in my area were able to sign up for the NEM 2.0 program just before the deadline, and that is bringing a boom business to reputable solar panel installers. Two contractors I talked to were not interested to bid, and the third contractor was very helpful and responsive, until I asked for alternatives to direct panel mounting that would have required up to 50 penetrations (for 13 panels). Too bad I am not 20 years younger to try the install myself. Hopeful I will find someone more experienced in dealing with TPO flat roofs when I restart my search again.