Solar Panel Question

[SteelPE]

I was recently asked to look at an existing metal building by a client. The client does not own the building, and at the time, I thought the client was going to lease the building from the owner. The addition of a new sprinkler system was part of the scope of work. Part of my due diligence required me to measure the existing roof frames and purlins. The building was constructed in 1989.

Code analysis revealed some issues with the roof (due to AISI code changes) but my analysis of the sprinkler system revealed that we were increasing the gravity load by 1% (which is under the 5% limit allowed in the IEBC). I wrote a letter of my findings which I gave to my client.

A few weeks later I found out that my client was looking to actually purchase the building and part of the purchase included a lease to a solar panel company (which had yet to be implemented). The lease was written in such a way to allow a 15% increase in the gravity loads on the building. From my analysis, I know this increase would require reinforcing of the existing roof, but no reinforcing was proposed. I informed my client that adding the solar panels to the roof is not a good idea and that they should negotiate their way out of the lease (they think this is possible).

Do companies that install these systems actually check to make sure the existing structures can support the added loads? Or do they just hope the structures can support the added loads? Or do they only care about adding to their bottom line?

FYI, I know specifically what my deficiencies are as I have a colleague who works in the metal building industry and can analyze these roof systems quickly.

 

[XR250]

In my area, they are required to get it checked out. I do a bunch of these for residential but never for a PEMB.

 

[Once20036]

The last time I worked on one of these things, the solar guy had an engineer they had been working with for years who would review the existing joists / structure and sign off on the added loads (in theory, the work isn't complete yet). I don't think that this was in their base contract, but they were happy to provide the service and clearly had been asked for it before.
I`m not sure how thorough they are, but we made it clear that there are numerous hung loads within the space that needed to be accounted for in their analysis.

 

[DenverStruct]

I don't typically design buildings but here is my thought. I think it depends on what controls the design of the roof? What live load do you typically put? If you cover the whole top with solar panel, technically you cannot have live load on your rooftop anymore so the design should still be OK? But if the roof top is controlled by something like snow, I would say you may have a problem because the solar panel will add weight and also accumulate more snow?

 

[WARose]

Do companies that install these systems actually check to make sure the existing structures can support the added loads? Or do they just hope the structures can support the added loads? Or do they only care about adding to their bottom line?

Since this solar power craze started (and don't even get me started on it).....I've had a number of panel installers call me for roof evaluations.

Whoever wrote that lease doesn't have a clue. You need to be sure you aren't connected with it in any way.....and be sure you document you've told them it would take a evaluation (on your part) to be sure of that 15%.

 

[JoshPlumSE]

Aren't solar panels a real red flag to building departments? I haven't worked any of these projects, but my impression (from a friend who added them to his house) was that these were a big deal to the building department. Not just the structural part, but also the electrical and fire safety aspects are as well.

Not saying that building departments are against them, but just that solar panels are very much on their radar for a number of reasons.

 

[Canuck65]

I have worked solar installation projects. Typical installations add in the range of 4 to 7 psf to the roof. If the solar installer has a snow study for their system, it generally shows that the snow accumulation doesn't increase as long as they conform to certain parameters. In my area it is mandatory to complete a structural assessment of the roof. I say assessment, instead of analysis for the moment. Sometimes it can be justified for an older building, where the original design codes were different, that the current design snow load is much less than the original design snow load. Sometimes the building is reroofed and a gravel ballasted system is changed for a non ballasted system, thus opening up extra dead load capacity. If the building was properly designed to an original design snow load that is 10psf more than current standards, there is likely room for solar. For a 1989 PEMB, I think you are out of luck for that argument and full analysis is warranted. As we find PEMB's a pain in #$@, we outsource the analysis to a PEMB specialty firm. They are quick, efficient and deal with PEMB's on a ongoing basis and have access to the MBS software. More often than not, reinforcement ($$$) is required before solar panels are put on PEMB's, there is virtually no extra capacity on these buildings. The solar company should absorb the cost of any engineering and upgrades to the roof required, this is typical for the larger type projects in my area.

 

[Mjkkb2]

New member here. I believe a good installer/supplier would ask for an engineer's opinion if the existing framing was questionable, but if the roof looks good (condition wise) they will install the panels without checking the framing. Their submittal (panel install drawings) will have requirements for attachment (unless ballasted system is used) to the framing members. It will also state that the roof members must be adequate to support the given loads.

The typical systems available currently do not add much weight to the roof and I don't think the added gravity weight is a problem for most building, however the PEMB systems are notorious for having no excess capacity so adding anything beyond the code minimum at the time of construction could be a problem. I also believe the bigger potential problems are the panels installed on elevated frames/racks where the loads are concentrated and there's a significant wind component. The uplift from a rack leg can be quite large and it introduces reverse bending in a roof member that is most likely unbraced on the bottom.

The above is just my local E coast experiance so it may not be accurate in other markets.

 

[SteelPE]

Canuck65, good information.

I have a unique experience here since I was ask about the ramifications of adding sprinklers to the building. I measured the existing purlin sizes and sent them off to my colleague for review and continued on to see what the IEBC said about my sprinkler situation. I'm in an odd position with this building but can justify adding the sprinklers through code references. However I know for a fact that a 15% increase will not fly without major reinforcement. I informed the potential buyer that they have two options:

1 Negotiate the existing building owner to terminate the solar lease prior to the sale
2 Reinforce the existing roof

I just find it odd that a solar panel company would enter into a lease with a building owner for a load increase of 15% without some investigation (FYI, no solar panels are on the roof...... yet). I have always wondered about these when I drive down the road and see all these building that now have solar panels. Seems like the dark side of the business that no one talks about.

 

[gte447f]

I did several roof evaluations for adding solar panels 6-8 years ago when solar seemed to be bursting onto the scene in my area, and I routinely received calls about roof evals for solar panels during that time. In my experience, it was a shell game with the loads to try to justify existing excess capacity in the roof. For example, comparing original code required loading to current loading, negating or reclassifying live load for dead load at solar panel locations, things like that, which have been mentioned in the posts above.
I personally never liked the idea of justifying a reduced live load based on the assumption that the solar panels basically block live load. It's logical, but I have always sort of viewed roof live load as a cya construction load, and you never know what some people will do during construction. Also, I don't know if code authorities would accept this logic.

If the shell game with the loads doesn't work out, then the scope for a true structural analysis of the roof load path expands substantially, and it seemed to me that there was never a realistic understanding of this or willingness to support this, in principal or financially, on the part of the owners and/or solar suppliers.

Curiously I never get calls about solar installations anymore. I suspect all of the suppliers in my area must have developed relationships with other engineer's that they preferred to work with, maybe because they had more lenient opinions about the roof evaluations. I also wonder if maybe things have changed in the way the codes address solar panels on roofs. For example, it could be codified that it is acceptable to reduce live load at solar panel locations.

 

[HuckleberryFinn]

Would any of you folks who have an existing relationship with someone who routinely evaluates PEMB's for upgrades/additional loads be willing to give me a referral? (Private message is fine if not a direct reply)? I have a client with a large existing (circa 1980's construction) single story industrial PEMB in California where the owner wants to add some new cooling units on the roof to support a new process line (I have tried to no avail to counsel them toward placing the units elsewhere - including new independent platforms/framing/etc...no luck).

Would be incredibly interested in exploring a SSE/EOR arrangement for this type of project and would love a referral if you guys are willing???

Thanks,

-Huck

 

[CCox]

Huck Finn, I have an excellent contact for you. I have used him to run analyses on projects ranging from enclosing open buildings to adding roof loads on existing buildings. Email me at cody@wavedesigngroupllc.com. I’ll give you his contact info. He is licensed in all 50 states and uses the MBS software.

Be really careful on PEMB’s with the plinths. If a PEMB is built more than 25 years ago, you will undoubtedly find the plinth too small and under reinforced.