Advice for residential flat roof installation in New England

[austinb]

Thanks J.P.M! Clarifications:

1) The initial proposal is for the panels to be a at 9 deg. tilt, though the design has not been finalized.
2) The system will be permitted by the building department, so those load calculations will be required to pull the permit. The preliminary design shows 129 ballast blocks (32 lbs each), with a total array pressure of 6.7 lbs/square foot.
3) The website for this ballasted system is at: https://ecolibriumsolar.com/ecofoot2plus/ and it shows video of how the system works.
4) The roof did originally carry an air conditioning system (compressor, external ducts, etc.), that was completely removed before the new rubber went down four years ago

Given your comments, it doesn't sound like this is a terrible idea overall... so that's encouraging.

[J.P.M.]

1.) Most roofs are flat. Many are oriented at an angle with respect to the horizontal. You have one that is mostly horizontal with the usual slight pitch of something like a degree or two or so to help with runoff/drainage. Some puddling is common and expected, mostly unavoidable and mostly harmless.
2.) For several reasons, I hope your panels will be at some angle to the horizontal, probably greater than 30 deg. or so.
3.) Ballasted systems without some fixation can still move/creep, even on mostly (but not completely) horizontal roofs.
Also, ballasted systems on (mostly) horizontal roofs need careful examination of the roof to ensure the roof can handle the added weight of the ballast, which can be quite significant, and also the other external loadings such as uplift from wind forces as well as consideration of the cyclic nature of those wind loadings, all of which were probably was not envisioned or designed for when the building was originally designed and constructed.
4.) Check with the building dept. for requirements for PV systems with respect to design and permitting requirements for PV systems, including roof loadings.

[austinb]

I am looking to have a 10KW system installed on a 1950's mid-century flat roof house in Rhode Island. The rubber roof is four years old and has only a very small amount of pitch. The rafters are 16" on center 2X12s.

We do get some pooling on the roof after a rain, but multiple roofers and an engineer have all advised me that this is totally normal and not to worry about it. We've owned the house for three years and have not had any leaks or problems.

I have had four or five estimates and settled on a company to do the installation. Currently, I'm waiting for their final design determination and not sure if they will go with a ballasted system (they use Ecofoot2+) or a penetrating rack (they use OMGRoofing).

I've been unsuccessful in my search for homeowners with solar installations on a flat roof. So far, I'm relying on the good word of the solar company salespeople who all assure me that there's nothing to worry about. However, I'm nervous about both options and am wondering if there are any experts out there who can provide some advice on things to look out for or insist upon.

Many thanks for any help!