Topic

It sounds like you're using a ballasted racking product, which is an excellent non-penetrative solution for flat roofs.  There are a few products available on the market, each with their own design specifications, so it's best to confirm with your manufacturer.

If, for example, you were using the AET Rayport product, AET recommends using blocks measuring 4" x 8" x 16" with a weight of 32 pounds.  AET provides engineering on a per-project basis, and this weight would be included therein.

If, on the other hand, you were using Unirac's RapidRac product, their Code Compliant Installation Manual, on Page 9, describes their blocks as "standard 'Cap Blocks' with the dimensions of 4" x 8" x 16" and having a weight of 26 lb."

Again, congratulations on your very exciting municipal project.