stamped racking plans
Must be stamped the rackings plans by an engineer before starting the construction?
That's entirely up to the AHJ. It may also depend on state law.
For what it's worth, in my experience, usually if you're doing a commercial building or a ground mount you will be required to show some engineering. (For the ground mount the main concern is soil and drainage, not racking.) If you're doing a residential rooftop project, usually not, especially if you can demonstrate the existing structure was built to code.
Most AHJs in my experience don't ask for a stamp on the racking if it's manufactured for the purpose and used as instructed.
Originally Posted by jaggedben
It also needs surplus load capacity for the self-weight of the modules and racking system.
If it is built to the code minimum of the current standard, so tightly that not one single psf of additional load can be added, you cannot put solar on it. Older buildings had more conservative safety factors in the codes at the time, so with the current standard, older buildings typically have surplus capacity.
To clarify: many AHJs ask us as a contractor to demonstrate the structural integrity, but usually don't require a structural engineer's stamp.
Originally Posted by Carultch
They ask us to certify the rafter size, spacing and spans, and they have guidelines for whether those specs pass muster without an engineer's stamp. (I consult those guidelines even when working with an AHJ who doesn't review it.) On unusual (e.g. Eichler) or substandard structures we often have to get an engineer's stamp (or upgrade the structure). The guidelines don't apply to ballasted systems and usually apply only to flush mounted systems (not tilt-up). This is in California where the state has issued quite a bit of guidance for how to expedite solar permits since there's a law that requires it for smaller residential systems.
Originally Posted by jjavier
Yeah like others have pointed out it really depends on the AHJ.
For example, in Seattle they have an guiding document on when a building permit is required. If for example, the pv system is not 18" over the roof line, and does not exceed 5psf, then a building permit is not required, only an electrical permit. Of course there are a bunch of other qualifying criteria. But in some cases, you could have a hybrid ballasted system (with some attachments) to get down to less than 5 psf and comply with their rule to not have a building permit.
However, I would still want an engineer's stamp to provide some level of comfort so I can sleep on those windy nights, that it won't be blowing off the roof. So regardless of the permit, I would want it stamped. But my opinion might differ based on the racking system, ballasted, sure lets get it stamped; fixed attached, probably not, especially on a newer built home and doing staggared attachment layouts 2 and 4' on centers, what I would call a conservative standard approach to fixed attached.
On a separate note, depending on the racking you are using, the company may already have stamped letters from your state, or even calculations and guiding tables on overhangs, spacing, cantilever, etc, on how the racking system can be soundly integrated into a building when their guidelines are followed. Unirac, Ironridge, and Snapnrack are few off the top of my head that I know have these resources available on their website.
Still, in my own opinion, I will usually opt for the extra $800-$1000 to have the design stamped by an engineer, depending on what it is. It is cheap insurance to know you are doing the job right, at least, according to the structural engineer.
We are looking for an engineer to stamp our ground racking system in Maine, Do you know one?
Originally Posted by jjavier