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Flat Roof High Wind Velocity Zone Advice

Bobguy

New Member
Joined
Nov 28, 2023
Messages
9
Location
Caribbean
I'm in the process of setting up my system, hung up on the mounting and looking for advice. I have a flat roof with 3x8 beams spaced at 32 inches that I would like to use. The roof has only a slight slope of 8-9 degrees and ideally I'd like to have 18 degrees tilt. Typically people here use basic L-bracket and rail but I'd like to get an extra 10 degrees of tilt. It is also a hurricane area.

Any advice on a mounting, rail system, or kit. Do I just stick with the current 8-9 degrees for a flat rail system that will keep the panels closer to the roof. What efficiency loss would I expect? Or do I try and find a system that I can tile and addition 8-10 degrees but may be more prone to fail in high winds? If I did the spacing and maths correct one of the rails would need to be about 5 1/2 inches than the other to get the extra tilt.

I feel confident on everything else for the system but stuck on the mounting. Any help would be greatly appreciated.
 
Any idea on a maximum design wind velocity? The devil is in the details! I would suspect that the roof will fail at the points of connection of the 3x8s and the top wall plate. Any additional lift from the desired increase in panel tilt will make those failure points more likely. It would be helpful if there is a continuous tie from the rafters down to the floor/slab, repetitve.

There is a "windstorm mitigation manual" floating around that is an excellent reference.

All that said, I would recommend you hire a structural engineer to look at it. If the cost of failure is high, the structural review will be cheap insurance!
 
Searching the forum I found a website to check and it isn't a huge annual efficiency loss. About 4% for the year whether it is tilted with the extra degrees or not. I would lose most efficiency during winter but that is when my energy demands are lower.

The site I used for comparison : https://re.jrc.ec.europa.eu/pvg_tools/en/
 
Any idea on a maximum design wind velocity? The devil is in the details! I would suspect that the roof will fail at the points of connection of the 3x8s and the top wall plate. Any additional lift from the desired increase in panel tilt will make those failure points more likely. It would be helpful if there is a continuous tie from the rafters down to the floor/slab, repetitve.

There is a "windstorm mitigation manual" floating around that is an excellent reference.

All that said, I would recommend you hire a structural engineer to look at it. If the cost of failure is high, the structural review will be cheap insurance!
The roof survived one category 5 (barely) just a little while back but didn't have solar on it. It is a concrete wall garage with wood roof. The beams are embedded in bond beam concrete walls. I think I won't deal with adding the extra tilt and keep the close to the roof. Looking for L-brackets with two lag bolts. I can also replace the facia around the edge of the roof to make it a little higher. I also bought some reasonable priced Q-Cell panels, and only 24, are going up there so not a huge hit if disaster strikes.
 

I think this is the mitigation manual I'm remembering.
We have quite a bit of data now for Puerto Rico and Virgin Islands in regards to uplift after the last storm.

If interested FEMA did a pretty good job on it if interested (below). The data models are buried pretty deep in the document.

 
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