Structure calculation for carport

[solar_newbie]

Hi,

My situation is I got kind of car port in the side yard and the backyard. One side is connected to the house. The other side has multiple big polls. It has composition roof and built around 2 years ago. However, when we built it, the purpose is to cover for rain and sun. It is strong to walk and run on like normal roof with few people as we build it with more wood than needed for normal roof.
I plan to put around 4 panels (160 lb) + racking structure (80lb) on top of them next year.
Now, I am looking the way to calculate structure integrity and how to prove that the carport can support the 240 lb on top of them.

Plus since the carport is flat, I would need to have some sort of angle mount. Could you suggest where to look ?


Thanks.

[foo1bar]

The other side has multiple big polls.

Do the polls show who's going to win next year's election?

Oh you meant poles. My bad.

Seriously though - I wouldn't give structural advice over the internet if I were qualified to do so. (Too much liability IMO)
And I wouldn't take structural advice from someone over the internet.

I believe you will have to look at the strength of each member (every piece of wood) and the forces on it. As well as the strength of each joint in each direction it can pivot.
And if I were looking at your plans I'd want to know how the poles are fastened to the ground. ex. what keeps them from jumping 8" to the left and landing off their foundation if there is a strong wind or an earthquake.

[solar_newbie]

Do the polls show who's going to win next year's election?

Oh you meant poles. My bad.

Seriously though - I wouldn't give structural advice over the internet if I were qualified to do so. (Too much liability IMO)
And I wouldn't take structural advice from someone over the internet.

I believe you will have to look at the strength of each member (every piece of wood) and the forces on it. As well as the strength of each joint in each direction it can pivot.
And if I were looking at your plans I'd want to know how the poles are fastened to the ground. ex. what keeps them from jumping 8" to the left and landing off their foundation if there is a strong wind or an earthquake.

Yeah Poles Poles are 8x8 treated wood. All are burry in the ground 5-6 inches concrete. The whole back/sides/front yard are covered with concretes. So, unless they are all broken in heavy earthquake, the poles will not go any where. Every 4 feet, I have 1 poles.
For the roof, every 1 feet I put 1 2x6 rafter. The only join is between the rafter and the 8x8 wood that is install on top of every 2 poles.
On top of rafter, it is a thick fly wood.
On top of fly wood, it is composite roof.

For me, I do not see any issue to put couple hundred lb equipment on top. However, I am not sure how to prove to the inspector.

[inetdog]

The inspector is likely to accept nothing less than sealed drawings from a professional engineer (PE), so I would start shopping around for one in your area.
He does not need to know much if anything about solar since he will just be covering the structural strength and not the electrical design.

The factors to be considered include dead weight, side force in high winds and uplift in high winds. (Does the roof have tie down straps to the poles to keep it from flying away, for example.)

PS: If you do not have dimensioned construction drawings of the structure as a starting point, it may cost you a lot more!
(Was there a building permit, if so you should have the drawings)

[solar_newbie]

Thank you. I guess this is the first things I would need to do at this moment.

[J.P.M.]

The inspector is likely to accept nothing less than sealed drawings from a professional engineer (PE), so I would start shopping around for one in your area.
He does not need to know much if anything about solar since he will just be covering the structural strength and not the electrical design.

The factors to be considered include dead weight, side force in high winds and uplift in high winds. (Does the roof have tie down straps to the poles to keep it from flying away, for example.)

PS: If you do not have dimensioned construction drawings of the structure as a starting point, it may cost you a lot more!
(Was there a building permit, if so you should have the drawings)

Depending on the projected size and type of carport and local code, it MAY not have needed a permit. The structural P.E. (if and likely needed for the solar work) will probably not need a lot of electrical info about the panels, but will need to know a lot about not only the panel weigh and dimensions, but also their orientation (tilt, azimuth) and quite likely some (perhaps) specific information about relative orientation to other structures and the other panels themselves to be able to calculate the best est. of dead, live, occasional, perhaps cyclic and other loadings on the structure induced by the panels and as a result of wind, seismic, etc.

Such design considerations are often ignored or treated as an afterthought, often due to ignorance, only to present unanticipated problems later in design/approval process. Ignore them at your risk.

Take what you want of the above. Scrap the rest.

[solar_newbie]

The carport does not need permit as long as it meets the city requirement of the location. I checked with the city and have contractor install it 2 years ago. I asked to have it builds strong as I paid for equipment and just hire them for labor. I would say it is stronger than my current home.
24 feet long x 8 feet width
9 poles of 8x8 installed each side with concrete leg and then 5-6 inches concrete cover as the part of putting 4000 square foot concrete work on the whole yards. Top they connect together with 8x8 wood.

I would not imagine, there is any issue to hold those panels.
But I am worried about the PE stamp as city told me that they do not allow quick solar process on any place beside the roof.

Even city official has not issues to walk through the car port before step up to my roof as the part of inspection the solar a month ago. He told me it is very strong and secure.
However, process is process .... I have no clue why roof is treat different from other structure for solar? Roof top solar can get approved in 1 hour or less..... It is unfair.

[foo1bar]

I have no clue why roof is treat different from other structure for solar? Roof top solar can get approved in 1 hour or less..... It is unfair.

I think because the roof/building had a full set of structural calculations done when it was put up.

Apparently your carport did not.

Which I think could mean that someone could put up a "carport" that was built out of 1x2's and throw panels on top. Then if it blew over in a stiff wind because of the solar panels and landed on the neighbor's car... Well, at least if I was the neighbor I'd be plenty upset with the bldg dept about allowing such stuff to happen.

[foo1bar]

I would not imagine, there is any issue to hold those panels.
But I am worried about the PE stamp as city told me that they do not allow quick solar process on any place beside the roof.

Document the design of the carport (possibly including pictures) and bring it in and ask.
It sounds like the poles are sufficient.
I'd make sure to include documentation of how each corner is fastened - soil-pole, pole-rafter and rafter-house.
And probably documentation of the flashing at the rafter-house interface would be good too. (That it won't rot out there in 10 years)

[J.P.M.]

Call the local authority, but do not be surprised if formal calcs. are required. Simply because someone thinks something must be OK because it "looks" safe or because it is, in some layperson's opinion, "overdesigned", or because someone "can walk on it", does not satisfy any engineering requirements I've ever worked to. There are building codes and structural requirements for reasons that many folks are clueless about, not the least of which involve this being a litigious society.