I am thinking about building (DIY) a carport.
A sketch of the area and some possible post locations is below.
It would be a simple structure. I'm envisioning a very lightweight roof of clear (tinted) corrugated plastic, slightly angled so that rain drains off the side farthest from the house. I don't plan to run the roof all the way to the house, thinking it will be about the same width as the garage (appx 12'). The roof length would be appx 20', from the garage to post "C". There may be some decorative element on the end of the roof facing the street. to conceal the corrugated, but nothing significant.
I'm hoping to use 4' x 4' posts. They could be fastened to the concrete driveway surface, or concreted into the soil next to the driveway. I prefer the former, since that soil is probably my neighbor's property.
I envision a beam (continuous, or sections) tying posts A, B and C together and to corner of the garage closest to post A. And, at 90 degrees, I envision a beam connecting post A to the house, a beam connecting post B to the house, and a beam connecting posts C and D to the house. Those beams are not shown in the sketch. I figure that having the structure tied to the house and garage in two axes will give me the necessary rigidity, so I won't have to triangulate or use thicker posts. On top of those beams, I can put a light framework for the corrugated.
And it is those beams that have me stalled. Posts A, B, and C are each appx 17' from the house. I can build up (laminate) a beam that long, but I wonder if it will sag.
Further, while the roof will ordinarily carry no load other than itself and some rain, it will be exposed to wind, and occasional snow.
The highest recorded wind gusts ever in Portland have been 70-80 mph (that's a 100 year storm around here) and in winter 30+ mph is not uncommon. I'm thinking in the 70 mph scenario the corrugated plastic would simply rip off before the wood structure would be damaged. Make sense?
As for snow, it is very infrequent here, like once every several years, but it does happen. We had a week of 12" snow last winter, and I suppose 18" is not inconceivable someday. I've read snow weighs 8 lb/cu ft so 12' x 20' x 8 = 1920 lbs.
What do you guys suggest I do about the beams? I could use two additional posts opposite from posts A and B, but would like to avoid it if possible. I can see them getting in the way.
Any other suggestions, thoughts? I will probably build one carport in my life and this is it, so I am by definition a newbie.
