Is my over hang designed properly?

I am thinking about building an overhang from our shed to park my trailers under. I am curious if my current design is structurally sound. I am building in southern Maryland so there is some snow but not much.
I would like to build 24 foot by 18 foot over hang. The slope of the roof would be on the 18 foot span. The 24 foot side would but up against my existing shed. The rafters would run the 18 foot span.
First is 6 4x4 posts sunk two feet in the ground enough? I think code in my area is 18 inches. One post on each corner and one in the front center and rear center.
Second do I need to use 2x6 or 2x8 for rafters? I am planning on puting the rafters 24" on center.
I plans to sheath it with plywood and shingle it with cheapo fiberglass shingles.
Is my plan sound?
Thanks Dan
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Home owner wrote:

Not enough information. Using 6 posts I see 8' between posts on the 24" side per your description. What are you bridging them with to support the rafters. Just as a WAG I would say that you need at a minimum 2x8 rafters.
If you need a building permit, draw your plans out and take them in. They will quite rapidly tell you if you are up to code. Of course the drawback is that you will wind up building way beyond what you consider adequate. In my case, for a 26x10' shed roof, had I built to their specs I could have parked a D6 cat on it.
Harry K
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I was thinking of running 2x6s along the front and back to hold up the raftres. I was thinking 4 12 foot 2x6. One on each side of the 4x4 with a seam in the middle of the structure. I am not sure I want to mess with getting a permit. But, unless I feel real comfortable witht he information I get I will go that route.
Also what should the pitch on the roof be at a minimum?
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i doubt if you will get a permit once you check and find out that you need a fabulous drawing (like a blueprint) and that you will have to build so it will last thru 100 year-storms.
since it's only to cover a trailer, it might now matter if a hurricane wind blows it away or collapses it. but i would listen intently to the advice you're getting and check those spans. bigger is better. bear in mind that a housing inspector might make you take it down so build it with bolts that you can remove if you have to. ....thehick
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frank-in-toronto wrote:

May not need blue prints. Many departments will accept well drawn plans done by home-owners. Mine will. They do need to be -well- drawn and require detail drawings of how you are going to frame corners, doors, etc. Must also have all construction materials specified as to size/type etc.
Harry K
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snipped-for-privacy@gmail.com says...

Your plan is not sound. First, you need to know the recommended snow load for your area. I doubt that it is a very high figure in Maryland, so let's use some common minimums for example, 10 psf dead load and 20 psf live (snow) load.
You won't even come close to spanning 18' using 2x8's on 16" centers, let alone 24". I just finished a 30' wide gable roof, and 2x8's on 16" centers just squeaked by the code for the 15' span.
And your cross members along the 18' edge would need to be quite substantial to span 8', they would require double 2x12's at least in my area.
Here is an online span calculator to play around with some figures:
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp
For starters use spruce-pine-fir in a #2 grade, that is the most common lumber in your area.
Dennis
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NO You need to contact your building department. Your design does not take into consideration, wind loading, and snow loading. I will bet you will end up with more like 2x10's 16" on center.
I built a patio cover, 12 feet wide by 14 feet long, 3/8 ply and rolled roofing. I need 1 4x6 post and a beam pocket attached to the house. I needed a 4x 10 beam to support the 2x8's 24" on center. I was lucky that the footing was already installed. Footings for a patio cover are 3 feet by 3 feet by one foot deep attached to the 4x6. The damn thing cost one hell of a lot more than I had envisioned during conception. Not sorry I spent the money, materials cost well over $5.00 bucks a square foot including the paint when I was finished.
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