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I have a 2-car attached garage but three cars in the household. While I'm obviously aware I can just leave the third car in the driveway, it inconveniently blocks the cars in the garage and in the winter it gets covered in snow.

I'd like to make a parking space on the side of my garage (most likely with pavers or concrete) but I'd also like to be able to put a roof over this space to keep the snow off.

If I do get a concrete slab poured, I could have them place some 4x4 post bases (like this or this, I'd imagine) to use on the one side, and then I think I'd have to install some kind of ledger board on the side of the garage and then of course build a simple slanted roof between the ledger board on the garage and the board running across the 4x4s on the other side.

Here's a picture of the side of the garage, and a terrible sketch of my 4x4 posts and my ledger boards (I'd probably use 3 posts, not 2, but the drawing was bad enough already...)

I'm not sure exactly what that would entail or if it's a bad idea to try to put a ledger board on the side of my garage- would I need to remove some of the vinyl siding, is that wall structurally supporting enough to handle the ledger board, etc.

If I couldn't put the ledger board directly on the garage itself, could I just put 4x4s on each side, slightly taller on the side near the garage?

Obviously this would all need to be approved by my town with a building permit, but I wanted to start planning this out and seeing what problems I might run into and how I should design this thing.

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This is highly dubious since you mention snow. The current garage sidewall is not high enough to support the high side of a shed roof over your proposed additional space, and the additional roof (if you just slap it on there anyway) will introduce additional snow-loading to the garage roof that it's probably not designed for. You can get some massive snow drifts in that configuration.

You would do better to build a totally separate structure away from the current garage. Once again, given the mention of snow, that structure would probably better be a garage - aside from people blindly following trends from elsewhere-that-it-does-not-snow-in, carports have never been all that popular in snow country because the car still gets snow on, around, and under it anytime the wind blows, so it's barely better than parking it out in the open.

  • Structurally, I agree with Ecnerwal's answer. But, I grew up in a house with a carport (in the Philadelphia region) and I have to disagree a bit as to the usefulness of a carport. Yes, wind will blow in a fair bit of snow on the sides depending on conditions and overhang, but the top of the cars in our case stayed in pretty good condition. This was especially valued during bouts with freezing rain and not having to scrape the windshields clear of ice. If @Joseph likes the idea, I would recommend it as a good balance if cost seems reasonable as opposed to another fully enclosed garage. – dmarietta Sep 29 '16 at 17:27
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I don't see why your idea would not work.

Yes, you will need to remove the siding where your ledger attaches. You will have several important considerations:

  • water intrusion at ledger board location. You will need to ensure that area is properly flashed and sealed, and try not to damage the waterproof membrane under your existing siding.
  • roof slope and design. Depending on your locale, you need to ensure the roof is designed to shed rain/snow properly.
  • structure strength, not just to support its own weight and snow load but for wind too.

You really ought to have an architect assess your design, he/she will have an engineer properly calculate foundation and structural member sizing for you.

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It's not clear to me that you have enough height to attach the carport as you propose. Based on the garage door visible (probably 7' high) I think it will be very tight once you take into account the slope of the carport roof (1:6 if using shingles) and the depth of the carport roof rafters. But it may work.

Also make sure you plan for the additional snow load that will be imposed on the shared wall. Depending on where you live that could be a considerable amount of additional weight. It might be easier to have the carport free-standing, that way you don't have to worry about compromising the garage's structure and getting the ledger flashing right.

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I think an easier solution is to not penetrate your current home. You have a system that works, so don't break it.

I would:

  • pour slab and use at least 8" posts for all four "corners.
  • have the height of the post go about 2 feet higher than gutter.
  • Run appropriate headers to carry roof load. Guessing these will be a good 9 feet in the air.
  • the roof would be a simple half-truss solution. Start off 2-3 feet higher on the left side (of your picture) and downslope away from your house. This will aesthetically look good. The left side can jut out to cover the gap plus a few inches to allow clearance for house and gutter.
  • The only downside is that your slab will probably need to be about a foot wider. This should be cheaper overall and look better. Also you will have a natural 2-3 feet on the left for storage without hurting the integrity of your house.
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It appears to me that your project will certainly work, especially if you install the posts to support the house side of the carport. There is no reason to jeopardize the integrity of the existing garage wall. I would check the building codes in your area, and considering the snow potential I would go with at least 2"x10" rafters. You might give yourself some peace of mind and use 6"x6" corner posts just to make sure the roof will support the weight. Sounds like a fun project and if done well, can add all the benefits of a regular garage without the additional costs.

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