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As described in this question, I'm planning to add an attached garage onto the side of my house. I'm looking for some guidance on how to attach it to the existing wall.

A bit of background about the existing house:

  • 2 story house (each level with 8' walls)
  • Exterior of the first floor is brick and the second floor is siding
  • Built in 2005
  • Exterior walls are made of 2x6's with insulation in between.
  • Existing roof trusses run parallel to wall in question

Relevant facts about the addition:

  • 10' walls
  • Lean-to roof
  • Interior ceiling of 10' with a small-ish attic above for storage

I'm considering using the existing wall as the interior wall of the new garage by cutting into the siding and attaching the roof rafters and ceiling/attic floor joists to the second floor wall framing. As I understand it, I think the only load this would be adding to that wall is a downward load since the ceiling rafters would counteract the lateral force that the roof rafters want to put on the wall (since that forms a right triangle). Especially since the existing roof trusses run parallel to the wall, I don't think there's very much load being placed on that wall and since they're 2x6's I expect it should hold that load without issue.

I'm sure before I do this I should get a qualified engineer to look at it and give me the go-ahead for my specific situation, but I'm hoping to minimize that cost by taking the plans to them already done and just needing their sign off on it (I'm not within city limits so permits and inspections aren't going to be an issue).

Bottom line question: Should I attach the roof/ceiling rafters to the existing exterior wall as described above or should I frame it as if that wall wasn't there (and it was a freestanding structure) and have the two load-bearing walls side-by-side?

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I would sketch out your plan to scale with dimensions and provide that drawing to your building department for your permit. I have done exactly what you are doing 3 times. Is your garage going to be totally enclosed? If it is the wall needs to be fire rated , this is not that hard removing the siding 2 sheets of Sheetrock with the seams staggered is what it took for me. On the one I added a door directly into the garage it had to have self closing hinges and be fire rated the other 2 had man doors out the back close to a entry door for the house. The best advice I can give is to make sure you use a wide flashing up under the house siding at least 4” up and 8” on top of the roof possibly taller if your wall is on the wind side. If the structure is going to remain open you may not need to have a fire rated wall but the ones I did were enclosed. Today any receptacles you put the garage will require GFCI protection even in the ceiling. If your plan doesn’t meet code they will red line it with a correction unless engineering is required then you will know you need to have it revised and stamped. I found my basic plan in a book back then laid it out and submitted I think they required a double cripple for the header but other than that it was approved.

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