I have a mud room that I'd like to make larger. By doing so I have to extend the floor out into the garage. Currently, there is a landing in the garage that is about 3 feet off the ground leading into the mud room. I want to remove the landing and wall/door leading into the mudroom and extending the floor into the garage by about 4 feet and adding non-load bearing walls to the new extension. Since the current walls in garage on top of the foundation, I need to find a way to support the new extended floor/walls. I'm looking for help on how to support a floor that will be about 3 feet off the ground.

Any thoughts?

closed as too broad by isherwood, ThreePhaseEel, Daniel Griscom, Machavity, mmathis Feb 1 at 15:55

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  • Hello, and welcome to Home Improvement. Unfortunately, this is too broad a question for our Q&A format. – Daniel Griscom Jan 31 at 0:19

A diagram with dimensions would help. But supporting the floor is the easy part - basically, you'll need to build a cripple wall, framed with 2x4 lumber, to support a rim joist that you'll hang your floor joists from. Set the cripple wall on a pressure treated plate lagged to the floor with concrete anchors. Floor joists will be sized with a span table Note that your garage floor should be sloped from back to front - you'll have to accommodate that in your framing to end up with a level floor.

You'll also have to determine if the wall at the back of the garage that you're intending to remove is load bearing or not. If so, that will be alot more work involving a licensed engineer, to figure out how to do that correctly. You'll also have to figure out how to support the new floor at that side, so you'll need to understand the framing & foundation of that wall.

Not sure where you're located, but most US building codes have specific rules about the walls between a garage and living space. Things like type & thickness of drywall, fire rated doors, sealed penetrations etc. You'd do well to check the codes for your community before you go to far.

  • Good answer, but I wonder about code with respect to supporting the floor on a slab. Technically you'd probably need footings underneath. – isherwood Jan 30 at 17:21
  • Yea, I'm not sure of that. But the load on it is minimal - basically just 4' of floor and a stick framed wall. I personally wouldn't be worried about it structurally - but code may say differently. – CoAstroGeek Jan 30 at 17:25
  • The issue would be seasonal floor movement in case the garage is unheated. Freeze/thaw cycles (and simple settling) could play havoc with drywall, etc. – isherwood Jan 30 at 17:28
  • Yea, that's a good point. You might have to cut some holes in the slab and put some piers down. At that point, he needs to talk to an engineer. – CoAstroGeek Jan 30 at 17:31
  • It sounds good to me for a non load bearing wall. I would think the the real problem would be the span of wall being removed probably is load bearing so a header of sufficient size would be needed to carry that load. – Ed Beal Jan 30 at 18:57

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