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Community and Q&A

Garage Renovation

sean_web | Posted in Building Code Questions on

My neighbors are renovating their garage into an inlaw suite. They’ve struggled for over a year–maybe two at this point–to lock down contractors, supplies, and working with the city inspector over permits.

They finally received materials but the inspector recently told them they will need to insulate the outside of the foundation. This would require them to trench around the entire structure, which would also mean tearing up some driveway, to put in foam board insulation.

My understanding is that the structure is old (likely 1920s) but solid. It’s probably around 24×20 with simple gable roof, and I believe it’s 2×6 24oc. I would guess….since it’s a garage….that it’s not a foundation but just a slab with frost walls on all four sides.

I think it’s ridiculous that the inspector wants them to do this. What if they were to simply put down 4in of polyiso on top the slab, and just put a floating floor over that? Wouldn’t that potentially meet code? We are Ohio/Zone 5 and I believe Ohio building code is IRC 2018. I know their plan is to otherwise insulate the walls and ceiling with code-compliant levels, but it sounded like they were not otherwise planning anything for the slab/floor.

That’s all the info I have on this project, but hoping that’s enough to maybe get some insight that could potentially help them.

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  1. plumb_bob | | #1

    The slab was not built with a dwelling unit in mind, so there are several issues that I could see concerning the existing slab: was there a granular layer or a poly sheet put down between the soil and concrete? If not, there could be issues with radon gas and/or moisture. Also, insulation levels must be addressed. If the unit is built correctly it will last for many years, and insulation levels should be able to achieve a minimum of energy efficiency and comfort. Even if this is not a concern for your neighbours, it could be for the next owners.

    There are always other options for any project, but they may be outside the scope of the code you are using, and require engineering.

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