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Discussion Starter · #1 ·
Hi all,

We live in southern Maine and have a 24’x30’ 2 story 2 car gambrel style detached garage 10’ away from our house. Garage was built around 98-99 timeframe. As far as we can tell and from the permit pulled on it, it’s on a 6”reinforced slab.

There’s roughly 400 sq feet of open space on the second floor of the garage that we’d love to turn into a couple of bedrooms by attaching the house (2 story cape with basement) and garage. However, code won’t allow attaching the house to a garage when it’s on a slab.

Is there any way to convert the existing slab to give it some type of footing like a 4’ frost wall or converting it to a frost protected shallow foundation? I’ve read about underpinning, but that seemed to be more about providing extra support for existing footings.

I know ideally we’d take the garage down and replace the slab to get it to code, it just feels like a terrible waste to tear the whole thing down when it’s already there.

Any thoughts?
 

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retired framer
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Underpinning is what you do when you need to lower a basement, make a foundation stronger or in you case make a slab frost proof.
Have you talked to the city about making the slab frost protected. Is that something they would consider?
 

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Discussion Starter · #3 ·
Underpinning is what you do when you need to lower a basement, make a foundation stronger or in you case make a slab frost proof.
Have you talked to the city about making the slab frost protected. Is that something they would consider?
I just talked to them and they said we could either retrofit with a 4’ frost wall or potentially add radiant heat to the the slab on the first level to keep it at 64 degrees.

Living in Maine ideally I’d prefer to stay away from heating the lower level 6 months out of the year just to park some cars in it. Where we’d have to add a 4’ frost wall already for the connection between the house and garage, I’m assuming it would be more economical in the long run to underpin the slab with a 4’ frost wall rather than continually heating the slab?
 

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Assuming that garage has no plumbing it would be an easy job for one of the "house moving" companies to slide it out of the way to give you access to build the required foundation and then slide it back. Worth talking to then to get an estimate.

Is the garage finished up and down? Even with the moving company the garage might need to be upgraded to meet today's codes, insulation, electrical, and heating.

You could also talk to an architect and see what a full detailed set of plans would cost. With plans you should slide right through the permit process.

Bud
 

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retired framer
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I just talked to them and they said we could either retrofit with a 4’ frost wall or potentially add radiant heat to the the slab on the first level to keep it at 64 degrees.

Living in Maine ideally I’d prefer to stay away from heating the lower level 6 months out of the year just to park some cars in it. Where we’d have to add a 4’ frost wall already for the connection between the house and garage, I’m assuming it would be more economical in the long run to underpin the slab with a 4’ frost wall rather than continually heating the slab?
Underpinning can cause other problems. Concrete wants to have smooth sides so ice can't form under irregular shapes. When you under pin dirt falls in the hole and you form up one side and pour concrete that fill all the gaps and holes in the fill. So you also want good drainage at the bottom.
 

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Discussion Starter · #6 ·
Assuming that garage has no plumbing it would be an easy job for one of the "house moving" companies to slide it out of the way to give you access to build the required foundation and then slide it back. Worth talking to then to get an estimate.

Is the garage finished up and down? Even with the moving company the garage might need to be upgraded to meet today's codes, insulation, electrical, and heating.

You could also talk to an architect and see what a full detailed set of plans would cost. With plans you should slide right through the permit process.

Bud
That’s a very interesting idea Bud, thank you. I found a local company that does both the moving and foundation work so I’ll talk with them to about cost to see if it makes sense vs starting over. The garage only has one circuit going into it and a line from our electric dog fence so there would be little to disconnect to move it. Most of the first floor walls and ceiling already have some R-13 insulation so we might be able to reuse that when drywalling it.
 

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That’s a very interesting idea Bud, thank you. I found a local company that does both the moving and foundation work so I’ll talk with them to about cost to see if it makes sense vs starting over. The garage only has one circuit going into it and a line from our electric dog fence so there would be little to disconnect to move it. Most of the first floor walls and ceiling already have some R-13 insulation so we might be able to reuse that when drywalling it.
You may want to look into the use of Mini- Piling.
 
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