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Community and Q&A

Converting a Garage into an Apartment

erock1297 | Posted in General Questions on

I want to convert a garage into a studio apt but the slab is 12” below the rest of the house. I want to raise the floor aprox 8-10 inches above the slab to create room for plumbing, proper fall for sewer junction and last but not least to avoid cutting through the slab. I will place a wood floor over the subfloor.

I am considering a few strategies to do this:
1) delta ms or fl moisture barrier with foamular 250 ngx then plywood then floor joists with plywood and wood flooring on top.
Is this overkill? Would I need to insulate between the joists? What thickness of insulation board would be ideal. Do I need to fasten the next to the floor? Wouldn’t that ruin the thermal and condensation barrier? Could I float it with two layers of plywood?

2) what if I simply used 2 layers of the NGX at 4” over the slab and delta ms or fl with plywood on top not fastened. Obviously taped and alternating seams? Maybe two layers of plywood?

3) could I place the delta ms or fl, sleepers and floor joists with insulation inside over that?

4) last maybe I just place the delta and some ngx and don’t raise the floor and suck it up and cut through the slab?

Lastly most cost effective method- the ngx at 4” is not cheap but compared to lumber and the ease of placement it might be worth it- not to mention the thermal value.  Any suggestions here would be appreciated.

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  1. PLIERS | | #1

    You are raising the floor 8-10 inches just for plumbing in a studio apartment. Sounds like a huge undertaking and prob overkill in insulation. Im confused on how this will avoid you cutting into slab if 8-10 inches still does not raise the floor above the rest of house, where is this sewer junction? Probably cheaper to use a pump to lift your plumbing up into the sewer. It is done all the time in basement bathrooms when sewer line is above the slab. If you need extra height you could platform just your plumbing fixtures not sure how this would look if it requires substantial height, a few inches for a toilet might be no big deal. They have toilets with built in pumps. Or just have a step up into the bathroom or kitchen.

    1. erock1297 | | #2

      That’s a good idea and a good point. The crawl space begins about 20 ft from the bathroom location. Maybe getting to 12 inches would be better or just using the pump toilet/shower system would be better. I’m sure the laundry and kitchen drains would start high enough that raising it would not be necessary. Thanks for the response. Any opinions on the slab insulation? Delta and ngx board- thickness?

  2. PLIERS | | #3

    There’s a lot of information on this site but if you are not raising the floor 8-10in I would think 1-2 inches of insulation and 2 layers of 1/2 inch plywood screwed together could float on top. No need for anything else underneath. Consider yourself lucky you must have a lot of ceiling space because I would like to do that with my slab

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