Thread: Garage Reno - Q re: habitable slab

Hi to all

I'm about to embark on converting one half of our double lock-up garage into a 'room' (habitable preferred). The house is 18 yrs old (we bought it 3 yrs ago). The garage is under the same roof line as the main house, gyprocked, two roller doors.
I have been speaking to the local council about habitable spaces\room for the proposed conversion and the main question cropping up is the garage concrete; whether it's habitable.

I have the house plans and how I'm interpreting it is that the garage slab is the same standard as the house (could be really wrong). There is a 100mm step-down into the garage when you enter the garage from the house.

So i guess my question is, how can I tell whether my slab is 'habitable'? What should i be looking for? I have attached House Plans and some photos. Certain parts of the plans have been blanked out for privacy reasons.

House Plans.pdf

The reason most garages have a step down is so that any fluids leaking from any vehicle do not run into the house. This may make it uninhabitable as you will not have this step into that room you are planning.

Drill a hole in the concrete and see how far down you have to go before hitting dirt.

Originally Posted by nace

So i guess my question is, how can I tell whether my slab is 'habitable'? What should i be looking for?

Most garage slabs don't have a plastic moisture barrier under them to help prevent damp, and are usually at the same level as the driveway, so you'll need to look at weatherproofing this also.

The reason Council is concerned about the slab being "habitable" is, does the slab have a plastic mositure proof barrier below it, to stop rising damp coming up through the slab causing and unhealthy situation should the floor of the new room be covered with carpet or similar. DON'T drill a hole through the concrete because if there is a barrier you just drilled through it destroying the integrity. The concrete slab when laid as a continuous pour will also act as a termite barrier, drilling a hole will be like an invite to raid your home. You need to determine was a plastic barrier installed below the floor. If you can dig down on the outside of the wall you might be able to find the orange plastic coming up from the underside of the footing. you won't be able to dig down to the bottom of the footing but if you can find the plastic at end end of the wall and perhaps in the middle it will give you a good understanding. Secondly and much easier get a 1m square peice of plastic and tape it to the top of the concrete making sure you continually tape it all round the perimeter. leave the plastic for about a week or two. If the slab has a moisture proof barrier the the plastic on top will not draw moisture to the surface, no barrier you will find moisture under the plastic. If you do end up with moisture you will need to apply a moisture barrier to the top of the floor before you apply any floor coverings. Use an epoxy moisture proof barrier NOT a moisture resitent barrier, there is a difference. Selleys or Bostick products do the job. Apart from the above you need to have a 2400mm floor to ceiling height and enough windows to provide light (10% of the floor area of the room) and ventilation (5% of the floor area). Enjoy your new room.

Holly crap Hoppy

Thanks for the tips, much appreciated. There are two existing windows (non-opening) which will be part of the new room space and a new stacker door system will go in at the opening. Just got to get this Permit application in.