Integral garage conversion.

Hi All

I'm about to convert my integral garage to a living space and would like some advice on insulation. The garage has 2 external walls, the longest wall (5m) is block and brick without insulation in the cavity. The shortest external wall (2.5m) will consist of the new infill wall of block/brick and insulation and a window. The floor is a concrete slab which I presume does not have any insulation below. There is a difference in height between the garage floor and the house floor of 80mm the front and 70mm at the back. Ideally I would like the floor in the house and the new room to be the same. A builder has quoted but is planning on using 25mm insulation in the floor with a screed on top, will this be enough to satisfy the BCO? I have heard of people laying rigid insulation onto the slab and laying chip board straight ontop. If this is a good idea will I need to self level the floor or will the 10mm difference not notice over 5m. Regarding the walls, will only the external wall need insulating? I was thinking of having them fit an insulated plasterboard. The ceiling is below a bedroom so I am pretty sure this will already be upto spec. Any advice on the whole subject of the conversion would be appreciated.

Thanks

Andy

BC will not accept 25mm insulation and a screed. You will have as thick insulation as you can fit under 18mm ply or chipboard. Not ideal but that's life! You could have say a 25mm high timber transition to get you a little higher under the doorway.

Separate insulation and foil backed plasterboard is cheaper than insulated plasterboard, although slightly more labour intensive.

You will have to check you have insulation in the ceiling and what it is, don't assume it just is.

Run you plans through with your Inspector before you do anything to check he is happy with your proposals, some are a lot more thorough than others and that is not necessarily a bad thing, ultimately the owness is on the homeowner to ensure compliance with Building Regulations not the builder. That said if you are not having drawings done for Building Control/for your builder to work off you should be working with a builder who knows the Regs inside out for garage conversions, from your post it would appear he is not. Tread carefully!

Thanks for the reply. I didn't think 25mm was enough. Is there an under screed foil available that would take the floor upto regs? What about the slope of the floor do you think it would notice with rigid boards layed on it? I was thinking that the plaster board option might save some space, the room is only 2.5m wide. Is the external wall the only one that needs insulating?

Thanks

No, there is no magic bullet solution here, you could maybe ask your inspector if you could increase the wall insulation to compensate but I wouldn't hold your breath. The wall between the garage and the house should not need insulating.

Using separate insulation and plasterboard is no thicker than insulated plasterboard.

10mm slope is not mahoosive over that room but you could shove some sand down or use a levelling screed if you really wanted to.

On a slightly different note, if you were having problems in upgrading the floor (with insulation and screed) due to levels, then you can look at using a "trade off" calculation, which SAP assessors use. You put as much insulation as you can on the floor and then you would look at upgrading the walls/ceiling with more than normal to make up for the loss to the floor. I've had it done a few times.