Garage project - Insulation and flooring.

11 Oct 2016
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United Kingdom

I'll give a little bit of background first..
We have an attached single garage to the side of our house. Originally it was not accessible from the house, with just an up-and-over door to the front and a rear door/window to the rear.

The previous owners converted the garage in a slightly strange manner. The rear half of the garage was turned into a utility room with an internal door into the house. The conversion is basically a stud/partition construction within the garage itself. The existing rear door now sits within this conversion and acts as a back door.

The front half is still garage and is accessed from within the utility room. It is un-modified. I can access the roof of the conversion for storage. I use this as a typical workshop/shed/storage place, and bung the washing machine in there.

I am looking to make this a bit more useful as a workshop, although not convert it fully into another room, with the following modifications.

-Raise the floor level from the concrete floor up to the level of the converstion. This is about 3 inches

-Insulate wherever possible.

Regarding the flooring. The concrete base hasn't ever shown signs of damp, so that leads me to suspect it has a DPM. Could I then just lay joists on the floor and add floorboards on top? Would it be beneficial to add some sort of insulation type material under here (Kingspan or polystyrene sheets)?

Insulation wise. I was thinking of fixing polystyrene insulation sheets on to the inside of the steel door, and then fixing some rubber draft proofing around the edges.
The other option would be to replace the steel door with a pair of side-hung wooden doors, similarly insulated.

Would polystyrene sheeting be beneficial between the rafters as well?

The plan is that this will not be a permanent habitable space, more a useful workshop that will be heated when necessary with a portable heat source.

Thanks in advance
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