Wall and floor insulation advice on extension

27 May 2004
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United Kingdom
We are planning to extend above and behind the garage and also convert most of the garage into a usable room. I would like the posibility of converting the garage back easily for future resale value.

The existing house is 16 years old and has 300mm thick walls, the garage only has 200mm thick walls which look like brick outside and concrete block inside.

1. There are obviously strict rules on insulation values for extensions, what will I need use to achieve these bearing in mind my walls are only 200mm thick in the garage ? How will this impact on the extension above the garage ?

2. Do I need to insulate the floor in the garage ?

3. How can I tell if there is an existing damp proof membrane in the garage floor ? (I think there is a DPC around the bricks)
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Not sure about doing this and then 'easily' turning it back into a garage later.
The floor will need raising, damp-proofing and insulating, which will be at least 8".
A brick retaining wall built along the entrance of the garage to house patio doors at the very least, plus the raised floor.
Then there's the ceiling height...
I think you'd need to look at digging the floor up and starting from a lower level, or you may be breaching the existing dpc and taking the floor higher than the one in the house.
And then you want to 'easily' remove this lot later?
Ring your Building Control, they'll give you solid, free advice. ;)

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