In an earlier contribution to this discussion,
wrote:

Does anybody know where I could possible get hold of cavity wall
specs ? basically I'm looking at managing a extension project myself
but I want to be sure that everything is done right and according to
BC. Some of the builders I have had in for a quote tell me that for
the floor be it solid or wooden, they have to dig about 8" down and
then build it up with a mixture of hardcore, insulation and DPM, is
this correct ?

Any advice/help will be greatly appericated.

How are you going about getting Building Regs approval for your extension?
Assuming you're in England or Wales (Scotland may be different) there are
two different approaches which you can adopt. The more usual one is to draw
up (or pay someone else to draw up) detailed plans which contain the full
technical details of how the building will be constructed - and get them
approved *before* getting quotes from tradesmen for the actual work. These
will contain details of the cavity wall construction, floor construction and
insulation, roof construcion, door and window specs, etc. - and leave little
room for argument.

The alternative approach is to do it on a Building Notice - where you submit
much less detailed plans and then negotiate each detail with the Building
Inspector as the work progresses. This gives you more flexibility to
'refine' the design but also makes it much harder to get fixed price quotes
from tradesmen because the BCO might insist that they do something they
weren't expecting, thus adding to the cost.

It's a good idea - especially if you're doing your own plans - to go to have
a chat with a BCO at your local council and find out exactly what they'll be
looking for before you start. If it's obvious from your approach that you
want to do it right, but are not quite sure what to do, I have always found
them to be very helpful and supportive. They'd rather help you get it right
first time than get into a dispute when they come to inspect something which
*hasn't* been done right.

If you're doing your own project management, this book
http://www.whsmith.co.uk/whs/go.asp?...220&Menu=Books is a
"must read". Looks like WHS are doing a good deal on it, or you'll probably
find a copy in your local library.
--
Cheers,
Roger
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