[Default] On Thu, 16 Aug 2012 08:59:31 +0100, a certain chimpanzee,
"David WE Roberts" , randomly hit the keyboard
and wrote:

We need SAP calculations for our extension - I assume because bi-folds are
over 25% of new floor area.

Can anyone recommend an online firm to do these?

Presumably you been asked to supply calculations to show that your
proposed extension performs no worse than a notional extension by your
Building Control section. This is shorthand for, "there's no way your
extension will comply with that much glazing, but I can't come out and
say it, so you have to get your own calcs to convince yourself".

If so, what they're looking for is the total additional heat loss from
an excess of glazing in Watts/degree C. You can then try and offset
this heat loss from elsewhere within the extension, or if not
possible, elsewhere in the building (e.g., additional loft insulation,
more efficient boiler, etc.).

If you know how to work out U-values (or your architect does), you
shouldn't need to go to the expense of getting two SAPs ('cos that's
what you'd need - one for the house + notional extension, & one for
the house with improvements + proposed extension).
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have I strayed"?