Claiming back VAT on extension

Hi
I have a client who is a VAT-registered partnership. They are currently building a brickwork extension for him to work at home properly, and it is attached to the house. (ie:not a posh shed in the back garden)
I would like to know the following:
Can he claim VAT back on build/labour? I have been assuming not, but can only find reference to residential new build/extensions for Jo Bloggs non-VAT registered or pre-fabricated, stand-alone, technically 'moveable' worksheds for business use. If someone could confirm I am on the right track (or not) it would be much appreciated
CGT; Can I assume that as long as the extension isn't solely for business use (ie: there is a bookshelf/telly in there, and future expenses are pro-rata'd to 95% CGT would not be an issue?
Thanks for your help,