In message , Kris
writes
Hi I have been looking at the posts regarding boarding out lofts and
have a question.
I plan to use the chipboard type floorboards to cover 70% of my loft.
At the moment the full loft has 100mm insulation and no vapor barrier.
if I put the boards down it will compress the insulation slightly (the
gap between the ceiling and the top of the wood is around 80mm. The
roof has no felt so the cement from the back of the tiles is all over
the insulation.

sounds like our loft, the old insulation was covered with the old mortar
from when the roof had been retiled.

As I am not boarding out the entire loft do I need to put a vapor
barrier down?

I didn't bother, I have lifted some of the boards since in the middle of
winter and there was no evidence of condensation.

How do I know weather the insulation needs replacing?

If it looks a bit tatty and a mess I'd replace it.

Actually what I did was lift the old insulation from the area to be
boarded, if the insulation in other areas wasn't too bad i left it.

I cleared out all the old mortar from between the joists (the worst part
of the job)

I laid new insulation (100mm) under the boards- I use battens to lift
the boards a little to avoid squashing the insulation, but it's of
probably of doubtful benefit.

I cross laid further insulation over the top of the other insulation in
the unboarded bits - I guess about 200-300 mm in total.
--
Chris French, Leeds