Weatherlawyer wrote:

I am planning on insulating my loft to the recommended 270mm, and
would also like to lay floorboards above the insulation so I can
keep using the loft for storage. The gap between the ceiling and
the top of the existing joists is 70mm, so there's 200mm to go.

First thing get the cheapest offer you can with the insulation. But
for heaven's sake phone around all the other places too first.
Builders merchants not only stock it they deiver.

Wickes deliver too, for a small fee. I'm not sure where all these "other
places" are. I don't know any reputable builder's merchants, and
wouldn't know how to tell if one *were* reputable. Wickes was
recommended to me by the nice man who did my central heating, and did a
very nice job of it too.

Secondly, why are you intent on adding timber? If you must walk
around up there for maintainance in the future all you need is a
walkway built up. If that. You could just lay a plank or two over the
wool.

As mentioned in my original post:

would also like to lay floorboards above the insulation so I can
keep using the loft for storage.

That's why I'm intent on adding timber

Remember there must be a draught in the roof at all times as the
amount of moisture that vents through it is quite amazing.

Yep, I wasn't going to lay the insulation all the way to the eaves, or
to the ceiling.

Third: However much you put up there at first, it will have shrunk to
a lot less after a few months settlement. Talk it over with the
salesmen in the timberyards you get quotes from. They will be far
more knowledgeable than staff at Wickes's or similar. Though I must
admit a few B&Q staffers I have met seemed on the ball.

Bugger, this was the sort of thing I was worried about. Will I need to
stick the timber up in the loft for a few months until it adjusts to the
weather conditions up there before I can cut and fit it?

Dave