Lobster wrote:
Dave Page wrote:

I was intending to replace the existing insulation - it's only
about an inch thick, dead old (over 10 years), and patchily
installed. Plus insulation seems to come (from Wickes at least, who
are selling rolls ad near-half-price until this weekend) in 170mm
and 100mm depths.

I wouldn't bother lifting the old stuff - 'orrible job, and it won't
do any harm being added to by what you're going to lay on top.

Frankly, it's all I can do to stop it blowing away in a draft.

I've used the Wickes stuff; it's still intended to be laid
perpendicularly (or orthogonally - FFS!) even if you're starting from
scratch (I think their instruction sheet says so).

Fair enough. In that case, I'm not sure what the best thing to do is; if
I lay the insulation perpendicular to the existing joists, I'm not going
to be able to get 270mm down over the existing joints (or a little way
either side) unless I lay *more* joisting over the top. Seems the best
thing to do might be to lay down the 100mm rolls *between* the existing
joists, lay another 200mm of joisting perpendicular to that (squishing
down some of the insulation beneath), and rolling the 170mm insulation
between the new joisting.

Still not too happy about your weight issue though, but I could be
wrong - hopefully someone with more knowledge than me will comment?

Well, if there's concern, I'll hold off for a little while until
consensus forms. Can't wait too long though, I want to make the purchase
before the Wickes special offer on insulation ends on Saturday, and I'm
busy all day Friday.

Dave