mlv wrote:
I'm going to re-insulate my loft. However, the joists are at non-standard
spacings (due mainly to additional joists being fitted for a loft
conversion), so the pre-cut rolls of fibreglass insulation are no use to me.

It used to be possible to buy uncut rolls of fibreglass insulation, but I
can't find them any more.

How do you mean, 'uncut'? Unless you mean the loose-fill granular stuff?

The rolls of fibreglass insulation are fairly 'flexible' in that within
reason they will fit between joist narrower than intended, and will bulk
up a bit (ie, get deeper, = more insulation). If they are way too wide,
just trim of the excess with a long carving knife while still rolled up
(like cutting a swiss roll!) - if you have non-standard spacings you can
be sure the surplus will be used up.

I'm going to lay two layers of 100mm thick and will want a considerable
quantity as the property is a bungalow.

The second layer should be laid at 90deg to the first, so you'll have no
joist issues there (and it will be much quicker to lay, too).

David