"Dave Page" wrote in message
...
Lobster wrote:

When topping up old insulation (Rockwool) it's normal and more effective
to lay the second layer perpendicular to the first.

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.

So you'd be better off fitting the new joists perpendicular to the
originals I'd have thought. However, your original ceiling joists are
not very meaty, so depending on the span, you may have a problem there,
if you are going to pile lots of new joists, floorboards and storage
items up there.

The joists are 14" / 355mm apart, so there are plenty of them (this is
particularly annoying since insulation roll seems to come in 400mm
widths). The thought of laying new joists crosswise is interesting, not
least because it would save me a few screws.

As it was, I'm not planning on putting too much weight up there, and was
considering only raising every other joist to save on timber. On the other
hand, the loft hatch is only 750mm wide, so if I want the boards to be
supported by three joists, I'll need to space the joists at roughly 350mm
anyway

Lay the joists at right angles and use joist hangers where they meet the
walls if any (gable end). Use 6" screws. Unifix supply these quite cheap.
Having the at 90 degrees reduces thermal bridging enormously.

There's one bit of information I'm missing; what sort of timber would be
appropriate for this job?

Just bog standard timber joists from the timber yard - haven't a clue
what species it is!

That sounds pretty useful. Wickes have some 40 x 100mm pre-cut 2.4m
lengths, I'll ask someone at the store whether it's suitable for my
purposes if it works out cheaper than a timber merchant.

Dave