"BigWallop" wrote in message
...

"David Hearn" wrote in message
...
Quick question about loft insulation.

I currently have 4" of 'loose' fibre glass insulation in a 1930's semi.
I
may add some extra joists at 90 degrees to add another 4" of insulation.
As
I understand it, its the air that gets trapped in the insulation that
provides the insulating effect. Therefore, there's no point in buying
the
thickest pack of insulation around and squash it into 4", rather get one
which is closest to the thickess I require. Should be cheaper (per m^2)
and
provide similar insulation to a thicker one squashed to 4". Or am I
wrong?

Thanks

D


Why are you going to lay another layer of joists ? Why not just roll your
new insulation at 90 degrees across the top of the existing stuff that's
already there ? The insulation doesn't need to be between joist to be
effective, in fact the looser and thicker it is, the better it works. The
fibre insulation is very cheap to buy on its own, so please don't go to
expense of laying joists on top of joists just to be able to squeeze
insulation between them. It's just not worth it.

I guess I assumed everyone would remember my other posts! I'm planning on
boarding out the loft, and therefore need the extra joists to add height for
additional insulation whilst hopefully providing a little extra strength.

D