"Peter Watson" wrote in message
...
In article ,
says...


But access to the edges doesn't have to be any thicker than the
thickness of
the boards, because you'd slide the boards in to the edges of the space.
Then just fix them down where it is most convenient to do so. If you go
with a flooring grade chipboard system, then the tongue and groove
around
the edges of the boards will be enough to hold them together in the
short
distances you can't reach right under the eaves. So you'll still
literally
be able to board the loft right out to the edges and make the space
between
the ceiling and the new loft floor into a sealed unit with the existing
insulation still between it.

I've been following this thread with interest as I'm in much the same
position as David. My house has 4x2 joists (not measured the spacing
yet) and I'd like to board at least the centre section but probably a
bit into the eaves as well. My original plan was the same as David's -
Put cross joist across the existong one to give extra height to allow
for more insulation and ventilation but I take your point about extra
loading.

I'm a bit confused about your previous advice here though - If I lay 4
inches of insulation between the joists and then board over am I likely
to run into condensation problems due to lack of ventilation to the
insulation? Is it generally OK if I were to not board over the bathroom
but to add extra insulation here instead?

I take your point about the boarding preventing air circulation and
acting as insulation but how does this compare with more fibre? The
current suggested minimum is 200mm (and I note that some people have
gone upto 450mm - Surely there's a law of diminishing returns here!)
The suggested solution would only have 100mm insulation, and boards?

Thanks,

Peter

As Andy Hall says, there is not a huge difference in the effect of laying
extra insulation when the same can be done by trapping the air between the
existing material with boards on top. The insulation works by stopping air
movement through the space between the boards and the ceiling, hence not
allowing colder air to travel through and cool the space down. The trapped
air is then heated by the very slow convection through from the room below
and has to stay where it is.

So by increasing the thickness of the insulation your actually just slowing
the air lose a very minuscule bit more than one layer does. But then your
giving yourself more work to try and increase the height of the space you
need before you can lay boards as a storage platform. Doing the math shows
that it is really not worth that kind of expense to gain so very little
more.