Hi,

Having clad my garage with celotex and plywood, I'm wondering how much
heat I need to keep it above freezing during the winter. I've looked
for u-values but I keep finding the value for 9" brick walls. I
thought a brick wall was about 4" thick. Are you laying walls with the
bricks "the wrong way round"? Or is a 9" brick wall, two courses of
brick next to each other, i.e. without a cavity?

Does anyone know the u-value for a single 4" thick brick wall?

I had a look at the calculator on the celotex web site but the example
it showed used no u-value for plywood. Is this because you need a much
greater thickness of wood before it has an insulating effect, or does
3/4" plywood have a u-value?

For the ceiling, I presume you discount the felt on the same basis
that it is too thin to have a significant effect?

TIA