DIYbanter - View Single Post

In article ,
says...

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.

Fair enough - What about the ventilaition issue though? My loft
curently is fairly sealed so I'm intending to fit ventilated soffits (in
the future) and not insulate to the very edge etc. Is boarding laid
directly over insulation with very little air gap likely to lead to
problems (condensation etc) later? If I lay less insulation to give an
air gap then I will lose any insulation properties that the boards give
as the air will no longer be trapped?

I don't really want to go the whole hog of laying plastic sheet (as a
vapour barrier) if I can avoid it hence my thought that the greatest
amount of 'damp' air is in the bathroom so I won't boasrd over that...

Thanks for the advice so far...

Peter