xavier wrote:

"G&M" wrote in message ...

"David" wrote in message
...


As a consequence of Part L, of the regs people give greater consideration

to

the underfloor insualation but the emphasis is not always there that if

you

do this then the vapour barrier is essential, it needs eduction of both

the

building insectors and the builders, who need to ensure that care is taken
to ensure an intact and well sealed membrane.


Absolutely agree. IME Rockwool is an absolute sod for holding
moisture and the wetter it gets, the better it gets at getting wetter
- if you see what I mean!

Question to all - if one is going to put in a membrane, would it be better
on top or underneath the floorboards ?

Obviously underneath is required if you want to show the floorboards but if
you have carpets or some other covering it seems to me that putting it on
top of the floorboards would keep moisture properly out .....
Any thoughts ?


The object of all this is to stop moisture laden air getting into the
sub floor space. If you put your dpm on top of the floor then this
will work. The problem is that at some stage in the proceedings
someone is going to come along and remove it (perhaps after you're
long dead and gone) because they won't realise the purpose of it. The
Rockwool still being there will then start the IC ball rolling!


whereas putting it underneath would still allow condensation on the
joists and underside of the boards - and then keep it there !

No. Not with insulation underneath. The boards would be warm and have an
upwards direction for moisture to migrate.


Visible condensation won't normally occur in the subfloor space if
it's ventilated adequately and the inclusion of a dpm separating it
from the living spaces will reduce the risk even further (as indeed
would another dpm over the actual ground itself). The Interstitial
Condensation ocurring because of previously mentioned circumstances is
the greater risk.

xav