I'm about to lay laminate flooring in a ground floor room. Room has a
suspended timber floor with cellar beneath. The existing floorboards are
tongue/groove in reasonable condition. The cellar isn't bone dry, but is
well ventilated.

I'm going to lay the laminate over fibreboard, as the existing floor
isn't snooker table flat, but well within 3mm/1m. Should I use a
polythene sheet dpm between the fibreboard and the existing floor? I
can't fully get my head round whether it's better to allow an element of
'breathing' (no dpm) and risk damage to the fibreboard/laminate. Or
protect the fibreboard and risk damage to the sub-floor. This thread
sums it up:

http://www.diynot.com/forums/floors-...boards.344586/

So, DPM or not?!

--
Cheers, Rob

On 28/12/2013 18:25, RJH wrote:
I'm about to lay laminate flooring in a ground floor room. Room has a
suspended timber floor with cellar beneath. The existing floorboards
are tongue/groove in reasonable condition. The cellar isn't bone dry,
but is well ventilated.

I'm going to lay the laminate over fibreboard, as the existing floor
isn't snooker table flat, but well within 3mm/1m. Should I use a
polythene sheet dpm between the fibreboard and the existing floor? I
can't fully get my head round whether it's better to allow an
element of 'breathing' (no dpm) and risk damage to the
fibreboard/laminate. Or protect the fibreboard and risk damage to
the sub-floor. This thread sums it up:

http://www.diynot.com/forums/floors-...boards.344586/



So, DPM or not?!


As things stand, the moisture content of the joists will be around 20%
average I would think, and the top side of the floorboards probably less
than 10%. It's anyone's guess whether the laminate will be more affected
by the cellar conditions or those above floor level. On balance I think
I'd go with the dpm over the fibreboard, or toss a coin :-)

On 29/12/2013 09:22, stuart noble wrote:
On 28/12/2013 18:25, RJH wrote:
I'm about to lay laminate flooring in a ground floor room. Room has a
suspended timber floor with cellar beneath. The existing floorboards
are tongue/groove in reasonable condition. The cellar isn't bone dry,
but is well ventilated.

I'm going to lay the laminate over fibreboard, as the existing floor
isn't snooker table flat, but well within 3mm/1m. Should I use a
polythene sheet dpm between the fibreboard and the existing floor? I
can't fully get my head round whether it's better to allow an
element of 'breathing' (no dpm) and risk damage to the
fibreboard/laminate. Or protect the fibreboard and risk damage to
the sub-floor. This thread sums it up:

http://www.diynot.com/forums/floors-...boards.344586/




So, DPM or not?!


As things stand, the moisture content of the joists will be around 20%
average I would think, and the top side of the floorboards probably less
than 10%. It's anyone's guess whether the laminate will be more affected
by the cellar conditions or those above floor level. On balance I think
I'd go with the dpm over the fibreboard, or toss a coin :-)

Thanks, yes, it all seems a bit imprecise! I think I'll do without and
keep an eye on the floor from below.

--
Cheers, Rob

There used to be some kind of stuff that allowed things to breathe without
letting water through. I don't recall what it was and I understand its main
drawback was that it did tend to degrade in 10 years or so, so maybe that is
why one does not hear of such things any more.
One assumes the Cellar is damp just because it lets some moisture in, not
due to condensation? If it is the latter a non permiable sheet could make
things worse.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"stuart noble" wrote in message
...
On 28/12/2013 18:25, RJH wrote:
I'm about to lay laminate flooring in a ground floor room. Room has a
suspended timber floor with cellar beneath. The existing floorboards
are tongue/groove in reasonable condition. The cellar isn't bone dry,
but is well ventilated.

I'm going to lay the laminate over fibreboard, as the existing floor
isn't snooker table flat, but well within 3mm/1m. Should I use a
polythene sheet dpm between the fibreboard and the existing floor? I
can't fully get my head round whether it's better to allow an
element of 'breathing' (no dpm) and risk damage to the
fibreboard/laminate. Or protect the fibreboard and risk damage to
the sub-floor. This thread sums it up:

http://www.diynot.com/forums/floors-...boards.344586/



So, DPM or not?!


As things stand, the moisture content of the joists will be around 20%
average I would think, and the top side of the floorboards probably less
than 10%. It's anyone's guess whether the laminate will be more affected
by the cellar conditions or those above floor level. On balance I think
I'd go with the dpm over the fibreboard, or toss a coin :-)

On Sunday 29 December 2013 11:11 Brian Gaff wrote in uk.d-i-y:

There used to be some kind of stuff that allowed things to breathe without
letting water through.

That sounds like Tyvek and other breathable membranes.
They are still very much in use - but I don't think they'd help for this
application - you really do want to block *vapour* not liquid water.

OP: I would add the DPM. I did in a similar scenario - floor in flat over
undercroft parking, not a dissimilar siutation to yours - ie damp could get
up into the subfloor from underneath.

It worked, no problems.

--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

On 29/12/2013 11:52, Tim Watts wrote:
On Sunday 29 December 2013 11:11 Brian Gaff wrote in uk.d-i-y:

There used to be some kind of stuff that allowed things to breathe without
letting water through.

That sounds like Tyvek and other breathable membranes.
They are still very much in use - but I don't think they'd help for this
application - you really do want to block *vapour* not liquid water.

OP: I would add the DPM. I did in a similar scenario - floor in flat over
undercroft parking, not a dissimilar siutation to yours - ie damp could get
up into the subfloor from underneath.

It worked, no problems.


And if it wasn't necessary, nobody knows (or cares)