Hi,

I live in a 1930s semi which has a void underneath the living room
that is about 6 foot deep. Although the wooden floor is carpeted,
would it help to insulate underneath the floor with something like
celotex between the joists? If so, do I need to leave a gap between
it and the floor and/or put any membrane layer somewhere? The void has
a concrete floor that has always been bone dry.

Grateful for any advice as to me the living room does not seem to heat
up to well.

TIA

ZeitGeist wrote:
Hi,

I live in a 1930s semi which has a void underneath the living room
that is about 6 foot deep. Although the wooden floor is carpeted,
would it help to insulate underneath the floor with something like
celotex between the joists?

Yes, definitely.

If so, do I need to leave a gap between
it and the floor and/or put any membrane layer somewhere? The void has
a concrete floor that has always been bone dry.

The void should be ventilated to teh outside world. it is advisable to
put a vapour barrier between the joists and the flooring above the
insulation.

What I would do is to lift the floor, nail battens to the joists to
support the insulation, at the right height to bring the celotex panels
flush with the joist tops, and then tape over the joists and panels with
celortex foil tape.


Grateful for any advice as to me the living room does not seem to heat
up to well.


The floor is less relevant than walls, typically, but easier to sort out.

TIA

On Wed, 07 Jan 2009 20:29:29 +0000, The Natural Philosopher
wrote:

The void should be ventilated to teh outside world. it is advisable to
put a vapour barrier between the joists and the flooring above the
insulation.

Do you mean that the vapour barrier should run underneath the floor
over the joists and insulation? i.e. directly beneath the
floorboards?

What I would do is to lift the floor, nail battens to the joists to
support the insulation, at the right height to bring the celotex panels
flush with the joist tops, and then tape over the joists and panels with
celortex foil tape.

And lay the barrier over that before putting the floorboards back
down?

I should have mentioned I can access the void and could work from
below without lifting the floorboards.

TIA

ZeitGeist wrote:
On Wed, 07 Jan 2009 20:29:29 +0000, The Natural Philosopher
wrote:

The void should be ventilated to teh outside world. it is advisable to
put a vapour barrier between the joists and the flooring above the
insulation.

Do you mean that the vapour barrier should run underneath the floor
over the joists and insulation? i.e. directly beneath the
floorboards?

yes.

What I would do is to lift the floor, nail battens to the joists to
support the insulation, at the right height to bring the celotex panels
flush with the joist tops, and then tape over the joists and panels with
celortex foil tape.

And lay the barrier over that before putting the floorboards back
down?

yes.

I should have mentioned I can access the void and could work from
below without lifting the floorboards.

Ah. In which case take a chance, and simply slap the insulation up and
between with a dab of no more nails?

And use some mastic to _utterly_ seal any gaps. Its not as good as
overall vapour barrier, but should be good enough.



TIA

On Wed, 07 Jan 2009 21:05:21 +0000, The Natural Philosopher
wrote:

(snip)

Many thanks for the info. Wil try and get round to it as soon as the
weather warms up a bit :-))

Best regards.

On Wed, 07 Jan 2009 20:29:29 +0000 The Natural Philosopher wrote :
What I would do is to lift the floor, nail battens to the joists to
support the insulation, at the right height to bring the celotex panels
flush with the joist tops, and then tape over the joists and panels with
celortex foil tape.

With a six foot void, make an access and work from below is probably
easier.

--
Tony Bryer, 'Software to build on' from Greentram
www.superbeam.co.uk www.superbeam.com www.greentram.com

In article , ZeitGeist
writes
On Wed, 07 Jan 2009 21:05:21 +0000, The Natural Philosopher
wrote:

(snip)

Many thanks for the info. Wil try and get round to it as soon as the
weather warms up a bit :-))

Celotex is the easy option but you could do it for a lot less with
rockwool,
you have plenty of working space and will have plenty of joist depth to
take the less effective insulation. You can support Celotex with slant
driven 4" nails or rockwool with hardboard and battens.

I have done this with fibreglass and didn't bother with the vapour
barrier.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

fred wrote:
In article , ZeitGeist
writes
On Wed, 07 Jan 2009 21:05:21 +0000, The Natural Philosopher
wrote:

(snip)

Many thanks for the info. Wil try and get round to it as soon as the
weather warms up a bit :-))

Celotex is the easy option but you could do it for a lot less with
rockwool,
you have plenty of working space and will have plenty of joist depth to
take the less effective insulation. You can support Celotex with slant
driven 4" nails or rockwool with hardboard and battens.

I have done this with fibreglass and didn't bother with the vapour barrier.

I think polystyrene is ok for ground floor

http://www.vencel.co.uk/products/insulation/

On 7 Jan, 20:15, ZeitGeist wrote:
Hi,

I live in a 1930s semi which has a void underneath the living room
that is about 6 foot deep. * Although the wooden floor is carpeted,
would it help to insulate underneath the floor with something like
celotex between the joists? *If so, do I need to leave a gap between
it and the floor and/or put any membrane layer somewhere? The void has
a concrete floor that has always been bone dry.

Grateful for any advice as to me the living room does not seem to heat
up to well.

TIA

Dear ZG
I disagree with the other posters for the following reason: the vapour
check needs to be on the warm side of the insulation and all timber
needs to be inside that or you will find a potential condensation trap
made
What to do? Slap 2" (or more up to 4") of TP 10 or the like (PU foam
with foil) UNDER the floor to the joists with long stainless fixings
(the pink ones used for outside insulation adapted to suit) or screws
and large 2" plate washers in plastic
Fill any gaps well but preferably dont have any - good interference
fits -
If gaps inevitable at say edges use foam gun above and below

That should do it

Make sure void is well vented to ouside

If you want a super job put rockwool addtionally in between the joists

Chris

wrote:
On 7 Jan, 20:15, ZeitGeist wrote:
Hi,

I live in a 1930s semi which has a void underneath the living room
that is about 6 foot deep. Although the wooden floor is carpeted,
would it help to insulate underneath the floor with something like
celotex between the joists? If so, do I need to leave a gap between
it and the floor and/or put any membrane layer somewhere? The void has
a concrete floor that has always been bone dry.

Grateful for any advice as to me the living room does not seem to heat
up to well.

TIA

Dear ZG
I disagree with the other posters for the following reason: the vapour
check needs to be on the warm side of the insulation

correct

and all timber
needs to be inside that or you will find a potential condensation trap
made

Wrong.

The point is to ckeep most and cold separate.

Since both are needed to get condensation.

Think roof rafters They are all on the cold side..

On Jan 7, 8:52*pm, ZeitGeist wrote:

What I would do is to lift the floor, nail battens to the joists to
support the insulation, *at the right height to bring the celotex panels
flush with the joist tops, and then tape over the joists and panels with
celortex foil tape.

And lay the barrier over that before putting the floorboards back
down?

If you use foil-backed Celotex (or Kingspan, which IME is more
robust), and tape the joints over the joists with foil tape, then you
have installed a vapour barrier.

Regards
Richard