I am making a lean-to pantry into part of a room. It has an uneven
single-skin external brick wall, rendered on the outside. I had
thought to build a stud wall an inch or so off the wall. The would
comprise studs with 2 inch Celotex between, and wainscotting (old
floorboards) over. Depending on how I deal with the eaves, the air
space behind could be ventilated or be dead. Should I put anything
between the stud wall and the brick wall, e.g. tanking or Tyvek, and
if so how should I attach it?

Regards
Richard

I had a customer with a similar situation which was resolved by fixing
a special plasterboard to the wall which incorporates a 20mm thick
layer of foam to insulate the wall and prevent moisture penetration.
Would be easier than building a stud wall.

On May 10, 9:57*pm, House martin wrote:
I had a customer with a similar situation which was resolved by fixing
a special plasterboard to the wall which incorporates a 20mm thick
layer of foam *to insulate the wall and prevent moisture penetration.
Would be easier than building a stud wall.

It's a very wobbly wall, and I want to get 50mm of celotex in there as
well....

Regards
Richard

geraldthehamster wrote:
I am making a lean-to pantry into part of a room. It has an uneven
single-skin external brick wall, rendered on the outside. I had
thought to build a stud wall an inch or so off the wall. The would
comprise studs with 2 inch Celotex between, and wainscotting (old
floorboards) over. Depending on how I deal with the eaves, the air
space behind could be ventilated or be dead. Should I put anything
between the stud wall and the brick wall, e.g. tanking or Tyvek, and
if so how should I attach it?

Regards
Richard

Definitely no. If youre going to fit a vapour barrier, it should be on
the warm side of the insulation.


NT

On 10 May, 22:49, geraldthehamster wrote:
On May 10, 9:57*pm, House martin wrote:

I had a customer with a similar situation which was resolved by fixing
a special plasterboard to the wall which incorporates a 20mm thick
layer of foam *to insulate the wall and prevent moisture penetration.
Would be easier than building a stud wall.

It's a very wobbly wall, and I want to get 50mm of celotex in there as
well....

Regards
Richard

Best to put half the thickness between the studs, the rest in front of
them, taped up to create a vapour barrier. Better still 50mm between
studs, 25mm over, or insulated plaster board screwed into the studs.
If there is a gap behind the studs, in theory it should be ventilated,
or some kind of cavity tray at the bottom and weep holes to the
outside. Depends how thorough you want to be.
Simon.

geraldthehamster wrote:
On May 10, 9:57 pm, House martin wrote:
I had a customer with a similar situation which was resolved by fixing
a special plasterboard to the wall which incorporates a 20mm thick
layer of foam to insulate the wall and prevent moisture penetration.
Would be easier than building a stud wall.

It's a very wobbly wall, and I want to get 50mm of celotex in there as
well....

Regards
Richard

If the battens are pre-drilled, you can use the fixing screws to adjust
the distance from the wall and pack out at intervals with filler.
Spending time getting the battens level usually means you don't have to
skim

In article
,
writes
On 10 May, 22:49, geraldthehamster wrote:
On May 10, 9:57*pm, House martin wrote:

I had a customer with a similar situation which was resolved by fixing
a special plasterboard to the wall which incorporates a 20mm thick
layer of foam *to insulate the wall and prevent moisture penetration.
Would be easier than building a stud wall.

It's a very wobbly wall, and I want to get 50mm of celotex in there as
well....

Regards
Richard

Best to put half the thickness between the studs, the rest in front of
them, taped up to create a vapour barrier. Better still 50mm between
studs, 25mm over, or insulated plaster board screwed into the studs.
If there is a gap behind the studs, in theory it should be ventilated,
or some kind of cavity tray at the bottom and weep holes to the
outside. Depends how thorough you want to be.
Simon.

I've got a similar situation but with restrictions on how thick I can
have the internal building.

I'm looking at dotting and dabbing 50mm celotex onto the wall, aiming to
leave 12mm ventilated behind, then cutting channels into the front of
the celotex at 600mm intervals (at the joins and in the middle of each
sheet) to take thin 20x80 battens. Battens fixed though the celotex with
frame fixings at regular intervals with 12mm plasterboard over the top
screwed into the battens.

The channelling of the insulation is a faff but the benefits I see are,
no wood on the wet side and something to fix shelves to on the outside.

Also, if the channels are foil taped before fitting the battens (under
rather than than on top) then a decent stud finder will pick up the lack
of foil at the battens for future fixing opportunities.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

fred wrote:
In article
,
writes
On 10 May, 22:49, geraldthehamster wrote:
On May 10, 9:57 pm, House martin wrote:

I had a customer with a similar situation which was resolved by fixing
a special plasterboard to the wall which incorporates a 20mm thick
layer of foam to insulate the wall and prevent moisture penetration.
Would be easier than building a stud wall.

It's a very wobbly wall, and I want to get 50mm of celotex in there as
well....

Regards
Richard

Best to put half the thickness between the studs, the rest in front of
them, taped up to create a vapour barrier. Better still 50mm between
studs, 25mm over, or insulated plaster board screwed into the studs.
If there is a gap behind the studs, in theory it should be ventilated,
or some kind of cavity tray at the bottom and weep holes to the
outside. Depends how thorough you want to be.
Simon.

I've got a similar situation but with restrictions on how thick I can
have the internal building.

I'm looking at dotting and dabbing 50mm celotex onto the wall, aiming to
leave 12mm ventilated behind, then cutting channels into the front of
the celotex at 600mm intervals (at the joins and in the middle of each
sheet) to take thin 20x80 battens. Battens fixed though the celotex with
frame fixings at regular intervals with 12mm plasterboard over the top
screwed into the battens.

The channelling of the insulation is a faff

You're not kidding.

but the benefits I see are,
no wood on the wet side

Why is the wet side wet? Is there penetrating damp from outside?

and something to fix shelves to on the outside.

Also, if the channels are foil taped before fitting the battens (under
rather than than on top) then a decent stud finder will pick up the lack
of foil at the battens for future fixing opportunities.

In article , Stuart
Noble writes
fred wrote:

I'm looking at dotting and dabbing 50mm celotex onto the wall, aiming to
leave 12mm ventilated behind, then cutting channels into the front of
the celotex at 600mm intervals (at the joins and in the middle of each
sheet) to take thin 20x80 battens. Battens fixed though the celotex with
frame fixings at regular intervals with 12mm plasterboard over the top
screwed into the battens.

The channelling of the insulation is a faff

You're not kidding.

Probably less than you think, the batten can guide a stanley knife to
for a perfect depth cut and the cutouts at a the edges are dead easy if
done before fitting. The centre sheet ones are aren't as easy but
celotex is so easy to sculpt that 5 mins per is an over estimate.

but the benefits I see are,
no wood on the wet side

Why is the wet side wet? Is there penetrating damp from outside?

Nope, figure of speech, but you can't assume that a the inside of a
single skin brick or stone wall will be bone dry for life so it makes
sense to cater for the worst case.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

On May 11, 11:00*pm, fred wrote:
In article , Stuart
Noble writesfred wrote:

I'm looking at dotting and dabbing 50mm celotex onto the wall, aiming to
leave 12mm ventilated behind, then cutting channels into the front of
the celotex at 600mm intervals (at the joins and in the middle of each
sheet) to take thin 20x80 battens. Battens fixed though the celotex with
frame fixings at regular intervals with 12mm plasterboard over the top
screwed into the battens.

The channelling of the insulation is a faff

You're not kidding.

Probably less than you think, the batten can guide a stanley knife to
for a perfect depth cut and the cutouts at a the edges are dead easy if
done before fitting. The centre sheet ones are aren't as easy but
celotex is so easy to sculpt that 5 mins per is an over estimate.

but the benefits I see are,
no wood on the wet side

Why is the wet side wet? Is there penetrating damp from outside?

Nope, figure of speech, but you can't assume that a the inside of a
single skin brick or stone wall will be bone dry for life so it makes
sense to cater for the worst case.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

Fred, I think you'd find it easier to fix a sheet of 25mm celotex to
the wall first (making sure to get it flat), then stick additional
sections of 25mm over the top, leaving gaps for your channels. Easier
than carving them out.

Your battens would be stronger, however, if screwed direct to the
wall. If you're worried about wood on the wet side, you could use
treated timber and/or put DPM behind it.

My problem with screwing battens to my wall is that the wall goes in
and out by an inch or more, which is why I'm thinking of building a
stud wall an inch or so out. Thinking about it, the air space behind
it will inevitably be dead, not ventilated, so I'm wondering about
filling it with expanding foam, behind the celotex. I searched the
group for opinions on how moisture-resistant expanding foam is, and
found asnwers ranging from "not very" to "completely waterproof" ;-)

Richard

In article
,
geraldthehamster writes

Fred, I think you'd find it easier to fix a sheet of 25mm celotex to
the wall first (making sure to get it flat), then stick additional
sections of 25mm over the top, leaving gaps for your channels. Easier
than carving them out.

Yes, that works too but 50mm celotex is cheap as chips as seconds
whereas 2x25mm is unlikely to be as cheap or as readily available as
seconds.

Your battens would be stronger, however, if screwed direct to the
wall. If you're worried about wood on the wet side, you could use
treated timber and/or put DPM behind it.

The main reason for having the battens close to the plasterboard side is
to provide direct support for shelving and with the bonus of being
easily detected (or undetected) if they're not foil taped over.

Yes, I agree it would be stronger overall with the battens closer to the
wall but I planned to have a hefty fillet of goop/fill'n'fix-foam
between the celotex and the wall directly under the battens to firm it
up and then have the benefit of stronger support for shelving on the
inside.

I'm not concerned about the wall being properly wet, keeping the wood on
the definitely-non-damp side was a secondary advantage.

My problem with screwing battens to my wall is that the wall goes in
and out by an inch or more, which is why I'm thinking of building a
stud wall an inch or so out. Thinking about it, the air space behind
it will inevitably be dead, not ventilated, so I'm wondering about
filling it with expanding foam, behind the celotex. I searched the
group for opinions on how moisture-resistant expanding foam is, and
found asnwers ranging from "not very" to "completely waterproof" ;-)

So why not take up the variable gap with fill'n'fix foam between the
celotex and the wall and then build a thinner frame structure on the
inside. My plan is to get strength by creating a composite structure.

Also, my feeling would be to leave the space open behind the celotex, an
air gap will always provide a barrier to damp penetration but if you put
something in the gap then is may pass damp to the inner leaf. FWIW, my
experience is that expanding foam is not closed cell and so could, in
the extreme, conduct moisture.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

On May 15, 6:45*pm, fred wrote:

So why not take up the variable gap with fill'n'fix foam between the
celotex and thewalland then build a thinner frame structure on the
inside. My plan is to get strength by creating a composite structure.

I'm not sure you aren't over-estimating the rigidity and levelness of
Celotex - if you jut stick it to a wonky wall, you;re liable to end up
with wonky Celotex. It's normally it's the wooden studding that will
provide a wall that's flat in all directions, with Celotex between and/
or over that. I think if I were you I'd use thicker battens, either
attached to the wall and packed out for levelness, or built as a
separate stud wall if your wall is too uneven. The foil on both sides
of the Celotex provides a vapour barrier from the inside as well as a
damp barrier from the outside - if you're worried about timber in
contact with the wall, use a DPM as well. Treated timber isn't such a
bad idea either. I just think this arrangement is more likely to give
you a flat wall. It's what I'm going to do anyway ;-)

Also, my feeling would be to leave the space open behind the celotex, an
air gap will always provide a barrier to damp penetration but if you put
something in the gap then is may pass damp to the inner leaf. FWIW, my
experience is that expanding foam is not closed cell and so could, in
the extreme, conduct moisture.

I've discovered today, through research at my local TP, that although
bog-standard expanding foam isn't claimed to be waterproof, the stuff
designed for fixing windows and doors is, although it doesn't expand
as much.

Regards
Richard