Hi,

I have a window in our living room that is in a prepared-for
French/patio door opening. However, as the opening just has an ordinary
window in it, the wall below the window is timber stud, 100mm void,
with painted timber cladding on the exterior. The piece of wall
(1.2x0.7m) under the window is very cold in the winter. I am also going
to move the radiator in that room to this piece of wall, and I don't
want all the heat going outside through the void! So, before I decorate
the room, I was planning on insulating it by placing 100mm mineral wool
in the void.

The void itself, obviously, is not ventilated. If I put a polythene
vapour barrier on the inside, will that be sufficient to avoid problems
with condensation? Is there a better way of doing this?

Thanks

Mark

Mark Hindley wrote:
Hi,

I have a window in our living room that is in a prepared-for
French/patio door opening. However, as the opening just has an ordinary
window in it, the wall below the window is timber stud, 100mm void,
with painted timber cladding on the exterior. The piece of wall
(1.2x0.7m) under the window is very cold in the winter. I am also going
to move the radiator in that room to this piece of wall, and I don't
want all the heat going outside through the void! So, before I decorate
the room, I was planning on insulating it by placing 100mm mineral wool
in the void.

The void itself, obviously, is not ventilated. If I put a polythene
vapour barrier on the inside, will that be sufficient to avoid problems
with condensation? Is there a better way of doing this?

Thanks

Mark

Personally I would a) use something with an even higher termal
resistance, such as Celotex or Kingspan, and b) ensure that there is an
air gap between the insulation and the outer wall.

On 8 Nov 2005 05:50:02 -0800, "Matt Beard" wrote:


Mark Hindley wrote:
Hi,

I have a window in our living room that is in a prepared-for
French/patio door opening. However, as the opening just has an ordinary
window in it, the wall below the window is timber stud, 100mm void,
with painted timber cladding on the exterior. The piece of wall
(1.2x0.7m) under the window is very cold in the winter. I am also going
to move the radiator in that room to this piece of wall, and I don't
want all the heat going outside through the void! So, before I decorate
the room, I was planning on insulating it by placing 100mm mineral wool
in the void.

The void itself, obviously, is not ventilated. If I put a polythene
vapour barrier on the inside, will that be sufficient to avoid problems
with condensation? Is there a better way of doing this?

Thanks

Mark

Personally I would a) use something with an even higher termal
resistance, such as Celotex or Kingspan, and b) ensure that there is an
air gap between the insulation and the outer wall.

50mm kingspan = 100mm rockwool for insulation purposes, minimum
recommend air gap = 50mm.

I'd use a "full fill" mineral wool, its cheeper. And then I'd clad the
inside of the whole wall in 50mm (or more) of kingspan. But the
cladding is maybe a bit more than you need.

Rick - who has IMM's views on insulation - more is better.

Rick wrote:

50mm kingspan = 100mm rockwool for insulation purposes, minimum
recommend air gap = 50mm.

Thanks.

Just so I'm clear -- what is the 50mm gap for?

I thought the gap would need to be ventilated to prevent condensation
forming. Or does it aid the insulation properties by avoiding bridging?

You didn't mention a vapour barrier. Is that just taken as read or not
necessary?

Mark

On Tue, 8 Nov 2005 19:44:08 +0000, Mark Hindley
wrote:

Rick wrote:

50mm kingspan = 100mm rockwool for insulation purposes, minimum
recommend air gap = 50mm.

Thanks.

Just so I'm clear -- what is the 50mm gap for?

I thought the gap would need to be ventilated to prevent condensation
forming. Or does it aid the insulation properties by avoiding bridging?

You didn't mention a vapour barrier. Is that just taken as read or not
necessary?

Mark

Kingspan is not a "full fill" insulation, which means its not
certified that it won't wick water, so you need a gap to maintain the
cavity & the waterproofness.

The "full fill" mineral fibers dont wick water, but there is a
difference between these, often sold as "cavity bats" and normal loft
mineral wool - you need to make sure you specify "full fill" at the
builders merchant.

I have no specific knowledge on vapor barriers in this application. I
did spend a long time researching the most cost effective insulation,
which is why I know this stuff.

Rick

On Tue, 8 Nov 2005 13:46:07 +0000, a particular chimpanzee named Mark
Hindley randomly hit the
keyboard and produced:

I have a window in our living room that is in a prepared-for
French/patio door opening. However, as the opening just has an ordinary
window in it, the wall below the window is timber stud, 100mm void,
with painted timber cladding on the exterior.

From inside out:
Plasterboard vapour barrier (polythene) ~140mm mineral fibre batts
or 70mm Celotex between studs, or fully fill between the studs with
mineral fibre batts and line internally with 25mm Celotex timber
sheathing (not necessarily plywood if not needed for structural
reasons, indeed, the more vapour permeable the better) vapour
permeable membrane (Tyvek, etc) (to allow vapour through but keep rain
and condensate out) drained and ventilated cavity (to get rid of any
moisture on the cold side of the timber frame) cladding.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"