Insulating 9" wall inside with air gap

[camerart]

Hi,
I want to add insulation, to a 9" outside wall, using celotex type insulation.

The building inspector, suggests battens, but I think the air can then only move vertically.
My idea is to stick rows and columns of hold off pads to the bare wall, with foam adhesive, so it's waterproof, then stick celotex onto the pads. This will allows air circulation. There has to be weep vents, or similar.
Does this seem ok?
Camerart

 

[noseall]

Hi,
I want to add insulation, to a 9" outside wall, using celotex type insulation.

The building inspector, suggests battens, but I think the air can then only move vertically.
My idea is to stick rows and columns of hold off pads to the bare wall, with foam adhesive, so it's waterproof, then stick celotex onto the pads. This will allows air circulation. There has to be weep vents, or similar.
Does this seem ok?
Camerart

Place or fix the Celotex against the wall, then fix the batten through and on top of the Celotex.

 

[camerart]

Place or fix the Celotex against the wall, then fix the batten through and on top of the Celotex.

Hi N,
There has to be a gap between the Celotex and the wall for air circulation.
Battens are linear, so the air can only move up and down, this is why I want to try pads.
C

 

[mikeey84]

Why do you think you need an air gap?

 

[camerart]

Why do you think you need an air gap?

Hi M,
I agreed this with the building control officer.
I also have to add bleed vents.
C

 

[noseall]

There has to be a gap between the Celotex and the wall for air circulation.

For what purpose?

 

[camerart]

For what purpose?

Hi N,
I had a lot of things, more complicated than this to put in front of the officer, so I agreed without question.
C

 

[camerart]

Hi,
I think in the building control officer's mind this little gap is a bit like a small cavity, for air circulation. Anyway keep them happy.

It was suggested that on the battens/pads, should be a dampproof membrane. As the next layer will be Celotex, does it need a membrane?
C

 

[Deluks]

I have noticed in recent, due to the increase in people wanting to insulate their homes, that this has become quite a contentious issue.

For every method suggested, someone will come along and say "that's wrong, you should be doing it this way"

The devil is in the details. What's the wall construction, what type of mortar, back to bare brickwork or rendered, gypsum, lime, what way do your joists run? wall orientation?

Popular YouTuber Charlie DIYte covers the issue in this video, lots of criticism and advice in the comments (He's changed his mind again since recording this video)

"The air gap needs ventilating" argument comes from the thinking behind cold roofs, but a wall isn't a roof and performs differently.

I expect it to be very difficult to make an air gap completely air tight. In most cases you'll have limited control as to what happens where it meets the floor and ceiling.

 

[George_engineer]

Why do you think you need an air gap?

Very little water gets through a 9" wall in fair condition. In my mind the gap comes about from the wall not being completely level, so when it's squared off, you will always have a nominal 10-25mm gap. But for waterproof insulation, the odd bit being in contact with the wall will not cause an issue. It wouldn't need ventilation.

The only time they would need ventilation is if there is reason to expect some level of penetrating moisture.

Vapour barriers are important (if not using vapour permeable materials like wood fibre, but that's
a whole different approach with no cavity/gap) and can be assisted with mechanical ventilation to keep humidity under control.

 

[camerart]

Very little water gets through a 9" wall in fair condition. In my mind the gap comes about from the wall not being completely level, so when it's squared off, you will always have a nominal 10-25mm gap. But for waterproof insulation, the odd bit being in contact with the wall will not cause an issue. It wouldn't need ventilation.

The only time they would need ventilation is if there is reason to expect some level of penetrating moisture.

Vapour barriers are important (if not using vapour permeable materials like wood fibre, but that's
a whole different approach with no cavity/gap) and can be assisted with mechanical ventilation to keep humidity under control.

Hi G,
I agree!
The wall is only damp due to condensation, not water. It's cold. but rearely gets rained on.
As this is not a difficult one to carry out, and the building control officer has agreed to other things, in the alterations, I'll just put a gap, and seal the Celotex gaps.
Thanks.
C

 

[JP_]

I expect it to be very difficult to make an air gap completely air tight

What is the point of an air tight air gap?

I stuck 50mm kingspan to my solid walls, over the plaster in some cases. Outside has had silicon render.
Touch wood, no problems so far. 5-6 years in.

I forgot to tell the building inspector though ...

 

[camerart]

What is the point of an air tight air gap?

I stuck 50mm kingspan to my solid walls, over the plaster in some cases. Outside has had silicon render.
Touch wood, no problems so far. 5-6 years in.

I forgot to tell the building inspector though ...

Hi J,
I have to make weep vents though the wall, and considering it's 9" the cements won't line up,, but hey ho.
There are lots of differences, in this house where the buildng inspector hasn't been informed, but if I carry out a short list, it will be all written off as ok. Previously the lack of Building control eveidence showed up in a survey for selling the property.
C

 

[JP_]

That makes sense, selling.
I don't plan to sell my bungalow anytime soon. I'll probably never sell it, that will be somebody else's job.
Hopefully the 20 year rule will apply by then!

 

[camerart]

I have noticed in recent, due to the increase in people wanting to insulate their homes, that this has become quite a contentious issue.

For every method suggested, someone will come along and say "that's wrong, you should be doing it this way"

The devil is in the details. What's the wall construction, what type of mortar, back to bare brickwork or rendered, gypsum, lime, what way do your joists run? wall orientation?

Popular YouTuber Charlie DIYte covers the issue in this video, lots of criticism and advice in the comments (He's changed his mind again since recording this video)

"The air gap needs ventilating" argument comes from the thinking behind cold roofs, but a wall isn't a roof and performs differently.

I expect it to be very difficult to make an air gap completely air tight. In most cases you'll have limited control as to what happens where it meets the floor and ceiling.

Hi D,
Watched 2x of his videos, very good, he seems to cover everything, thanks.
C