Insulated Plasterboard on Solid External Walls - Could cause damp?

[ToastyToes]

Hi all,

We are doing a major renovation to our 1890s Victorian. Its a typical terrace style but unusually detached. We haven't lived in it yet but expect it to be chilly due to the solid walls.

We are already installing 80mm PIR boards between the ground floor joists and 100mm Rockwool between the floors.

In addition to this I am considering using 38mm plasterboard and PIR insulation on all external walls to both the ground floor and first floor rooms.

I've read that this could cause condensation between the insulation and external wall resulting in damp walls.

Is there any evidence of this?
What can I do to prevent damp occurring?
Is there another way to efficiently insulate my house?
Have you done this and what is the outcome of it?

Thanks!

 

[Bonni]

I would consider the solid wall as the outer leaf, so I wouldn't attach and plaster boards to it. I would consider Metal C 50mm Stud wall, put 50mm kingspan in, plaster board over and keep it 20mm to 50mm of off the solid wall (clear cavity).

 

[Notch7]

I've read that this could cause condensation between the insulation and external wall resulting in damp walls.

I think it depends whether the walls suffer rain renetration and dampness appears on the internal faces. If thats the case, it would probably be evident on the plaster.

If dampness is due to interstitial condensation, that can be prevented by correct detailing.

The most efficient internal wall insulation is to apply celetex directly to the whole wall, with no gaps, tape all joints. Then screw 50 x 25 or 50 x 19 battens laid flat and plasterboard on top.

If you have time, fix a board of celetex to a wall screw with some battens so its tight. Seal all edges. After a cold wet spell you could remove and see if there is any evidence of damp.

 

[foxhole]

Hi all,

We are doing a major renovation to our 1890s Victorian. Its a typical terrace style but unusually detached. We haven't lived in it yet but expect it to be chilly due to the solid walls.

We are already installing 80mm PIR boards between the ground floor joists and 100mm Rockwool between the floors.

In addition to this I am considering using 38mm plasterboard and PIR insulation on all external walls to both the ground floor and first floor rooms.

I've read that this could cause condensation between the insulation and external wall resulting in damp walls.

Is there any evidence of this?
What can I do to prevent damp occurring?
Is there another way to efficiently insulate my house?
Have you done this and what is the outcome of it?

Thanks!

Where is it suggested insulation can cause damp?

 

[motorbiking]

If the insulation is poorly fitting such that you get warm air flow between the cold outer wall and the insulation, then its possible to get condensation between the surfaces. As long as its fitted properly it should be fine.

 

[SFK]

Toes,
Regarding your question "Have you done this and what is the outcome of it?", have a look at this:
http://jack-kelly.com/insulating_our_victorian_living_room
SFK

 

[JP_]

I am in the process of fitting 50mm kingspan to external solid walls. Use lots of Everbuild Pinkgrip foam to stick the insulation to the wall, then tape all joins, and then more pinkgrip to fix plasterboards to the insulation. Idea is that no moisture lade air from inside will get through that - the kingspan has vapour barrier each side. Also careful to seal gaps at the bottom and tops of boards.

Not fully tested yet ... but did the first room last winter and no sign of problems there.

Also insulated under the floorboards (again, taping everything).

I think the thing about condensation was interstitial condensation if you use too much insulation. 40-50mm was quoted somewhere as being ideal, any more and the external walls will stay too cold and moisture will be more likely to enter the wall and condense at the dew point. 50mm lets some house warmth to penetrate into the walls. Apparently.

 

[motorbiking]

You can also use a few slim frame fixers to hold until bonded. Push them in flush and just skim over.

 

[JP_]

Toes,
Regarding your question "Have you done this and what is the outcome of it?", have a look at this:
http://jack-kelly.com/insulating_our_victorian_living_room
SFK

and this!
https://www.diynot.com/diy/threads/my-rotten-floor-s.491659/page-5

although not great pics of the actual wall insulation part ... some newer pics just added here:

https://photos.app.goo.gl/tSGFt3HD2CWY7sGa9

 

[ToastyToes]

I would consider the solid wall as the outer leaf, so I wouldn't attach and plaster boards to it. I would consider Metal C 50mm Stud wall, put 50mm kingspan in, plaster board over and keep it 20mm to 50mm of off the solid wall (clear cavity).

Thanks for the suggestion but this will reduce the internal floor space too much.

I think it depends whether the walls suffer rain renetration and dampness appears on the internal faces. If thats the case, it would probably be evident on the plaster.

If dampness is due to interstitial condensation, that can be prevented by correct detailing.

The most efficient internal wall insulation is to apply celetex directly to the whole wall, with no gaps, tape all joints. Then screw 50 x 25 or 50 x 19 battens laid flat and plasterboard on top.

If you have time, fix a board of celetex to a wall screw with some battens so its tight. Seal all edges. After a cold wet spell you could remove and see if there is any evidence of damp.

Would you screw the batterns straight through the insulation into the brick wall behind?

Toes,
Regarding your question "Have you done this and what is the outcome of it?", have a look at this:
http://jack-kelly.com/insulating_our_victorian_living_room
SFK

Thank you for this. Very informative.

I am in the process of fitting 50mm kingspan to external solid walls. Use lots of Everbuild Pinkgrip foam to stick the insulation to the wall, then tape all joins, and then more pinkgrip to fix plasterboards to the insulation. Idea is that no moisture lade air from inside will get through that - the kingspan has vapour barrier each side. Also careful to seal gaps at the bottom and tops of boards.

Not fully tested yet ... but did the first room last winter and no sign of problems there.

Also insulated under the floorboards (again, taping everything).

I think the thing about condensation was interstitial condensation if you use too much insulation. 40-50mm was quoted somewhere as being ideal, any more and the external walls will stay too cold and moisture will be more likely to enter the wall and condense at the dew point. 50mm lets some house warmth to penetrate into the walls. Apparently.

I wouldn't want to add more then 25mm as it is a large cost and will reduce the internal floor space too much.

 

[ToastyToes]

and this!
https://www.diynot.com/diy/threads/my-rotten-floor-s.491659/page-5

although not great pics of the actual wall insulation part ... some newer pics just added here:

https://photos.app.goo.gl/tSGFt3HD2CWY7sGa9

This is great thank you

 

[foxhole]

I am in the process of fitting 50mm kingspan to external solid walls. Use lots of Everbuild Pinkgrip foam to stick the insulation to the wall, then tape all joins, and then more pinkgrip to fix plasterboards to the insulation. Idea is that no moisture lade air from inside will get through that - the kingspan has vapour barrier each side. Also careful to seal gaps at the bottom and tops of boards.

Not fully tested yet ... but did the first room last winter and no sign of problems there.

Also insulated under the floorboards (again, taping everything).

I think the thing about condensation was interstitial condensation if you use too much insulation. 40-50mm was quoted somewhere as being ideal, any more and the external walls will stay too cold and moisture will be more likely to enter the wall and condense at the dew point. 50mm lets some house warmth to penetrate into the walls. Apparently.

Rubbish, if wall is insulated then no moist air can get to any cold surface beyond it.

 

[foxhole]

Thanks for the suggestion but this will reduce the internal floor space too much.



Would you screw the batterns straight through the insulation into the brick wall behind?



Thank you for this. Very informative.



I wouldn't want to add more then 25mm as it is a large cost and will reduce the internal floor space too much.

25mm would be a waste of time needs at leat 40-50mm to have any value.

 

[ToastyToes]

25mm would be a waste of time needs at leat 40-50mm to have any value.

Surely 25 is better then 0. But I get your point. If I am going to put the effort and funds into 25mm, it might as well be 50.

 

[wwwebber]

Did exactly this to our 1880s house renovation. We had plasterboard backed with 50mm insulation dobbed & dabbed to all internal outside facing walls. We did have damp previously and simply had the walls sealed with a damp proof scratch coat (cant remember what it is was called exactly) up to 1m all the way around. House was very cheap to heat afterwards, quiet and zero issues with damp for the 10 years we lived in it. Good luck