Internal Insulation for solid brick walls - Which way would be best way to do it?

[Hightowermark]

Hi,

Recently moved house into a 1900's house (Semi). And the main gable wall needs to be insulated. There is also a slight bowing to the wall, this had been checked by a structural engineer prior to purchase and no issues has not moved in over 70 years. And he was perfectly happy to sign it off for mortgage etc. So the wall in no level there is about 3" in the centre to the two sides. This wall is 7m long.

So options are

1) Full stud wall (3"x2" treated) with top and bottom plates, PIR insulation inside the studs, taped, vapour barrier and then plasterboard
2) Batten the wall (treated 2x2) fit 50mm PIR in the gap, then flip PIR vertical so it's now 100mm and then plasterboard

Option 1 would leave a small gap in the centre as the stud would be level, how would you fill this?
Option 2 would leave the curve

Or if anyone has any other ideas or advice it would be most welcome

Thanks

 

[George_engineer]

Option 2. Don't buy an old house and expect true and level walls... hard enough to achieve in a new build...!

 

[oldbutnotdead]

Go option 1 BUT 75mm between the studs then 25mm over studs (reduces cold bridging) then pb. Push the 75mm back to fill the gap as much as possible.
Or option 2 but pack the battens off the wall in the middle.

 

[Hightowermark]

Thank you. I think i prefer a stud wall. So you fill the whole void with 75mm in-between the studs and then another 25mm vertical.

Would a vapour barrier be needed for this before the plasterboard?

 

[cdbe]

I thought the modern way was to foam it on, easy to level and avoids cold bridging.

 

[mrrusty]

My point of view on this seems to disagree with everyone else's. I have fairly recently internally insulated a 1902 semi that had a small cavity which is very well ventilated. I discussed the potential for controlling interstitial condensation with my local building control and also read up a fair bit (heritage house etc). The conclusion we came to was insulating the internal face of the cavity wall was OK because any condensation in the wall would be evaporated away by the air movement within the ventilated cavity.

You have a solid wall. It's obviously thicker - is it rendered externally or bare brick? For sure, unless you can totally air-seal the wall from internal air (very difficult in an old property) then you WILL get condensation forming on the inside face of the now colder solid wall (colder because it's insulated from the internal warmer air)- dew point of ambient air (20ish deg @60% RH) is in the order of 12 degrees. You wall will easily get to this behind the insulation. On the basis there will be condensation you have to consider how that can be removed. It might evaporate slowly through the wall (but won't if the outside is rendered or sealed) or it could be evaporated by air movement in a ventilated cavity between the wall and your new insulated stud wall.

This construction of insulated timber frame, then ventilated cavity, then a brick skin is the way modern timber houses are built. If they have to have a ventilated cavity, why would you think a conversion of an existing solid wall would not?

I admit I have never insulated a solid wall, but can confirm that after 4-5 years or so the internal insulation on our small-cavity wall is working well. I also have a pretty good understanding of condensation control from my merchant navy days because condensation in holds can ruin cargoes, so was very much part of my training.

 

[oldbutnotdead]

Thank you. I think i prefer a stud wall. So you fill the whole void with 75mm in-between the studs and then another 25mm vertical.

Would a vapour barrier be needed for this before the plasterboard?

Not if you seal all the joints in the 25mm layer but you can stick one on if you want.

 

[oldbutnotdead]

My point of view on this seems to disagree with everyone else's. I have fairly recently internally insulated a 1902 semi that had a small cavity which is very well ventilated. I discussed the potential for controlling interstitial condensation with my local building control and also read up a fair bit (heritage house etc). The conclusion we came to was insulating the internal face of the cavity wall was OK because any condensation in the wall would be evaporated away by the air movement within the ventilated cavity.

You have a solid wall. It's obviously thicker - is it rendered externally or bare brick? For sure, unless you can totally air-seal the wall from internal air (very difficult in an old property) then you WILL get condensation forming on the inside face of the now colder solid wall (colder because it's insulated from the internal warmer air)- dew point of ambient air (20ish deg @60% RH) is in the order of 12 degrees. You wall will easily get to this behind the insulation. On the basis there will be condensation you have to consider how that can be removed. It might evaporate slowly through the wall (but won't if the outside is rendered or sealed) or it could be evaporated by air movement in a ventilated cavity between the wall and your new insulated stud wall.

This construction of insulated timber frame, then ventilated cavity, then a brick skin is the way modern timber houses are built. If they have to have a ventilated cavity, why would you think a conversion of an existing solid wall would not?

I admit I have never insulated a solid wall, but can confirm that after 4-5 years or so the internal insulation on our small-cavity wall is working well. I also have a pretty good understanding of condensation control from my merchant navy days because condensation in holds can ruin cargoes, so was very much part of my training.

Yes the whole solid wall insulation thing is a bit up in the air.
The advice I was given was either make sure there is no gap (so no room for large volumes of waterladen air) or if there is a gap make sure it is ventilated. Time will tell...