Condensation Worries With Internal Wall Insulation

[Mr Sparkle]

A company is proposing to install internal wall insulation on the external walls of my family members house.

The property is a victorian building with solid walls and lime plaster

The company state that they will install battens onto the wall, then place insulated plasterboard on top. This will then be tape and jointed before plastering

What I want to know is that if the existing plaster is hollow

1. Should I remove all the lime plaster, so that they attach the battens directly to the brickwork?

2. Should I insist of plastering the plasterboard with lime plaster (for breathability) or will gypsum be okay?

3. The property needs a rewire plus additional sockets on these external walls. So Should I chisel out the walls now for the backbox? or is the void between the plasterboard and brick work enough to install a dry lining backbox

4. If the plasterboard is cut e.g. for the backboxes, will this cause thermal bridging/ condensation and possible mould behind the plasterboard?

 

[JohnD]

Do the rewiring first. You will probably not need to chase out for boxes as they will be within the new lining. Ask in the "electrics UK" section.

 

[endecotp]

1. Should I remove all the lime plaster, so that they attach the battens directly to the brickwork?

I don’t think so; the screws will go through the plaster into the brick.

2. Should I insist of plastering the plasterboard with lime plaster (for breathability) or will gypsum be okay?

The insulation is a vapour barrier, so making the skim layer breathable won’t change anything.

If you believe that the wall needs to breath, you should use vapour-permeable insulation (e.g. mineral wool, wood fibre, etc.)

3. The property needs a rewire plus additional sockets on these external walls. So Should I chisel out the walls now for the backbox? or is the void between the plasterboard and brick work enough to install a dry lining backbox

What thickness of insulation is proposed?
If they are using a sensible amount, the depth of the back box will fit within that.

4. If the plasterboard is cut e.g. for the backboxes, will this cause thermal bridging/ condensation and possible mould behind the plasterboard?

Care is required to get this right.

 

[mikeey84]

Removing the plaster will mean the insulation takes up less of the room. Its not going to make a huge difference, but every little helps.

Additionally this is an activity that will need to be inspected by a building control officer, so ensure the contractor is handling this, or ensure its arranged

 

[Mr Sparkle]

Thanks guys

 

[Mr Chibs]

If you choose the batten method, you can mount the back boxes onto a batten attached to the frame work, that way you can use metal boxes that are sat on wood.

 

[mrrusty]

You may find this helpful https://www.siniat.co.uk/en/downloa...lues?rev=d744a5f1-272c-4f07-82be-3b9e716b887e
IMHO you need a definite cavity behind the insulation, and if this is ventilated, all the better. You will be sealing the wall from the room. If the wall is also rendered on the outside - i.e. sealed, and/or has been pointed in cement rather than the lime the original solid wall would have been pointed in, then IMHO there is a risk of damp within the wall, either through interstitial condensation, or penetration which cant subsequently escape - the moisture gets trapped in the wall and can't get out because both sides are sealed.

IMHO, internal insulation when you have a ventilated cavity is sensible, because the ventilated cavity will draw away both interstitial condensation and penetration damp. However, with a solid wall it is a different kettle of poisson. More info here:- https://www.heritage-house.org/damp...ed-consequences-of-solid-wall-insulation.html