Best way to internally insulate solid walls

[Red15]

Hi, the walls in our house have been fitted with a damp proof membrane on the walls on the ground floor and the first floor (the type you might see used in basements) this is fitted straight to the wall and then battened and plasterboarded over.

I have just started removing the plasterboard and have seen that there are a lot of water droplets holding between the damp proof membrane and the wall is giving off a damp smell.

(This work was all carried out by previous owners)

I am planning on removing it all and using kingspan/celotex type insulation but what is the most effective way of fitting it without causing any further issues afterwards.

I was originally thinking about battening the wall and then fitting 62.5mm insulated plasterboard to it but the price of insulated plasterboard is twice the price of buying insulation and plasterboard seperate.

Should I leave an air gap between solid walls rather than tightly fitting insulation against it to prevent the solid wall sweating internally?

Should I fit vents in the plasterboard wall to allow air to get into created cavity?

Should I construct a 2x2 stud wall and inch or so off the solid wall to leave a cavity and fill the frame with 50mm insulation and plasterboard over?

whats the best method?

 

[jeds]

Not a good idea to create cold side voids AND cut off evaporation routes. Recipe for condensation. Better option is to place PIR insulation tight against the wall. You then have three options; you could board over with plasterboard but, be warned, drilling, plugging and screwing through 75mm board+insulation is very difficult to do without the screwhead pulling through the board. Wide-head screws is an option and I've known people add washers but it's still a tricky business. Much better plan is to batten over the insulation or, better still, board over with 18mm OSB. Plasterboard is then fixed with standard driwall screws. The OSB option has the advantage of providing a decent fixing later for screwing stuff to the wall. Use a spray on tack adhesive to hold the insulation in place while you mess around with battens or OSB.

 

[Bod ...]

I did thus last year. Forgot what it called.

Kitchen I have insulated 2 externals walls in my kitchen and 1 in my living room.

Also in doing my Kitchen I have replaced all the 15mm hot feeds to taps with 10mm feeds and insulated them from a manifold.

Next year I'll insulate the spare room and hopefully fit triple glazing.View attachment 284297View attachment 284325

 

[Red15]

Not a good idea to create cold side voids AND cut off evaporation routes. Recipe for condensation. Better option is to place PIR insulation tight against the wall. You then have three options; you could board over with plasterboard but, be warned, drilling, plugging and screwing through 75mm board+insulation is very difficult to do without the screwhead pulling through the board. Wide-head screws is an option and I've known people add washers but it's still a tricky business. Much better plan is to batten over the insulation or, better still, board over with 18mm OSB. Plasterboard is then fixed with standard driwall screws. The OSB option has the advantage of providing a decent fixing later for screwing stuff to the wall. Use a spray on tack adhesive to hold the insulation in place while you mess around with battens or OSB.

Thanks for the reply, why would you suggest to fit the insulation tight to the wall rather than batten or frame first to leave a gap/cavity and then insulation?

 

[robinbanks]

Much better plan is to batten over the insulation

This also helpfully creates a service void in which cables and pipes can be run

 

[Brigadier]

Not a good idea to create cold side voids AND cut off evaporation routes. Recipe for condensation. Better option is to place PIR insulation tight against the wall. You then have three options; you could board over with plasterboard but, be warned, drilling, plugging and screwing through 75mm board+insulation is very difficult to do without the screwhead pulling through the board. Wide-head screws is an option and I've known people add washers but it's still a tricky business. Much better plan is to batten over the insulation or, better still, board over with 18mm OSB. Plasterboard is then fixed with standard driwall screws. The OSB option has the advantage of providing a decent fixing later for screwing stuff to the wall. Use a spray on tack adhesive to hold the insulation in place while you mess around with battens or OSB.

Won't the screws (mechanical fixings, and being right through to the (cold wall), form "cold bridges"?

 

[jeds]

Won't the screws (mechanical fixings, and being right through to the (cold wall), form "cold bridges"?

In theory yes but not to any measurable effect. The cross section area of the screw is very small and the screw shaft warms as it gets closer to the inner surface. This is a standard specification - well proven.

 

[Brigadier]

In theory yes but not to any measurable effect. The cross section area of the screw is very small and the screw shaft warms as it gets closer to the inner surface. This is a standard specification - well proven.

I might be overthinking it but, I'd be gutted if I'd put all of that effort in, only to have cold (read, damp / mouldy) spots coming through......

(Having seen the lengths people go to, to avoid cold-bridging in other applications).

 

[jeds]

Thanks for the reply, why would you suggest to fit the insulation tight to the wall rather than batten or frame first to leave a gap/cavity and then insulation?

Leaving a gap on the cold side creates an unventilated void which will run with condensation. Even a small gap does the same but the smaller the gap the less volume of vapour and the problem reduces to a point of insignificance.

PS. made even worse if you also 'waterproof' the cold surface, blocking off any chance of outward evaporation.

 

[robinbanks]

Having seen the lengths people go to, to avoid cold-bridging in other applications

Building a passivhaus, yes..

 

[robinbanks]

Leaving a gap on the cold side creates an unventilated void which will run with condensation

But if it's unventilated, where does the moisture laden air come from to supply the cold surface with vapour to condense?

 

[jeds]

But if it's unventilated, where does the moisture laden air come from to supply the cold surface with vapour to condense?

Being unventilated really just means there is no deliberate flow of air though the void, but that does not stop vapour permeating. It's impossible to hermetically seal a void like that. Vapour will find a way in around the edges and possibly even through the materials.

 

[oldbutnotdead]

You can make your own insulated plasterboard easily enough (PIR, non-solvent adhesive, 12.5mm boards).
You can dot and dab this composite to your solid walls- no problem with damp leaching through the 'dots' to the plasterboard, the PIR is not porous. This works very well if the brickwork is a bit poor.
Downside is electrical services need a hole in the insulation.