Insulating behind plasterboard on studs

eoghan1985

I've got a house with external insulation, with a single story extension out back (also externally insulated). The single story extension has plasterboard on studs with about 2 inch gap. The thing is cold air seems to be getting in behind the plasterboard from the flat roof ventilation, negating the external insulation.

Does anyone know of a way to insulate this gap, by pumping or something in between the studs? The missus has totally forbidden me from damaging wall but I could drill holes and polyfill them.

Any recommendations for products to fit this or even pointers to a company to do it would be great

decky1

when she's out at the bingo take them down and put up some 'Warmboard.

eoghan1985

decky1 wrote: »

when she's out at the bingo take them down and put up some 'Warmboard.

Might just about get me killed if she found out. Also warmboard doesn't stop the cold draft behind the plasterboard, which some sort of fill material would

_Brian

You could carefully drill at skirting board level and use cans of expanding foam.

It would be slow, but it can be done.

fred funk }{

_Brian wrote: »

You could carefully drill at skirting board level and use cans of expanding foam.

It would be slow, but it can be done.

Jesus no. You could end up destroying the walls. Ever see how powerful expanding foam is? It would push out the plasterboard.

_Brian

fred funk }{ wrote: »

Jesus no. You could end up destroying the walls. Ever see how powerful expanding foam is? It would push out the plasterboard.

If indeed there is a gap behind the boards the foam will expand up into this space rather than forcing out the boards.

Calahonda52

_Brian wrote: »

You could carefully drill at skirting board level and use cans of expanding foam.

It would be slow, but it can be done.

Jesus no - eile - because of the fire regs, which may be an issue here.

OP: you need to solve the wind problem so we need more intel on the wall structure from outside in

EWI
Plaster
Block
cavity ?
Block
plaster/skim?
Studs
Plaster board
skim

then take off one of the wall vents and check if the vent is fully ducted to side face of the plasterboard

If the fire regs were followed, there should be a solid batten across top and bottom, stopping draughts coming down

eoghan1985

Calahonda52 wrote: »

Jesus no - eile - because of the fire regs, which may be an issue here.

OP: you need to solve the wind problem so we need more intel on the wall structure from outside in

EWI
Plaster
Block
cavity ?
Block
plaster/skim?
Studs
Plaster board
skim

then take off one of the wall vents and check if the vent is fully ducted to side face of the plasterboard

If the fire regs were followed, there should be a solid batten across top and bottom, stopping draughts coming down

Ok, there's
EWI,
9 inch cavity block,
Studded gap
Plasterboard,
Skim.

The vent is blocked off from cross venting inside the plasterboard like you said. Like there's a blast of cold air out of sockets on wall opposite the vent, which would double rule that out

The draft is coming from the flat roof, which is fibre glass. I presume that there is a path from the in roof ventilation above the roof insulation down, but I cannot get access to the roof without a major deconstruction, which would also not be allowed

listermint

At this point id be putting in an inspection hole at the top of the wall to the left or right of that socket *vertically up to review where the air is coming from and check for cross battening at the top of the plasterboard where it meets the ceiling.

That will guide you for next steps.

You wont be able to progress this by just looking at the walls you will need to cause some inspection damage

Could be waaay off with my idea, but could you not drill a hole at the top, and pour a load of beads in? And seal it up?

https://www.adverts.ie/furniture/polystyrene-beads-ideal-for-bean-bags-filling/3327890

whizbang

Your problem is the cavity block walls. Who the hell puts EWI onto a cavity block wall..?

dathi

whizbang wrote: »

Your problem is the cavity block walls. Who the hell puts EWI onto a cavity block wall..?

https://passivehouseplus.ie/magazine/new-build/ground-breaking-housing-scheme-captures-one-developer-s-journey-to-passive

these guys are doing it on new build and external insulation is the recommended way of insulating cavity blocks in renovations

whizbang

EWI is fine in a new build, where the top of the block is capped and insulated

In an existing build, the cavity is open at top. Any heat saved by ewi simply flows up through the cavity, and out. Into your vented unheated attic space if you are lucky.

Also look at the buildup from the floor joists.
Usually a line of 4" solids on edge outside, and rough cut solids on the inside between joists. Continue again with the Cavity blocks on top, and now there is a massive airflow from between the joists up into the cavity, and out the top again.

How many holes are drilled into the cavity from inside for years and years. Waste pipes all perfectly sealed from outside, never on inside..

listermint

whizbang wrote: »

Your problem is the cavity block walls. Who the hell puts EWI onto a cavity block wall..?

Huh!?