Insulating External Walls in an early 1990's hollow block built house

alias no.9

We're in the process of buying an early 1990's semi in Dublin. Needless to say, despite the fact that the rest of the country were building cavity walls back then, Hollow blocks were still de-rigueur in Dublin. The external walls are battened and slabbed with presumably a hopeless sliver of glass wool in between the battens.

The plan is to get the house right before moving in and insulation is a concern. I'm inclined to strip back the plasterboard and start again. I'm looking for opinions on the best way to go about it, should I...

[1] Strip back to the battens and fit insulated plasterboard directly to the battens, if so, should I replace the insulation between the battens too?

[2] Strip back to the bare wall and fit insulated plasterboard to directly to the bare wall? What should I have done with electrical cables in this case, have them chased into the wall (can that even be done with hollow blocks)?

[3] Leave well enough alone?

The plan is to replace the windows and external doors too in order to improve the air-tightness because they're fairly tired despite being double glazed.

Catfirelily

Take it back to the walls,you can cut a channel in the back of the insulated slabs for the conduit and socket boxes if necessary. Or dab and stick the slabs over them then tag the slabs. Mightn't be any harm to have the cavities pumped with insulation aswell. Or go for the external insulation.

alias no.9

Catfirelily wrote: »

Take it back to the walls,you can cut a channel in the back of the insulated slabs for the conduit and socket boxes if necessary. Or dab and stick the slabs over them then tag the slabs. Mightn't be any harm to have the cavities pumped with insulation aswell. Or go for the external insulation.

Don't think you can pump the cavities in hollow blocks. Would go with external but the front is a mix of brickwork and tile.

Catfirelily

Insulated boards inside would work out cheaper if you don't mind losing the space

alias no.9

The stairs is on the party wall, so the smallest rooms have just one external wall with the larger rooms having two so we should be ok for space.

MicktheMan

alias no.9 wrote: »

[1] Strip back to the battens and fit insulated plasterboard directly to the battens, if so, should I replace the insulation between the battens too?

[2] Strip back to the bare wall and fit insulated plasterboard to directly to the bare wall? What should I have done with electrical cables in this case, have them chased into the wall (can that even be done with hollow blocks)?

[3] Leave well enough alone?

The plan is to replace the windows and external doors too in order to improve the air-tightness because they're fairly tired despite being double glazed.

No 3 might be your best option until you have it properly assessed for heat loss. It might very well be an air tightness issue (draughts) rather than an insulation one. If the walls are bare block at the back of the dry lining then your external walls are porous to air (i.e. no effective air barrier. Without first addressing this with a good scratch coat or grey sand/cement plaster layer, no amount of insulation will be effective.

Internal drylining increases significantly the risk of interstitial condensation and mould at the back of the dry lining (regardless whether a vapour barrier is installed) and if was my home, I would get the air tightness issue sorted first and when funds allow externally insulate and replace the windows at the same time (there are different finishes including brick slips available for external insulation).