Question on Insulation and Plasterboard in extension

Rew

We have a dodgy extension that we inherited from the previous owners. The main problem is that during the winter if we have a lot of people in the room it gets condensation spots appearing all over the walls. As far as I can see its where they have dabbed the board to the brick walls. If i take off a socket or light switch there is a small air gap and then blocks. I know that part of the problem is ventilation. There is no wall vent but there are 2 veluxes that would be set to vent generally.

I want to rectify the situation and im comfortable with pulling down the plaster work and reslabbing with kingspan backed boards. However I don't know is this the correct approach so im looking for a bit of advice.

Should I:

1) pull down existing plaster work, put up a dampproof membrane, kingspan and plasterbaord (is the damp proofing required?)

2) Put kingspan backed board directly onto the existing plasterwork

I think a wall vent is a given either way.

Any help appreciated.

DublinDilbert

Vapour barrier has to be on the warm side of the insulation, not the cold side. There should be a vapour control layer on the insulated slab you buy, between the plaster board and the insulation, so its closest to the room.

Oh and you'll notice a massive difference in that room.

L1979

Dot and Dab is used in houses all over the country without leading to condensation problems. If you were to use an insulated slab it would even achive a higher u-value if dot and dabbed (well according to literature).

I would start by installing a wall vent first, to see if this resolves condenation problem, or at minimum do both in tandom. But i wouldnt add to the problem by insulating alone.

Rew

L1979 wrote: »

Dot and Dab is used in houses all over the country without leading to condensation problems. If you were to use an insulated slab it would even achive a higher u-value if dot and dabbed (well according to literature).

I would start by installing a wall vent first, to see if this resolves condenation problem, or at minimum do both in tandom. But i wouldnt add to the problem by insulating alone.

As I said already the vent is a given but I suspect that the walls aren't properly insulated in the first place (if at all). We have already had to rectify issues with the roof and we suspect that the whole extension was badly done.

I'm leaning toward using insulted slab over the existing plaster work and and living with the loss of 50 or 60mm all round.

L1979

I insulated with an insulated slab 62.5mm thick (12.5 plaster + 50 insulation). Ripped out existing plasterboard and knocked off dabs. Then i dot and dabbed insulated boards up. I wouldn't recommend leaving existing plasterboard (even if it would be alot less messy) as you want to make sure you have an effective mechanical fixing into the blockwork to meet fire regulations.

If you read the research on condensation, cold briges etc, from what i remember, there is a higher incidence of condensation as a result of the insulated slab, where the insulation layer thickness exceeds my 50mm thickness. That was what was the deciding factor for me.

Good luck with the project.

Try fitting a vent first, you may find it sorts the condensation out. We have an apartment and it was plagued with condensation. We had 4 inch vents drilled into the lounge, hall and bedroom walls and hey presto, not more condensation problems at all. Holemasters did it for us - super service

Rew

Deleted User wrote: »

Try fitting a vent first, you may find it sorts the condensation out. We have an apartment and it was plagued with condensation. We had 4 inch vents drilled into the lounge, hall and bedroom walls and hey presto, not more condensation problems at all. Holemasters did it for us - super service

Condensation is only part of it. Its the way that it forms in spots all over the walls like the room has caught measles. I dont think ther eis much if any insulation behind the blocks.