Very Old Insulating Boards? Remove and replace with new insulation boards? Or leave?

Hi folks.

I'm getting some insulation boards put on internal cold walls and re-plastering.

One room with external wall has must be very old plaster board with what looks like at least an inch of polystyrene on it? It must be at least 20 years old, but much older, 40 years? Has anyone seen these boards before?

As there's an existing gap between the plaster/polystyrene board and the wall I don't think it has much affect at all?

Should I put new insulation boards over the top of it? Or remove the old boards completely and then put on new insulation boards and re-plaster?

I'm thinking to leave a space between the two layers of insulating board and the wall isn't a good idea?

Thanks.

10-10-20

If it's an option, I'd remove the older boards and have some newer PIR based boards installed as the thermal performance will be much better than polystyrene and you won't double your space losses.

The newer boards will have a vapor control layer while the older may not, that should help with reducing any condensation within the wall.

@10-10-20

@10-10-20 Thanks for that. I think I'll remove them. The room, an old garage conversion, was always cold and I don't think the old plaster/polystyrene had as much effect as newer boards. Thankfully there was never a problem with condensation. Keeping the space loss down is a big consideration too.

10-10-20

https://www.boards.ie/discussion/comment/120325079#Comment_120325079

It's not a holistic solution - you're not addressing some of the other reasons why that room is probably cold, but it should be an improvement at least. Do have the plasterer confirm that you're going to gain here by moving from polystyrene to PIR (by looking at the depth of insulation).

A 50.5mm insulated plasterboard would give you 12.5mm of plasterboard and 38mm (1.5") of PIR. They also come in 62.5mm.

Example: https://brooksonline.ie/xtratherm-thin-r-thermal-liner-dot-dab-xt-tl-up9895-c

Calahonda52

1: you cant put insulation over skimmed PB

It needs to come off, render the blocks with sand cement to make them airtight and then put on the new gear.

block is not airtight