Replacing Polystyrene Insulation

[doigy99]

Hi,

I am decorating a small room at home and noticed that previous owner had battened an internal wall that is opposite an external wall and filled with polystyrene and then covered with plywood and wallpapered over this.

I guess the fact that this wall is opposite the outside this was done to provide extra insulation.

My question is really around if I should just put some plasterboard onto the battens and keep the polystyrene in situ and keep it cheap and simple or whether I should buy some Celotex PIR of around 25mm and replace the polystyrene and plasterboard onto the battens instead to bring the insulation up to more modern standards.

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[Someone-Else]

if I should just put some plasterboard onto the battens and keep the polystyrene in situ and keep it cheap

It's up to you.

1) How much will the plasterboard cost
2) How much will the celotex cost
3) What will the heat gain by each be

[Grendel]

Plasterboard might give you a better surface to decorate than the ply but if you’ve only just found this then the ply looks to have been doing it’s job. Celotex will give a better degree of insulation but from what I’ve read it gradually over about 7years gives off the manufacturing gases , replaces that with air at which point it’s not much better than polystyrene. The only advantage might be the foil coating reflecting radian heat . I’m also not sure but possibly the polystyrene is more flammable if that might be an issue but again the plasterboard would largely mitigate that issue. Really it comes down as SE days to how much you want to spend…