Julestools

Thanks Mike for a very helpful reply. Yes, this is part of an extensive refurb, including a roof upgrade later this year, and floor levelling and insulating currently underway. I am confident about the air tightness of the walls so currently not seeing a need to remove the plaster, but perhaps a condensation risk assessment may be a good idea, as Redbeard suggests. Breathable paint, no probs! Thanks again👍

Good point.. And yes I might be overyhinking it! We're they using vcl to keep moist air out, or somehow making it breathable I wonder?

Insulated stud sounds good, though someone suggested spacers at intervals to bring the studs away from the wall to minimise bridging. Then wool can go behind and between studs too. Intello is clever indeed! Would you regard pb with, say, the more porous 'one coat' plaster on it, breathable enough, or not?!

Thanks Redbeard. So would using Intello increase the chances of a dry healthy wall and insulation space if using not-so-breathable plasterboard and plaster?

Hi all, I want to add internal wall insulation to my 1970's block cavity walls. The cavities were filled with a mineral wool type fluff in the 90's, which appears to be dry where I've been able to see it and there is no evidence of damp or mould in or on the walls. The external render is also in good shape. We are leaning toward a stud frame fixed to the inside of the external cavity walls with mineral wool bats like knauf RWA45 or RS45, with plasterboard over. Our reasons being, it's cheaper than using celotex or insulated plasterboard, it's a breathable option which, from what I gather, would carry less risk of issues with condensation and mould and we don't mind losing a bit of internal space. I'd love to hear your thoughts and knowledge on this approach to internallly insulating cavity walls. Is it a good idea to do it at all? Is a vapour-open breathable approach better, or should I use a vapour barrier, as some manufacturers suggest? Any and all thoughts welcomed! Cheers, Jules

OK, if it'll do no harm with the old dpm also present below the slab. Thanks.

Thanks for the reply Jimbo. Yes, taped pir will do that, but I was talking about the dpm under the slab. Kingspan and others spec a dpm laid over the slab, before the pir goes down, which may be pointless if the old dpm seems effective despite it's age. I was just wondering if should trust the old dpm or not, or lay a new one over the slab anyway, just to be on the safe side. Cheers.

Hi everyone, I'm just starting to renovate our new home, a funny old bungalow built in 1973 which has an uninsulated concrete floor. After a bit of sds poking around in a few places I can confirm a dpm is present under the slab, it's clear and looks like 1000g.. definitely not 1200g, it turns up where the slab meets walls and ends in the vicinity of the bitumous dpc, but is not lapped/connected to it. Despite the fact that the dpm thickness and it's installation isn't ideal, the floor seems really dry, with no signs of past or present damp or mould. I taped a big square of polythene to the concrete in a couple of spots for a couple of days; there was no sign at all of any moisture/condensation or damp. After some levelling of the screed, I'll be fitting a floating floor with pir boards, taped, with 22mm chipboard t&g flooring on top. The question is.. Can I trust that old dpm?.. given that the floor seems very dry, or should I lay a new 1200g dpm over the screed to be on the safe side before the Insulation goes on?... Also, if the old dpm is still effective, as it seem to be, could a second dpm over the slab cause issues, given that the slab would then be vapour-closed on both sides? Oh what joy it is to be an indecisive over-thinker😂 I'm really looking forward to hearing people's thoughts on this one. Thank you.