insulation behind plasterboard

benson1980

Hi all,

Getting there with our bathroom renovation and ripping everything out. After removing the tiles it was clear I needed to get the room re-boarded, so I'm completely stripping it down and taking down all of the old plasterboard. Whilst I'm at it, I know the general consensus is to insulate. As per the photo, I do have a bit of insulation, so the only external wall here is the one with the window, and it's a dormer upstairs so the void behind all the pipework is essentially the roof/eaves....



What would people recommend? There is a degree of diminishing returns here as this is the only room at the front of the house where I'm ripping the plasterboard out, and in the grand scheme of things it's a pretty small area. I was therefore wondering if there was a simple roll-type product I could just wedge between the studs that would more or less stay in place, but not something like celotex which seems a bit overkill and time consuming. I have considered insulated plasterboard but I can't really reduce the width of the room due to bath size which is already on the smaller side.

Would something like this work?

https://www.travisperkins.co.uk/cavity-and-internal-wall-insulation/knauf-insulation-dritherm-37-cavity-insulation-slab/p/9000199446

FreeBear

benson1980 said: What would people recommend?

I was therefore wondering if there was a simple roll-type product I could just wedge between the studs that would more or less stay in place, but not something like celotex which seems a bit overkill and time consuming.

I would have suggested PUR/PIR (Celotex) type boards - They are not difficult to cut to size (use a sharp serrated kitchen knife), and fill any gaps with expanding foam. In terms of cost, performance, & ease of use, PUR is twice as good as fibreglass for the same thickness, and 30% better than polystyrene. OK, OUR boards are 25-50% more expensive depending on where you buy, but these things are always a trade-off - Using PUR/PIR, you stand a better chance of getting close to the building regs targets with the space available.

Bendy_House

The stuff that's there is pretty useless.

If you really don't want the cost of PUR, then how about Jablite, the 'rigid' expanded polystyrene sheet? Again, easy to cut to fit snugly between the studs, sealed top, bottom, sides and to eachother using a bead of exp foam, tapped in until flush with the front of the studs, and then overboard with foil- backed p'board. 
3" thick studs? So ditto Jablite - it'll all be nicely ventilated from behind.

I think this will be pretty effective, and bathrooms are rooms where you don't really want cold spots.

theonlywayisup

Personally I would use something like Actis Hybris.  Celotex is a nasty thing to cut and the wastage is phenominal.  Actis can be cut with a toothless saw and for that void you would be ok with 75mm.  Info here https://www.insulation-actis.com/files/actis/pdfs/en/installation-guidelines/ACTIS-literature-HYBRIS-installation-guidelines-PZ509-112018.pdf

If you do go down the Celotex route then make sure you fit it correctly. It must be 100% snug to the studs otherwise it has no insulating value at all. Cut off too much and you've got to find a smaller hole to shove it in.

FreeBear

theonlywayisup said: Personally I would use something like Actis Hybris.  Celotex is a nasty thing to cut and the wastage is phenominal.

hrmmm... Interesting stuff - With a u-value of 0.033W/m²K, is is about the same as Jablite (polystyrene), and similarly priced. Wastage would be about the same for any rigid sheet.

Celotex, if cut with a standard wood saw makes a lot of mess (as would polystyrene), hence my suggestion to use a sharp serrated kitchen knife - Minimal mess, and if you plan your cuts in advance, wastage is kept to a minimum.

benson1980

Ok thanks all- I will have another look. The other issue I have is the copper pipes coming down the loft give me a space to back of plasterboard of around 10mm, near the ceiling. I guess I could always cut some kind of channel in the back of that particular bit. It’s also messy with all the pipe work in general hence why I was thinking non rigid sheet type insulation as I can work it around the pipes a bit rather than just cutting loads of sections out. But, points noted….

thanks again.

Bendy_House

I'd never heard of that stuff, TOWIU.

With that sort of trimming, Benson, both Celotex-type and Jablite are really pretty easy to handle. I laid microbore pipes in a 100mm layer of Celotex floor insulation by cutting a 'V' into the surface to around a third depth using a 'snap-off' craft knife, so it had a long enough blade length. The long V section lifted out cleanly, so all I then needed was to widen the bottom of the V to take the pipes, trim the matching amount of the tip of the removed V, and press it back into place with a thin bead of adhesive. Nigh-on invisible.

That Hybris material is certainly interesting, but I think would be tricky to work around pipes. If this were mine, I think I'd still go with Jablite of whatever thickness (depth) the studs are, and cut with a craft-knife so very little mess. Cutting channels for the pipes is also easy - cut a V as mentioned above, widen the slot to take the pipes as snugly as possible, fit these sheets from inside the eaves until the front edge is flush with the studs as before, trim away whatever is needed from the removed V lengths in order to accommodate the pipes, and push back into place with a couple of beads of Stixall or similar on the matting surfaces. If the V springs out before the adhesive sets, temporarily fit battens along the front of the studs to hold them in place.

Then foil-backed p'b.

Jobbie jablited.

theonlywayisup

The beauty with Actis Hybris is that you can use the 'leftovers'.  So long as the strips all butt up then it will not lose any Uvalue. Which means there can be zero wastage.  It isn't messy and there is no dust.  It is very simple as it's just a concertina makeup, so you can shove it almost anywhere.  It is very easy around pipes, you shove it in when compact and then pull it up/down to fill the void - no channels or bits to cut out.

Down here in Cornwall it is used by nearly all the timber frame companies.  

There is another layer you can add - a bit like a duvet - called Actis H Control, which pushes the Uvalue further.   Our holiday lets were built using it (and Hybris) and the U value is 0.12 - bearing in mind they are 10 years or so old, I think that's brilliant!