seems to be a lot of choice.

i have a freezing and dampish downstairs loo, which used to be outside but now part of the conservatory.

it is single story, tacked on the side of the house, and I’m pretty sure single skin.  It is pretty small so space is at a premium.  I think the damn is most likely from condensation from the rest of the house.

so before I refurb I’d like to insulte it a bit.  My idea is to take off the old plaster which is about 100mm thick and then fit an insulated board to the outer wall and the ceiling.  I could go much thicker on the ceiling.

so what type of board do I want?  I presume I need some sort of vapour barrier?

I’d use polyuthethane backed plasterboard for that or use Recticel/Celotex/kingspan with water-resitant plasterboard glued on top. Both have vapour barriers. Use the shiny aluminium side on the inside.

Unless it’s timber frame you won’t need a vapour barrier on the walls, but it’s a good idea to fit one on the ceiling.

As for what insulation type: As space is a premium, you’d want to go PIR, such as Kingspan as it has a better thermal conductivity than mineral wool.

The trouble with insulating a single-leaf wall is you want to create a cavity so if any moisture does work it’s way through the brickwork it drips down the cavity and is caught by a cavity tray, which can then be drained by weepholes through the perpends in the brickwork. Of course, this will lose you space in the room, but British Gypsum do independent wall lining systems for this.

Failing that, an insulated plasterboard, such as Kingspan K118 would probably do the trick.

thanks, what’ the minimum depth that would make a difference?  and when you fit do you make it flush with the floor?  I think I read about leaving a small gap but can’ find the referece again.

as for fitting is it best just to glue it with no nails or drill / screw in place?

Fit as thick as your available space will allow.

Have a look at the Kingspan website: They have lots of fitting guidelines.

https://www.kingspan.com/gb/en-gb/products/insulation/insulation-boards/kooltherm/kooltherm-k118-insulated-plasterboard

Your current wall is probably less than R=0.4. 30mm of polyurethane is R=1.3, 60mm is R=2.6 and so on. R0.4 + 2.6 = 3 which is a good level for a wall. It’ll divide heat loss by at least six.

If the wall is dry apart from condensation as you suggest then glue will be fine. If you use half a dozen lumps per board then you’ll leave a small air gap so there will be enough circulation. There are Youtubes showing how to do it, I followed the Recticel ones. Where I was worried about damp I used a metal frame, and a 27 layer multi-layer insulator which takes the same space, 60mm, for R3. It was much more hassle and I wouldn’t bother again as it turned out that all the damp was condensation. I took a board off to check after a year and the wall behind it was completely dry.

thanks chaps, what about the ceiling?  rather than pull the old ceiling down could I just overboard with kingspan like k118 again?

at the moment the toilet can be 10 degrees colder than the rest of the house and has and old cast iron cistern in there which can be dripping wet with condensation.

Yeah, fitting on adhesive “dabs” will create a small ventilation space behind the insulation. You could also fit to 25mm treated softwood battens, if space allows.

The hardest part will probably be making sure the joints are well taped and sealed. You could then either paint the plasterboard or skim first.

Yeah, K118 on the ceiling as well: It contains an integral vapour control layer. To ensure it acts as a vapour barrier, you need to properly tape the joints again.

Is the roof ventilated? if not, condensation in between the joists could be an issue once you’ve insulated.

Or tile straight onto the plaster board as it’s a toilet.

Edit: the cistern will still drip with condensation, that’s due to a cold object at mains water temperature (which is probably less than 10°C in Winter) in warm humid house air. The walls and ceiling will be dry though.

no obvious signs of ventilation for the roof space.  it’ very small, like a brick lean to on the side of the house.  one side is the loo and the other side an old pantry, which I’m not planning on doing anything to just yet.

basically not much bigger than a large cupboard but does have z small window and trickle vent

wondering if I should put a fan in there too whilst I’m at it

A trickle vent is adequate in a toilet. The roof space will be OK if there’s no way warm humid air from the house can get into it. Make sure the ceiling in the pantry and toilet are well sealed.

A word of warning, once you start this insulation lark you realise just how much differnce it makes and you’ll end up doing the whole house. (winky)

Can you add insulation externally? This would allow much more depth and therefore performance.

If you have a gable wall you could put an air brick in to provide some roof ventilation.

Technically, a toilet should have at least an intermittent extract fan, providing no less than 15l/s extract.

Can you add insulation externally? This would allow much more depth and therefore performance.

You can, but it would probably be more complicated as you’d have to finish it somehow; probably using an insulated render system, or timber weatherboarding on battens, which would all significantly add to the cost.

Technically, a toilet should have at least an intermittent extract fan, providing no less than 15l/s extract.

Isn’t that just for a new house, not existing?

morning can’ insulate externally as this side is built right on the boundary.  I am half thinking about it for the rest of the house as the top half is pebble dash and mock Tudor and will need some tlc at some point

I may leave the ceiling void alone for now, it looks well sealed and must have been like that for a good length of time