Internal insulation of Bathroom

[wookey]

I think that trick without the waterprofing bitumen will work very well too (possibly better). i.e just put insulation against the wall (XPS) and gravel in front of that. Dramaticaly reduces the thermal bypass through the bottom corner of the wall into the cold surface ground, and keeps the wall much dryer. Relatively simple job.

[Greenbeast]

Thanks guys, behind the bathroom is my veg patch, so i won't have to ruin any grass but i will have to empty a waterbutt and move it temporarily.
Not a bad idea though.

Wookey, what are your thoughts on the method of insulating that i'm choosing? the cross-battening with an sealed air gap?
Also what about the type of insulation, i.e. between mine and TwoHorsePower's suggestion

[wookey]

Hmm, 9" solid wall, partly underground. Does it have a DPC? I have no direct experience of such things. I think adding the XPS and drainage outside is very important in this case. All that extra soil, whilst being awkward from a damp control POV is good in terms of insulation :-)

I think your scheme should work, so long as it really is sealed. I am always nervous of air gaps myself and have avoided them here, but if you have wonky walls then they are unavoidable, and relatively small ones can be OK (e.g the 16mm in double-glazed windows). With potentially damp walls it is important that the moisture can get out somewhere (or at least that it doesn't freeze and has nothing to rot). So treated battens are in order. The horizontal battening should be effective in minimising circulation. Why are you putting in vertical battens rather than butting up sheets? Just seems like an extra gap to potentially let water vapour pass through, and a thermal bridge. If the wall is really soggy then I'd wonder about using breathable insulation and not trying to keep it all in. The problem is that none of that stuff is as good as PUR for a given thickness, except spacetherm and that's awfully expensive.

[Greenbeast]

I don't know about the DPC, opne would hope so!
I will definitely follow that course of action for out side, but it may have to wait a couple of months

As for the vertical battens, not sure now that you mention it. I think it was to help in putting up noggins for hanging things on the wall (basin, etc...), but i've since thought about timber going right back to the brick for that (stronger and i will just insulate around it)
I guess i can just buy plasterboard screws long enough to go through the insulation.

Although i was planning on putting 100mm insulating/VCL tape across from sheet to sheet (i.e. over the batten) anyway.
It would reduce cold bridging if i did away with them, i guess

It's never easy is it!?

[Greenbeast]

I'm now literally 2-3 weeks from doing this job.

Need to work out the fine details.
I'm going to batten the walls to leave an air gap behind the insulation, i will make sure there is no path for air to move around the sheets into the cavity.
This way i can gain insulation value without shelling out more money on thicker sheets.

I've been reading up and it seems i have to worry about interstitial condensation and should not go below a U value of 0.45.

I've got a few questions
1) Does this matter on a party wall? Should i insulate at all on that wall in fact?
2) There's two external walls, one is double skin and one is single skin, I assume if i've got the space and money i should buy thicker insulation for the single skin wall to bring it down to 0.45?

Anything else i need to think about


Thanks

[tony.]

Greenbeast,

I would insulate to a depth as much as you can afford to loose from the finished room dimensions, bearing in mind door openings, window openings and existing sockets,switches that might have limited length on them to relocate.

I recently removed lath and plaster from my coomed ceiling and from the walls, fitted 100mm celotex boards inbetween  rafters and timber partition studwork.

I sealed this with about 30 tubes of clear silicone, and a lot of expanding foam, i will now get a foam gun for better control, as i think i wasted more than used.

All joins were taped with silver foil and finally i used 12.5mm foil backed plasterboard, with the perimeter of the boards siliconed in place.

Everything was finally wet plastered.

Its made a huge difference.

On the external wall i kept the insulation off the wall 50mm(this wall was behind a existing coomed ceiling so would never be seen or touched again) i just fitted the boards tight and foamed them into place. A cupboaard was built in front of this wall.

Got so much insulation left over, im fitting it in the loft, rather than throwing it away or free cycling

Good luck

Tony

[Greenbeast]

Does this advice not ignore the risk of interstitial condensation?

When you say you kept the boards off the wall by 50mm on the external wall, do you mean in the same way that i intend to have an air gap behind my insulation?

re: foam gun, good idea, i recently got one with this job in mind and have been draft proofing around the house, much better than standard throw-away jobbie.

[tony.]

Greenbeast,

My plasterboard is foil backed so acts as a vapour barrier.

The celotex is foil backed on both sides and is completely sealed so no warm air can enter.

I have left the 50mm gap between the rafters and the back of the insulation to allow air movement, but this air will be unheated.

I think this is fine, unless !!!

Tony

[Greenbeast]

yes i was planning on foil backed celotex with taped joints