Insulating an old bathroom

[mikeey84]

elements board, as it adds insulation properties.

Mine were similar to elements boards. Marmox multi boards. Cheaper too!!

 

[yorksbuilder]

Good to know. No more ply also do the similar board now too, NMP insulation board

 

[Elsa TLC]

I've used Prowarm on the external walls of my bathroom.
I wanted you use Rubber flooring but I can't find the colour I want.
I generally fit Vinyl to my bath / shower rooms for customers.
So will do this on mine too. Vinyl is anti slip and warm on the feet. It's not a massive insulation but it's better than a kick in the shins.

However I'd recommend Rubber floor if you can get the design and colour you want.

 

[Elsa TLC]

An insurance job i did.

 

[Ivor Windybottom]

Elements board is one of many equivalent brands. It's all generically known as tile backer board. It's available in various thicknesses, you could use a thicker sheet on the external walls for more insulation. It's rigid, waterproof and insulates.

I wouldn't use it on the floor. I have no evidence to say it's a bad idea but I just don't like the idea of walking on tiles that are on top of foam. It sounds like a recipe for future problems to my old-fashioned brain.

 

[yorksbuilder]

Use 6mm no more ply cement board on the floor. You can insulate under the floorboards if you want.

 

[Craig24]

Thanks everyone.

What would be the best option for external walls that are just going to be plastered? Should I still use the XPS board and skim over or is there a better or cheaper way?

 

[Ivor Windybottom]

Yes there's a better way... fully tile!

Whatever the insulation, the external wall will always be the coldest, so it's the place all the moisture from the air will condense and gather. If it's tiled it will gather as droplets then dry or at worst run onto the floor. If it's painted it will absorb, even into bathroom paint, and and develop into black mould.

If you really don't want tile then probably insulated plasterboard. But plasterboard in a bathroom is generally as terrible an idea as painted walls.

 

[Craig24]

I also have a narrow cavity. On the window outside wall I have 72.5mm insulated PB (60+12.5) fixed direct, on the shower outside wall I have 2x3's on edge filled with PIR and overboarded with tilebacker cement board. It's been a perfect solution - we don't get condensation on the walls at all even with long showers - our extract is an inline over the shower cubicle. My house relies on the ventilated cavity to control interstitial condensation caused by the insulation resulting in colder internal walls. ( that's the theory anyway - so far so good). I would not consider CWI for this reason.

Thanks for the reply. I like this idea but am worried that adding insulation will move the dew point to the cavity, meaning my cavity will get wet and it isn’t ventilated. I was hoping by building a stud wall and adding PIR, I could add a full moisture barrier to the whole wall before overboarding, does this sound correct?

 

[mrrusty]

I like this idea but am worried that adding insulation will move the dew point to the cavity, meaning my cavity will get wet

I think there is always a danger of overthinking it. If you have a sealed surface - tiles, boarding, insulation the chances of running up against serious interstitial condensation issues are probably minimal. It's good to think about it, but nothing is ever perfect. I would crack on and use whatever insulation method is easiest for you, and just take a little time to seal the joints to minimise the amount of bathroom air that can get behind the wall surface through gaps/ceiling/floor.

In my own house, I had a plan, thought about the risks, did the best I could to mitigate them, and so far all is good. But, I have no idea if the risks I mitigated were real or imagined - all I know is I don't have problems.

 

[JohnD]

I like this idea but am worried that adding insulation will move the dew point to the cavity,

The external leaf will be coldest, except when sun is shining on it, and the internal leaf a bit warmer.

If you have sealed the internal face with tiles, I don't see that there will be much moisture from inside the house migrating through the wall.

 

[noseall]

Thanks for the reply. I like this idea but am worried that adding insulation will move the dew point to the cavity,

Eh?

 

[Craig24]

Eh?

At the moment condensation is happening on the cold interior walls of the bathroom, by introducing insulation, I am worried condensation would now happen at the next coldest point (the cavity). Maybe I am wrong, just something I have read.

 

[JohnD]

At the moment condensation is happening on the cold interior walls of the bathroom, by introducing insulation, I am worried condensation would now happen at the next coldest point (the cavity). Maybe I am wrong, just something I have read.

But you're going to provide good ventilation, to extract the water vapour, aren't you?

The steam won't penetrate the walls much.

Interstital condensation in a brick wall is rarely seen away from cold stores.