Period House - Insulation

fx83wab

Am looking at insulating a 120+ year old house and have seen Calsitherm, Gutex etc. So here I need to strip off the existing plaster, install the insulation and then lime plaster over it. That seems to be the only option and think I've got my head around that.

What I'm wondering about is insulating the bathroom. I will be tiling the walls, so is there any point in going down the whole breathable insulation route, if I'm just going to put tiles on top of it, which won't be breathable?

Calahonda52

whats the wall construction from front to inside?
what aspect is the bathroom wall?

fx83wab

solid blocks, no cavity

west and south (2 walls)

Yellow_Fern

It is not the only option but external is usually best. Will all bathroom walls be tiled?

BryanF

Yellow_Fern wrote: »

It is not the only option but external is usually best. Will all bathroom walls be tiled?

Ewi is hardly best in this case? Given what the OP said about the rest of the house?

OP,
I would continue with the breathable insulation through out, if space isn’t tight you could use metal studs with cement fibre board, to hold the tiles, I found the bathroom roll on tanking system great, it wasn’t big money.

fx83wab

Thanks for the responses.

External insulation is not an option due to the brickwork.

Bathroom will be completely tiled.

I suppose what I'm struggling to understand is what is the point of breathable insulation, if I'm going to go ahead and put a non-breathable material (i.e. the tiles) on top of it?

BryanF

fx83wab wrote: »

Thanks for the responses.

External insulation is not an option due to the brickwork.

Bathroom will be completely tiled.

I suppose what I'm struggling to understand is what is the point of breathable insulation, if I'm going to go ahead and put a non-breathable material (i.e. the tiles) on top of it?

It’s still relevant, the point of the insulation breathability is to allow any moisture that gets into the wall build-up to get out.

fx83wab

Bear with me here, I'm pretty useless at this kind of stuff.

Scenario 1, breathable
Moisture from outside penetrates brick, hits the breathable insulation and penetrates it and then hits the tiles and is stuck. To get back out, has to go back through insulation and brick.

Scenario 2, non-breathable
Moisture from outside penetrates brick, hits the non-breathable insulation. To get back out, only has to go back through brick. Easier to get out.

Where is my logic going wrong?

BryanF

1. Why would the moisture be stuck at the back of tile? The breathable insulation absorbs and slowly releases moisture back out through the wall.

2. The breathable insulation slows the creation of condensation on the cold internal brick surface, that would otherwise occur with ‘ploy’ based insulation’s and lead to mould etc.

Let’s stop for minute, calling this insulation ‘breathable’, why not research ‘hygroscopic insulation’?

The wood fibre’s, calcium silicate’s, etc, even cellulose! allows moisture to be absorbed and dispersed, and keeps internal humidity low, until the external conditions change, and the wall can ‘dry out’, ie the wall remains ‘vapour open’ and the hygroscopic insulation and brick / render function together.

Found this on the first page of searching ‘hygroscopic insulation’
https://www.bre.co.uk/filelibrary/pdf/projects/low_impact_materials/IP18_11.pdf

You’ll get lots of peer reviewed studies also.

sydthebeat

fx83wab wrote: »

Bear with me here, I'm pretty useless at this kind of stuff.

Scenario 1, breathable
Moisture from outside penetrates brick, hits the breathable insulation and penetrates it and then hits the tiles and is stuck. To get back out, has to go back through insulation and brick.

Scenario 2, non-breathable
Moisture from outside penetrates brick, hits the non-breathable insulation. To get back out, only has to go back through brick. Easier to get out.

Where is my logic going wrong?

"Breathable" goes both ways.
It allows vapour to travel from internal to external without condensation due to energy flux (energy travels from warm to cold), in the majority of the time. In the minority the time (warmest summer days) there is a risk of condensation occurring the other way ie the extrenal is way warmer than they internal therefore the energy flux is in the other direction.
Breathable construction allows these situations to occur without trapping condensate within the construction.

"non breathable" is basically accepting that condensation will occur, and building to stop it entering the internal.
The problem with non breathable is, in that minority of situations during the warmest summer days, condensation gets trapped on the opposite side of the vapour barrier and can't go anywhere... Ergo mould, fungi, sick building etc. This is especially risky in single leaf porous constructions such as solid brick. At least a cavity construction has the ability to drain to the external.