Breathable external wall insulation / insulated lime render options - Diathonite vs??

[renovator123]

Any suggestions or feedback for comparing breathable EWI options for a home aiming for EnerPHit (U 0.15).

 

These options we are looking at:

* Diathonite (clay/cork/lime)

* CorkSol / SprayCork - how does it compare to Diathonite?

* Wood boards eg Steico, Gutex (Pavatherm prices seem crazy) - durability? Bowing? Water ingress?

* Supasoft (recycled PET) 

* Superfoil is advertised as breathable 

 

All seem very similar U value, prices vary a lot and Diathonite installers are hardest to find.

 

We have ruled out thermafleece wool for reasons I won't get into here.

 

This is to go under render (existing concrete based render is cracked and will be removed first), for an old house (500-600mm solid walls) with no damp proof course.

 

IWI we have ruled out due to construction/layout and internal issues. It's a semi with very limited space on one side (under 100mm thickness needed).

 

Anything extremely durable and really good for non-coastal but very windy area would be good.

[Redbeard]

EWI? - Supasoft? Superfoil? Can they be used for EWI? Why would you? I cannot see the logic in using a floppy insulant for EWI, necessitating studs and render-board.

 

Wood-fibre is good. Cork board is good, but IME a bit more expensive. Diathonite I have not used, but EBS say it can be used for EWI as well as IWI. See 'luneretrofit' for details of it sprayed on.

Lune Retrofit

https://luneretrofit.com

 

Don't know Cork Sol.

Hope that helps a bit.

[Iceverge]

Acrylic render over EPS would be far cheaper for EWI and well tested. 

 

I put the word "breathable" in the bin a few weeks ago along with "thermal mass" and "eco". Unfortunately it doesn't mean much.

 

You just get materials with various levels of vapour permeability .How they are

stacked in a wall, along with the heat gradient, the internal and external atmospheric conditions and all important airtightness determines if the wall will accumulate moisture leading to issues.

 

EWI is tremendously safe from a moisture perspective as the dew point never reaches in to the structure. The wall will never get damp so it really doesn't benefit to make it from expensive materials of higher vapour permeability. 

 

Not the case with IWI obviously. 

 

 

 

[Roger440]

19 minutes ago, Iceverge said:

Acrylic render over EPS would be far cheaper for EWI and well tested. 

 

I put the word "breathable" in the bin a few weeks ago along with "thermal mass" and "eco". Unfortunately it doesn't mean much.

 

You just get materials with various levels of vapour permeability .How they are

stacked in a wall, along with the heat gradient, the internal and external atmospheric conditions and all important airtightness determines if the wall will accumulate moisture leading to issues.

 

EWI is tremendously safe from a moisture perspective as the dew point never reaches in to the structure. The wall will never get damp so it really doesn't benefit to make it from expensive materials of higher vapour permeability. 

 

Not the case with IWI obviously. 

 

 

 

 

The OP says wall has no DPC. So the wall will be damp/wet to some extent. EPS will trap that in the wall. As well as the acrylic render.

 

With a DPC, sure.

 

 

 

[Roger440]

3 hours ago, renovator123 said:

Any suggestions or feedback for comparing breathable EWI options for a home aiming for EnerPHit (U 0.15).

 

These options we are looking at:

* Diathonite (clay/cork/lime)

* CorkSol / SprayCork - how does it compare to Diathonite?

* Wood boards eg Steico, Gutex (Pavatherm prices seem crazy) - durability? Bowing? Water ingress?

* Supasoft (recycled PET) 

* Superfoil is advertised as breathable 

 

All seem very similar U value, prices vary a lot and Diathonite installers are hardest to find.

 

We have ruled out thermafleece wool for reasons I won't get into here.

 

This is to go under render (existing concrete based render is cracked and will be removed first), for an old house (500-600mm solid walls) with no damp proof course.

 

IWI we have ruled out due to construction/layout and internal issues. It's a semi with very limited space on one side (under 100mm thickness needed).

 

Anything extremely durable and really good for non-coastal but very windy area would be good.

 

How will you stop the new (lime?) render cracking and allowing water in?

 

I see Carrington Lime are running practical courses on insulating traditional walls.

Edited February 1 by Roger440

[Iceverge]

23 minutes ago, Roger440 said:

 

The OP says wall has no DPC. So the wall will be damp/wet to some extent. EPS will trap that in the wall. As well as the acrylic render.

 

With a DPC, sure.

 

 

 

 

A DPC isn't magic. 

 

It simply stops moisture being pushed up through a wall by a high water table. 

 

A french drain outside would solve this. 

 

 

[RobLe]

Without a DPC i suggest only use materials that do not wick water, and are not damaged by water.  My experience of eps is that it’s very resilient against water, and I’m unconvinced about natural materials - cork or wood fibre in the same circumstances.  Nb:  ive used diathonite internally, and platinum eps externally - all just diy.  Eps is by far the easier to use.  If you’re avoiding it for eco reasons, check your assumptions - the jury is out on what the upfront carbon emissions are of the different materials, hence which is the more ‘eco’.   Eps might be made of oil, but wood fibre takes a lot of kiln drying.

[Roger440]

35 minutes ago, Iceverge said:

 

A DPC isn't magic. 

 

It simply stops moisture being pushed up through a wall by a high water table. 

 

A french drain outside would solve this. 

 

 

 

Magic no. But damn good at stopping moisture.

 

A french drain, in most cases will not solve this. Imporove? Maybe. Solve. No. Not unless you are building in a desert. Sadly, it rains here a fair bit. Ground is always damp.

 

 

 

 

 

[Roger440]

26 minutes ago, RobLe said:

Without a DPC i suggest only use materials that do not wick water, and are not damaged by water.  My experience of eps is that it’s very resilient against water, and I’m unconvinced about natural materials - cork or wood fibre in the same circumstances.  Nb:  ive used diathonite internally, and platinum eps externally - all just diy.  Eps is by far the easier to use.  If you’re avoiding it for eco reasons, check your assumptions - the jury is out on what the upfront carbon emissions are of the different materials, hence which is the more ‘eco’.   Eps might be made of oil, but wood fibre takes a lot of kiln drying.

 

That makes no sense.

 

With no DPC the wall is wicking water already to some extent. Where will it go if you stick EPS in front of it?

 

If you stick a load of damp clothes in a plastic bag and hang it on the washing line, what do you think will happen?

[RobLe]

Eps does breathe very well, it’s not XPS which is like a plastic bag.  Of course the render must be breathable too.  And it doesn’t mind being wet in the slightest - it won’t rot, while natural materials might, that would be my worry.  Happy to be shown to be wrong, I’m just a cautious diy-er. 

 

[SimonD]

Like others have suggested, don't discount EPS. It's far cheaper than the other options, more installers, probably more resilient than say wood fibre, especially if in a windy area where there is risk of wind driven rain.

 

If using wood fibre and there is dampness at the bottom of the wall, it is possible to use EPS towards the bottom and wood fibre further up. Indeed this is recommended if the EWI falls below about 300mm above ground level. I have EPS along the lower portion of my wood fibre wall for a significant proportion of the house, including the whole plinth.

[renovator123]

On 01/02/2024 at 19:02, Redbeard said:

EWI? - Supasoft? Superfoil? Can they be used for EWI? Why would you? I cannot see the logic in using a floppy insulant for EWI, necessitating studs and render-board.

 

Wood-fibre is good. Cork board is good, but IME a bit more expensive. Diathonite I have not used, but EBS say it can be used for EWI as well as IWI. See 'luneretrofit' for details of it sprayed on.

Lune Retrofit

https://luneretrofit.com

 

Don't know Cork Sol.

Hope that helps a bit.

 

The walls are nothing close to level so a flexible insulation allows you to fill any gaps and level things out. EPS or other boards must have the gap between them and the wall fully filled. It's a period house that was built as both vapour open and breathable and keeping it that way it's going to cause its less problems. 

 

[renovator123]

On 02/02/2024 at 09:12, SimonD said:

Like others have suggested, don't discount EPS. It's far cheaper than the other options, more installers, probably more resilient than say wood fibre, especially if in a windy area where there is risk of wind driven rain.

 

If using wood fibre and there is dampness at the bottom of the wall, it is possible to use EPS towards the bottom and wood fibre further up. Indeed this is recommended if the EWI falls below about 300mm above ground level. I have EPS along the lower portion of my wood fibre wall for a significant proportion of the house, including the whole plinth.

 

Yes about the lower walls, something not so vapour open it needed for the lower part of all of this, I should have said. Diathonite Demix and tanking are needed for the bottom 30cm+ for at least some part of the house given about a third sits on a concrete slab over rammed earth and house is 1830s and has never seen a DPC. 

 

By "breathable", think "vapor open". Figures for vapour permeability by diffusion and air tightness values are available for all the materials mentioned, although some (foil quilt and Supasoft) have to be filled in specific ways for EWI - supercoil have a breather quilt for instance. Currently we actually have some damp in a fully internal supporting wall coming up from this. Hopefully we will be getting this resolved as part of the work. The electric back box for unused sockets have rusted a second time after having measures done to fix it before.

[renovator123]

On 02/02/2024 at 07:45, RobLe said:

Eps does breathe very well, it’s not XPS which is like a plastic bag.  Of course the render must be breathable too.  And it doesn’t mind being wet in the slightest - it won’t rot, while natural materials might, that would be my worry.  Happy to be shown to be wrong, I’m just a cautious diy-er. 

 

 

Lime is extremely alkaline which discourages fugus/mould/rot but the additional breathable means the damp has somewhere to go (via diffusion) which right now it's the case with the concrete render slapped on the external walls. Externally it will be coated to keep out driving rain.

[renovator123]

On 01/02/2024 at 23:02, Roger440 said:

 

Magic no. But damn good at stopping moisture.

 

A french drain, in most cases will not solve this. Imporove? Maybe. Solve. No. Not unless you are building in a desert. Sadly, it rains here a fair bit. Ground is always damp.

 

 

 

 

 

 

I live on a hill in one of the wettest parts of the uk, but the water runs down the hill into a river and French drains are typically as part of that, it is not such as issue with the type of ground and the fact it's so steep - it would be an issue if we had chalk ir clay but we don't. It drains without a problem.

 

DPCs are perfectly good when you have cavity walls and a fairly modern build and you don't have any rooms below outside ground level.

 

It's not exactly practical to expect a DPC on 600mm limestone and cob with render and gypsum plaster to keep the wall dry, especially not when you do not have a floating floor or real foundations - we've been down that route and not had it work. So the focus needs to be on what materials work for the existing building and the limitations of it. Keeping 100% of damp out is highly unlikely so going with traditional but updated building products means moving further to vapour open, and MVHR (heat recovery ventilation) will be reducing any excess humidity further, although I doubt we will see damp on internal walls in the same way later.

[renovator123]

On 01/02/2024 at 19:02, Redbeard said:

EWI? - Supasoft? Superfoil? Can they be used for EWI? Why would you? I cannot see the logic in using a floppy insulant for EWI, necessitating studs and render-board.

 

Wood-fibre is good. Cork board is good, but IME a bit more expensive. Diathonite I have not used, but EBS say it can be used for EWI as well as IWI. See 'luneretrofit' for details of it sprayed on.

Lune Retrofit

https://luneretrofit.com

 

Don't know Cork Sol.

Hope that helps a bit.

Interesting, thanks. We are facing similar issues.

Diathonite is actually a range of products with Thermactive being IWI and Evolution being EWI, plus extra products for areas with a lot of salt crystals, a tanking solution and top costs. They do a top coat cork spray which can be colored and is less prone to cracking and better able to move with minor movement compared to most render.

 

I think we have given up with CorkSol, U value is not a good and they don't seem so good at getting back to you, and unsure of the quality / consistency of it. 

 

Another Diathonite EWI case, the House at the Northern Gate has it too (far North of Scotland and coastal).

 

https://www.fca-magazine.com/features/product-specific-features/1396-ecological-building-systems-cumbrian-period-property-overcomes-issues-of-damp-and-mould-in-major-renovation

[Iceverge]

12 hours ago, renovator123 said:

live on a hill in one of the wettest parts of the uk, but the water runs down the hill into a river and French drains are typically as part of that, it is not such as issue with the type of ground and the fact it's so steep

 

Whats your understanding of french drain?

 

This confused me a bit.

[renovator123]

Update: we weren't impressed at all with the Cork Sol info and found it easier to get Diathonite installers. The other options seem rarely used externally and won't help so much with air tightness or mould. Diathonite is excellent, not fully cured for a few months (but dry to touch and re-coatable).

We had advice that we should have XPS plinth across the bottom where we get a lot of water spray - on to get a bead on it so that the XPS can be recoated in future years/decades if there is water damage. The same top coat is on both and it looks awesome. We had a few external concrete window sills so got those knocked out and replaced with XPS, which is ridiculously loud when it rains (or was until the top coat was on).

 

Diathonite has greatly improved the air tightness (less drafty), and the mould situation too (because it's alkaline and because damp can move to the outside). It's a colored top coat so no painting needed. To keep moisture moving from inside to outside needs lime plaster or similar, although there's still a lot of benefits with gypsum... a lot of internal plaster is persistently mouldy or blown so needs sorting anyway. One part is so mouldy that the metal edging under the plaster has rusted through.

 

It's very noticeable how warm it is overnight and the phase shift of the thermal mass.

 

No good pics yet since top coat is still in progress and has to dry gradually before you get to the final color. It's already much better than the concrete render (which had a lot of damage). Diathonite evolution is a sandy color going on, drying to light grey. Top coat is by Lime Green in woad blue. The window bands need reforming unless you want to just paint them on after.