ICF cladding for Nudura/Thermohouse - internal and external options

[Indy]

There have been a few of these on the forum recently, but rather than hijack those - thought I would start my own as my query is slightly different.

 

Fairly settled on going for an EPS type system - either Nudura or Thermohouse (if I can afford the latter!). Wanted to understand the options there are for both internal and external cladding.

 

Internal - fairly straightforward in the sense that we'll get plasterboard and then normal plaster and paint on top. Would this be a sensible approach to have an airtight home to almost PH levels, that work with MVHR? Would the plasterboard wall be strong enough to take the weight of usual fixings on the wall (discounting the kitchen units, where I've been told we can put up an OSB to take the weight).

 

External - this is more confusing. We're going for a white render finish and the recommendation from both companies is to render directly on top of the EPS (with the usual base coat applied). Even with the silicone render and the hygrophobic properties that are touted, I'm not sure I trust this enough to not have a proper rain screen. We're not going for a timber clad look, its smooth render on the majority of the building. What are the options here - something like fireproof cement board and render on top of that? Something else that I'm not aware of? Or am I being too pessimistic and render on top of EPS is sufficient?

 

Pics for reference 

https://ibb.co/k1tHrNX
https://ibb.co/vj1hnm1

 

 

[Russell griffiths]

Your icf house should be airtight without any internal finish. 

I tested mine before plasterboard and got a good score, 

big mirrors, cupboards, flatscreen telly, fix a chunk of 5/8 ply behind the plasterboard, then just board over. 

 

Externally, mine sat outside with no external protection for 3 years, you can stand there with a hose on it if you want, you won’t get any water penetration if you pick a good icf and if you detail the window and floor junction correctly. 

The only thing that hurts it is UV. 

[Indy]

4 hours ago, Russell griffiths said:

Your icf house should be airtight without any internal finish. 

I tested mine before plasterboard and got a good score, 

big mirrors, cupboards, flatscreen telly, fix a chunk of 5/8 ply behind the plasterboard, then just board over. 

 

Externally, mine sat outside with no external protection for 3 years, you can stand there with a hose on it if you want, you won’t get any water penetration if you pick a good icf and if you detail the window and floor junction correctly. 

The only thing that hurts it is UV. 

So render over the EPS ICF is waterproof enough? How about structural rigidity - i.e. if you hit the side of the walls with a hammer or something heavy, would the EPS crumble or get dents? Or does the render 'harden' and provide a protective layer?

[Nickfromwales]

4 minutes ago, Indy said:

So render over the EPS ICF is waterproof enough? How about structural rigidity - i.e. if you hit the side of the walls with a hammer or something heavy, would the EPS crumble or get dents? Or does the render 'harden' and provide a protective layer?

Render IS waterproof, which is why it gets applied!  

Yes, point impact would damage this with relative ease, but you can apply additional layers of base coat and mesh to 'beef' this up.

If you want to take a hammer to it, not much will withstand that tbh, but render over a cement board would be an option.

Visit a house with render over EPS EWI and see for yourself that it is quite robust. If you are crap at parking and hit the corner of the house........use the bus  

[FM2015]

Both Nudura and Thermohouse should be fairly airtight as standard.  Check best practice for each product on sealing openings, required vents etc

 

Internal

Plasterboard straight over.

Plywood beneath plasterboard mentioned already for fix to.  Really heavy items could be fixed to timber secured directly back to concrete in chases.  It's not just the weight, is it static or dynamic?  We have a climbing wall fixed through ICF....not you average kitchen cupboard full of baked beans.

 

External

Most EPS based blocks are classified impervious until finished.

Most thin coats are locally repairable but tough as the proverbial.

Check with warranty issuer and product manufacturers for appropriate brands.  Not all EPS/XPS are the same density and this can impact the quality of bond.

Sadly this last point seems to change depending on area, warranty, wind direction.

Getting this choice right though could eliminate the need to cement board everywhere.  And I would suspect repair could be more involved.

 

Edited May 17, 2022 by FM2015

[Mako]

23 hours ago, Indy said:

So render over the EPS ICF is waterproof enough? How about structural rigidity - i.e. if you hit the side of the walls with a hammer or something heavy, would the EPS crumble or get dents? Or does the render 'harden' and provide a protective layer?

Hmm, that’s the weak part of EPS or even XPS cladding, the compression strenght it’s not strong enough to withstand any impact. I have seen kids playing bow and arrow games at a council estate where they applied EWI System.

the arrows where penetrating the render with ease.

render is only cosmetic really.

 

[Nick Laslett]

EPS lack of strength is a double edged sword. It may be easily damaged, but it is also easily repaired. The concrete core is the structural element.

You could go to great lengths to protect the EPS, but it is only the insulation layer. 
 

Think of it like plastering plasterboard. The plaster gives the plasterboard a hard shell, without it, it is easily dented. You don’t put cement board in front of plasterboard, then plaster. (Maybe this is a bad analogy?)

 

Every system has its strengths and weaknesses, don’t use ICF if you are worried about what will happen to the external EPS layer, or go to great lengths to remedy this weakness. 

Edited May 18, 2022 by Nick Laslett

[Mako]

3 minutes ago, Nick Laslett said:

EPS lack of strength is a double edged sword. It may be easily damaged, but it is also easily repaired. The concrete core is the structural element.
 

Easily repaired yes, but it would involve rendering again as the patch work can’t be matched, as render will bleach in time.

done it in the past, you will need to paint over with silicone paint at very least.

[Mako]

On 17/05/2022 at 22:33, Nickfromwales said:

Render IS waterproof, which is why it gets applied!  

Yes, point impact would damage this with relative ease, but you can apply additional layers of base coat and mesh to 'beef' this up.

If you want to take a hammer to it, not much will withstand that tbh, but render over a cement board would be an option.

Visit a house with render over EPS EWI and see for yourself that it is quite robust. If you are crap at parking and hit the corner of the house........use the bus  

Hmmm, render it’s not quite waterproof it’s classed as water repellent, if you render your basement walls it will leak, because

render absorbs water, but because its applied vertically water will run off it. And it will dry quick after that.👍

[Nickfromwales]

17 minutes ago, Mako said:

Hmmm, render it’s not quite waterproof it’s classed as water repellent, if you render your basement walls it will leak, because

render absorbs water, but because its applied vertically water will run off it. And it will dry quick after that.👍

OK, you got me  I should have said rain / weather proof. I’ll get my coat. 

[FM2015]

20 hours ago, Mako said:

Hmm, that’s the weak part of EPS or even XPS cladding, the compression strenght it’s not strong enough to withstand any impact. I have seen kids playing bow and arrow games at a council estate where they applied EWI System.

the arrows where penetrating the render with ease.

render is only cosmetic really.

 

EPS and XPS used in ICF is denser than that used in EWI.

 

That's 4 abbreviations in one sentence.  Which is three too many!

[Babak]

I am using TH and the fabric has been built. Rendering using EWIPro silicone in a few weeks. So this is what has and has not worked well:

 

- Do a lot of research about getting a building warranty if applying render direct to walls. A couple of large insurance companies (eg LABC warranty) now all but refuse to insure this except under some impossible conditions.  

 See example here.

- I have opted for an architectural warranty which covers direct render to ICF.

- I did have the option for leaving a vent gap between the wall and the render using battens and render boards but somehow that defeats the purpose. Plus with 150mm EPS there will be a lot of long and thick screws into concrete, both expensive and slightly impacting insulation values.

- my EPS walls are all scratched (seriously), pushed in, damaged, etc. not in a big way of course. Any serious damage can be fixed with low expansion foam. But when different renderers came for quotes, they were not worried at all whatsoever. They said the first base layer will smooth everything out.

- I understand you can hose wash the silicone render within reason. So it is water resistant enough. However it MUST be applied well. EPS is NOT waterproof, I have seen it in action. It is not porous like plaster at all, but water will get through it eventually. Remember the old white foam coffee cups?

- very critical to make sure openings are sealed well. Goes without saying. Remember there is no air gap like a two leaf wall, so sealing has to be much better.

 

- I plan to glue plasterboard direct to EPS with some screws into galv steel for good measure. But remember, if you were to fix heavy stuff, the plasterboard and the glue may take the weight, but the EPS could get ripped. Very unlikely to happen with normal loads though. With thermohouse there is only 50mm EPS inside the house so is easier to reach the concrete core where you have to. I have also used sterling board for heavier stuff as suggested already, fixed to concrete using thick hammer fixing for my plant room walls.

 

- for external render I have the option of using double scrim for additional strength. But just can’t see too many cars driving into the walls, so am taking a small risk…

 

- thin coat silicone appears best for EPS.

 

- if you have neighbours across the fence when you design the house, make sure the architect looks at fire spreading regs.

 

- for windows, thermohouse is not really the most impressive out there in terms of product support. Most other providers offer their window jamb system and kit.
 

- for doors and windows, make sure you choose a system which integrates well with ICF. Assuming you will go for low u value windows, they are often different from standard windows. So do not make assumptions. Eg with my Rationel windows, they want to place the entire weight of triple glazed windows on the base, possibly over a few spacers. ICF EPS is not designed to take that type of load and will give over time. My solution is to replace the EPS above the concrete on openings with thinner EPS 300 or 400, with a 10mm layer of cement or timber on top of it. To take the point load of the spacers.

 

- think what you want to hang outside and allow for it at concrete pour time. Also for any holes in the wall, etc.

 

- good luck.
 

- on a separate note, if you are aiming for low u value house, then be prepared to argue with heating engineers who will (likely) use standardised parameters to work out your heat demand. I ended up registering as a reseller with a main brand so could enter my own house parameters. Yes, those with 30 years of heating design may still want to use heat demands from 30 years ago (no disrespect to those good advisers, but personally I gave up with JG and NuHeat for underfloor heating, though I am sure it was my bad luck.

same with boiler/heat pump. I had to insist over several calls and after emailing informative documents, before my heat pump guys incorporated MVHR efficiencies into their air volume change calculations….

 

 

 

 

[Nick Laslett]

On 27/06/2022 at 23:02, Babak said:

I am using TH and the fabric has been built. Rendering using EWIPro silicone in a few weeks. So this is what has and has not worked well:

 

- Do a lot of research about getting a building warranty if applying render direct to walls. A couple of large insurance companies (eg LABC warranty) now all but refuse to insure this except under some impossible conditions.  

 See example here.

- I have opted for an architectural warranty which covers direct render to ICF.

- I did have the option for leaving a vent gap between the wall and the render using battens and render boards but somehow that defeats the purpose. Plus with 150mm EPS there will be a lot of long and thick screws into concrete, both expensive and slightly impacting insulation values.

- my EPS walls are all scratched (seriously), pushed in, damaged, etc. not in a big way of course. Any serious damage can be fixed with low expansion foam. But when different renderers came for quotes, they were not worried at all whatsoever. They said the first base layer will smooth everything out.

- I understand you can hose wash the silicone render within reason. So it is water resistant enough. However it MUST be applied well. EPS is NOT waterproof, I have seen it in action. It is not porous like plaster at all, but water will get through it eventually. Remember the old white foam coffee cups?

- very critical to make sure openings are sealed well. Goes without saying. Remember there is no air gap like a two leaf wall, so sealing has to be much better.

 

- I plan to glue plasterboard direct to EPS with some screws into galv steel for good measure. But remember, if you were to fix heavy stuff, the plasterboard and the glue may take the weight, but the EPS could get ripped. Very unlikely to happen with normal loads though. With thermohouse there is only 50mm EPS inside the house so is easier to reach the concrete core where you have to. I have also used sterling board for heavier stuff as suggested already, fixed to concrete using thick hammer fixing for my plant room walls.

 

- for external render I have the option of using double scrim for additional strength. But just can’t see too many cars driving into the walls, so am taking a small risk…

 

- thin coat silicone appears best for EPS.

 

- if you have neighbours across the fence when you design the house, make sure the architect looks at fire spreading regs.

 

- for windows, thermohouse is not really the most impressive out there in terms of product support. Most other providers offer their window jamb system and kit.
 

- for doors and windows, make sure you choose a system which integrates well with ICF. Assuming you will go for low u value windows, they are often different from standard windows. So do not make assumptions. Eg with my Rationel windows, they want to place the entire weight of triple glazed windows on the base, possibly over a few spacers. ICF EPS is not designed to take that type of load and will give over time. My solution is to replace the EPS above the concrete on openings with thinner EPS 300 or 400, with a 10mm layer of cement or timber on top of it. To take the point load of the spacers.

 

- think what you want to hang outside and allow for it at concrete pour time. Also for any holes in the wall, etc.

 

- good luck.
 

- on a separate note, if you are aiming for low u value house, then be prepared to argue with heating engineers who will (likely) use standardised parameters to work out your heat demand. I ended up registering as a reseller with a main brand so could enter my own house parameters. Yes, those with 30 years of heating design may still want to use heat demands from 30 years ago (no disrespect to those good advisers, but personally I gave up with JG and NuHeat for underfloor heating, though I am sure it was my bad luck.

same with boiler/heat pump. I had to insist over several calls and after emailing informative documents, before my heat pump guys incorporated MVHR efficiencies into their air volume change calculations….

 

 

 

 

Great post with lots of useful information. We just had our EWIPro rendering done about a month ago. All seems to have gone well. 
 

I don’t know how important it is to the long term quality of the application of thin coat render systems. But I had to impress upon my render crew that they needed to brush down the EPS, as it had been in the sun for 6 months and had a thin coat of eps dust. I think with a regular EWI job, the EPS has not been up for very long, whereas with ICF, there can be a significant time gap. 

[Babak]

On 03/07/2022 at 18:39, Nick Laslett said:

Great post with lots of useful information. We just had our EWIPro rendering done about a month ago. All seems to have gone well. 
 

I don’t know how important it is to the long term quality of the application of thin coat render systems. But I had to impress upon my render crew that they needed to brush down the EPS, as it had been in the sun for 6 months and had a thin coat of eps dust. I think with a regular EWI job, the EPS has not been up for very long, whereas with ICF, there can be a significant time gap. 

That’s a really good point. My renderers are supposed to commence in a couple of days so will ask the same. The build was finished in March so it has not been under the sun - certainly summer sun - for that long, but definitely a good point, thank you!

 

 

Edited July 9, 2022 by Babak