External Insulation and Stone

Troy2013

We hope to soon be in a position to externally insulate our house and build an extension. Fingers crossed!! The extension was originally going to be cavity wall (250mm cavity filled with bonded bead) but our Engineer feels it is better to externally insulate the extension and old building together rather than try tie in two different insulation methods.

The u-values seem to make sense as does the ease of building but we have one concern- we had planned to have one stone faced wall to break up the elevation of the house. My understanding is that we can't use natural stone if we go with external insulation and this leaves me worried that stone cladding won't provide suitable water tightness or look great. Our Engineer is a person who errs very much on the practical rather than the aesthetic side of things and so I would love to hear the opinions of anyone who has used stone cladding on external insulation?

Thanks for any advice/opinions.

Calahonda52

IMHO, with the emphasis on the H, as one of those erring engineers, these stone clad walls look naff:D

Do the EWI properly, making sure it goes up inside soffit and ties in with properly done roof insulation

chillit

Hi Troy

I have seen plenty of stone cladding attached over external insulation. This is quite common in mountainous areas of Europe where the standard external render would not survive several months of snow cover lying against the render.

First they attach the external insulation with adhesive to the wall in the usual way. Then they attach a metal mesh (50mm x 50mm square mesh). This mesh is held onto the wall using the mechanical fixings that are also used in Ireland. The mesh forms a structure for the stone to be attached to.

I can't comment if this approach is suitable for Ireland where we probably get a lot more horizontal driven rain that these European areas would. But it works for them and I have never heard any reports of damp problems.

Please note that the stone they use is fully grouted. It would not be a dry stone type finish like you see in Ireland. Sometimes they use a manufactured stone cladding (these look much better these days) and this is attached and grouted almost like tiles would be.

Troy2013

Calahonda52 wrote: »

IMHO, with the emphasis on the H, as one of those erring engineers, these stone clad walls look naff:D

Do the EWI properly, making sure it goes up inside soffit and ties in with properly done roof insulation

Thanks Calahonda52, glad to hear I'm not alone in thinking stone cladding might look terrible. I would hate to do all the work and then have the house stand out for all the wrong reasons.

We are trying to ensure the EWI will be done correctly and so we are extending the roof and digging up the footpaths to allow the EWI be fitted down to foundation level. It will never be like a new build but one can try!

Troy2013

chillit wrote: »

Hi Troy

I have seen plenty of stone cladding attached over external insulation. This is quite common in mountainous areas of Europe where the standard external render would not survive several months of snow cover lying against the render.

First they attach the external insulation with adhesive to the wall in the usual way. Then they attach a metal mesh (50mm x 50mm square mesh). This mesh is held onto the wall using the mechanical fixings that are also used in Ireland. The mesh forms a structure for the stone to be attached to.

I can't comment if this approach is suitable for Ireland where we probably get a lot more horizontal driven rain that these European areas would. But it works for them and I have never heard any reports of damp problems.

Please note that the stone they use is fully grouted. It would not be a dry stone type finish like you see in Ireland. Sometimes they use a manufactured stone cladding (these look much better these days) and this is attached and grouted almost like tiles would be.

Hi Chillit, thanks for taking the time to reply.

In relation to the mesh fixings you mention, if they are fixed with metal wall ties to the original block wall would this not create a huge thermal bridge through the external insulation? Also, can this method be used with natural stone (grouted/pointed like you said) or does it also have to be cladding? I will definitely run this idea past our Engineer if it is possible with natural stone.

I was thinking that we might render the EWI like normal or put felt as a water barrier and then stone face the wall to try ensure driving rain doesn't cause a problem. Although, the manufacturers of the EWI seem to believe the water won't penetrate through the whole insulation even if some water ingress happens.

sydthebeat

chillit wrote: »

Hi Troy

I have seen plenty of stone cladding attached over external insulation. This is quite common in mountainous areas of Europe where the standard external render would not survive several months of snow cover lying against the render.

First they attach the external insulation with adhesive to the wall in the usual way. Then they attach a metal mesh (50mm x 50mm square mesh). This mesh is held onto the wall using the mechanical fixings that are also used in Ireland. The mesh forms a structure for the stone to be attached to.

I can't comment if this approach is suitable for Ireland where we probably get a lot more horizontal driven rain that these European areas would. But it works for them and I have never heard any reports of damp problems.

Please note that the stone they use is fully grouted. It would not be a dry stone type finish like you see in Ireland. Sometimes they use a manufactured stone cladding (these look much better these days) and this is attached and grouted almost like tiles would be.

just note that this method would most probably pertain to a structural stone such as fernhill which is certified to be used as a standalone masonry leaf.

random rubble stone such as manor stone etc wouldnt be certified for use in that manner and would require a structural substrata

also, if youre putting a stone external finish.. why not just build a cavity wall?

Metric Tensor

I agree with syd ... why not build a pseudo or indeed full cavity wall with the stonework as the external leaf. It will require wall ties but all cavity walls have wall ties and thermal bridging through correctly selected ties is small.

Troy2013

Metric Tensor wrote: »

I agree with syd ... why not build a pseudo or indeed full cavity wall with the stonework as the external leaf. It will require wall ties but all cavity walls have wall ties and thermal bridging through correctly selected ties is small.

sydthebeat wrote: »

just note that this method would most probably pertain to a structural stone such as fernhill which is certified to be used as a standalone masonry leaf.

random rubble stone such as manor stone etc wouldnt be certified for use in that manner and would require a structural substrata

also, if youre putting a stone external finish.. why not just build a cavity wall?

Thanks for posting.

Metric Tensor, in relation to a pseudo wall- do you mean that we build the block on flat wall externally insulated and then in front of the insulation we build another wall (perhaps block on edge) to tie the stone work to?

In my opening post I did mention that we were originally going to build a cavity wall but our Engineer has come back to us saying he would prefer to use external insulation on both new extension and old house rather than switch between cavity wall and external insulation.

Sydthebeat- A cavity would be the easiest method of achieving the stone faced wall we are looking for but I was just seeing if any others had used stone with external insulation before we confirmed which type of wall/insulation we were going with. I had a quick look at the fernhill stone website that you posted, thanks. Just one more question, is stuctural stone a type of stone that you can use on its own and therefore doesn't need to be tied to any other structure for stability?

chillit

Troy2013 wrote: »

Hi Chillit, thanks for taking the time to reply.

In relation to the mesh fixings you mention, if they are fixed with metal wall ties to the original block wall would this not create a huge thermal bridge through the external insulation? Also, can this method be used with natural stone (grouted/pointed like you said) or does it also have to be cladding? I will definitely run this idea past our Engineer if it is possible with natural stone.

I was thinking that we might render the EWI like normal or put felt as a water barrier and then stone face the wall to try ensure driving rain doesn't cause a problem. Although, the manufacturers of the EWI seem to believe the water won't penetrate through the whole insulation even if some water ingress happens.

the wall fixings are the plastic type provided by EWI companies like weber, baumit etc. I don't believe that the thermal bridge if significant. By the way these fixings should be used with basic external wall insulation anyway. In Europe I have never seen them install external wall insulation with just adhesive. Also regarding the stone I have seen installed it is generally only on the ground level walls so you would need to consider the weight of the stone if installing at a higher level. One for your engineer I would say.

I can't comment on the water barrier. What I have seen installed didnt include a 'specific water barrier but local conditions might not have as much driving rain as Ireland.

Metric Tensor

Troy2013 wrote: »

Metric Tensor, in relation to a pseudo wall- do you mean that we build the block on flat wall externally insulated and then in front of the insulation we build another wall (perhaps block on edge) to tie the stone work to?

If, as syd says, you use a "structural stone" this can be a leaf on its own outside the insulation. You wouldn't need a block at all.

Regardless of what way you build it it will be necessary to tie it through the insulation to the other leaf of the same wall.

This is where the wall ties come in. Once you're at that point then of course you start to think why not just build a standard cavity wall and then you are back to the reasons your engineer originally recommended discounting it .. i.e. continuity of insulation.

So no solution is perfect but they all have advantages and disadvantages.

Troy2013

chillit wrote: »

the wall fixings are the plastic type provided by EWI companies like weber, baumit etc. I don't believe that the thermal bridge if significant. By the way these fixings should be used with basic external wall insulation anyway. In Europe I have never seen them install external wall insulation with just adhesive. Also regarding the stone I have seen installed it is generally only on the ground level walls so you would need to consider the weight of the stone if installing at a higher level. One for your engineer I would say.

I can't comment on the water barrier. What I have seen installed didnt include a 'specific water barrier but local conditions might not have as much driving rain as Ireland.

I know the fixings you are talking about- they seem to be referred to as a mushroom fixing and that is definitely what is being suggested to tie the External Insulation to the walls. The stone will be only be ground floor level as our extension is single story. I think from all the advice that we will probably revert to a cavity wall for the new extension so we can have the natural stone. Thanks for your help!

Troy2013

Metric Tensor wrote: »

If, as syd says, you use a "structural stone" this can be a leaf on its own outside the insulation. You wouldn't need a block at all.

Regardless of what way you build it it will be necessary to tie it through the insulation to the other leaf of the same wall.

This is where the wall ties come in. Once you're at that point then of course you start to think why not just build a standard cavity wall and then you are back to the reasons your engineer originally recommended discounting it .. i.e. continuity of insulation.

So no solution is perfect but they all have advantages and disadvantages.

It definitely seems like there is no easy solution to it unless we just render the house- which we all think will be a bit bland. At this stage I think I am back to a cavity wall for the extension and the various detailing to try tie in the external insulation. Thanks for all your help.