Closed cell spray foam in cavity walls

[Gus Potter]

On 02/11/2022 at 18:24, SteamyTea said:

There possibly are problems there.

Steamy, it all sounds like a can of worms.

 

On 02/11/2022 at 18:24, SteamyTea said:

but would be fun to find out.

 

Yes.. If you are talking about say a ground bearing floor slab that has PIR under then the possibility that the PIR could shrink.. due to a change in the chemical structure, could cause a potential issue say in 20 to 30 years time.

 

If you extrapolate this further then could the chemical structure change such that say the material completely fails and turns to dust. You could apply this to a lot of products we use.. EPS for example.. we just have to partly rely on past experience of the perfomance of the material or similar materials, the expertise of the "Chemists" when developing new formulas and the knowledge and experience of the people developing the test and validation procedures.

 

In terms of how SE's may approach this. I'll work in kg a bit as this may help BH members get a feel for the "weight" of things.

 

Take an insulated ground bearing slab or say an ICF structural raft foundation that both sit on a layer of insulation. Say the insulation is 150mm thick PIR with a compressive strength of 150 kPa ( 150 kN/m^2 ~= 15 tonnes per m^2) at 10% compression. Now say we load up the insulation at 15 tonnes per m^2. 10% of 150mm is 15mm. To carry the full load the insulation is going to compress down by 15mm.

 

Iif we had say a concrete slab that was isolated from everything else and we could guarentee that the load was always going to be perfectly uniform then in theory we could maybe get it to work and just let it slab  / house move up and down by 15mm. But in real life we have concentrated loading, loads that occur at the edges. These types of uneven loads could introduce a potential 15mm differential movement.. thus we could need a serious concrete slab with a lot of rebar and invite other problems.

 

Then you have to add to that the fact that the ground under the insulation may also settle, swell and shrink as moisture levels change say. The building above will also be moving about thus in some cases you could suddenly end up with 40 - 50mm of movement if all the cards fall the wrong way.

 

In the round as a rule of thumb a medium sized house can cope with say 20 -25mm of movement over all, say corner to corner before bad things start to happen... a few cracks accepted. Yes we can design for more movement if need be.. but that all adds to the cost.

 

Now on slabs and ICF raft founds in particular we say.. we may need a raft as the allowable ground bearing capacity of the soil is say 60 kN/m^2 =~ 6 tonnes per m^2. Now you may have a soil report that mentions a presumed allowable soil bearing capacity. This value is a prediction of what load you can put on the soil without it settling / compressing by more than 25mm.. and / or not completely failing.

 

Now you can see that we have 15mm compression of the insulation and potentially up to 25mm in the soil = 40mm + plus any say other superstructure shrinkages / movements.

 

To come up with some sort of initial answer we say.. Let's look at the insulation. What compressive strength will it have at 2% compression say. 10% gives 15mm thus 2% would be 3mm. We assume the insulation behaves like an elastic band so the response is linear. At 2% compression we can load the insulation by 150 kPa x 2% / 10 % = 30 kPa. Then we could say the soil has an allowable bearing capacity of 60 kN/m^2  based on 25mm of settlement so half that (as that is what the insulation can carry) gives 12.5mm of settlement.

 

It's a massive simplification but for ease of argument just add the insulation and soil movement together = 3.0mm plus 12.5  = about 15mm. That we could live with as a starting point.

 

BUT.. all of the above is based on a building being fully loaded for often a long time.. Clay soils can often take a high short term load as they can't settle until the water is squeezed out.

 

So in summary we kind of design for full loading which does not happen very often so that is maybe why we  get away with the insulation shrinking a bit and not see it cropping up a big construction/ design problem?

 

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21 hours ago, saveasteading said:

big issues due to shrinkage of the pir within the roof panels

Yes can't quite remember the max lengths but there are a number of guidance notes published by the SCI / BRE that mention designing in movement joints in the roof.

 

I'll dig out the info when I get a chance.

 

I think if you follow this guidance the shrinkage of the PIR roof panels can end up being a mute point.

 

If you have an long shed / office say with glazing panels you need to make sure you put in enough movement joints so you dont' jamb the doors and break the glass. It should be obvious that if you don't put enough joints in the roof then something is going to give.

 

 

 

On 19/10/2022 at 13:31, SimonC said:

In my renovation and extension project of a 1960s detached house I'm considering closed cell spray foam insulation to fill the existing unfilled cavity walls

 

A dilemma I face is that my timber floor joists are built into the external walls in my 1960's brick cavity walls. The joist ends are not wrapped, they may have a splash of bitumen but I doubt it.

 

The cavity is drafty but that is why maybe the timbers have lasted so long.

 

Also I have a timber wall plate that is built into the inner leaf of masonry which is the main load bearing element. Any rot here is going to cause the building / walls / roof to settle badly.. very badly.

 

I too have been mulling over filling the cavity but I just can't convince myself that it's a safe thing to do.

 

I would have a look at how all your structural elements interact with the walls before progressing.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Radian]

9 minutes ago, Gus Potter said:

Also I have a timber wall plate that is built into the inner leaf of masonry which is the main load bearing element. Any rot here is going to cause the building / walls / roof to settle badly.. very badly.

 

Just how common a practice was this - and why the (expletive deleted) did they do it? Was it some kind of shortcut to hold the joists in place while they infilled with bricks? It just boggles my mind.

[SteamyTea]

7 minutes ago, Gus Potter said:

In terms of how SE's may approach this

So halve the loads and hope for the best.  What we usually did.

I am not sure how elastic PU foams are, when I say elastic, I actually mean work evenly within the theoretical elastic limits.  I think by the time you get to the nasty end of Young's Modulus, the point of no return has been reach and the material will fail rapidly.  You only got to bend, or shock a sheet to see how easily it can snap.

I don't know much about expanded and extruded polystyrenes, had to make some tooling for some once, but never even say the production process.  They feel more compressible than expanded PU, but fingertips can easily be tricked by a softer feeling material. 

[Radian]

13 minutes ago, SteamyTea said:

I don't know much about expanded and extruded polystyrenes

Our house has a measly 50mm thick sheet of XPS laid on block and beam, topped with flooring chipboard. It's been down for the best part of 25 years now. Every morning when I come downstairs I can hear/feel the chipboard settling. It's only first thing, once walked on it's fine. It's almost as if the chipboard lifts up slightly overnight. Can't figure it out, or think if its always been like this or not.

[SteamyTea]

7 hours ago, Radian said:

It's only first thing

Thermal or moisture expansion and contraction maybe?

[Radian]

2 hours ago, SteamyTea said:

Thermal or moisture expansion and contraction maybe?

I wouldn't expect such a big change in dimension based on those variables but it does indeed seem as if a space has opened up between the chipboard and XPS sheet overnight.

[saveasteading]

11 hours ago, Gus Potter said:

If you have a long shed

Built one 200m long once*. There was a complete movement joint half way, on the basis that the expansion of the roof would cause too much stress or deflection of the structure. Each half had its own stability.

The roof was doubke skin with fibregalss, so no concerns re pir.

 

* going back for a tape or pencil left at the other end was good exercise.

 

[Gus Potter]

On 03/11/2022 at 22:08, SteamyTea said:

So halve the loads and hope for the best.  What we usually did.

I am not sure how elastic PU foams are, when I say elastic, I actually mean work evenly within the theoretical elastic limits.  I think by the time you get to the nasty end of Young's Modulus, the point of no return has been reach and the material will fail rapidly. 

Good point. PU foams may behave more like say stainless steel or cold formed steel.

 

For all. A typical steel beam you get for your house is quite stretchy (elastic) and you can load it up a fair bit until it starts to "yield" . If you take the load back off it before it gets to the yield point it will return to it's original shape if say the masonry above allows it to.

 

But stainless steels and cold formed steels are different. The elasticity changes depending on the load.. how "stretched / compressed they are. Have been lazy and copied a graph off internet below that shows you how carbon steels behave linearly up until a defined yield point but stainless does not. Cold formed steels are similar but the shape is a little different. Youngs modulus E is the stress / the strain.

 

 

Now it may be and I suspect as @SteamyTea is alluding to? is that PU foams and say EPS may have a similar behaviour to stainless steel in that they may not be quite as elastic as we think when heavily loaded on a long term basis.

 

Now you may have wondered in my previous post about why I chose a value of 2% compression to get a bearing capacity... a spin off is that we are not pushing the insulation that hard in terms of it's elastic performance. In some way we are mitigating / minimising risk where we are not quite sure just how well a material may behave when pushed to the maximum declared manufacture's loadings. 

On 04/11/2022 at 09:40, saveasteading said:

Built one 200m long once

That's a long building. On something like that you could have a lot of changes in the ground, need free movement joints, big floor slabs that will shirink a lot end to end and thus the roof should be designed to move / have joint's that suit the building under.

 

I thing the roof sheets tend to move less than the building underneath so they don't dominate the movement  / settlement design.

On 03/11/2022 at 22:05, Radian said:

Just how common a practice was this

Quite common up my neck of the woods. After the second war there was a drive to upgrade the housing stock and re purpose the factories that had been concentrating on the war effort. This manifested in what we call "non traditional housing"

 

To us now it seems "daft" but back then there was a great need to provide houses that were forecast to have a lifetime of 20 - 50 years. Remember that a lot of folk were living in slums, outside toilets and so on. My house would have seemed like paradise at the time.

 

My ex council house is now some 55 - 60 years old... but know if I insulate the wrong way it and rot the built in wall plate there will be trouble.

 

 

 

[SteamyTea]

Just by chance this bit if foam had washed up. Probably bouncy from a small boat.

Can see that the surface has degraded and the initial mounding was sub standard.

 

 

 

[jayc89]

I understand that PIR relies on gases within it to provide its thermal properties and over time this gas leaches out, resulting in a similar K value to EPS. Would this be the same for spray foam?

[DundeeDancer]

We don't seem to have any good installers in Scotland yet. I had one guy visiting my development today and then he ran away as soon as I said there was 20mm polystyrene boards in the cavity already, so it's just the rest of the cavity to fill, another 80mm of the 100mm cavity.  The installer was saying that's not possible but I had already been told by the isothane manufacture that it is possible.  The installer also was unwilling to give me a ballpark price, I wonder how much it is on avarage per-meter-cubed for this closed cell foam.

 

Would be great to get the foam installed, the brick work is quite porous and the wind just seems to get into the cavity and takes the heat away from the walls.

[Roger440]

3 minutes ago, DundeeDancer said:

We don't seem to have any good installers in Scotland yet. I had one guy visiting my development today and then he ran away as soon as I said there was 20mm polystyrene boards in the cavity already, so it's just the rest of the cavity to fill, another 80mm of the 100mm cavity.  The installer was saying that's not possible but I had already been told by the isothane manufacture that it is possible.  The installer also was unwilling to give me a ballpark price, I wonder how much it is on avarage per-meter-cubed for this closed cell foam.

 

Would be great to get the foam installed, the brick work is quite porous and the wind just seems to get into the cavity and takes the heat away from the walls.

 

Was anyy explanation offered as to why the cavity alreadt having insulation in it was an issue? Doesnt make sense?

[DundeeDancer]

6 minutes ago, Roger440 said:

 

Was anyy explanation offered as to why the cavity alreadt having insulation in it was an issue? Doesnt make sense?

 

He said he would not be able to guarantee that there won’t be voids in the insulation if the polystyrene boards had possible moved. I suggested the foam expanding force should move any loose boards firmly against the inner cavity wall and so it shouldn’t be an issue but he said he wasn’t interested in such a job.  I said well maybe in a few years time there will be better techniques  for this type of scenario but he just disagreed and said it was impossible, with that mind-frame I thought it best not to discuss it any further and thanked him for his time.

[Roger440]

2 minutes ago, DundeeDancer said:

 

He said he would not be able to guarantee that there won’t be voids in the insulation if the polystyrene boards had possible moved. I suggested the foam expanding force should move any loose boards firmly against the inner cavity wall and so it shouldn’t be an issue but he said he wasn’t interested in such a job.  I said well maybe in a few years time there will be better techniques  for this type of scenario but he just disagreed and said it was impossible, with that mind-frame I thought it best not to discuss it any further and thanked him for his time.

 

Thanks. Given it goes in as a liquid, it still makes no sense!!

[DundeeDancer]

1 minute ago, Roger440 said:

 

Thanks. Given it goes in as a liquid, it still makes no sense!!

 

I know, but he was like 7 foot tall and a foot wider than me and he didn't look like he wanted to talk sense so I made a tatical retreat 😊 

[embra]

@DundeeDancer did you manage to find any other suppliers willing to work with you?

 

@SimonC did you get anywhere with your search for information?

 

I am in a similar situation (~25mm foam boards in ~100mm cavity of my 1990s built house) and looking for options to improve wall insulation, and airtightness as a bonus.

Edited July 11, 2023 by embra

[SteamyTea]

On 24/11/2022 at 21:23, DundeeDancer said:

I had one guy visiting my development today and then he ran away as soon as I said there was 20mm polystyrene boards in the cavity already, so it's just the rest of the cavity to fill, another 80mm of the 100mm cavity.  The installer was saying that's not possible but I had already been told by the isothane manufacture that it is possible.

I am with the installer here.

Having made tooling for blowing expanding and structural PU, inserts, which the existing sheets are, will cause problems.

Isothane are probably talking about reactivity between different materials, and not the practicalities of installing.

Generally, when expanding flexible PU is moulded, it is poured into an open mould, then the mould is closed and clamped.  Vent holes are usually added after a few trial shots to remove air/gasses where voids appear.

Voids are not always caused by the liquid resin unable to reach an area i.e. flow around a solid insert.  They are often caused by the ongoing shrinkage after initial curing.