Closed cell spray foam in cavity walls

[SimonC]

On paper the advertised benefits of closed cell spray foam insulation for a cavity fill appear compelling: good thermal efficiency; airtightness; vapour barrier; and strength.  When used in a cavity fill I liken it to SIPs but rather than being sandwiched between OSB the insulation sandwiched between brick and block.  One clear downside is price, though to my mind the price comparison is not as simple as contrasting the material price, since when correctly installed spray foam has the potential to fill the whole cavity and eliminates the burden of careful installation detail and time/labour cost of the brickie.  

 

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 (around 3" cavity) and the cavity in the new extension walls (around 4").  This approach would allow for the construction of new walls with an unfilled cavity (opting to use appropriate wall ties) and then subsequently all wall cavities could filled by a specialist contractor.  However, I have some concerns.

 

First concern: If closed cell spray foam insulation is as good as it says on paper, then why is this not widely used in the UK construction industry?  It seems commonplace to use spray foam insulation in USA and Canada, and if there were significant defects in the product I imagine it would have prevented continued use not to mention the litigious culture that exists over there.  The manufacturers I'm considering (Icynene, Isothane, BASF Walltite, Swis Synthesia) have various certifications (BBA, Kiwa, NSAI) for their respective products.  I have also read a few members on this forum who have indicated they used it in their projects and I would be very interested to hear of any direct experience - good or bad - with closed cell spray foam insulation being used as cavity fill retrofit or for new build. 

 

Second concern: Breathability of the building.  The popular criticisms levied at closed cell insulation seem to target increased risk of mould, condensation and rot - though I think these are primarily issues from bad roof installations rather than cavity fills.  In my project, if the building's wall cavities were filled with closed cell insulation (and potentially the roof as well to create a thermal envelope - the roof is to be replaced as part of a loft conversion in the scope of works giving some control over the design of the new roof construction), plus having a desire to adopt an airtightness strategy to reduce uncontrolled airflow, then there is a clear need for controlled mechanical ventilation.  This mandates an appropriately designed MVHR system - and to that end I've been chatting with Patrick at Heat, Space and Light who has provided a proposal for a Zehnder MVHR system.  My concern is will MVHR be sufficient to mitigate the potential adverse issues?  It is rarely clear from critical commentary whether there was an appropriate ventilation strategy in place which caused the mould, condensation, or rot linked to the spray foam insulation or indeed whether the installation was performed correctly.  The suppliers I have spoken with so far assure this is not an issue, though theirs is perhaps a bias view.

 

I would be grateful of your experience of using closed cell spray foam insulation in the cavity walls, or in the roof.  Any lessons learned or construction advice.

 

Thanks in advance.  

 

 

[Mr Punter]

I think some lenders and insurers don't like spray foam in the roof as there have been cases of poor installation and specification where the timbers have been affected.

[SimonC]

6 hours ago, Mr Punter said:

I think some lenders and insurers don't like spray foam in the roof as there have been cases of poor installation and specification where the timbers have been affected.

 

Thanks, I need to read up again on the lenders and insurance issue.  

 

I thought the standing objection to SPF in the roof was primarily due to bad roof installations rather than the product.  Specifically in those circumstances where SPF had been directly sprayed onto the roof membrane and/or tiles omitting a ventilation gap leading to the possibility for condensation potentially leading to rot in the roof timbers.  A solution would be to include a 50mm ventilated void directly below the roof membrane - Fusion Insulation have a vent spacer to fit between the wall plate and ridge beam which provides the necessary air gap (http://www.fusioninsulation.com/thermal-insulation.html).  

 

However, the alternative approach I’m considering for the roof build up would be to install OSB sarking boards over the roof rafters, then a vapour permeable membrane, then counter battens, tile battens and finally clay roof tiles.  The SPF would be installed under the sarking OSB and between the rafters that would be much like a SIP roof panel, then an airtightness membrane, then plasterboard.

 

Of course, if there is a blanket ban on SPF from lenders and insurers then the use of SPF is a non-starter.  I would be interested to hear how other forum members have overcome the matter.

 

 

 

 

[IanMcP]

On 19/10/2022 at 22:59, SimonC said:

 

Thanks, I need to read up again on the lenders and insurance issue.  

 

I thought the standing objection to SPF in the roof was primarily due to bad roof installations rather than the product.  Specifically in those circumstances where SPF had been directly sprayed onto the roof membrane and/or tiles omitting a ventilation gap leading to the possibility for condensation potentially leading to rot in the roof timbers.  A solution would be to include a 50mm ventilated void directly below the roof membrane - Fusion Insulation have a vent spacer to fit between the wall plate and ridge beam which provides the necessary air gap (http://www.fusioninsulation.com/thermal-insulation.html).  

 

However, the alternative approach I’m considering for the roof build up would be to install OSB sarking boards over the roof rafters, then a vapour permeable membrane, then counter battens, tile battens and finally clay roof tiles.  The SPF would be installed under the sarking OSB and between the rafters that would be much like a SIP roof panel, then an airtightness membrane, then plasterboard.

 

Of course, if there is a blanket ban on SPF from lenders and insurers then the use of SPF is a non-starter.  I would be interested to hear how other forum members have overcome the matter.

 

 

 

 

 

 

did you get anywhere on if SPF on the roof is a go for lenders ? Seems solid info is hard to come by.. 

[Iceverge]

A mate used open cell Isothane in his pitched roof. He was pleased with it AFAIK. Good for airtightness and ease of install. Safe for use with timber as it's breathable. Lots of trimming and wastage however, not terribly good for decrement delay and not cheap. 

@Gone West did his previous house entirely in it I think. 

 

Blown cellulose would be by my choice. But would require an airtight membrane installed beforehand. 

 

Re: closed cell in the cavity it was 4 times the price of EPS beads and with our wide cavity of 250mm I was concerned of structural damage due to shrinkage. 

 

 

[Radian]

13 minutes ago, Iceverge said:

Re: closed cell in the cavity it was 4 times the price of EPS beads

You'd really have to be able to justify that for a 0.026W/mK to 0.032W/mK advantage. And given the risk of structural damage due to shrinkage or expansion through incorrect application, I'd be very cautious indeed.

[Seren161]

Is it this polyurethane stuff.. Recent article claims that main issue is the fact that it makes it difficult for surveyors to properly assess structural integrity with subsequent mortgage issues. 

I just have screenshot but you can probably find the article as relatively recent 

[Roger440]

I looked at this in our current house for the cavity, though the prime driver was, because of the risk of flooding, the normal options were not viable.

 

Also, and i was specifically looking at BASF walltite, it is water proof. So would help resist the passage of water through the wall.

 

The OP didnt mention the construction of his 60's house. But if its brick/block, inner leaf and outer, to me it looks like a great idea. Cost aside of course.

 

Im again considering it at the new place, this time because of the risk of wind driven rain. Though the available tables rate EPS beads as a better option in these circumstances. Which makes no sense to me at all.

 

I certainly wouldnt use it in a roof at all. Or probably in a timber framed house.

 

[Radian]

20 minutes ago, Roger440 said:

 

Im again considering it at the new place, this time because of the risk of wind driven rain. Though the available tables rate EPS beads as a better option in these circumstances. Which makes no sense to me at all.

I think the issue is in the inability of the external masonry to dry out. Some residual air circulation remains in EPS fills.

[Gone West]

13 hours ago, Iceverge said:

@Gone West did his previous house entirely in it I think. 

I used Icynene for the walls and roof in an I-beam timber portal frame house. I've not used Isothane so don't know anything about it. Icynene is very good for airtightness and remains rubbery and flexible after it has set. The OP PMd me and I sent details.

[SimonC]

On 19/10/2022 at 15:27, Mr Punter said:

I think some lenders and insurers don't like spray foam in the roof as there have been cases of poor installation and specification where the timbers have been affected.

 

I have reached out to the main national players in SPF for their commentary and ended speaking direct with a very helpful chap at ECON Polyurethanes who are the BASF Walltite distributor.  He reported that the industry is taking urgent action to put in place an accredited scheme for spray foam installers that will meet the needs and assurances required by lenders and insurers.  An industry panel has already been setup and convened comprising representatives from lenders, insurers, manufacturers, distributors and installers.  The chap I spoke with is sitting on this panel so I feel this information is reliable and the good news is the panel are aiming to deliver the scheme in Q2 next year.  I got the impression that the scheme will deliver not just installation guidelines but also result in something like a certification pack containing relevant documentation/photos about the install that would create a form of provenance to stay with the property.  

 

From my perspective (yet to begin works) this is good news but I'm not clear how it will benefit existing installations.  It might be that in some circumstances this could be retrospectively done where the build has been well documented and the spray foam was installed by accredited companies, though that is just my supposition. 

 

 

 

[SimonC]

On 26/10/2022 at 19:12, Iceverge said:

A mate used open cell Isothane in his pitched roof. He was pleased with it AFAIK. Good for airtightness and ease of install. Safe for use with timber as it's breathable. Lots of trimming and wastage however, not terribly good for decrement delay and not cheap. 

@Gone West did his previous house entirely in it I think. 

 

Blown cellulose would be by my choice. But would require an airtight membrane installed beforehand. 

 

Re: closed cell in the cavity it was 4 times the price of EPS beads and with our wide cavity of 250mm I was concerned of structural damage due to shrinkage. 

 

 

 

I have not discounted EPS beads or cellulose at this stage; still asking questions and gathering data.

 

Getting indicative prices for SPF is the next step.  As I see it the price differential is not just reflected in the dollar amount as it includes some potentially quantifiable benefits, such as contributing to airtightness.  And in present economic circumstances the payback period for either is getting shorter - if next years 75% price hike materialises without any government intervention then I'm looking down the barrel of an annual combined gas and electricity bill of over £10k. 

 

Peter ( aka @Gone West ) was kind enough to send me some information on his build and reported that he was able to achieve an airtightness of 0.47 ACH by using open cell SPF without membranes or tapes.  I'm not expecting I will be able to achieve that in my 1960s renovation and extension but hope that by using a considered approach to the materials it could help to make a significant difference.  

 

 

 

[SimonC]

On 26/10/2022 at 19:30, Radian said:

You'd really have to be able to justify that for a 0.026W/mK to 0.032W/mK advantage. And given the risk of structural damage due to shrinkage or expansion through incorrect application, I'd be very cautious indeed.

 

I'd like to understand how to avoid structural damage - do you have experience of shrinkage or expansion in SPF and what went wrong?  Are these issues solely related to closed cell and as result of poor installation, or are they a generic property of the product so will closed cell shrink over time regardless of how well it was installed?  I thought I might be able to mitigate the risk of poor installation by only using an insurance backed and accredited installer from one of the main players i.e. Icynene or BASF Walltite?

 

Do products like SIPs, which are essentially closed cell PU sandwiched between OSB, also suffer from these adverse effects?

[SimonC]

On 26/10/2022 at 21:46, Roger440 said:

I looked at this in our current house for the cavity, though the prime driver was, because of the risk of flooding, the normal options were not viable.

 

Also, and i was specifically looking at BASF walltite, it is water proof. So would help resist the passage of water through the wall.

 

The OP didnt mention the construction of his 60's house. But if its brick/block, inner leaf and outer, to me it looks like a great idea. Cost aside of course.

 

Im again considering it at the new place, this time because of the risk of wind driven rain. Though the available tables rate EPS beads as a better option in these circumstances. Which makes no sense to me at all.

 

I certainly wouldnt use it in a roof at all. Or probably in a timber framed house.

 

 

On paper I'm in a lower banded flood zone near the River Thames albeit 1/4 mile away from the river and the immediate area has never flooded.  Closed cell could give a bonus in that regard but frankly I'd prefer not to test it. 

 

The walls are brick/block cavity.

 

For the roof the main adverse issues seem to stem from SPF applied direct to roof tiles or non-breathable roofing membrane.  I'm planning for a roof build up with OSB sarking boards over the roof rafters, then a vapour permeable membrane, then counter battens, tile battens and finally clay roof tiles.  The SPF would be installed under the sarking OSB and between the rafters that would be much like a SIP roof panel, then an airtightness membrane, then plasterboard.  When I ran this construction detail by the chap from ECON Polyurethane he saw no issues and suggested that sarking board might be unnecessary provided the membrane detail was adequate (usual caveats it was not binding advice) though I like the idea that sarking board will add strength and create an enclosed 'panel' in the warm roof.

 

 

 

[Iceverge]

4 hours ago, SimonC said:

m planning for a roof build up with OSB sarking boards over the roof rafters, then a vapour permeable membrane, then counter battens, tile battens and finally clay roof tiles.  The SPF would be installed under the sarking OSB and between the rafters that would be much like a SIP roof panel, then an airtightness membrane, then plasterboard

 

I was attracted to spray foam too when i began looking at this way back when.

 

However, after lots of reading blown cellulose beats it in almost every regard. 

 

It will fill every gap. It is great for airtightness, it is cheaper, better decrement delay. Better fire resistance. No off gassing. No mess, no waste. The list is longer if you want me to continue. 

 

 

 

 

[jayc89]

On 27/10/2022 at 08:24, Gone West said:

I used Icynene for the walls and roof in an I-beam timber portal frame house. I've not used Isothane so don't know anything about it. Icynene is very good for airtightness and remains rubbery and flexible after it has set. The OP PMd me and I sent details.

 

Isn't Icynene open-cell whereas Isothane is closed-cell? I assume the former would also provide a higher U-value, like for like. 

[Gone West]

24 minutes ago, Iceverge said:

 

I was attracted to spray foam too when i began looking at this way back when.

 

However, after lots of reading blown cellulose beats it in almost every regard. 

 

It will fill every gap. It is great for airtightness, it is cheaper, better decrement delay. Better fire resistance. No off gassing. No mess, no waste. The list is longer if you want me to continue. 

 

 

 

 

The reason I didn't use blown celulose was because I was worried about sagging and thermal bypass. Strangely enough I was talking to a friend a couple of days ago who used Warmcel in her build twelve years ago. She had recently uncovered some internal walls and found large cavities in the Warmcel which she said surprised her because it had been put in under such high pressure. She is going to hire a thermal camera to check the external walls. She had also used Icynene in the external walls of a detached studio in the grounds. One advantage of Icynene is that you can see the coverage before it's covered up.

As for blown cellulose:-

It certainly doesn't fill every gap in all cases.

I doubt it's better for airtightness.

I don't know about the cost comparison.

Blown cellulose is better for decrement delay, but the importance of decrement delay is dependent on the situation of the property.

As the insulation is encapsulated, fire resistance is a bit of a red herring.

Off gassing of Icynene is complete in 48 hours.

There can be a lot of work involved in trimming Icynene with the associated waste.

We also looked at blown mineral fibre which would have been my second choice.

 

[SteamyTea]

5 hours ago, SimonC said:

like to understand how to avoid structural damage - do you have experience of shrinkage or expansion in SPF and what went wrong?

We used to work on 3% shrinkage when moulding polyurethanes. Some mixes where better than others.

If you have ever wondered why new furniture has cushions that seem tightly fitted, and old furniture seems loose on the bench part, this is down to long term shrinkage. 

In the late 1980s,  melamine powders where introduced into the mix to help with fire retardancy. This caused mixing problems (wear on mixing head and the pumps), this could make the curing inconsistent.

An inconsistent mix causes uneven curing, adhesion failure and excess heat spots, all things that need to be avoided with sprayed products.

 

When foam is moulded, or sprayed, there is an initial rapid expansion. As curing takes place, there is then a rapid contraction as the blowing agent (a gas) is released and thermal contraction takes place. Then a slow contraction takes place over time, usually months.

One material we used carried on contracting at about 0.5% a year, for a decade at least.

 

Long term contact with moisture, or even just high humidity causes polymers to break down. Excess temperature can cause initial softening, then brittleness.

 

As much as I like polyurethane polymers, and there are literally hundreds on the market, I would be reluctant to use them as insulation. Great initially, long term they absorb about 10% of their mass in water, then, with thermal cycling, disintegrate.

 

I have a feeling that a polyurethane is not allowed in aeroplanes as a structural element (skinned wings), though may be wrong on that.

[jayc89]

49 minutes ago, SteamyTea said:

We used to work on 3% shrinkage when moulding polyurethanes. Some mixes where better than others.

If you have ever wondered why new furniture has cushions that seem tightly fitted, and old furniture seems loose on the bench part, this is down to long term shrinkage. 

In the late 1980s,  melamine powders where introduced into the mix to help with fire retardancy. This caused mixing problems (wear on mixing head and the pumps), this could make the curing inconsistent.

An inconsistent mix causes uneven curing, adhesion failure and excess heat spots, all things that need to be avoided with sprayed products.

 

When foam is moulded, or sprayed, there is an initial rapid expansion. As curing takes place, there is then a rapid contraction as the blowing agent (a gas) is released and thermal contraction takes place. Then a slow contraction takes place over time, usually months.

One material we used carried on contracting at about 0.5% a year, for a decade at least.

 

Long term contact with moisture, or even just high humidity causes polymers to break down. Excess temperature can cause initial softening, then brittleness.

 

As much as I like polyurethane polymers, and there are literally hundreds on the market, I would be reluctant to use them as insulation. Great initially, long term they absorb about 10% of their mass in water, then, with thermal cycling, disintegrate.

 

I have a feeling that a polyurethane is not allowed in aeroplanes as a structural element (skinned wings), though may be wrong on that.

 

Wouldn't that ultimately render all floor slabs that are insulated using PIR useless over time? Surely there would be reports of slabs installed 10, 15 years ago now having problems?

[SteamyTea]

7 minutes ago, jayc89 said:

 

Wouldn't that ultimately render all floor slabs that are insulated using PIR useless over time? Surely there would be reports of slabs installed 10, 15 years ago now having problems?

There possibly are problems there.

Usually they use 'aged' foams, which have already shrunk quite a bit. 

It may also be hard to tell if a slab has shrunken or dipped a few millimetres over a decade or two. Buildings do that anyway.

A good SE should have designed for shrinkages I would have thought ( @Gus Potter, @saveasteading).

What most likely happens is that the shrinkage is uneven, so some parts will pull away from the slab, other parts will be compressed a bit more.

hard to tell without sawing a slab open, but would be fun to find out.

[Iceverge]

1 hour ago, Gone West said:

She had recently uncovered some internal walls and found large cavities in the Warmcel which she said surprised her because it had been put in under such high pressure

 

That's interesting, it is susceptible to poor installers. I think getting the required 60kg/M3 density ( from memory) is not a task for an amateur.  

 

Blowing it behind a semi transparent membrane as dense as possible and then allowing it to settle for a couple of weeks before topping up if needed before boarding seems to be a good technique. 

 

Cost at last check was €27/m2 +vat for a 200mm TF wall at 600mm cc. 

 

We have 450mm in our attic that was blown in at low density. It has settled somewhat. Maybe 50mm, I will check, but that was expected and allowed for. 

 

All of the best airtightness results I know of < 0.15ACH use cellulose with the exception of that archive building that used spray airtightness paint. I think when it's really properly packed it seals any tiny holes in the airtight layers. 

 

Longevity of actual insulation is an understudied area I think though. I'm going to have a good look at our blown bead walls when I pick up my thermal camera. 

 

 

 

 

 

 

 

 

 

[Gone West]

1 hour ago, Iceverge said:

 

That's interesting, it is susceptible to poor installers. I think getting the required 60kg/M3 density ( from memory) is not a task for an amateur.  

 

Blowing it behind a semi transparent membrane as dense as possible and then allowing it to settle for a couple of weeks before topping up if needed before boarding seems to be a good technique. 

 

Cost at last check was €27/m2 +vat for a 200mm TF wall at 600mm cc. 

 

We have 450mm in our attic that was blown in at low density. It has settled somewhat. Maybe 50mm, I will check, but that was expected and allowed for. 

 

All of the best airtightness results I know of < 0.15ACH use cellulose with the exception of that archive building that used spray airtightness paint. I think when it's really properly packed it seals any tiny holes in the airtight layers. 

 

Longevity of actual insulation is an understudied area I think though. I'm going to have a good look at our blown bead walls when I pick up my thermal camera. 

 

 

 

 

 

 

 

 

 

The blown mineral fibre system I looked at thirteen years ago used a semi transparent membrane which I thought was a good idea.

As always there are many ways to skin a cat, and several work well, but none are perfect.

[saveasteading]

5 hours ago, SteamyTea said:

A good SE should have designed for shrinkages

A good SE is unlikely to hear of any such allegation, and usually isn't responsible for insulation levels.

My business was mostly very big sheds. A slab over 25 x 25 or so  doesn't need insulation. The walls and roof do. We had a relationship with a specialist manufacturer who promoted fibreglass throughout. They bought in pir sandwich panels if the client required, BUT insisted on complete movement joints in the roof every 40m. Why, I asked the development Engineer.  The gist was that some huge building by someone else had (allegedly) big issues due to shrinkage of the pir within the roof panels. Crazing and crumpling of the roof  and leaks apparently ensued. As there was a big legal case and a private settlement, nothing was published, but our people learnt what they could, and decided that they would assume shrinkage and design a sliding joint for roofs.

 

We used sandwich panels a few times, without problems, but never dissected an older building to look for problems.

 

Yes I think it shrinks.  We did use pir under the slab for smaller buildings  The pir has a plastic sheet over it so it isn't tied to the concrete slab, so there will be gaps rather than crazing.

But perhaps the pir behaves differently next to the colder ground.

Nobody has any incentive to check.

If there are known issues they are not publicised.

 

With this in mind, for our current steading project we used 2 thinner layers of pir, with staggered joints. The heat losses  if any, will be minimal.

[jayc89]

9 hours ago, saveasteading said:

A good SE is unlikely to hear of any such allegation, and usually isn't responsible for insulation levels.

My business was mostly very big sheds. A slab over 25 x 25 or so  doesn't need insulation. The walls and roof do. We had a relationship with a specialist manufacturer who promoted fibreglass throughout. They bought in pir sandwich panels if the client required, BUT insisted on complete movement joints in the roof every 40m. Why, I asked the development Engineer.  The gist was that some huge building by someone else had (allegedly) big issues due to shrinkage of the pir within the roof panels. Crazing and crumpling of the roof  and leaks apparently ensued. As there was a big legal case and a private settlement, nothing was published, but our people learnt what they could, and decided that they would assume shrinkage and design a sliding joint for roofs.

 

We used sandwich panels a few times, without problems, but never dissected an older building to look for problems.

 

Yes I think it shrinks.  We did use pir under the slab for smaller buildings  The pir has a plastic sheet over it so it isn't tied to the concrete slab, so there will be gaps rather than crazing.

But perhaps the pir behaves differently next to the colder ground.

Nobody has any incentive to check.

If there are known issues they are not publicised.

 

With this in mind, for our current steading project we used 2 thinner layers of pir, with staggered joints. The heat losses  if any, will be minimal.

 

That was my original intention, prior to considering spray foam. It seems there is no silver bullet out there, unfortunately. 

[saveasteading]

1 hour ago, jayc89 said:

 no silver bullet out there

Knowledge, quality control and pragmatism. An alloy.