Advice Needed - Cold Bridge Behind Full Fill PIR Insulation

[Johnny Jekyll]

ADVICE NEEDED PLEASE..!

The walls on our detached 3 bed new build are made up of (from in to out): 100mm medium dense blocks, 100mm cavity with full fill PIR insulation (cavities are more like 115/120mm wide), 100mm medium dense blocks (no thermalite has been used). We are at block course 14 of 23, so already towards the top of the house. The problem is the insulation has not been fitted tight to the inner leaf. We have a 10mm gap behind the insulation to the inner leaf in numerous areas. This will likely cause a cold bridge. I of course wish we could start again, and use wider cavities with EPS beads but we are where we are. Any ideas to stop the potential cold bridges?

 

 

The options I see are:
1 ) Try and spray foam filler or EPS beads down the back of the insulation already installed, although I don't think this will get very far down.  
2 ) Fit the full fill insulation tight to the inner leave from this point up (of course).
3 ) Insulate internally using some sort of insulated plasterboard / PIR / wool / thermal liner / foil insulation (we don't have much room internally though).
4 ) Insulate externally using some sort of external wall insulation (although this may require planning permission - and lots more money I don't have).

 

Any help / advice you can offer is much appreciated please. Freaking out...!

[ETC]

Get the brick/block layers to take it down and rebuild it with the insulation tight against the inner leaf. They should have been using wall ties with retaining discs on them. Not acceptable to you or to Building Control.

[Johnny Jekyll]

1 minute ago, ETC said:

Get the brick/block layers to take it down and rebuild it with the insulation tight against the inner leaf. They should have been using wall ties with retaining discs on them. Not acceptable to you or to Building Control.

 

Thanks for the reply, but taking down isn't an option. This full fill doesn't require the wall ties with retaining discs (I know the ones you mean). Need to solve this retrospectively.

[Iceverge]

what a pity. you really have my sympathy.

 

@ETC is unfortunately right about this, can you elaborate on why it is not an option?  It can be psychologically extremely difficult to undo work to put it right but it’s the proper, and often the cheapest thing to do. 

 

Cold bridging is probably the wrong term here. “Thermal looping“ is a better one, 

 

A quick google turned this up. There are other sources of info. 

https://www.kore-system.com/blog_list/cavity-wall-insulation-the-devastating-effects-of-thermal-looping/

 

Simply put what has been done will probably half or worse the performance of your wall.

 

My neighbour used Technitherm poured closed cell foam in conjunction with 100mm PIR in a 150mm cavity. It was successful as far as i know. 

However your remaining cavity sounds too thin for this to be an option.

 

Other ideas that come to mind. 

 

1. Can you drill holes in the mortar joints externally and push the boards tight to the inner leaf? Use closed cell spray foam then to pin them in place and hope it spreads enough to do the job? Walltite are one supplier. I think this is your best option.

 

2 . Remove all the boards via the top of the cavity and window and door jambs and use beads? 

 

3. With extreme diligence air seal the cavity wall both externally and internally to prevent external air from entering the cavity.  Difficult to do properly and not a 100% solution. 

 

 

[markc]

Agree with all of the above, there is no magical gadget that will crawl around the cavity doing what the brickies should have done in the first place,they either didn’t bother or didn’t understand what and how insulation works.

why is taking down not an option? It is the easiest and cheapest solution.

[Brickie]

If taking down cannot be done,how about isolated removal of individual blocks on the external leaf to allow access to the affected areas? 
‘Full fill’ in this scenario is a commonly used misnomer & Id say the retaining clips definitely are required for the system to stand a chance of working. 
Im really not a fan of it,to be honest. The real world installation just never tallies with how good it looks on paper. 

[Johnny Jekyll]

Thanks everyone, very helpful and honest feedback. I researched and planned so much but practical application is another animal altogether. I would love to take down and start again, but family and other circumstances mean it's just not an option. I'll do my best to fill gaps where possible.

 

Moving forward. The house will be pretty airtight once I'm finished on the inside. And we are using an MVHR. Considering this may I ask 2 questions:

1 ) Surely using insulated plasterboard, thermal liner, or battens with thin PIR / wool / foil insulation on the inside will help? Form a barrier against the blocks from the inside?

2 ) Our plan is for underfloor heating. Should we continue with this or move to radiators?

 

Thanks very much. 

[Johnny Jekyll]

QUICK QUESTION GUYS.

Looking at my insulation gaps today, what about pouring sand down the back of the insulation where the gaps are? Would that at least fill some of the gaps, and help with the thermal looping?

[Brickie]

I’m confused-if you can pour sand down behind any given board can you not lever it back tight against the inner skin?

[Johnny Jekyll]

Just now, Brickie said:

I’m confused-if you can pour sand down behind any given board can you not lever it back tight against the inner skin?

Yes I understand your question.

Problem is we are 17 blocks up, so near the top. And the brickies didn't do the best job of cleaning the mortar in the cavities on the way up.

Some sections are not too bad. Other sections definitely need filling behind.

Can't find where to buy EPS beads (in the next 2 days as we are laying again on Monday)?

Thinking of ways to fill the gaps?

Insulation manufacturer says using insulated plasterboard inside will help. Do you agree with that?

[Declan52]

Just use insulated plasterboard on the inside is the easiest option. Not the cheapest but it is what it is. If you take it all down and do it again some boards will end up the same. It happens all the time, it really shouldn't but that's the joys of building.

[Johnny Jekyll]

4 minutes ago, Declan52 said:

Just use insulated plasterboard on the inside is the easiest option. Not the cheapest but it is what it is. If you take it all down and do it again some boards will end up the same. It happens all the time, it really shouldn't but that's the joys of building.

 

Do you think the insulated plasterboard will do a good job in solving the cold bridge problem? Common sense says yes but you're a lot more experienced on this than me. 

[Declan52]

Out of all your options it's the only one that I would choose. More expense for you though. 

Is it on every wall or just a few sections?? Shine a torch down the cavity and see how many boards kick out indicating they aren't flush with the wall.

Have you said to the builder you ain't happy with this aspect???

[Johnny Jekyll]

2 minutes ago, Declan52 said:

Out of all your options it's the only one that I would choose. More expense for you though. 

Is it on every wall or just a few sections?? Shine a torch down the cavity and see how many boards kick out indicating they aren't flush with the wall.

Have you said to the builder you ain't happy with this aspect???

 

It's a long story, I won't bore you with it.

It's messy all over. So I'm going to install the insulated plasterboard all over the inside perimeter. It costs what it costs.

I'm just furious about the whole thing...!

[Brickie]

1 hour ago, Johnny Jekyll said:

I'm just furious about the whole thing...!

I can’t imagine the stress you’re under at the moment-can you post some pictures to see if there are any hacks we can suggest to achieve better performance from what’s already built?

[Mr Punter]

If the insulation is contiguous, with no gaps between the boards, there should not be massive amounts of outside air circulating between the boards and the blockwork.  For the rest of the wall, make sure the blockwork is built up with wall ties and retaining clips and mortar cleaned off as it progresses.  I think that dry sand may cause issues should you need to drill through the wall in future.  Also, if the gap is quite wide you would need lots.

[Johnny Jekyll]

I guess sand could act as a bridge for damp so maybe that's not the best idea. Please correct me if I'm wrong on this. I have tons of it on site.

I guess grey EPS insulation beads would help but just can't find them anywhere (except installers). Could buy bean bag beads from ebay or amazon but believe they're a fire hazard.

Photos attached, you can see the space behind the boards to the blocks (medium dense, not thermalite).

Insulated plasterboard is at the top of my list at the moment.

[Mr Punter]

It doesn't look too bad to me.  No gaps between boards.  I would be tempted to squirt in some low expansion foam or squash in some Rockwool to form a continuous barrier at this level and get them to fit the boards a bit snugger for the rest.  Also, make sure that at the top the cavity is very well sealed.

Edited October 13, 2021 by Mr Punter

[ETC]

Remove as much of the cavity insulation as you can and pump the cavities. Or discount the insulation already installed, speak to your SAP assessor to run a new SAP with internal wall insulation. Guessing an insulated plasterboard thickness is a waste of time - the TER/DER needs to work with this new thermal element. As an aside I’d be a bit concerned if the boards were - at some time in the future - slip, touch the inside of the outer leaf and act as a bridge for moisture/water to pass across the cavity.

[ETC]

Having looked at the photographs it doesn’t look that bad.

 

Have you tried pulling it in?

 

Could you drill a few holes at say 1200mm horizontal and 900 mm vertical centres in the inner leaf from the ground floor up and pull the insulation towards the inner leaf and mechanically or glue fix to the inner leaf?

 

Just a thought.

 

what breed of insulation did you use?

[ADLIan]

See this far too often with this type of product, only real solution is to rebuild. What manufacturer is it from? You could ask them for advice on install instructions along with BBA certificate - may give you leverage with contractor. Assume you currently have a U-value of 0.19/0.20 expect this to increase to 0.23/0.24 (the theoretical correction for bad install). SAP assessor will be able to run the numbers and see what insulated plasterboard would get you back to 0.20 or better.

[Johnny Jekyll]

Thanks guys.

Project was well planned. SAP passes on paper without any insulated plasterboard (did 7 different assessments during planning).

Using Cavity Therm (great science behind the product and seems superb if installed correctly).

The ties cut through the ridges and jamb the insulation in place. It won't move let alone slip.

I've spoken with them. They say insulated plasterboard should help with this.

I'm just a bit of a perfectionist. Quite funny really how things turn out. We're gonna live in it so I just want it warm for myself.

Think I'll stuff some rockwool down the backs where possible, and be very diligent from this point up.

Insulated plasterboard is the answer for me.

 

 

[Johnny Jekyll]

33 minutes ago, Mr Punter said:

It doesn't look too bad to me.  No gaps between boards.  I would be tempted to squirt in some low expansion foam or squash in some Rockwool to form a continuous barrier at this level and get them to fit the boards a bit snugger for the rest.  Also, make sure that at the top the cavity is very well sealed.

 

May I ask how you properly seal the cavity at the top?

[Brickie]

Is it yourself or the bricklayers installing? 
That top sheet needs to come out,the snots cut off flush & cleared & then reinstalled tight. From here on,tell them you want the cavity side of the inner leaf pointed AND brushed off,as if it were face work. When they object,tell them you’ve no choice but to insist on it as,left to their own devices,they give you the work you’ve shown. 

[Johnny Jekyll]

2 minutes ago, Brickie said:

Is it yourself or the bricklayers installing? 
That top sheet needs to come out,the snots cut off flush & cleared & then reinstalled tight. From here on,tell them you want the cavity side of the inner leaf pointed AND brushed off,as if it were face work. When they object,tell them you’ve no choice but to insist on it as,left to their own devices,they give you the work you’ve shown. 

Thanks Brickie. I'm all over it from this point up that's for sure.