PIR in cavity wall and avoiding air gaps

[Valinor]

Due to site constraints we had to do the outer skin first, and will be now adding the insulation and building the inner skin from Celcon blocks. A few questions I have which I would appreciate any advice on ?

 

How come in some images the insulation doesn't go to the bottom of the cavity? Wouldn't that reduce the wall's insulation properties? Is there anything wrong with going all the way to the bottom of the cavity?

 

As I'll have to cut and place the insulation in the cavity before we lay each course of blocks against it, I was wondering whether it matters which side of the insulation I place tape on. As in, looking at the illustration below, from left to right, would this be ok at preventing airflow?

bricks - 25mm void - 75mm PIR - tape - Celcon blocks. 

Or should I go to the effort of trying to tape on the side with the 25mm void?

 

Any tips for making sure there is no gap between the PIR and Celcons when doing it in this order? Anything I should pay attention to when helping the brickie? I would have much rather had the Celcons up first and been able to place the PIR against them etc, but that wasn't possible. 

 

Thanks!

 

[Declan52]

The gap left at the bottom is for droppings of motar. It's a standard detail. 

When you say your going to have to cut the PIR insulation what do you mean?? 

Are you buying 8*4 sheets and cutting these up as that will be disastrous. If you intend to use PIR insulation in a cavity then you buy the cavity boards. They are 450mm high so suit wall tie spacing. Plus they are tongue and groove. Your never going to be able to cut sheets up and somehow tape the joins up with the outside skin already built. 

If the brickie  doesn't push any motar out when bedding the wall or setting down the block then the cavity boards will be tight but being realistic not every board will be. 

For this build your best bet would be getting beads blown in. 

[Valinor]

3 minutes ago, Declan52 said:

The gap left at the bottom is for droppings of motar. It's a standard detail. 

When you say your going to have to cut the PIR insulation what do you mean?? 

Are you buying 8*4 sheets and cutting these up as that will be disastrous. If you intend to use PIR insulation in a cavity then you buy the cavity boards. They are 450mm high so suit wall tie spacing. Plus they are tongue and groove. Your never going to be able to cut sheets up and somehow tape the joins up with the outside skin already built. 

If the brickie  doesn't push any motar out when bedding the wall or setting down the block then the cavity boards will be tight but being realistic not every board will be. 

For this build your best bet would be getting beads blown in. 

 

Thank you for taking the time to reply

 

Unfortunately we purchased all insulation before the March price rise, we've got 450mm x 1200mm though without tongue and groove as those were too expensive (we went for Recticel Eurowall - PIR Cavity Wall Insulation Board)

 

When talking about cutting I meant for all the areas around a window opening or where building control specified more brick ties (where I imagine I can insert a knife into the PIR and the wall tie will go straight through. 

 

I still want to tape the joints of the factory perfect edges etc. 

 

To prevent the brickie pushing mortar out the back - would it make sense to try and convince him to bed the mortar more to the inside, with there being less of it on the insulation side and likely to push out that way? Or would that weaken the walls too much from a structural point of view?

 

 

[Declan52]

Cut the boards with a hand saw.

Physically there is no way your getting your hand down a 25mm space to put tape on the joins without pushing the wet blocks out of plumb. 

They will bed the wall like that but with the best will in the world unless your paying mega bucks for him to clean each and every bed as he goes and double checks each board and lift off some blocks then some are going to have gaps.

[Brickie]

I’ve been put in this scenario myself-it’s an absolute #**#ache. 
As Declan said-blown in beads or full fill cavity batts are the practical solution. Otherwise,you’ll end up with an improperly inststalled,underperforming insulation system. 
If the PIR has gone up in price & is still packaged,would you not get the majority of your money back?

[Valinor]

11 hours ago, Declan52 said:

 

 

3 hours ago, Brickie said:

 

 

Thank you for both your replies! Yes PIR has gone up in price and that's a very good idea. Will need to mull it over as I do appreciate the insanity of trying to do it as it was originally planned!

 

 

[Johnny Jekyll]

Valinor, my walls are going up as we speak, I'm using full fill PIR insulation, cost me a fortune. The whole thing has been a complete and utter nightmare. My first self-build, 3 years in planning, bought into the science of everything, had multiple site meetings in the months running up to the build, had everything on site ready, colour coded notes for everyone. My architect said in 50 years he's not seen anyone better prepared. Totally pointless. It just doesn't work practically with the way the trades work, and they will not adapt to you. For example if brickies are on price work, all they want to do is lay brick, and QUICK. Air gaps, mess, thermal looping, you'll get the lot, even if you try to do the insulation yourself (I've been fitting my PIR myself around them since the first row). If you have the time, sell your PIR, at a loss if necessary. Get the brickies to concentrate on laying brick straight and accurate, lay the wall ties properly, wipe mortar away on all sides. Once they're off site, pour EPS beads in from the top ensuring all gaps are filled. I've debated and been advised by our knowledgeable friends on here to take mine down and start again. Not an option for me, so I've paid fortunes for full fill PIR, now I'm going to have to pay lots more and install insulated plasterboard on the inside to reduce the cold bridge effect, and lose internal space for the pleasure. EPS beads all the way.

[Iceverge]

Beads or batts or closed cell foam. 

 

Rigid insulation has no place in a cavity wall. Blockwork is almost impossible to get to a perfect smooth finish with no mortar droppings. 

 

 

[Digmixfill]

On 10/10/2021 at 22:26, Valinor said:

Due to site constraints we had to do the outer skin first, and will be now adding the insulation and building the inner skin from Celcon blocks. ?

On 13/10/2021 at 15:40, Johnny Jekyll said:

Valinor, my walls are going up as we speak, I'm using full fill PIR insulation, cost me a fortune. The whole thing has been a complete and utter nightmare.

 

I'm a good way through putting up my internal walls and creating a cavity against an existing outer wall and I agree with @Johnny Jekyll it's been a pain. I'm the brickie, so no problems with me re-laying blocks umpteen times, or removing deformities on the blocks to get things as straight as I can for the PIR boards, but truly a pain.

 

Beads or injected/poured PIR if a ever get the silly idea to do this again.

 

[CalvinHobbes]

Could you not have resold the insulation you bought and use beads with the money?

 

[Digmixfill]

I could have, yes.

Having started I decided to carry on with the boards. ?

 

Edited November 13, 2021 by Digmixfill

[ruggers]

On 13/10/2021 at 15:40, Johnny Jekyll said:

Valinor, my walls are going up as we speak, I'm using full fill PIR insulation, cost me a fortune. The whole thing has been a complete and utter nightmare. My first self-build, 3 years in planning, bought into the science of everything, had multiple site meetings in the months running up to the build, had everything on site ready, colour coded notes for everyone. My architect said in 50 years he's not seen anyone better prepared. Totally pointless. It just doesn't work practically with the way the trades work, and they will not adapt to you. For example if brickies are on price work, all they want to do is lay brick, and QUICK. Air gaps, mess, thermal looping, you'll get the lot, even if you try to do the insulation yourself (I've been fitting my PIR myself around them since the first row). If you have the time, sell your PIR, at a loss if necessary. Get the brickies to concentrate on laying brick straight and accurate, lay the wall ties properly, wipe mortar away on all sides. Once they're off site, pour EPS beads in from the top ensuring all gaps are filled. I've debated and been advised by our knowledgeable friends on here to take mine down and start again. Not an option for me, so I've paid fortunes for full fill PIR, now I'm going to have to pay lots more and install insulated plasterboard on the inside to reduce the cold bridge effect, and lose internal space for the pleasure. EPS beads all the way.

 

I'm looking to start a 100mm pir partial fill this year. How does EPS beads compare in price compared to PIR sheet, do the plan needs changed much? Can you also use this with facing brick exterior as theres a lot of mortar with potential to let in more water than a rendered finish.

[Iceverge]

You'll need to bump the cavity to 150mm between the leafs.  You prob have this anyway

 

I haven't seen any examples of moisture getting across the cavity with beads that were installed correctly. Normally it's because of a badly fitted cavity tray, mortar bridging the cavity or an unsuitable mineral wool pumped into a very narrow cavity. 

 

There's a few threads here about boards in the cavity. Have a read through. 

 

 

 

[SBMS]

2 hours ago, ruggers said:

 

I'm looking to start a 100mm pir partial fill this year. How does EPS beads compare in price compared to PIR sheet, do the plan needs changed much? Can you also use this with facing brick exterior as theres a lot of mortar with potential to let in more water than a rendered finish.

So we’ve just been down this route. Initially we were going 100mm pir but after looking into it decided to go blown EPS beads. I increased cavity to 150mm (should be fine if you’ve standard width foundations). Ours is also exterior facing brick. 

Cost difference: 

272 m2 of cavity insulation required : about £4900 plus the labour for the brickies to fit.
 

Pumped insulation by outside specialist contractor - £4200 - with a 25 year guarantee. 
 

Means the build will go up quicker (brickies just focus on laying block and brick) and have a much greater chance of a fully, well insulated cavity. 
 

FYI the beads are water resistant and don’t transfer water across the cavity. Water that does get into the cavity naturally flows down the beads between the balls rather than across the cavity. 

[Simplysimon]

why oh why do you still build with a block inner leaf instead of a timber kit down there? move into the 20th century folks, heaven forbid, you could actually move into the 21st century with i beam kits......... ?

[SBMS]

4 minutes ago, Simplysimon said:

why oh why do you still build with a block inner leaf instead of a timber kit down there? move into the 20th century folks, heaven forbid, you could actually move into the 21st century with i beam kits......... ?

Risk of rot

Poorer sound insulation

Timber fraction to insulation ratios need considering

Some Mortgage lenders don’t like (at least want an outer brick leaf)

Issues with shower movement

 

Each or these can be argued against I know, Im merely pointing out that you cant evangelise a construction method to the exclusion of all others.

Went through a lot of research when looking at construction methods for our new build but came back round to traditional. 

 

That’s not to say that there’s some great advantages to timber frame. But timber frame is hardly new or innovative, like all things there are a hundred factors to consider (one of them being whether you’re in a wet climate!) when considering any individual build. 

 

 

[Simplysimon]

3 minutes ago, SBMS said:

Risk of rot

dpm, dpc and a well fitted and sealed vcl - negligible chance

 

4 minutes ago, SBMS said:

Poorer sound insulation

300mm+ i beams exceedingly good sound performance

 

5 minutes ago, SBMS said:

Timber fraction to insulation ratios need considering

see above, 350mm i beam with blown cellulose = 0.1

 

6 minutes ago, SBMS said:

Some Mortgage lenders don’t like (at least want an outer brick leaf)

well put an expensive rain screen around it then, you are already

 

7 minutes ago, SBMS said:

Issues with shower movement

????

 

8 minutes ago, SBMS said:

cant evangelise a construction method to the exclusion of all others.

i'm not, it you lot griping about how difficult it is to fit insulation to an inner leaf blockwork wall and considering eps blown beads and hoping your price work brickie isn't leaving snotters to bridge the cavity, i'm putting foward a build method to mitigate these issues.

 

15 minutes ago, SBMS said:

(one of them being whether you’re in a wet climate!)

along with the lake district and wales, scotland does have its fair share of rain, usually driven on a strong breeze as has been shown over the last week or so ?

[Johnny Jekyll]

54 minutes ago, SBMS said:

So we’ve just been down this route. Initially we were going 100mm pir but after looking into it decided to go blown EPS beads. I increased cavity to 150mm (should be fine if you’ve standard width foundations). Ours is also exterior facing brick. 

Cost difference: 

272 m2 of cavity insulation required : about £4900 plus the labour for the brickies to fit.
 

Pumped insulation by outside specialist contractor - £4200 - with a 25 year guarantee. 
 

Means the build will go up quicker (brickies just focus on laying block and brick) and have a much greater chance of a fully, well insulated cavity. 
 

FYI the beads are water resistant and don’t transfer water across the cavity. Water that does get into the cavity naturally flows down the beads between the balls rather than across the cavity. 

 

Excellent response. Perfectly explained.

[SBMS]

17 minutes ago, Simplysimon said:

dpm, dpc and a well fitted and sealed vcl - negligible chance

 

300mm+ i beams exceedingly good sound performance

 

see above, 350mm i beam with blown cellulose = 0.1

 

well put an expensive rain screen around it then, you are already

 

????

 

i'm not, it you lot griping about how difficult it is to fit insulation to an inner leaf blockwork wall and considering eps blown beads and hoping your price work brickie isn't leaving snotters to bridge the cavity, i'm putting foward a build method to mitigate these issues.

 

along with the lake district and wales, scotland does have its fair share of rain, usually driven on a strong breeze as has been shown over the last week or so ?

I did say all the TF drawbacks could be mitigated! Every construction method has its drawbacks. You’ve just listed ways to combat some of the drawbacks with timber frame. The same can be done for brick and block - or ICF - or SIPS or whatever really. They all have pros and cons. 
 

Downsides to brick and block can be mitigated in exactly the same way - but doesn’t mean I think everyone should build brick and block (and that those that don’t aren’t in the 20th/21st century ?)

[ruggers]

@SBMS I'll be similar wall area as yourself, actually around 40m2 less. I've been reading some of the posts on here, had a look over the Kore system website but it says that for the West coast area its severe wind driven rain zone and a render finish is required instead of brick finish. The cavity is already 150 for the partial fill. It's hard around here to get any labour to do anything different to traditional. Most people won't entertain wet plaster only board skim, PIR all the time if not timber frame which I looked and it was at least 20k more for the build. 

 

Reading some older posts I seen two comments I didnt understand one mentioning to sleeve all pvc cabling coming into contact with the beads and another saying any opening DPC to be laid flat. I will have to check that again.

[Ian]

On 10/10/2021 at 22:26, Valinor said:

 

bricks - 25mm void - 75mm PIR - tape - Celcon blocks. 

Or should I go to the effort of trying to tape on the side with the 25mm void?

 

Probably too late for the OP (I’m not here very often these days as it’s now 5 years since I finished my own build) but for the benefit of anyone else contemplating a masonry cavity wall, the Approved Docs for England (not sure about Scotland) expressly require a minimum cavity width of 50mm. The alternative is full-fill insulation.

The relevant bit of the regs is Part A, Page 14, Sections 2C8. It’s also in Part C, Page 32, Section 5.15 together with diagrams showing the options.

Edited February 24, 2022 by Ian

[Ian]

39 minutes ago, Ian said:

Probably too late for the OP (I’m not here very often these days as it’s now 5 years since I finished my own build) but for the benefit of anyone else contemplating a masonry cavity wall, the Approved Docs for England (not sure about Scotland) expressly require a minimum cavity width of 50mm. The alternative is full-fill insulation.

The relevant bit of the regs is Part A, Page 14, Sections 2C8. It’s also in Part C, Page 32, Section 5.15 together with diagrams showing the options.

Extra Note: in Exposure Zone 4 (see page 35 of Part C) the minimum residual cavity is 75mm if you’re building a masonry cavity wall using facing bricks.

Edited February 24, 2022 by Ian

[SBMS]

8 hours ago, ruggers said:

@SBMS I'll be similar wall area as yourself, actually around 40m2 less. I've been reading some of the posts on here, had a look over the Kore system website but it says that for the West coast area its severe wind driven rain zone and a render finish is required instead of brick finish. The cavity is already 150 for the partial fill. It's hard around here to get any labour to do anything different to traditional. Most people won't entertain wet plaster only board skim, PIR all the time if not timber frame which I looked and it was at least 20k more for the build. 

 

Reading some older posts I seen two comments I didnt understand one mentioning to sleeve all pvc cabling coming into contact with the beads and another saying any opening DPC to be laid flat. I will have to check that again.

Not sure about the DPC but I believe there was evidence in the 70s and 80s of the plasticiser in the PVC cable migrating into the beads if in contact, and degrading the EPS. I don’t think that’s an issue anymore, I think there’s a chemical additive in the beads to mitigate this (anyone confirm this?). If you were really worried, then just put any cables in some 15mm pipe through your cavity - we are probably just talking about wall lights and maybe outdoor sockets? Anything else going outside should probably be armoured. 

[ruggers]

I'd be more concerned about it being the other way affecting the cable, it was in the small print when i looked on the kore website. Sleeving would get around this anyway as you say. 

 

[Sophiae]

On 23/02/2022 at 22:16, Simplysimon said:

why oh why do you still build with a block inner leaf instead of a timber kit down there? move into the 20th century folks, heaven forbid, you could actually move into the 21st century with i beam kits......... ?

Can you fit a steel beam on top of that? I have 4m bifold doors to that wall.