Building Regs - Cavity Wall Insulation

[jayc89]

We're not discussing building regs with our Architect. We're going for a traditional cavity wall construction (for a multitude of reasons I won't go into here). I touted the idea of a 175mm cavity using blown EPS beads once the cavity is constructed and closed. He's less keen on EPS beads, worrying that it's effectively done blind and he believes there's also a risk of slumping over time.  Ultimately he's left the ball in my court.

 

Is there are evidence out there to mitigate his concerns? Whilst I could of course "over-rule" him, I'd prefer to work with him rather than against him.

[Temp]

As I understand it the grey coated bead systems are OK, the blown fibre systems can be a nightmare if they get wet and are more prone to slumping.

 

Are you rendering the outside? Bricks can be very porous and there is a risk of water bridging the cavity when you fully fill it. Again the coated bead systems have a better reputation than others. Installers are meant to check if your house is in an exposed location before installing full fill systems to reduce the risk of damp bridging. Rendering effectively stops this being an issue.

 

If your cavity is 175mm you could consider 125mm PIR sheets. If installed correctly the U-Value should be at least as good as 175mm EPS. You might even be able to use 150mm PIR but keep knocking the snot off the wall ties.

 

I'm convinced that poor installation let's down many good intentions. You don't want your builder trying to stuff sheet insulation down the cavity because the brick layers got too far ahead. Ideally you want then fixing it to the block inner leaf with nice tight butt joints before the outer leaf is built.

[Mr Punter]

I am doing a 150mm cavity with beads on a project.  The brickwork is getting a coat of StormDry.  I will watch the bead installer to make sure they have got to all the voids.  I may suggest to them that we will use a thermal image camera on completion.

[Radian]

I've just been around my property that was recently pumped with graphite coated EPS beads and in the handful of places I could examine with my borescope, it was thoroughly filled. TBH, I can't see how anyone could really do a bad job. The stuff goes in at around 100PSI and as a result goes in very thoroughly. Our tiny 1990's 50mm cavity is about as challenging as it could get but In a big cavity I just can't see how it could fail so long as they're systematic with the injection point location and spacing. They just keep pumping until the backpressure forces the lance back out. The injection system also mixes in a PVA binder that makes the EPS into a solid block once dry. That looks to be very effective, the odd escape here and there was well stuck together. I'd just keep an eye on the PVA delivery tank.

[PeterW]

1 hour ago, jayc89 said:

He's less keen on EPS beads, worrying that it's effectively done blind and he believes there's also a risk of slumping over time.  Ultimately he's left the ball in my court.

He’s never seen it done then ..! Get it done from the inside when you’ve just got blockwork and the windows and doors in, and make sure you close the cavity top with something like a cavity sock as otherwise it will go everywhere ..!! As @Radian says, this is 100PSi and the guys we use are very efficient - where are you im the U.K. ..?

[jayc89]

34 minutes ago, PeterW said:

He’s never seen it done then ..! Get it done from the inside when you’ve just got blockwork and the windows and doors in, and make sure you close the cavity top with something like a cavity sock as otherwise it will go everywhere ..!! As @Radian says, this is 100PSi and the guys we use are very efficient - where are you im the U.K. ..?

 

East Yorkshire so only a couple of hours away from you, do you think you guys would travel that far?

[jayc89]

1 hour ago, Temp said:

As I understand it the grey coated bead systems are OK, the blown fibre systems can be a nightmare if they get wet and are more prone to slumping.

 

Are you rendering the outside? Bricks can be very porous and there is a risk of water bridging the cavity when you fully fill it. Again the coated bead systems have a better reputation than others. Installers are meant to check if your house is in an exposed location before installing full fill systems to reduce the risk of damp bridging. Rendering effectively stops this being an issue.

 

If your cavity is 175mm you could consider 125mm PIR sheets. If installed correctly the U-Value should be at least as good as 175mm EPS. You might even be able to use 150mm PIR but keep knocking the snot off the wall ties.

 

I'm convinced that poor installation let's down many good intentions. You don't want your builder trying to stuff sheet insulation down the cavity because the brick layers got too far ahead. Ideally you want then fixing it to the block inner leaf with nice tight butt joints before the outer leaf is built.

 

This is exactly my concern. With the best will in the world I don't see the builder paying enough attention to butting up the PIR boards, which I don't want.

[Iceverge]

+1 for beads. 

 

Very fill fill. I checked our 250mm cavity. By drilling test holes. 

 

Some PVA was missing beads fell out where I cored a hole. Make sure you have all penetrations sorted first. 

 

 

[Radian]

35 minutes ago, Iceverge said:

+1 for beads. 

 

Very fill fill. I checked our 250mm cavity. By drilling test holes. 

 

Some PVA was missing beads fell out where I cored a hole. Make sure you have all penetrations sorted first. 

 

 

The matrix it creates is very fragile when exposed but gains stability in a contained volume. I may be wrong but I think it's more to do with slump prevention than stopping spillage.

[PeterW]

1 hour ago, jayc89 said:

 

East Yorkshire so only a couple of hours away from you, do you think you guys would travel that far?

They are Sheffield based so pretty sure they do

[jayc89]

9 hours ago, PeterW said:

They are Sheffield based so pretty sure they do

 

Would you minding sending me their details? Here or DM would be great.

[PeterW]

3 hours ago, jayc89 said:

 

Would you minding sending me their details? Here or DM would be great.

https://www.jjcrump.com/

[jayc89]

Thanks, another concern was the additional costs of wall ties, lintels, cavity closers etc. Has any one done the maths on how much extra a wider cavity cost them? I assume there are savings to be had with EPS beads, presumably, cheaper than K106 boards. 

[PeterW]

Nothing … or a very small cost !

 

You can use standard stainless ties - 275mm are about 1p different depending on where you buy from. Lintels in 175mm cavity can be done using a 165mm cavity lintel or you could design it at 165mm cavity and still get decent uValues 

[Iceverge]

Or use off the shelf precast lintels separately for both leafs.

 

Standard practice here. 

[jayc89]

On 06/10/2022 at 12:50, PeterW said:

Nothing … or a very small cost !

 

You can use standard stainless ties - 275mm are about 1p different depending on where you buy from. Lintels in 175mm cavity can be done using a 165mm cavity lintel or you could design it at 165mm cavity and still get decent uValues 

 

Minimum u-value here is 0.18 which I believe means we'd need a minimum cavity of 170mm. Given the digger bucket size, 175mm would make the most sense. 

 

I dropped the insulation company an email asking for some advice/materials to pass back to our Architect, so we'll see what they say. 

[markc]

Given the digger bucket size, 175mm would make the most sense. ?

Excavations will never be within or even near to 5mm tolerance. Yes to being careful and not needing loads of extra concrete but never dig undersize, a bit of extra mass fill is much cheaper and easier than going back to straighten or widen trenches

[JackofAll]

On 05/10/2022 at 21:20, Iceverge said:

+1 for beads. 

 

Very fill fill. I checked our 250mm cavity. By drilling test holes. 

 

Some PVA was missing beads fell out where I cored a hole. Make sure you have all penetrations sorted first. 

 

 

 Sorry to be piggy backing on the OP but am  curious if you would go with beads again, as opposed to full fill batts?

[Iceverge]

2 hours ago, JackofAll said:

 Sorry to be piggy backing on the OP but am  curious if you would go with beads again, as opposed to full fill batts?

 

 

Batts are good if you install them properly. 

 

Beads are more tolerant of less exacting workmanship. 

 

We used beads to about 600mm below floor level in the cavity to reduce the thermal bridge there. Similar to the Denby Dale detail but much less labour. 

 

 

 

[JackofAll]

1 hour ago, Iceverge said:

 

 

Batts are good if you install them properly. 

 

Beads are more tolerant of less exacting workmanship. 

 

We used beads to about 600mm below floor level in the cavity to reduce the thermal bridge there. Similar to the Denby Dale detail but much less labour. 

 

 

 

So you would go with beads again on that basis.

[Iceverge]

Yes. 

 

Just make sure all your penetrations are done before blowing. 

 

Also you'll need to keep cavity ties clear. Cavity boards to catch mortar or a wash down daily of the ties with a before the mortar dries. 

 

 

 

[JackofAll]

1 hour ago, Iceverge said:

Yes. 

 

Just make sure all your penetrations are done before blowing. 

 

Also you'll need to keep cavity ties clear. Cavity boards to catch mortar or a wash down daily of the ties with a before the mortar dries. 

 

 

 

Thanks for that, am strongly thinking of cavity batts(250mm) imagine would add to sound insulation inside the building but can see the convenience of beads. 

[Iceverge]

A wide cavity with full fill will transfer almost zero sound whatever you choose. 

 

Reveals, heads, jambs, windows doors and the roof buildup will be far more important. 

 

If you'd prefer batts go for it. @Tony and @joe90 have had some success. I believe. 

[joe90]

1 hour ago, Iceverge said:

and @joe90 have had some success. I believe. 

Oh yes, 200mm batt filled cavity works a treat 👍

[jayc89]

On 07/10/2022 at 09:57, Iceverge said:

Or use off the shelf precast lintels separately for both leafs.

 

Standard practice here. 

 

Only works if the outer leaf is to be rendered, or hidden in some other way though, not facing bricks?