How to close this cavity

[Radian]

Can anyone suggest how I can retrospectively close the cavity of the internal gable inside this building?

 

Here it was - at the perfect time to close it...

 

Same location from the inside - after it was too late:

 

The gap between the attic truss and wall is too tight to work-in a typical plastic/foam cavity closer while making sure it's a good seal.

 

This last photo was taken above the car parking side of the garage so is effectively permanently open to the outside air and it's obviously leaking air into the occupied side like crazy.

I can work insulation in between the truss and wall but the cavity would remain an open route to air movement into the insulated zone on the other side of the wall.

[tonyshouse]

Is there no cavity insulation in there at all? 
 

best plan might be to thermally line the gable wall internally joining up with the insulation barrier in the walls and ceilings 

[Radian]

It's an empty cavity. But it was just a garage built 23 years ago. The problem with doing anything with the occupied half is it's all finished and furnished now. I would therefore like to do any remedial work in the unused half.

 

There's already a doorway in the gable so the plan is to partition off a further 2m to make a store room that will be insulated. At least this should reduce losses through the cavity.

[PeterW]

10mm masonry bit, cheap garden spray, box of gun foam and a decent gun and some patience ..!

 

Drill holes about 150mm apart at probably 100mm from the timber line, then get the sprayer lance in the hole and give a decent squirt of water into the cavity. Follow with the foam gun and don’t be shy with the pressure and you’ll start to create an insulated line along the ridge as the foam creates a barrier. 
 

Other option is to get one of the blown bead installers to fill the whole wall - may not be that cheap though for such a small wall. 

[tonyshouse]

The cavity is what I call an ‘in house winter cooling system’, full of draughts, cold, allows convection and even if you seal the top, still very likely draughty and cold.

[Radian]

14 minutes ago, PeterW said:

10mm masonry bit, cheap garden spray, box of gun foam and a decent gun and some patience ..!

 

Unless there's a better solution, this will have to be the answer. My only worry is verifying that the fill is continuous - I will try my inspection cam to see if I can get a view from around the end of the wall.

 

8 minutes ago, tonyshouse said:

The cavity is what I call an ‘in house winter cooling system’, full of draughts, cold, allows convection and even if you seal the top, still very likely draughty and cold.

 

Yeah, like having a fireplace chimney in reverse. If I do go down the squirty foam route as suggest by PeterW it wouldn't be too much extra to run horizontally at floor level. The door opening already closes the cavity in the middle 0.8m so I could, in theory, isolate the complete triangular wall. Then when I complete the store area I would have continuous insulation ?

[Radian]

Just poked phone between truss and wall (where the orange arrow is above) to snap this photo:

 

The edge of the outer sheet of roof insulation is visible (100mm Kingspan). There's quite some gap between the edge of the concrete blocks and the underside of the breather membrane because the roof pitch was altered by a couple of degrees. If I could make a right-angled lance to inject the squirty foam I could aim it at the insulation and build off it to close the cavity as well as making a continuous seal - although I can imagine it getting out of control and contacting the membrane.

 

I guess this could also be a possibility if I drilled injection holes and squirted through those instead. But what harm, if any, might there be in getting foam on the membrane?

Edited December 27, 2021 by Radian

[tonyshouse]

I would use rockwool quilt stuffing it in til no more wants to go in 

[Radian]

13 hours ago, tonyshouse said:

I would use rockwool quilt stuffing it in til no more wants to go in 

 

Would be quite easy to do - but would that make an airtight seal?

 

P.S. I've been reading through Draughtbusters. Very useful info there. It also left me feeling angry that dot & dab isn't outlawed by now. All our previous properties were sand cement plastered but the builder of our current property pushed us hard to have drylining despite me asking for traditional plaster when I looked into this newfangled practice (23 years ago). I wish I had persisted but excuses about the length of time it would add to the build conned me into it. Conned, because they overran by 6 months anyway, and I have greatly regreted it ever since.

 

Because of this experience, I specified that our recent garage extension be hard plastered where possible. But I wasn't able to control the installation of the specified insulation or detailing of air-tightness. More regrets.

[tonyshouse]

Shall we go for 100,000 signatures and get it outlawed by parliament ?

[tonyshouse]

That’s two so far then, thx  ?

[Mr Punter]

Perhaps blown cavity wall insulation  - either beads or fibre - would be an idea.

[Radian]

20 minutes ago, tonyshouse said:

That’s two so far then, thx  ?

 

? I can definitely persuade mrs. and junior to sign-up as well. Just to shut me up if nothing else.

 

18 minutes ago, Mr Punter said:

Perhaps blown cavity wall insulation  - either beads or fibre - would be an idea.

 

I wonder what the installers would do about the fist-sized gap all along the top of the wall? Or would they just stop pumping when it started to snow...

 

I have often seriously considered bonded EPS bead fill for the main house and adding this small job inside the garage might well be cost-effective (I'm sure it wouldn't if they had to turn up to do just 24m2). But I think I have a few problems here that rule it out...

1. We live in zone 4 (very severe exposure to wind and rain)
2. High water table on heavy clay (have seen standing water about 200mm below DPC in cavity)
3. 'T' Shaped House with multiple electric cables crossing a cavity to get from consumer unit in side wing to main house.

If, however, filling the cavity meant not living in the plasterboard tent I might look in to it further...

[tonyshouse]

That would insulate but not really close the cavity, if I were having it done I would stuff the top of the cavity full of rockwool first as above. 

[Mr Punter]

9 minutes ago, Radian said:

I wonder what the installers would do about the fist-sized gap all along the top of the wall? Or would they just stop pumping when it started to snow...

 

The squashed in mineral wool as suggested by @tonyshouse would hold it in place.

[Radian]

But what about the breather membrane under the battens/on top of the trusses? That's only 25mm beneath the slates so could push on them if, in turn, it was pushed by the mineral wool.

[tonyshouse]

Technically yes, in practice not a problem.

[Radian]

48 minutes ago, tonyshouse said:

Technically yes, in practice not a problem.

 

Maybe I'm overthinking things as usual. But what about my 3 point concerns about EPS cavity fill? Am I overthinking that as well?

 

I honestly wouldn't trust the advice given to me by any installation company so I'm kind of paralysed on making a decision about this. Back in 1997, when the house was built, building regs. mandated insulation in cavities but somehow our builder got away with leaving it out of half the house. To clarify, the main part of the house has an inner and outer leaf of lightweight block (thermalite?) with an empty cavity and the outer leaf was clad with Purbeck sandstone. The abutting wing is is brick/PIR in cavity/lightweight block. TBH I can't feel any difference between rooms in either half. Both have fresh air vents built into every electrical faceplate.

 

The sandstone facade seems pretty watertight - where I have had occasion to break in to it, I've not seen any evidence of water penetration. However, I remember the brickie's laughing at how ridiculously absorbent the lightweight blocks were.

[tonyshouse]

Eps beads can and do deplasticise pvc cables but if this a problem we would be hearing about problems, the idea is that the cables become brittle and loose their insulating properties but you need more than long term exposure to a once touching pvc cable, not enough deplasticisation ever happens. 
 

[TonyT]

Cables shouldn’t be run in the cavity, the only exception is tails passing from the meter box to the consumer unit.

[matthyde83]

8 hours ago, TonyT said:

Cables shouldn’t be run in the cavity, the only exception is tails passing from the meter box to the consumer unit.

And exterior lighting with cables passing through the cavity?

[Radian]

9 hours ago, TonyT said:

Cables shouldn’t be run in the cavity, the only exception is tails passing from the meter box to the consumer unit.

 

The cables don't run in the cavity, they cross it - much like the tails from the meter. Imagine if you built an extension on the side of a house and brought all the services in through it. That's how our house was built. If I go up into the main attic and look down the cavity I can see all the cables crossing between the two halves.

 

Our previous house built in the 1980's has bonded EPS cavity fill (and sand cement plaster and was so much more comfortable!). We still own it and rent it out and when we recently upgraded the FCU from the original cartridge fuse model the damage to the tails and ring final cables was very evident from contact with EPS. That house was built to a similar plan to our current house with a side extension and cavity crossing cables. That's why I'm being so cautious here.

 

OK, so let's say I take the short-term view (I don't have another 40 years to consider here after all) and forget all about point 3. What about points 2 and 1?

[TonyT]

2 hours ago, matthyde83 said:

And exterior lighting with cables passing through the cavity?

They aren’t run in the cavity, just pass through the cavity as you say so fine, if I knew I was going to be doing cavity fill I may look at a way of protecting cables from polystyrene to stop the green goo issue later

 

 

 

[matthyde83]

1 hour ago, TonyT said:

They aren’t run in the cavity, just pass through the cavity as you say so fine, if I knew I was going to be doing cavity fill I may look at a way of protecting cables from polystyrene to stop the green goo issue later

 

 

 

 

Maybe some conduit through the wall for the wires to pass through then seal / fill?

[WGL]

What roof tile type do you have? If it's anything other than slate, I'd tackle it from above. But not everybody wants to climb around on a roof, so understand if that's not an option