Block and Block with 180mm cavity instead of Isotex ICF

[Nickfromwales]

32 minutes ago, Dave Jones said:

no batts to keep cavity clean while being built etc.

It's the brick-layer that keeps the cavity clean  Plus the batts do not fully fil the void so crap will still fall down it if there's poor house-keeping on site. Most decent builders don't let too many snots / debris get into the bottom of the cavity, but the cavity often goes substantially lower than DPC to allow for some crap to go down and collect. 

[joe90]

23 minutes ago, Nickfromwales said:

It's the brick-layer that keeps the cavity clean

Yes my brick layer was great at this and installed the batts as he went (inner skin already built) and he could reach to retrieve any that fell onto the batts.

25 minutes ago, Nickfromwales said:

Plus the batts do not fully fil the void

Mine did.

26 minutes ago, Nickfromwales said:

the cavity often goes substantially lower than DPC to allow for some crap to go down and collect. 

Below DPC my cavity was filled with XPS rather than weak mix to avoid a thermal bridge.

[Dave Jones]

3 hours ago, joe90 said:

Below DPC my cavity was filled with XPS rather than weak mix to avoid a thermal bridge.

 interesting, how did that work stopping the cold bridge to footings ?

 

Having to use marnox blocks to achieve this on ours and they are horrendously expensive....

[Dave Jones]

4 hours ago, Nickfromwales said:

It's the brick-layer that keeps the cavity clean  Plus the batts do not fully fil the void so crap will still fall down it if there's poor house-keeping on site. Most decent builders don't let too many snots / debris get into the bottom of the cavity, but the cavity often goes substantially lower than DPC to allow for some crap to go down and collect. 

 

150 batt 150 cav etc.

[joe90]

2 minutes ago, Dave Jones said:

interesting, how did that work stopping the cold bridge to footings ?

Similar to this…..

[Dave Jones]

you have cold bridging there. we are delinking the footings with Marmox block here to avoid it. bloody expensive too

 

[Nickfromwales]

34 minutes ago, Dave Jones said:

bloody expensive too

But very good at knocking that on the head right at that location.

[LSB]

our batts totally fill the cavity, 150 mineral wool. 

 

[Nickfromwales]

42 minutes ago, LSB said:

our batts totally fill the cavity, 150 mineral wool

 

I always thought that mineral wool would convey / bridge damp. 
 

[ADLIan]

Mineral wool slabs are treated with a water proofing agent. They have to pass a very extreme BBA test to prove they work, do not allow moisture to pass and get certification.  They can normally be used below dpc 

[LSB]

6 minutes ago, ADLIan said:

Mineral wool slabs are treated with a water proofing agent. They have to pass a very extreme BBA test to prove they work, do not allow moisture to pass and get certification.  They can normally be used below dpc 

no moisture anywhere near, no rain for 4+ weeks and covered anyway and not below DPC

 

[Dave Jones]

20 minutes ago, ADLIan said:

Mineral wool slabs are treated with a water proofing agent. They have to pass a very extreme BBA test to prove they work, do not allow moisture to pass and get certification.  They can normally be used below dpc 

 

all i will say is they get soggy as buggery when it rains...

 

They are still the least worst option though.

[Sophiae]

Feeling more confused now. 
like the idea of all of them but essentially it is down to the skill of the brick layers. 
not sure how comfortable that makes me feel to have to rely on other peoples’ work ethics when some have already failed me big time. 
 

I’ll read again and check the feasibility of each if all 3 options can achieve the same U-Value 

[joe90]

10 hours ago, Dave Jones said:

all i will say is they get soggy as buggery when it rains...

Well my brick layer was not convinced about full fill with batts but they do have a bba certificate. The outer wall was brick and one wall faced west and it was near the coast in Cornwall and after a very wet winter the bricks were sodden. I then installed the ASHP which meant I had to core drill that wall and when I put my hand in the hole the inner face of the bricks were sodden but the batts had absorbed no water vat all, to protect the bricks on the face (possible spalling) I coated the wall in water proofed and the rain then rolled off it like glass.

 

13 hours ago, Dave Jones said:

you have cold bridging there.

I would suggest the cold bridging is minimal, the soil temp at depth is quite stable and above air temp in cold weather, like the wall ties ( I decided the cost of special wall ties was not worth their minimal effect) suffice to say that over the 6 years I lived there the heating from my 4Kw ASHP only came on in Dec and Jan for short periods .

[Dave Jones]

On 14/06/2023 at 08:22, joe90 said:

Well my brick layer was not convinced about full fill with batts but they do have a bba certificate. The outer wall was brick and one wall faced west and it was near the coast in Cornwall and after a very wet winter the bricks were sodden. I then installed the ASHP which meant I had to core drill that wall and when I put my hand in the hole the inner face of the bricks were sodden but the batts had absorbed no water vat all, to protect the bricks on the face (possible spalling) I coated the wall in water proofed and the rain then rolled off it like glass.

 

I would suggest the cold bridging is minimal, the soil temp at depth is quite stable and above air temp in cold weather, like the wall ties ( I decided the cost of special wall ties was not worth their minimal effect) suffice to say that over the 6 years I lived there the heating from my 4Kw ASHP only came on in Dec and Jan for short periods .

 

interesting about the wet cav, do you have to reapply the treatment annually ?

 

ref cold bridging, your detail fails current sap specifically 1A and 1B. Photographs have to be provided showing how the cold bridge has been mitigated now. 

 

The plus side of marmox allows the doors to fully sit on the external skin and still be thermally broken and fully in the insulation envelope. Here is the detail, we have level threshold so the marmox wont be seen as its underground.

 

[JohnMo]

On 13/06/2023 at 18:28, Dave Jones said:

you have cold bridging there. we are delinking the footings with Marmox block here to avoid it. bloody expensive too

 

Just reading this thread. Mine is similar to the image also. I filled my cavity with PIR.  The area circled and blocks directly below, I used Thermolite blocks and doing the calculations (sideways and downwards) I found there was less of a cold bridge when I compared to Marmox.  I also used Thermolite at the thresholds for the same reason.

[Big Jimbo]

To be honest the above looks like a cold bridge. Screed, 25mm upstand, then through the block, and into the cavity. That picture above shows the door frame sitting outside the cavity, not within it. Expensive marmox block doing very little.

[Big Jimbo]

If I am sinking my doors into the floor. I usually do like the picture. Because of the depth of cills available, I usually find that door frames end up sitting forward of the cavity regardless of size. I also try and improve the head and reveals. Providing everything is nice and tight, I have never had my screed cracking.

[Dave Jones]

2 hours ago, JohnMo said:

Just reading this thread. Mine is similar to the image also. I filled my cavity with PIR.  The area circled and blocks directly below, I used Thermolite blocks and doing the calculations (sideways and downwards) I found there was less of a cold bridge when I compared to Marmox.  I also used Thermolite at the thresholds for the same reason.

 

thermo's will get you a sap fail for mitigating cold bridging as they don't stop it.

 

The stock marmox detail is a little wrong for us as it doesn't show the screed and insulation travelling over the cavity. it looks like this for door reveals.

 

An upstand isnt really needed in the reveals but without the marmox you are directly heating the ground outside with your slab. not a good idea.

 

 

 

[Dave Jones]

2 hours ago, Big Jimbo said:

If I am sinking my doors into the floor. I usually do like the picture. Because of the depth of cills available, I usually find that door frames end up sitting forward of the cavity regardless of size. I also try and improve the head and reveals. Providing everything is nice and tight, I have never had my screed cracking.

 

so your fitting your cills below DPC or your FFL is above dpc ?  definitely cold bridging there as the screed is exposed to an external wall albeit not a lot.

 

marmox solution keeping a consistent DPC and mitigating cold bridging is better solution albeit more expensive.

[Big Jimbo]

@Dave Jones So i know that if i replaced my outside leaf cut block with a marmox block, my thermal losses would be better. It's just so bloody expensive. 

Apols re your first pic. It didn't look you had anything in the cavity. Lets face it what normally happens is that the perimeter insulation  and floor insulation is only taken around the inner block wall, and the void is just filled with bloody concrete. 

Will you also do some work to improve the thermal losses to the door frame sides, and head. If they are not sitting 30mm into the cavity that is a building regs fail.

[JohnMo]

1 hour ago, Dave Jones said:

thermo's will get you a sap fail for mitigating cold bridging as they don't stop it.

Why don't they stop it?

 

Thermolite thermal conductivity is 0.14 and they are 215mm high while Marmox is 0.05W/mK, but 65mm high. So resulting U valve is lower for the Thermolite block - 0.65 compared to 0.77 for the downward direction.

 

I think sideways they are similar, but any insulation in the cavity will stop sideways anyway.

[Dave Jones]

1 hour ago, Big Jimbo said:

@Dave Jones 

Will you also do some work to improve the thermal losses to the door frame sides, and head. If they are not sitting 30mm into the cavity that is a building regs fail.

 

Correct if they were windows!

 

The reveals do not need anything more than the normal insulated closers to pass regs as the doors are a decent U value already. We will be dabbing 25mm insulated plasterboard on every reveal anyway because why not.

[Dave Jones]

1 hour ago, JohnMo said:

Why don't they stop it?

 

Thermolite thermal conductivity is 0.14 and they are 215mm high while Marmox is 0.05W/mK, but 65mm high. So resulting U valve is lower for the Thermolite block - 0.65 compared to 0.77 for the downward direction.

 

I think sideways they are similar, but any insulation in the cavity will stop sideways anyway.

 

no, its there to stop the ground pulling heat out through it as well as the conc below. thermos are nowhere near that good especially when they get soaked which will be nearly all the time when underground. Like already said a SAP fail so not an option.

 

Not worth skimping/bodging really, other areas can easily save the cost of marmox.

[JohnMo]

1 minute ago, Dave Jones said:

 

no, its there to stop the ground pulling heat out through it as well as the conc below. thermos are nowhere near that good especially when they get soaked which will be nearly all the time when underground. Like already said a SAP fail so not an option.

 

Not worth skimping/bodging really, other areas can easily save the cost of marmox.

Why would they be soaked, they are inside. If they are wet you have bigger issues.

 

Why a SAP fail?