Thermal bridge on ground floor under load bearing partition

[davejura]

Looking for ideas on how to prevent this please. I'm looking at Marmox Thermoblocks, but they seem to be hard to come by and expensive. Any cheaper easier to come by solutions? Our floor is suspended  beam and block if that makes a difference.

[tonyshouse]

Between the beam and wall or between beam and block and sub structure? 

[Miek]

Foamglass perinsul. Also expensive 😞

 

 

 

[davejura]

It's a load bearing partition running the length of the house. Directly above a spine wall, on top of the beam and block.

 

[PeterW]

So usually you leave the blocks out and build off the spine wall below and infil either side with cut blocks if needed. Never seen a structural wall with a beam and block sandwich as there will be voids under the blocks. 

[matthyde83]

I’ve used Marmox and impressed with them so far.  Very easy to lay and nice and square to start the walls off.  I’ve used them all round and seemed to get a decent price.  I’ll dig out where from. 

[davejura]

On 06/05/2022 at 22:46, PeterW said:

So usually you leave the blocks out and build off the spine wall below and infil either side with cut blocks if needed. Never seen a structural wall with a beam and block sandwich as there will be voids under the blocks. 

That's interesting that the engineers didn't specify this as they have been OTT with almost everything else! It's timber frame, so a timber load bearing wall. Maybe the calculations were OK for it? I guess the beams will be spreading the load anyway.

[JohnMo]

I used thermolite blocks, topped with engineered concrete blocks 65mm thick.  This gave a good fixing point for the walls above.

 

Floor build up from top is 100mm concrete screed, 200mm PIR insulation.  So the thermolite block starts above the insulation.  Gives an effective downward u value of around 0.7 at the stub wall.

[Kelvin]

On 07/05/2022 at 08:06, matthyde83 said:

I’ve used Marmox and impressed with them so far.  Very easy to lay and nice and square to start the walls off.  I’ve used them all round and seemed to get a decent price.  I’ll dig out where from. 

Hi. Could you share where you got the Marmox blocks from? 

[matthyde83]

On 15/10/2022 at 12:04, Kelvin said:

Hi. Could you share where you got the Marmox blocks from? 

 

Sorry for delay.  We got them from Ecomerchant 

[Canski]

As a Bricky I haven’t seen them until this year then whallop they are on every site. Easy to lay but when you come to cut them at corners or bond them you need to be selective with your cutting. There are little pillars in them that a hand saw will not get through. I’ve not tried a stihl saw yet but we get round it with a 3/4 and a 1/2 if you know what I mean. On my place I will use a thermalite block to the perimeter and notch them around the beam and block ends and run them along any parallel beams.
 

PS I haven’t bought any yet so no idea of cost.  

[matthyde83]

They aren't cheap but I think have been great.  Yet to see how much difference they make thermally but the must do!  Great at door thresholds too.  Another benefit we've seen is it stops the blocks soaking up water from the floors.  They'd have been saturated with the amount of water we've had in there until the roof was on.  

[JohnMo]

My original plan was marmox, but when I did quite a few calculations comparing to thermolite, I chose thermolite.

[Tom]

We went for thermolite instead of marmox for our build. U-value about twice as much as the marmox iirc, but they are twice as thick, so in the end it all worked out pretty much the same

[Dave Jones]

10 hours ago, Tom said:

We went for thermolite instead of marmox for our build. U-value about twice as much as the marmox iirc, but they are twice as thick, so in the end it all worked out pretty much the same

 

Just for clarity, thermolite blocks are nearly twice as bad as marmox for insulation purposes. For the few that are used on the ground floor its a false economy to skimp.

 

https://www.ecomerchant.co.uk/pub/media/productattachments/files/11_19.pdf

 

https://www.forterra.co.uk/wp-content/uploads/2021/10/Thermalite-brochure-web.pdf

[JohnMo]

28 minutes ago, Dave Jones said:

Just for clarity, thermolite blocks are nearly twice as bad as marmox for insulation purposes

 

Not correct, from the marmox data sheet.

 

0.065m/0.078W/mK = 0.8mK/W convert to U value, 1/0.8=1.25

 

From the other datasheet

0.215/.15 W/mK = 1.43mK/W

convert to U value, 1/1.43=0.7

 

Thermolite is in fact nearly twice as good for reducing the heat loss, even with a worse conductivity.  Because they are 215mm high compared to 65mm. 

 

It's the size that matters!

 

 

[Dave Jones]

13 minutes ago, JohnMo said:

 

Not correct, from the marmox data sheet.

 

0.065m/0.078W/mK = 0.8mK/W convert to U value, 1/0.8=1.25

 

From the other datasheet

0.215/.15 W/mK = 1.43mK/W

convert to U value, 1/1.43=0.7

 

Thermolite is in fact nearly twice as good for reducing the heat loss, even with a worse conductivity.  Because they are 215mm high compared to 65mm. 

 

It's the size that matters!

 

 

need to compare like for like. 

[Russell griffiths]

11 hours ago, Canski said:

As a Bricky I haven’t seen them until this year then whallop they are on every site. Easy to lay but when you come to cut them at corners or bond them you need to be selective with your cutting. There are little pillars in them that a hand saw will not get through. I’ve not tried a stihl saw yet but we get round it with a 3/4 and a 1/2 if you know what I mean. On my place I will use a thermalite block to the perimeter and notch them around the beam and block ends and run them along any parallel beams.
 

PS I haven’t bought any yet so no idea of cost.  

Put one a day in your sandwich box and you won’t need to buy any 🤣

[Nickfromwales]

11 hours ago, Canski said:

As a Bricky I haven’t seen them until this year then whallop they are on every site. Easy to lay but when you come to cut them at corners or bond them you need to be selective with your cutting. There are little pillars in them that a hand saw will not get through. I’ve not tried a stihl saw yet but we get round it with a 3/4 and a 1/2 if you know what I mean. On my place I will use a thermalite block to the perimeter and notch them around the beam and block ends and run them along any parallel beams.
 

PS I haven’t bought any yet so no idea of cost.  

Hope you're going with Beamshield / other for that B&B deck? Cold ventilated sub-floors are the last option if I specify a foundation system for a client!!

[JohnMo]

1 hour ago, Dave Jones said:

need to compare like for like.

No you need to compare as built, with as built.  If I had done what the architect had suggested, the performance would not of been as good as the final solution, which was also easier and way cheaper to install.

[BenP]

Cheapest place I found for Marmox at the time:

 

https://www.tilefixdirect.com/marmox-thermoblock-load-bearing-thermal-insulation-block-100mm-140mm-sizes/

[Tom]

3 hours ago, Dave Jones said:

 

Just for clarity, thermolite blocks are nearly twice as bad as marmox for insulation purposes. 

Ummm, isn't that what I said? But as I, and subsequently others, have said, the thermolite blocks are significantly thicker, so the actual performance of the insulating layer is about as good. For a lot less bunce.

[JohnMo]

3 minutes ago, Tom said:

actual performance of the insulating layer is about as good

Read my post above - thermolite are nearly twice as good as marmox. 

 

Plus if your screed thickness is greater than 65mm thick, there is still a thermal bridge below the marmox block as it doesn't overlap on to the insulation.

[Tom]

Sure, also available in 100mm and 140mm thickness though.

I think we're on the same side of this argument though.. Basically, thermolite for a self-builder, marmox for an architect on an expense account

[Kelvin]

2 minutes ago, Tom said:

Sure, also available in 100mm and 140mm thickness though.

I think we're on the same side of this argument though.. Basically, thermolite for a self-builder, marmox for an architect on an expense account

 

Are they? There's 65mm standard thickness and an extra thick block at 100mm. Widths are 100mm, 140mm, and 215mm