Marmox or Thermalite

[matthyde83]

I'm just finalising my foundation details and I hope someone can help me make a decision...

 

Do I emlpoy Marmox Thermoblocks on the inner leaf at the insulation level or simply use thermalite or similar below.  Can anyone help with the potential performance of the two different methods?  I expect it to be significantly cheaper to use thermalite blocks.  Traditional slab build up of 200mm with 200mm insulation above.  Also I've drawn the Marmox block at 215 tall below but it's 65mm so ignore that.

 

[Mr Punter]

The Marmox is far better at insulating and eliminating the cold bridge.

[matthyde83]

35 minutes ago, Mr Punter said:

The Marmox is far better at insulating and eliminating the cold bridge.

“far” better sounds like I’m going to make the more expensive choice then…

[JohnMo]

The way I looked at this. The thermal bridge you are mitigating is downwards to the ground.

 

Comparing Marmox and Thermalite "R values", Marmox is approx 3x better.  But thermolite blocks are more than 3x as thick (215 compared to 65).  So the resulting u value is better for the Thermolite block, certainly no worse.

 

Thermolite easier to install and get hold of, cheaper to purchase, win, win.

 

[matthyde83]

2 hours ago, JohnMo said:

The way I looked at this. The thermal bridge you are mitigating is downwards to the ground.

 

Comparing Marmox and Thermalite "R values", Marmox is approx 3x better.  But thermolite blocks are more than 3x as thick (215 compared to 65).  So the resulting u value is better for the Thermolite block, certainly no worse.

 

Thermolite easier to install and get hold of, cheaper to purchase, win, win.

 

 

That seems to make sense... 65mm marmox 0.05, 215mm Aircrete (10N) 0.19.  So Marmox is slightly better at 3.3x BUT if it's courses below and then courses in insulation layer say 3 courses the aircrete will be much better.

[SuperPav]

I mean that logic does sort of make sense... except you're not substituting 215mm of thermalite for 65mm of marmox, you're substituting 65mm of the thermalite course for 65mm of marmox (which is much better) and then still getting the benefit of the remaining 150mm of thermalite below it...

 

Whether it's worth it or not really depends on the rest of the house, and how much perimeter you have to cover with it. Marmox thermoblock is very satisfying to lay though! (or maybe that's just a placebo side effect of its expense...)

[Mr Punter]

2 hours ago, JohnMo said:

The way I looked at this. The thermal bridge you are mitigating is downwards to the ground.

 

The thermal break only works when it is in line with the floor insulation.  Anything below will be subject to heat loss sideways into the slab or sub base.  @matthyde83 has a 200mm insulation layer so will be OK but would be better with Marmox.

[matthyde83]

2 hours ago, Mr Punter said:

 

The thermal break only works when it is in line with the floor insulation.  Anything below will be subject to heat loss sideways into the slab or sub base.  @matthyde83 has a 200mm insulation layer so will be OK but would be better with Marmox.

Understood.  So you would recommend thermalite up to insulation layer then a layer of Marmox rather than another thermalite in line. 

[JohnMo]

Also missing from your drawing and worth noting if you are doing any calculations, is there will be an insulation upstand from the insulation below the screed, to screed top, against the wall, I used 70mm PIR.  But is more normal to use 25mm