GF insulation & screed: 75mm + 45mm screed vs 95mm + 25mm liquid screed

[bmj1]

Hi all,

 

We've got the following two options, please can you advise ?

 

Option 1

1. Kingspan K103 at 75mm depth
2. 45mm to 65mm of sand/cement screed with hardener

 

Option 2

1. Kingspan K103 at 75mm depth
2. 2nd layer of floor insulation at 20mm depth
3. 25mm to 45mm of Liquid screed

 

Thought process is:

1. The K103 is already purchased and on-site, so no option to go with a different product
2. This would be a significant improvement in performance: u value goes from 0.158 -> 0.138
3. A liquid screed would conduct more heat into the building, rather than below the house, so would be more efficient to run

 

Key notes:

1) This is on Ground Floor. Construction is beam and block.

2) We have UFH.

 

Questions:

1) Does this make sense ?

2) Is there a disadvantage to a liquid screed ?

3) Are there any issues with laying a 20mm depth PIR on top of a 75mm depth PIR ?