Floor insulation for UFH for new extension- Urgent advice required please.

[ab12]

In the middle of having a kitchen extension. Brickie has nearly built up to damp. I have opted for the following floor make:

 

150mm hardcore

50mm sand blinding

2000 g  (500 mu) DPM

100mm concrete slab

1200g (300 mu) DPM

100mm   OR 130mm  OR  150mm insulation

DPM unsure about the g or mu value  may choose 1200g or even thinner?

75mm non liquid screed over UFH to reach finish floor level

 

I'm confused about the insulation part. Need to reach U value 0.18. 

 

walls, all exposed to outside with Cavity of 150mm between outer and inner walls.

 

Dimensions of internal  leaf walls are 5.6m by 3.49m , Area to be insulated: 19.54 m2. Exposed perimeter is 14.69m. PA ratio is 0.75.....can get

U value 0.17 with 100m Cellotex 

U of 0.14 with 130mm Celltotex

U 0f 0.12 with 15omm Cellotex

 

I have already purchased 6 sheets 2400mm by 1200mm Cellotex. 

Is it worth going the extra mile and have extra insulation so either 130mm or 150mm laid in 2 layers,

so 100mm sheets laid first followed by 30/50mm sheets 

OR 30/50mm sheets first followed by 100 mm sheets.

 

Please let me know your thoughts. Workers coming and laying hardcore and sand, I may need to dig a little bit more of the floor  if go for 150 mm insulation OR I can sacrifice on sand blinding layer by choosing 30mm sand blinding instead of 50mm sand blinding without needing to dig any more floor.

 

 

 

 

[JohnMo]

Double post