U values

[Mike_scotland]

Hi Group,

 

Me and my partner are currently working through our building warrant and SAP calcs stuff,

 

What would be a good u value or thickness of insulation for the ground floor with UFH? Would 150mm be a enough? 

 

 

[Mr Punter]

Yes, 150mm is good.  PIR is a bit better than XPS for the thickness, but costs more.

[Mike_scotland]

So far our builder has suggested i think 

 

The external walls will be frametherm 32 150mm thick, horizontal FF ceiling 2layers totalling 400mm wool and sloping parts of ceiling will have PIR board (150mm) with 2^nd board (20mm)over the face.

 

Its all about the sap guy but i want a good insulated house, just lookong for past experiences 

 

Mike 

[A_L]

22 minutes ago, Mike_scotland said:

The external walls will be frametherm 32 150mm thick

This is relatively poor at probably not lower than U=0.25

 

25 minutes ago, Mike_scotland said:

horizontal FF ceiling 2layers totalling 400mm wool

If this DIY shed loftwool, thermal conductivity 0.044W/m² .K then the U-value will be around 0.13

 

31 minutes ago, Mike_scotland said:

sloping parts of ceiling will have PIR board (150mm) with 2^nd board (20mm)over the face.

U--value around 0.20-0.22

 

With the floor area and external perimeter I can calculate a U-value

[Mike_scotland]

Ermmm i think its 19m length by 7.5m wide.

 

Floor area is about 230m2 or therby.

 

The architect reckons a B rated house but maybe not of really poor insulation.

[A_L]

If the ground floor is a 19 x 7.5 metre rectangle, 150mm of PIR or anything else of equivalent thermal resistance will give a Passivhaus level 0.11 U-value.

 

Personally I think you need another 100mm on the walls and 75mm on the sloping ceiling (same material) to get U values down to 0.12/0.14

Edited March 9, 2021 by A_L
minor typo

[Mike_scotland]

Yeah it is a rectangle, roughly  19m by 7.5m its 1.5 storey.

 

I will wait and see the SAP calcs and then ask what the price would be to upgrade the insulation.

 

So what is a good thickness level for roof, sloping ceiling, walls and floor? Or u value.

 

Thanks,

 

MIKE