What alternatives and why?

[Makeitstop]

Hi all,

 

Just looking to line things up for a kitchen extension, and want to get some views on insulation choices. So far, the buildups look like those set out below, but I'm open to adjusting to whatever, should smarter choices be possible and the clear way to go.

 

Structure is simple brick / block construction with 340mm cavity walls. Floor is block and beam, off rc beam sat on piling. Roof is warm flat. I guess there is scope to adjust from what I've got here, so please feel free to share any thoughts on what and why.

 

Wall buildup….

 

U-value 0.21W/m2k

 

12.5mm PB

100mm Celcon high strength Block

90mm Kingspan kooltherm K108

50mm cavity

Facing brick to match existing.

---------------------------------------------------------

Floor buildup….

 

U-value 0.18W/m2k

 

65mm screed

PE sheet separating layer

100mm Kingspan kooltherm K103 board

Visqueen gas membrane / similar

Beam and block

------------------------------------------------------------

Roof buildup…..

 

U-value 0.15 W/m2k

 

GRP

18mm ext ply

Min 180mm kingspan thermaroof

Tyvek VPL

18mm ext ply / firring with fall to 1:40

47 X 220 Rafters @ Max 400mm centres

12mm pb.

[crispy_wafer]

I think the first thing on there that leaps out, would be the Kingspan cavity wall insulation,

 

Being honest with you, that unless your laying the blocks and fitting it yourself dont bother you'll be disappointed with the builders/labourers attempt at it.  It's expensive stuff and to see it installed incorrectly will make your head wobble.  It's an extension so should be fairly simple to keep on top of the workmanship, but still...  Full fill Beads, or batts at 140mm shouldnt be too bad.  What's the rest of building like?

 

If you can, get a bit more insulation in the floor.  How are you intending to heat the space?

[Makeitstop]

I did wonder about the walls and thought that an alternative to the pir may be a smarter choice, and this is why I posted this up. My only concern is... what is there that competes in terms of efficiency, and, is there any viable option.

 

Same applies to the floor, as I have the option of adjusting depth there, as nothing is down yet, apart from piling, so could in theory get more insulation in by ensuring the rc beam is set lower, or below damp blockwork allows for it.

 

The existing house is simple brick / block construction and is approx 6/7 years old. The heating is gas c/h, so the system will be extended to serve the additional area.

 

 

Edited November 23, 2021 by Makeitstop

[JohnMo]

I would look to increase the floor insulation to 200mm of PIR.  Use  2 layers of say 100mm each with staggered joints at the different layers.  This should get a U value around 0.1.  Almost half your floor heat loss, for very little outlay

 

Same with the roof increase to 200mm