House Insulation Values

[richo106]

Hi All

 

We are in the planning stages of our renovation and I am writing the spec for our builder/BC

 

The house will be heated using an ASHP so wanted to achieve a good level of insulation, what are peoples opinions on the current insulation level I have opted for? Are the U-values low enough for a low temperature ASHP to be suitable? downstairs is UFH and upstairs planning to use heat pump convectors

 

We don't want external wall insulation so have opted for IWI

 

Just wanted some other opinions before I sent it 

 

So far these are my insulation levels and U values for the different areas of our house:

 

Pitched Roof (General Loft): U-Value = 0.13

·         150mm Isover Spacesaver between joists

·         200mm Isover Spacesaver over joists

 

Pitched Roof (Bedroom Vaulted Ceiling): U-Value = 0.14

·         120mm Celotex XR4000 between rafters (400 centres)

·         50mm PIR Backed Plasterboard (PL4050) screwed to rafters

 

Downstairs Walls (Existing Bungalow): U-Value = 0.20

·         Brickwork 103mm

·         Cavity 80mm with 80mm blown insulation

·         Brickwork 103mm

·         50mm PIR Backed Plasterboard (PL4050) dot and dabbed

 

New Upstairs Walls (above existing bungalow): U-Value = 0.18

·         Brickwork 103mm

·         Cavity 80mm with 75mm Isover CWS32

·         Blockwork 100mm

·         50mm PIR Backed Plasterboard (PL4050) dot and dabbed

 

New Double Extension: U-Value = 0.18

·         Brickwork 103mm

·         Cavity 100mm with 90mm Celotex Thermaclass cavity wall

·         Blockwork 100mm

·         12.5mm Wallboard dot and dabbed

 

Ground Floor Slab

·         150mm MOT

·         100mm Concrete Slab

·         200mm PIR Insulation – Celotex XR4200

·         75mm Screed

 

All help and advice greatly appreciated 

 

 

[JohnMo]

Ground slab should be giving you a good u value circa 0.1, get that put down in 2 layers with staggered joints, with all gaps foamed, top layer tapped.  It will need a polythene sheet over the PIR and under the UFH pipes.  The UFH pipes can be stapled to PIR through the polythene.

 

Wall I try to improve u values if you can.  Your new walls could you use thermolite blocks for one of the skins?  Also the cavity with Celotex Thermaclass may be better with blown insulation or in Rockwool or similar as it's easier to construct (brickies likely to make to a mess of it).

 

Not a huge fan of dot and dab.  I did battons, and dry lined, but if you are plastering on top of plasterboard, why not just plaster the walls, you will get less air leakage overall.

[richo106]

21 minutes ago, JohnMo said:

Ground slab should be giving you a good u value circa 0.1, get that put down in 2 layers with staggered joints, with all gaps foamed, top layer tapped.  It will need a polythene sheet over the PIR and under the UFH pipes.  The UFH pipes can be stapled to PIR through the polythene.

OK I am awaiting info regarding the U-Value on that so I will definitely mention that

21 minutes ago, JohnMo said:

 

Wall I try to improve u values if you can.  Your new walls could you use thermolite blocks for one of the skins?  Also the cavity with Celotex Thermaclass may be better with blown insulation or in Rockwool or similar as it's easier to construct (brickies likely to make to a mess of it).

Yes that is with thermolite blocks, I will mention to the builder regarding Thermaclass...I spoke to saint-gobain technical advice so they specified their products. I will look into rockwool or similar

21 minutes ago, JohnMo said:

Not a huge fan of dot and dab.  I did battons, and dry lined, but if you are plastering on top of plasterboard, why not just plaster the walls, you will get less air leakage overall.

Would you batten all the walls including where I would use 50mmPIR plasterboard?