Cavity insulation and internal insulation

Tim Robbins

HI,

I have 100mm Mannox cavity insulation. Thermal conductivity 0.022 (see: https://www.uvalue.ie/products/quinn-foil-faced-full-fill-cavity-wall-pir-boards).

I am wondering how far this is off latest building reg?

And on the internal leaf if I have 2*2 battons and then put insulated plasterboard rather than plasterboard. IT would be a narrow enough insulated plasterboard e.g. 29mm from u value here https://www.uvalue.ie/images/uploads/product/UValue_Warmline_PIR.pdf IT is 9.5 plasterboard, 20mm foam same thermal conductivity is 0.022.

is this a good solution?

https://www.corebuild.ie/mannok-polyiso-8-x-4-100mm-sheet?gclid=Cj0KCQjw3JanBhCPARIsAJpXTx7HVmXmQO4mgB6aEwI5bw88v_fDeM8NNOE2VELqjEP7CFP5utCmaUgaAsWoEALw_wcB

Calahonda52

U value calculation methods set out in TGD part L

sydthebeat

the first thing we need to know is, is this a new build dwelling, or an extension or renovation?

mickdw

If new build, you need a DEAP calculation. What you suggest likely meets minimum wall spec but DEAP will consider everything as a whole including heating, ventilation, build fabric etc and confirm compliance or not.

Tim Robbins

https://www.boards.ie/discussion/comment/121132768#Comment_121132768

I ended up with using 25mm foam board and 12.5mm plasterboard in a 37.5mm warm board.

I calculated the R value as:

97mm cavity insulation with 0.022 thermal conductivity is R value = 4.4

25mm warm board insulation with 0.022 thermal conductivity is R value = 1.17

U value = 1 / (4.4 + 1.17) = 0.179

Not including plasterboard, sand cement, two bricks, and 25mm air gap. But it would be lower e.g. 0.17 if we did.

sydthebeat

Well you obviously need to include everything to calculate the wall U value.

0.18 would be very borderline for compliance

Tim Robbins

https://www.boards.ie/discussion/comment/121133072#Comment_121133072

Absolutely. But once I was under 0.18 I was happy enough.

The other walls in the house are 90mm insulation internal BER is B1, and the house is gas heated (with solar help for hot water). I feel most important thing is you are not making house worse.

Tim Robbins

https://www.boards.ie/discussion/comment/121132741#Comment_121132741

Extension. Adding 50 square metres to a house that is 112 metres. Already BER B1.

It was too much hassle to go with air pump as felt the rest of the house was not high enough spec.

Goal was to keep it BER B1 at a minimum and anything else was a bonus.

I'll just include other information in case anyone in similar situation.

Flat roof insulation is 150mm rigid, warm roof. U value is 0.147.

Windows Munster Joinery, triple glased munster joinery 1.1 u value. Note: deliberately avoided dermot bannon massive windows as feel there is no point doing this as this kills your over all room u-value.