you only do it once but what? - internal insulation

[rob dayglo]

Hi All, so I am internally fitting out my timberframe house. To meet the SAP requirements the frame has 140mm mineral wool insulation, then the vapour barrier then counterbattens 24mm deep, creating an air gap then standard 12.5mm plasterboard. 

 

However I now see that there are alot of self builders filling the air gap between the vapour barrier and plasterboard. So my first thought is to fill it with 12mm PIR board as I have a good price on 25mm roofing batten and the building budget is getting very tight.

 

So the questions are.

Is it worth doing?

What would be the most cost effective material to use? (I considered SF6 Superfoil but its £5.63m2 compared to 12mm PIR @ £3.70m2

 

All advice gladly received

 

 

 

 

 

[Thedreamer]

9 minutes ago, rob dayglo said:

Hi All, so I am internally fitting out my timberframe house. To meet the SAP requirements the frame has 140mm mineral wool insulation, then the vapour barrier then counterbattens 24mm deep, creating an air gap then standard 12.5mm plasterboard. 

 

However I now see that there are alot of self builders filling the air gap between the vapour barrier and plasterboard. So my first thought is to fill it with 12mm PIR board as I have a good price on 25mm roofing batten and the building budget is getting very tight.

 

So the questions are.

Is it worth doing?

What would be the most cost effective material to use? (I considered SF6 Superfoil but its £5.63m2 compared to 12mm PIR @ £3.70m2

 

All advice gladly received

 

 

 

 

 

 

I used 25mm PIR after 140 mineral wool. I used frametherm 35 and 32 elsewhere, if I could go back I probably would have used frametherm 32 through out.

 

Joints on PIR taped with an air tightness barrier for critical areas. 

 

Then battened for plasterboard. 

 

Probably could have pull some additional insulation in between battens. Wasn't going for a really high spec just a little bit above building control.

 

I would try and make up your budget elsewhere and increase the insulation spec.

 

 

[Thorfun]

I've not started yet but my plan is to put 140mm Frametherm 32 between the external wall studs, then cover that with 50mm or 80mm (undecided yet) PIR, then put airtight membrane, battens for the service void, then plasterboard.

 

seems a pretty standard wall makeup and is used by MBC. 

 

it'll cost more but as @Thedreamer alluded to, I think it's best to get the fabric right and try and save money elsewhere.

 

I'd love to get rid of the PIR to reduce the requirement of oil based products but I feel some insulation is required to reduce the cold bridging from the stud work and 140mm of Frametherm 32 doesn't give the U-values I'm after.

[ProDave]

I am not sure 140mm of mineral wool in the frame, on it's own will even meet building regs now?  that was the standard spec nearly 20 years ago.  I would definitely want to over sheet the frame with something to improve on that.

 

What's going on the outside of the frame?  Brick or block or something else?

[redtop]

e have 140mm rockwool between the studs of the external frame and then 140mm of woodfibre insulation on the outside of that, then VPL, battons and cladding.  Moving inside from the rockwool we have vapour proof OSB, 25mm battons for service void and then plasterboard.  I wouldn't want any insulation in the service void as I would be worried about condensation issues, plus I would worry about removing the point of the service void in the first place (easy for services installation and later changing). We may use insulated plasterboard

[A_L]

Hello, if your current build-up meets building regs then you have a decision to make. Reducing the width of the service cavity reduces its contribution to the overall thermal resistance of the whole but this would be greatly outweighed by adding 12mm of PIR. Given the details  that you have provided there could be a reduction in U-value of around 0.05W/m².K which equates to an energy saving of around 2.5kWh/m².yr. (Central England/Full SAP)

[rob dayglo]

20 hours ago, rob dayglo said:

Hi All, so I am internally fitting out my timberframe house. To meet the SAP requirements the frame has 140mm mineral wool insulation, then the vapour barrier then counterbattens 24mm deep, creating an air gap then standard 12.5mm plasterboard. 

 

However I now see that there are alot of self builders filling the air gap between the vapour barrier and plasterboard. So my first thought is to fill it with 12mm PIR board as I have a good price on 25mm roofing batten and the building budget is getting very tight.

 

So the questions are.

Is it worth doing?

What would be the most cost effective material to use? (I considered SF6 Superfoil but its £5.63m2 compared to 12mm PIR @ £3.70m2

 

All advice gladly received

 

 

20 hours ago, rob dayglo said:

PS outer skin is block and momocouche render