boarding out new extension

[scfc151]

not sure which part of the forum this belongs....
im having an extension built on an existing garage. it has 80mm cavity so i think building regs will want some insulation on the inside. it will be block and render (except the boundry wall) which will be brick.
i am going to try and do as much as i can on the inside myself to save on labour costs
so my options are:

• dot and dab insulated plasterbord (foil backed so vapour control is sorted
• timber batten and insulsted inbetween with a vapour barrier membrane between the timber and boards.

if the walls are straight i was thinkin this would be straight forward
im trying to find the most cost effective method.
do i need an air gap behind pir board? my thoughts were if i used 2" battens with either 25mm pir and 25mm air gap or 50mm rockwool, as far as i can see this gives roughly the same r value. however rockwool is a lot cheaper. am i on the right track?

 

[bobasd]

do you mean your convertin a garage into a living space?

 

[scfc151]

no sorry im going straight up extending over the garage. it already has 80mm cavity wall

 

[bobasd]

your extending the house over the garage, typicly an en-suite bedroom?
- all the work will be more or less at first floor level an up?

 

[scfc151]

yes thats right. ensuite bedroom and walk in wardrobe

 

[^woody^]

Is someone drawing plans or are you making it up as you go?

 

[scfc151]

no its all being done properly. drawings, buildings regs. im getting the builders to complete the shell and im project managing the inside. so im trying to research the most cost effective way of boarding the inside with additional insulation

 

[^woody^]

no its all being done properly. drawings, buildings regs. im getting the builders to complete the shell and im project managing the inside. so im trying to research the most cost effective way of boarding the inside with additional insulation

But that's the designers job. Surely he knows the most cost-effective way better than some ramdom people pin the internet.... otherwise why would you be paying him?

The point is, design should be comprehensive and not a case of "we do this for the garage, and this for the bedroom, and this for the ...."

 

[scfc151]

dont worry about it. my architect has designed the building so i can have it built. im project managing the inside. knowing that i need slightly more insulation inside im just trying to work out the most cost effective method to do this

 

[noseall]

• dot and dab insulated plasterbord (foil backed so vapour control is sorted

You can't D&D foil backed boards. Non-foil boards are dab-able but require supplementary mechanical fixings due to the risk of popping.

You'll need summat like 62.5mm (overall) thick insulated plaster boards and a couple of boxes of fixings.