Help me interpret our insulation requirements

[Arron]

Hi. We are building a house and are required to insulate the walls as follows, quoting from our Basix:
R3 (3.4 including construction)

My Interpretation of this statement is that counting all the elements of construction from the very inside of the wall to the exterior the total R value must be R3.4.

We have NRG Greenboard on much of the walls which - looking at the spec sheet and considering our method of construction - gives us the following.

External air firm R0.03
Render system. R0.02
Greenboard 100mm. R2.60
Sisalation wrap. R0.48
Cavity and frame. R0.17
10mm plasterboard. R0.06
Internal air film. R0.12

Giving total value of R3.48

At first sight, this seems to mean we have hit the required R value. Is this correct ?

Second question. Insulation is relatively cheap, and we have very large walls facing west with no eaves. Is there any value in upping the R value by, perhaps, putting some R1.5 or R2.0 batts into these walls. Will it make the walls perform better and will we be more comfortable? Or is there some reason it may have a negative effect or no effect at all?

Cheers
Arron

[Beardy]

Regardless of your target R rating I would be putting batts in your frame as it is the closest element to your interior and good value for money
You may even consider acoustic batts if you have a potential noise issue, I also like to put them in internal common walls between bedrooms or backing onto a washing machine etc

[q9]

Second question. Insulation is relatively cheap, and we have very large walls facing west with no eaves. Is there any value in upping the R value by, perhaps, putting some R1.5 or R2.0 batts into these walls. Will it make the walls perform better and will we be more comfortable?

Dear Dog, yes!

Western facing walls soak heat from the sun and radiate it into your living space. Do it.

[rwbuild]

Do it!!
Make sure you use the appropriate breathable sarking or you could end up with mildew problems

[Arron]

Thanks for the replies guys. I expected that more is better but was mainly just checking to make sure there were no issues that might arise that I hadn’t considered, especially wrt moisture issues.

How about my first question ? Any answers to whether I have hit the appropriate R level (leaving aside the fact that as I have the opportunity to exceed it then I definitely should)?

Cheers
Arron

[yvan]

Regardless of your target R rating I would be putting batts in your frame as it is the closest element to your interior and good value for money
You may even consider acoustic batts if you have a potential noise issue, I also like to put them in internal common walls between bedrooms or backing onto a washing machine etc

Yes to acoustic batts. We didn't have any installed in the walls of our bath and shower rooms. It is amazing how much the sound an unfurling roll of loo paper gets amplified in the cavity of the walls... DAMHIK !!!

[62woollybugger]

When I was doing energy efficient building design, as part of a TAFE course I was doing, we were told that to keep heat in, in a cold climate, use bulk insulation (batts) & to keep heat out in hot climates use reflective insulation. Batts insulate by absorbing the heat, which will radiate into the house at night. I used something similar to these Concertina Foil Batts | Going Solar in the west facing walls of our last house & it made a huge difference. I stapled them to the wall studs when I renovated the kitchen & dinning room.

[yvan]

Are these Concertina Foil batts used together with or without insulation batts?

Cheers Yvan

[62woollybugger]

Are these Concertina Foil batts used together with or without insulation batts?

Cheers Yvan

Without, they need an air gap either side to work. If you go down the page in the link I posted to the section on using them in walls, it explains it all.

[Salv]

Do it!!
Make sure you use the appropriate breathable sarking or you could end up with mildew problems

+1

As dwellings have come to incorporate higher levels of insulation and become more airtight, the problem of moisture accumulation from condensation has increasingly raised its ugly head. One-way breathable sarking (vapour permeable construction fabric) is specifically designed to mitigate this problem.

BTW, whilst the law of diminishing returns applies (say, R5.48 versus R3.48), insulation is relatively cheap and effective for the life of the building. Make sure bulk insulation is installed with its uncompressed width retained so far as possible and with a minimum of gaps around building elements and services such as plumbing, electrical wiring etc. Gaps in insulation in particular will lead to a disproportionate reduction in overall performance.

Cheers