Retrofit wall insulation - weatherboard home

Hello,

I live in Melbourne. I am currently stripping out plaster in a granny flat as ceiling plaster was damaged due to water damage from an old roof that was replaced. It is a new skillion roof with insulated roofers blanket and r2.5 earthwool underneath it. I would ideally like to install wall insulation and do my best to keep in warmth in winter and if possible keep heat out in summer.Hence I have begun stripping out wall plaster also whilst this is not damaged.

In reading about construction methods I understand best case scenario I should have sarking/reflective foil between the studs and weatherboards (that I can not do), an air gap then bulk insulation then gyprok.

I have found:

1. standard 900mm studs in the walls
2. No sarking or reflective foil as it is an older building
3. I have some gaps between weatherboards, some knots that have shrunk and some drill holes for wall vents that I do not want to keep.

I wanted to install something like Earthwool from Bunnings but my concerns are:

1. Given the gaps in the weatherboard and no sarking or reflective foil that water ingress will be an issue
2. That moisture build up / condensation will be an issue without sarking reflective foil and could cause rot
3. Placing an air gap in the walls for effectiveness of the insulation
4. Installing a vapour barrier between insulation and the plaster?

So what I am asking is what is the best way to proceed. Some thoughts I have are:

1. Using a external cladding filler to fill the gaps in the weatherboard
2. Whether I should install sarking / reflective foil by abutting to the weatherboards and stapling to the studs? Should I try to do this with an air gap / spacers? Would the shiny side face out or in? What could i use as spacers?
3. Then install insulation?
4. Then install vapour barrier on internal side of the studs? Would this be reflecitve foil shiny side facing the eatherboards or some other product?

Any help for this complete novice would be much appreciated.

Wow that's a tricky one, not sure if anyone does it here in Oz, but a spray foam insulation like they use in the states would be ideal.

Failing that there is a polystyrene foam about 10mm thick with a foil face, maybe that could be cut between studs and placed hard against the cladding, and then the installation batt against that??

Might be worth seeking advice from a few insulation companies to pick their brains further?

Sorry not much help I know

Kind Regards

James Mason - Our Build.

www.renovationjunkies.com.au

www.ourbuildhandyman.com.au

Thanks James for your feedback.

I am looking into retrofitting sisilation as a u-shape between the studs. Then putting in some insulation. I think the batts are a little better than the spray in solutions. Also it seems better since I am going to the trouble of ripping out internal walls

Thanks