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Should we add a vapor barrier, sarking and insulation to a weatherboard house?

Am doing some Reno's of an old weatherboard house and have discovered no sarking/vapor barrier/insulation anywhere.

We have mould issues in the bathroom and on the ceiling of most rooms about a foot from the perimeter wall. Our bathroom fan vents into the roof cavity, and there is no rangehood/vent in the kitchen. I do a lot of slow cooking, particularly in winter, with pots on the stove boiling for hours, leading to some moisture on the walls and windows.

My plan is to totally redo all the drywall, tiling, and waterproofing in the bathroom, install a bathroom fan and rangehood that vents to outside, and install a whirlybird on our roof.

Not sure if I should also look at wall insulation/vapor barriers/whatever. Seems to be a lot of discussion about correct insulation of air/water barriers (semi permeable vs non permeable, inside wall ve outside wall)

We live in climate zone 6 (south coast NSW) and run the Air conditioner all day in summer, and most days (reverse cycle) in winter.

We are about to renovate our kitchen and bathroom (both have an external wall)

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Comments

MitchellMc

Welcome to the Bunnings Workshop community @diyaaron. It's wonderful to have you join us, and many thanks for your question about insulating your home.

Adding sarking, a vapour barrier, and insulation to your weatherboard house would be an excellent idea, especially considering the mould and moisture issues you’re facing.

Sarking, such as Ametalin 1500mm x 30m SilverSark HD Reflective Roof and Wall Insulation , can create a water-resistant barrier behind your weatherboards while reflecting heat and providing a level of thermal insulation. This is especially valuable in your climate, where air conditioning is used year-round, as it helps reduce both cooling and heating costs.

A vapour barrier, like Ametalin 1370mm x 30m VapourTech Brane VHP Vapour Permeable Wall Insulation, can help prevent condensation and moisture from entering your walls. In climates with mixed hot and cold conditions, a semi-permeable barrier is ideal, allowing some vapour to escape while preventing bulk moisture buildup, thereby reducing the risk of mould.

Insulation is also important for controlling indoor temperatures and preventing condensation caused by temperature differences between indoor and outdoor spaces. Products such as Earthwool R2.0 90 x 580 x 1160mm 21.5m² Insulation Wall Batts are a good choice for thermal comfort and energy efficiency.

In addition to these measures, ensuring proper ventilation in your bathroom and kitchen is vital. Installing vents that expel moisture outside, combined with a whirlybird on the roof to ventilate the roof cavity, will help reduce moisture build-up and further prevent mould issues. With these renovations, including the planned fan and rangehood installation, you’ll not only improve airflow but also greatly enhance your home’s overall comfort and energy efficiency.

Please let me know if you have any further questions.

Mitchell

tomgg

https://www.workshop.bunnings.com.au/discussion/comment/42599#Comment_42599

Are all three recommended, and in the order described E.g. Starting from the external cladding, then the sarking, then the vapour permeable barrier, and then the batts in between the joists?

Tom.

EricL

https://www.workshop.bunnings.com.au/discussion/comment/89735#Comment_89735

Hello @tomgg

Welcome to the Bunnings Workshop community. It's sensational to have you join us.

You can use Ametalin SilverSark HD, Ametalin VapourTech Brane VHP, and Earthwool R2.0 Wall Batts in a wall system, but not in the order you listed. Each product has a different purpose, and getting the order right is important for keeping moisture out, staying warm, and following the building code (NCC 2022).

Starting from the outside, the wall should begin with the external cladding, such as brick, timber, or metal sheets which protects the building from weather and damage. Just behind that, you should install the Ametalin VapourTech Brane VHP. This is a special type of wrap that stops rain from getting in but still lets water vapour inside the wall escape. It helps the wall "breathe" and stops mould or damp from building up. It must go on the outside of the frame, directly behind the cladding.

Inside the wall frame, you can place the Earthwool R2.0 batts between the timber studs. These are thick insulation batts that help keep heat in and reduce noise. They work well with the VapourTech wrap because they also allow moisture vapour to pass through if needed. After that, the wall is finished off with internal wall sheeting like plasterboard.

The Ametalin SilverSark HD is a shiny foil wrap that reflects heat and is mostly used in roofs or behind brick walls. It does not let moisture escape, so it can trap water inside the wall if used the wrong way. It’s not recommended to use SilverSark HD in the same wall as VapourTech Brane VHP unless it’s a special brick veneer setup, where SilverSark sits between the bricks and the timber frame, but not alongside a vapour-permeable wrap. To be safe, always check the installation guides, NCC rules, or ask a professional before starting your project.

If you need further assistance, please let us now.

Eric