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

[diyaaron]

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) 

[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