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How to insulate a wall?

Living room wall has been stripped back to repair termite damage, so taking opportunity to insulate the wall. It’s an older weatherboard house, with no insulation wrap. I have read where someone stapled aircell insulation as a vapour/air barrier in the cavities before insulating with batts, can anyone give me advice on this? Thanks in advance.

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MitchellMc

Hi @joputra,

This discussion has led me to research further into moisture and vapour barriers within a home.

Some things I've learned are:

The right building wrap and installation location is dependent on which climate zone you live in. In a tropical climate, the hot outside air carries a large amount of water vapour. This condensates when it meets a surface cooled by conditioned air inside. In colder areas, condensation works in reverse. This time it’s the warm interior air that holds high levels of water vapour. This condensates when it meets a cooler surface close to the outside of the building.

Vapour barriers need to be installed on the warm side of the insulation and can lead to mould and timber decay if installed on the incorrect side. In cold climates, they are to be installed on the inside of the insulation (next to the internal wall lining). In warm climates, on the outside of the insulation.

Commonly reflective foil wraps are alright to use in warmer climates and they block external vapour entering the cooled home. However, in colder climate zones where internal heating is used a vapour-permeable wall wrap is required for moisture control.

Avoid gaps in all types of insulation and barriers. Even a small gap can greatly reduce the insulating value and the properties of a vapour barrier. Ametalin 72mm x 50m Reinforced Insulation And Ducting Tape can be used to seal and join vapour barriers.

In summary, the sarking or vapour barrier needs to be installed on the correct side of the insulation for the climate of your area. Depending on where the barrier is to be installed it might need to be permeable to allow moisture to escape the interior of the dwelling. Incorrect location or the type of barrier used can lead to trapped moisture, mould and damage.

In your situation, if there were only insulation batts there previously or there are no pre-existing moisture issues with the wall I would advise installing just the insulation batts. There is no requirement to add a barrier when installing batts unless there is moisture permeating the exterior cladding. In your case given there is an additional aluminium cladding, excessive moisture within the cavity might not be an issue at all.

Mitchell

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MitchellMc

Welcome to the Bunnings Workshop community @joputra. It's great to have you join us and many thanks for your question.

Whether it is possible to install a vapour/air barrier prior to insulating or not, you would need to consider what benefit that would have to the over-all house in such a small location. Generally, the vapour barrier/air barrier/sarking would be installed to the whole house on the outside of the studs under the weatherboard providing a significant benefit to a home.

With some work, you could certainly cut the Aircell up into pieces that will fit inside the stud work and staple them into place prior to using insulation batts. As an air barrier that could certainly reduce any existing issues if you diligently fit and staple it into place. However, having a solid barrier will always be more effective than cutting pieces, unfortunately, this is just not possible with the studs installed.

As a vapour barrier stapling it in place now will do little to prevent moisture build-up or transfer. The timbers will not be protected where they contact the weatherboards and will simply transfer moisture themselves.

Let me mention the knowledgable members @Brad, @JDE and @Kermit to see if they had any suggestions about retrofitting insulation to a property.

Please let me know if you need further information or had any questions.

Mitchell

joputra

The house has aluminium cladding over the original weatherboards ( not sure if that makes a difference ) would it be ok just to add the batts without a barrier then? I wonder what others have done?

MitchellMc

Hi @joputra,

This discussion has led me to research further into moisture and vapour barriers within a home.

Some things I've learned are:

The right building wrap and installation location is dependent on which climate zone you live in. In a tropical climate, the hot outside air carries a large amount of water vapour. This condensates when it meets a surface cooled by conditioned air inside. In colder areas, condensation works in reverse. This time it’s the warm interior air that holds high levels of water vapour. This condensates when it meets a cooler surface close to the outside of the building.

Vapour barriers need to be installed on the warm side of the insulation and can lead to mould and timber decay if installed on the incorrect side. In cold climates, they are to be installed on the inside of the insulation (next to the internal wall lining). In warm climates, on the outside of the insulation.

Commonly reflective foil wraps are alright to use in warmer climates and they block external vapour entering the cooled home. However, in colder climate zones where internal heating is used a vapour-permeable wall wrap is required for moisture control.

Avoid gaps in all types of insulation and barriers. Even a small gap can greatly reduce the insulating value and the properties of a vapour barrier. Ametalin 72mm x 50m Reinforced Insulation And Ducting Tape can be used to seal and join vapour barriers.

Mitchell

joputra

Thank you so much, think we’ll just go with the batts then, so helpful 👍

woodenwookie

Have you thought about maybe using the polystyrene insulation often used under floor? It often has a water protective layer which would help. Just give it gaps around wires and hot water pipes.

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