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Wall Insulation Types

Similarly to how your roofing needs to be insulated, a home’s walls are another face exposed to the natural elements and will be the likely culprits of letting hot or cold air into your home if left uninsulated.

Wall insulation can save about 15% on heating and cooling costs. Common wall types for residential homes have an insufficient R-value on their own, requiring additional insulation material to be installed. The required R-value is dependent on the climate you are located.

Weatherboard walls

Typical weatherboard walls sit at around R0.45 for thermal resistance and require added insulation. Filling the cavity with bulk insulation is the way to go, ensuring it fits well, without compressing or gaps. A vapour control layer like a permeable wall membrane is needed to prevent mould forming.

For information on installing insulation batts in a weatherboard wall have a look at this Bunnings video

Brick veneer walls

Brick veneer walls typically have the same thermal resistance as weatherboard walls at R0.45. However, brick walls release and absorb heat at a slower rate than weatherboards. As the R-value is low it must also be supplemented with insulation.

Wall-wrap products can be used with at least 100mm overlap around joints with approved adhesive tape. Insulation batts can be installed between the studs fitting to the wall frame thickness well, avoiding compression and air gaps. A rigid foam board can provide better insulation and be installed between the brick and wall frame. In cooler environments, you can also include a foil face to the interior, or you can install this with conventional bulk bats in the wall frame, though these are not used together.

Using PIR and PUR or XPS boards, or foil-faced boards with an air gap of 25mm on the outside of studs can help reduce thermal bridging in colder climates. This results in a higher total R-value than placing insulation between the studs. Don’t forget to allow sufficient space to lay the outside brick skin and keep in mind that brick cavity ties will also need to be included typically through sheet joints.

Cavity brick walls

Cavity brick walls have the same R value as brick veneer walls and again will need additional insulation.

Often foam boards or cavity fill are used, of either loose-fill or injected foams. Reflective layers require sufficient air gaps to function properly. It is important to check installation requirements for your climate.

Cavity fill insulation in double brick walls ups the total R value to approximately R1.3 though it depends on the depth of the cavity and hence thickness of the insulation. Cavity fill must be water-repellent. Also, before going ahead with cavity fill, double check with your local building regulations on whether it is allowed or not.

Solid walls

A solid wall is one without a cavity, such as a concrete block or panel, stone, mud brick, a solid brick construction, or rammed earth (also known as pisé). these walls typically have a R value of R0.3 to R0.4 and in most climates will need additional insulation. Insulation can be installed on the inside or outside, however, be sure to not insulate the inside of thermal mass walls. This will insulate the thermal mass from the interior, wasting any benefits it would otherwise provide.

Typical insulative materials used include rigid foam boards, bulk batts between battens, and inward facing foil-faced foam boards with an air gap of at least 15mm. Internal walls will typically be insulated by plaster board bonded to rigid foam. External walls can have bulk batts fixed between battens and covered with an appropriate water control layer.

Internal walls

Internal walls only need additional insulation if they’re adjacent to an “unconditioned” room, or a room that will not be heated or cooled throughout the year, like a garage or storeroom. These walls can be insulated just the same as external walls as listed above.

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