Retrofit Wall Insulation for Existing Homes: Everything You Need to Know


A large proportion of Australian homes are under-insulated. Unfortunately, this means many Australians experience uncomfortable indoor temperatures year round and are paying more on their electricity bill than they should be. This is particularly an issue in older homes where wall insulation is missing or has lost its effectiveness. Without adequate wall insulation, you could be losing as much as 25% of your home’s heat in winter and gaining up to 25% more heat in summer.

If your home is uncomfortably cold in winter, unbearably hot in summer and difficult to heat up or cool down, chances are you need to replace your wall insulation. It’s one of the best ways to regulate temperatures effectively, cut your power bill down and do your bit for the environment. Installing insulation in new homes during the construction phase is simple and efficient, but insulation can also be retrofitted in existing homes. If you suspect your wall insulation is missing or isn’t doing its job properly, stay tuned. Below we cover some of the most important factors you need to know to get started retrofitting your home with wall insulation.

Why Should I Replace My Wall Insulation?

Adequate wall insulation will make a tangible difference to the temperatures inside your home. Wall Insulation is built to last for years. However insulation that is 10 years or older may need to be checked for damage, mould or rodents. Over time, the R-Value of insulation products may decrease, meaning they will be less effective at resisting the flow of heat. This is usually due to compression, moisture or movement creating gaps in the insulation. Rotting or damaged insulation should be completely removed and new insulation then installed into the area.

What’s the Best Wall Insulation?

From fibreglass batts to blown-in cellulose, spray foam and foil backed insulation – there’s a huge range of insulation types. Below we run through some of the most popular products used in wall retrofit applications.

  1. Insulation BattsInsulation batts are a type of bulk insulation which are pre-cut to fit in between the wall joists. They are most commonly made from glasswool (aka fiberglass), polyester and rockwool. Insulation batts tend to be inexpensive, effective and have a high fire rating. Specialised acoustic batts also provide noise reducing effects. If you are living in a home without wall insulation, then your best option is to remove the plaster and install insulation batts in the cavities.
  2. Blow-In CelluloseBlow in cellulose insulation requires more effort to install than insulation batts because training is required before using the blow machine.In Australia, retrofitting existing walls with blown-in cellulose is an expensive process. As cellulose insulation is manufactured from ground up paper it has a lower fire rating. Overall, this product is quite effective but has a short lifespan and can get blown around leaving gaps between the insulation material. The actual technique required for effective blown-in insulation is also often overlooked. If the insulation is blown against a joist and compacts, it will be significantly less effective!
  3. Spray FoamSpray foams are more expensive compared to the other options and must be installed by a professional. In general, spray foams have a longer lifespan, are permanent and will not sag or lose their R-value over time. Spray foams come in two forms; open and closed cell structure. Open cell foam has air gaps inside the material and occupies more space per weight. As the foam expands it fills the air spaces and prevents air draughts. Closed-cell foam is more common and denser giving it a higher R-value rating. Retrofitting existing walls with spray foam insulation is very expensive, which is why we generally recommend installing glasswool insulation batts.

Batts vs Blown-In

Let’s take a look at how batts stack up against blown-in insulation over a number of categories.

  1. When to InstallThe perfect opportunity for installing wall insulation batts is during a major renovation project or extension with brick-veneer or weatherboard walls. When the wall-lining is not being removed, blown in insulation can be used and the small insulation particles will conform to the cavity space. However, this is generally an expensive way to insulate your walls.
  2. Ease of InstallationBatt insulation can be installed as a DIY project or by a professional. Batts are easy to handle and come pre-cut to fit in between the wall joists of most Australian homes. For hard to reach or awkward spaces, batts can be easily cut into the right shape. This is by far the most cost-effective way to insulate your home. Blown insulation usually requires a professional to install it with specialised equipment. Access to the cavity is gained through lifting tiles above the wall cavity or creating a small hole from the exterior side of the wall.
  3. CostIn Australia, batts are a cost-effective option compared to blowin-in insulation. Additionally, batts can be installed as a DIY project which can help bring costs down even more.
  4. EffectivenessBatts provide excellent resistance to heat flow and also offer acoustic benefits. They come in a wide range of R-Values to suit your needs and budget. Blown in insulation is also quite effective, but care needs to be taken when installing that the particles are not blown out of place. Furthermore, if any moisture is collected by the blown insulation as it passes into the wall cavity, the performance will be compromised.
  5. LongevityInsulation batts are much more durable and long lasting than blown in insulation. Batts are more likely to stay in place and continue providing thermal resistance long after blown insulation has stopped performing. Over time, blown-in insulation can settle or move downwards in the wall cavity, leaving pockets of air at the top. These pockets of air allow major heat loss and gain. This is less of an issue in ceiling spaces, but for walls blown-in insulation poses a major disadvantage.
  6. Fire RatingsIn general, batts outshine blown in insulation when it comes to fire safety. Cellulose blown-in insulation is manufactured from ground up paper and therefore has a much lower fire rating. Glasswool and Rockwool batts have particularly high fire ratings and won’t produce any toxic smoke in the case of a fire.

How to Retrofit Wall Insulation the Right Way

When it comes down to it, batts offer greater value for money, superior durability and long lasting performance. If you have decided to retrofit wall insulation during a major renovation, batts are the way to go.

During your renovation project when wall cavities are exposed, insulation batts are pressed between the joists and can be strapped into place. It is important that batts are not compressed and that there are no gaps left during installation. Insulation should be shaped and fit behind any electrical and plumbing work and if required, the batts can be trimmed to an appropriate size. A good rule of thumb is to oversize your cut by 10mm to ensure a snug fit. Any off cuts can be used to fill gaps around windows and doors.

If you plan to do the installation yourself, make sure you read up on our DIY guide to ensure the best outcomes. Poorly installed insulation will be less effective. Also make sure you use the necessary safety equipment. Gloves, safety glasses and long sleeves are highly recommended.

Wall Insulation Batts – Brand Comparison

Insert Video – Pink Batts vs Earthwool vs Bradford Insulation

Pink Batts made by Fletcher Insulation are glasswool insulation batts, made from up to 80% recycled glass material. The new soft touch technology gives the insulation a low-itch feel making it easy to install. They are lightweight and firm batts which keep their shape once installed and have a lifespan of up to 50 years.

Knauf Earthwool is a glasswool insulation product and is the least itchy of the three brands. It is made of 80% recycled glass and has no added formaldehyde. It is odourless, rot proof and does not sustain vermin, thus being an attractive product for older houses.

CSR Bradford has been manufacturing insulation in Australian for over 80 years and has a large variety of insulation products on offer. When properly installed Bradford insulation can be expected to last as long as your home!

4 thoughts on “Retrofit Wall Insulation for Existing Homes: Everything You Need to Know

  1. Tom Cooper says:

    Hi guys. I am tackling this job in my own weatherboard cottage built in the early 1960s. The weatherboards are pretty easy to remove, just need to be gentle as to not split them. I had to remove them to see the size of the space between the studs. A few hours to remove, a few hours to put in the insualtion and a few hours to replace the boards and job done really

    • Pricewise Insulation says:

      Hi Tom,

      Thanks for sharing this with us! It’s great to hear that you could reuse the same weatherboards without having to replace them. The process you have described is a really effective way to insulate the exterior walls of a weatherboard house.


      • Annabelle says:

        Good to read that Tom was able to install batts by removing a few weatherboards to insert the batts.
        I need a tradie to do this, any recommendations? Thanks Annabelle

        • Pricewise Insulation says:

          Hi Annabelle,

          Thanks for your question. If you live in Melbourne then we recommend Van Oord Building ( If you live elsewhere in Australia then we would recommend a quick Google search to find a local tradie. Feel free to contact us on 1300 729 639 if you have any further questions. Cheers!

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