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

retrofit wall insulation

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

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! Choose between Bradford Gold and Bradford Polymax Insulation for your residential build.

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

    • Pricewise Insulation says:

      Hi Sally, insulating existing walls with blow-in insulation is difficult because of all the timber joists that are in the way. There are companies that do this (such as Enviroflex in Melbourne), however it is quite expensive. If you are renovating then one option is to remove the plasterboard or weatherboards, install R2.5HD Knauf Earthwool Insulation Sound Shield Batts and then install new plaster and weatherboards. We understand that this is not an easy or cheap solution, however once it’s complete the insulation is designed to work effectively for decades. Feel free to give our team a call on 1300 729 639 if you have any questions.

      Pricewise Insulation

  1. Rose says:

    I would like to upgrade my external wall insulation in my existing home without needing to remove plaster walls. My main aim is to reduce traffic noise from outside. Is that possible?
    If so is there any concerns and would it affect the wiring in the walls
    Also would it void my structural guarantee?


    • Pricewise Insulation says:

      Hi Rose,

      Thanks for your question! If you have timber cladding on the exterior of your home then this could be removed and the insulation can be installed this way. Another option would be to get the insulation blown into the wall cavities, but this is an expensive option and not so common in Australia. In terms of the structural guarantee, you would need to talk to a builder or engineer about this. Feel free to contact us on 1300 729 639 if you have any questions!


  2. Chris Mitchell says:

    Hello, what is the best way to reduce as much noise as possible coming through the internal plasterboard walls I share with the townhouse next to me. I plan on staying here for 5+ years, so want to get a solution to the noise problems I am having!

    • Pricewise Insulation says:

      Hi Chris,

      This is a great question. We would recommend removing the plaster on the partitions wall and installing R2.7HD Knauf Earthwool Sound Shield Insulation. For added benefits you could also install new soundproofing plaster instead of regular plaster along the partition walls. You could also look at installing R4.0 Sound Shield Insulation in your roof space, as this will help to reduce noise travelling into your townhouse this way. Feel free to contact our team on 1300 729 639 if you have any further questions. Cheers!

  3. Jen says:

    I live in an apartment on a main road and although I can hardly hear my neighbours, the traffic noise from outside is quite audible. I have double glazed windows including sliding doors to the balcony that faces the main road. Unsure if it’s the sliding glass doors that need to be upgraded or if I need to insulate my walls. Ideas on how to check?

    • Pricewise Insulation says:

      Hi Jen,

      Thanks for your question. If you already have double glazed windows along the side of the house facing the road, I would start by trying to improve the quality of the seals around the windows and doors. This is typically an area where you can get a sound entering the house. You might want to look at taking the architraves off around the doors and windows and sealing those as well to stop noise leakage.

      If you have weatherboards or other light weight cladding on the outside of the house, putting insulation in the walls will help with the sound of the traffic, however if your house if brick then insulation won’t make a huge difference. I would suggest that you start with the windows before considering other options.

      Kind regards,

    • Les says:

      Hi Jen,
      Frequently when homes are being energy rated for the building permit, external sliding glass doors are omitted from being double glazed, due to weight and cost, so check that you door is double glazed too, but all of what Paul said is valid also.

  4. George says:

    Our house in North Western Sydney was built in 1999. It doesn’t have any kind of insulation (sarking, ceiling and wall). Can you please suggest some ideas to insulate our house? Does the foil insulation underneath the tiles (without removing the tiling) help? I am planning to install ceiling insulation. What should be the R value. I believe the wall insulation is nearly impossible without removing the plaster board. Thanks.

    • Pricewise Insulation says:

      Hello George,

      Generally if you want a good result in the ceiling, we would look at installing bulk insulation batts, or a combination of the sarking with bulk insulation batts. We recommend installing R4.0 ceiling insulation or higher in Sydney. For the best thermal results we would recommend R5.0 or R6.0 batts.

      You can retrofit sarking, and this will help with radiant heat, you can also look at roofing blanket with foil facing. As for the walls you can look for someone that install blow-in insulation, however this is generally quite an expensive option. If you wanted to use batts you would have to remove the plasterboard, so this is best to do when completing other renovation works. Feel free to give our team a call on 1300 722 639 if you have any further questions.

  5. Jay says:

    We have 25 years old modern brick veneer double story home which we built. How can we insulate our walls? We plan to live here for another 20 years. What options we have?

    • Pricewise Insulation says:

      Hi Jay,

      Thanks for your question. Insulating walls in an existing home is never easy, especially in Australia where blow-in wall insulation is both uncommon and very expensive. Basically your best option would be to remove the plasterboard, install R2.5HD Earthwool Sound Shield Wall Insulation and then install new plaster. The best time to do this would be during renovations when all the furniture and other items have been removed. We hope this helps! Feel free to contact us on 1300 729 639 if you have any further questions. Cheers!

  6. Mary-Ann says:

    We are renovating our 1930’s-40’s? house and whilst in the process of removing the old horse hair plaster and replacing it with gyprock we are going to retrofit the external walls with some Bradford polymax R2.5 wall batts, the thing is with the recent continuous wet weather we are having in Northern NSW we have noticed quite a lot of wet areas (from the inside) on the external timber cladding, should we be trying to put some sort of barrier between the timber cladding and the polyester batts?

    • Pricewise Insulation says:

      Hi Mary-Ann,

      Thank you for your question. If you are noticing that wet areas on the inside of the cladding I would suggest that you retrofit a vapour permeable membrane (eg Ametalin Brane VHP) to the inside of the frame before you install the batts. Just make sure that the wrap is installed with the print facing the cladding so that it performs its function as water barrier properly. Feel free to give us a call on 1300 729 639 if you have any further questions. Cheers!

  7. David Hancock says:

    Hi, we have a 70s brick house. The main bedroom is south facing with 3 external walls, all with no wall insulation. I’m assuming the best way to insulate the walls is to remove the Gyprock, insulate and re-gyprock the wall? Please confirm. As an alternative, we are looking at cladding the house. Can the insulation be added between the cladding and external brick instead?

    • Pricewise Insulation says:

      Hi David,

      Thanks for your question. The easiest option would be to remove the plasterboard, install wall insulation and then replace the plasterboard. Installing insulation between the bricks and cladding is also an option, however this install method is prone to moisture issues and you will need to take care to maintain sufficient air gaps. If you are seriously considering this second install option, then we would recommend talking to one of our insulation specialists first. Please give us a call on 1300 729 639 during business hours.


  8. Amanda says:

    What is the price difference in retrofit blow in insulation and removing internal plasterboard putting in batts then replacing plasterboard? Just use the example of 7m long wall by 2.3m high.

    • Pricewise Insulation says:

      Hi Amanda,

      Thanks for your question. To retrofit blow-in wall insulation costs about $50 per m2 in Melbourne, Australia. By comparison R2.5 thermal and acoustic wall insulation batts cost around $8 per m2, plus the cost of the new plasterboard. Removing the existing plaster and installing new insulation batts and plaster would work out considerably cheaper than blow-in wall insulation.

      Wall insulation batts also offer a higher thermal and acoustic performance than blow-in insulation, due to their higher densities. Feel free to give our team a call on 1300 729 639 if you have any further questions.


  9. Michelle says:


    My home is built in 2015 and based on the house plans it seems the builder had put in a foil insulation sheet in the wall cavities. I had asked two companies to come provide me with a quote.

    1) company 1, blow in wool, drill into wall to pump in, said that it would not be possible with my home as I already have foil insulation between the cavity walls.

    2) company 2. Polystyrene balls, pumped in through roof by removing roof tile. I advised them about the foil insulation between the cavity walls and they said there balls would not affect it.

    When I was doing some reading, it said that if anything touches the foil insulation it deems them as negligible and do not provide any insulation anymore.

    I would really like your advice, my house feels cold and I was really keen to get some insulation between the wall cavities but now I’m not sure if it will be possible or any value added?
    I am in Perth WA

    Thanking you for your time 🙂

    • Pricewise Insulation says:

      Hi Michelle,

      What you mentioned about the foil losing its R-value when other insulation is installed against it is correct. Foil insulation does require a reflective air cavity for it achieve its stated R-value.

      However, by filling the cavity with bulk insulation you will most likely end with with a higher total R-value for the wall. Your walls are currently around an R1.0 to R1.5. Filling the wall cavity with a blow in insulation such as the Knauf Jetstream will help you achieve an overall R-value of R2.5 to R3.0.

      There are a few other things that you could do to improve the energy efficiency of your home, including installing some extra ceiling insulation and sealing gaps around your doors, windows and other gaps around the house. Feel free to give our team a call on 1300 729 639 if you have any further questions.


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