How to Retrofit Roof Insulation

how to retrofit roof insulation

More than any other place in your home, it’s critical that the roof is insulated. That’s because the roof is responsible for the most heat loss and gain in a home – as much as 35%!

When a building is being constructed, insulation can be installed simply as part of the building process. However, what happens when you want to retrofit roof insulation in a pre-existing building or replace the insulation in an older home? And is it worth the investment?

Can You Retrofit Roof Insulation?

To retrofit insulation means installing insulation in a home after it has been built as opposed to installing during the construction phase in a new home. Ceiling/roof insulation is fairly simple to install in existing homes provided there is enough room in the roof space for the necessary manipulation of insulation materials.

How to Install Roof Insulation Batts

The most convenient time to retrofit ceiling insulation is during renovations when the plaster has been removed, giving easy access to the ceiling cavity. You can also retrofit roof insulation through the manhole or an access hole in the roof that you can create by taking off a roof sheet or sliding back some roof tiles.

Choosing The Right Insulation Products

The best roof insulation for your home will depend on a number of factors including your geographical location, budget and personal preferences. Some of the most popular retrofit roof insulation products include:

Glasswool Ceiling Batts – Made from recycled glass materials, glasswool ceiling batts have excellent thermal performance and are easy to handle and great for DIY projects. To reduce noises from airplanes or heavy rain, you might consider investing in specialised acoustic ceiling batts to help create a quiet, peaceful indoor environment for your home.

Polyester Ceiling Batts – Pre-cut to fit most Aussie ceilings, polyester ceiling batts are made from recycled plastic materials and have none of the itch factor associated with more traditional glasswool products. They are non-allergenic and contain no breathable particles, making them a good choice for people with asthma or dust allergies.

Reflective Foil Insulation (or Sarking) – With a thin layer of reflective foil, this insulation product is installed in the roof to help reflect radiant heat from the sun away from your home and is particularly effective for homes that receive a lot of heat in summer. Some insulation products combine foil insulation with bulk insulation for a 2 in 1 product.

Please note – Foil insulation is not suitable as an insulation product on it’s own, it does a slightly different job to standard insulation batts. For best results, both foil (or sarking) and insulation batts of choice should be used!

Choosing the Right R Value and Saving on Energy Bills

Whatever insulation products you choose, make sure you get the right R-Value based on your location and climate zone. 

In Australia, every insulation product is given an R-Value which indicates how effective it is at preventing heat loss and gain. The higher the R-Value, the greater the thermal performance of the product which means less heat loss during winter and less heat gain during summer.

For ceiling insulation in Australian homes, we recommend a minimum R Value of R4.0. However, if you live in a cooler location such as Melbourne, Sydney or Adelaide, we recommend upgrading to R5.0 or R6.0. Upgrading to the highest R Value that you can afford will lead to greater energy efficiency and more savings on your power bill year round.

Replacing Vs Topping Up Old Insulation

A lot of people want to know if you can add new insulation to existing ceiling insulation. In some cases it is possible to top up existing insulation with new insulation. Although old insulation will have a lower R Value than when it was first installed, it often still has some insulating power left and may help increase the total R Value when combined with new insulation.

If the existing insulation in your house is damaged, mouldy or rodent-infested, you should get it removed completely before installing new ceiling batts. Similarly, if your ceiling has suffered damage from a storm or plumbing leaks, these should be completely fixed before installing new ceiling batts.

Can You Spray Insulation Into an Existing Ceiling?

Spray foam insulation is a type of insulation that is sprayed into the roof space using a specialised machine. Although spray foam insulation might be the most convenient choice for ceilings which can’t be safely accessed any other way, you will usually get higher level results with insulation batts.

For more information about how spray insulation stacks up against insulation batts, check out our article on expanding foam vs insulation batts.

Video: What to Check Before Buying Roof Insulation

How Do You Insulate an Existing Roof?

Step 1. Gather your materials, including safety gear, utility knife, a long stick and a wooden plank to kneel on. Ensure the power is switched off.

Step 2. Load the insulation into the roof before taking it out of the packaging. Insulation batts are compress packaged and can expand a lot once taken out of the packaging. If the manhole into the ceiling is too small to load insulation through, you can access the roof space by taking off a roof sheet or sliding back some tiles.

Step 3. Start by placing the batts between rafters around the perimeter of the roof. Make sure they cover the top plate of the wall. Use your long stick to help you push the batts into place.

Step 4. Begin installing the middle of the roof, working from the furthest point back towards the manhole or opening in the roof.

Step 5. Leave appropriate gaps around downlights and fans. Fill any other gaps with cut offs to ensure there are no gaps left as this can compromise the effectiveness of your insulation. If you have any leftover insulation, you can leave it on top of the other batts.

Best Practices For When You Retrofit Roof Insulation

When retrofitting ceiling insulation yourself, make sure you follow the following best practices to ensure you stay safe and get the optimal results from your insulation.

  • Use appropriate safety gear, including safety glasses, gloves and dust mask. 
  • Avoid installing during the hottest part of the day as the roof cavity can become very hot.
  • Ensure the power is switched off before you start working in the roof.
  • Ensure there are no gaps between ceiling batts.
  • Do not compress ceiling batts – this will compromise their performance.
  • If there is existing insulation and it is below the top of the rafters, install the batts between the rafters on top of the old insulation. If the old insulation is flush with the top of the rafters, the new insulation can be installed on top of the rafters.
  • Leave appropriate clearings around downlights.

For more information about retrofitting ceiling insulation, check out our RETROFITTING CEILING INSULATION GUIDE or get in touch with our friendly team.

Video: How to Install Roof Insulation

Buy Roof Insulation Online Today

If you’re looking for quality and affordable retrofit roof insulation products, Pricewise Insulation has a wide range of options which perform well in Australian climates all year round. If you live in the Sydney or Melbourne regions, our insulation installers can help you get the job done effectively.

Place an order online today or call us on 1300 729 639 to speak with one of our insulation specialists about your project.

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