R2.5 Ceiling Insulation

R2.5 batts – a cheap solution

R2.5 insulation batts are the cheapest ceiling product available on the market. They are suitable in hotter regions such as Brisbane and Darwin, although we generally recommend opting for a higher R-value. Insulation is a once off investment!

Which brand is best?

If two products have the same R-value, then their insulating performance will be the same. No certified insulation brand is better than the other – it all comes down to the R-value. Each of the brands we sell meet the Australian Standard AS/NZS 4859.

Choosing an R-value

Australia is divided into a number of climate zones which help determine which insulation is best for each region. In the hot climates up north, properly installed reflective foil insulation is as important as bulk insulation products such as glass wool or polyester.

R2.5 Roof and Ceiling Insulation

Some ceilings, in particular flat pitched roofs, are almost impossible to insulate after plaster – there is simply not enough room to manoeuvre in the roof space.

The usual solution is to install the insulation from underneath in between all the joists, before the plaster is installed.

This can seem a daunting prospect, and you may well be better off hiring a professional installer to do it for you. But if you’re feeling adventurous, here are a few tips to help get you started.

Installing Ceiling Insulation before Plaster


  • 1 x Sharp Knife
  • 2 x sticks, approx. 1.5 metres long
  • 1 x dust mask
  • 1 x “A frame” ladder
  • Plastic Strapping or industrial sticky tape
  • 1 x industrial stapler (if using plastic strapping)

After opening one bag of insulation, take a batt in one hand and your two sticks in the other, and poke the sticks into the centre of the batt. Push it up between the joists, hold it in place with one stick and use the other to tuck the batt into place so that it lies suspended between the joists.

Depending on the spacing between the joists, you may need to cut some batts to size. To start with you may need to use a ladder to measure how much you need to cut, but with some practice you should find that you will be able to size it up accurately without the assistance of a tape measure.

Key tips:

  • Only cut insulation against wooden joists or on a piece of wood on the floor, concrete will quickly blunt your knife
  • The insulation will only sit for a few days before it starts to sag, so remember to run strapping across the joists if the plaster will not be installed within the next couple of days.
  • Leave gaps around where downlights and vents are going to be, these will often be marked on the floor
  • Only open one bag at a time; glasswool tends to become more floppy the longer it sits outside a bag, making it harder to install.

Good luck!