The Better Way to Insulate Your Roof

When it comes to choosing home insulation the rule of thumb has always been to choose the highest ‘R-value’ that you can afford. R6 batts cost more than R4 and provide better insulation. In the long run however, the energy savings will far out way the initial cost of purchasing the more expensive batts.

Most companies will tell you that when it comes to home insulation that this is all there is to it. Unfortunately however, it is not that simple. The timber joists in the ceiling still allow heat to transfer in and out of your home.

There is a much better way to insulate your home. Using lower ‘R’ rated batts, but in two layers.

Instead of laying R6 batts between the timbers in your ceiling and leaving it at that which will allow for the thermal bridging and heat loss, you can instead use R3 batts between the wooden timbers and then crisscross these R3 batts with R4 batts over the top.

Crosshatching two layers of insulation results in a substantial improvement in insulation efficiency.

In any average Canberra roof the space will consist of timber joists spaced at either 450, 600 or 900mm intervals. When added together these timbers take a surprising amount of ceiling space, none of which is insulated in a standard batt installation.

Basically for every square meter of roof at least 5% is timber and as high as 10% if the timbers are spaced only 450mm apart.

If you’re only laying one layer of insulation between the joists, the best you can do is insulate 95% of the roof.

Thermal bridging

Heat can move in and out of a house anywhere where it is not properly insulated. This can happen through roof timbers also. This effect is what is known as thermal bridging.

We have a great tool that can calculate the figures for you exactly but basically if you stick with R6 batts laid in a standard configuration between the joists leaving the tops of the timbers exposed to thermal bridging you will end up with a resistance value of only R4.1. It also gets worse with the timbers closer together, at timber spacing of 450mm the R6 batts reduce to effectively on a resistance value of R3.2. 

Our installation guide talks about crosshatching in more details. If you haven’t done so already, download a copy below.

Need to find out more? Get all the information in our installation guide