Home Building Project – Insulation Batts

Over the next couple of editions of the DirectBuild Newsletter, it is proposed to look at the different components of the building project and possible factors with regard to the thermal performance of your home.

In this edition, we are going to address Insulation Batts which are a simple but effective product when installed correctly.

A lot of the design and construction methods used today have come about following a period of trial and error. Even now with over 40 years of fibreglass insulation batts use, Architects, builders and home owners are still using this bulk insulation product incorrectly.

The original thought behind the insulation batt was to provide a resistance barrier (R rating) to minimise the transfer of hot or cold external temperatures to an internally temperature controlled zone. The thinking was that the higher the R value the better the transfer resistance factor. This is not necessarily the case. Correct installation of the insulation batts is critical.

For example, if you over-insulate a dwelling without the correct passive performance (shading, window placement, ventilation) you might form an oven or esky effect. Similarly, trying to squash R3.0 insulation batts (approximately 132mm thick) into a 90mm timber frame wall will not only lessen the benefits of the R3.0 batts, you will waste money. Insulation batts are designed to be installed as loose and fluffy as possible so that the millions of air gaps can do their resistance job effectively. Once you squash the batt to make it fit, those air gaps just become a bridge for moving the temperature. Same with old sagging dust covered ceiling batts. They will help but only partly.

Further, insulation batts must fit snugly. If you allow any more than 5 percent of space around the insulation batt, you will lose anywhere up to 40 percent of the benefits. So taking the time to ensure correct installation of the correct R rated batt is essential.

Long term the correct installation of bulk insulation batts is paramount to the thermal performance of residential dwellings.

To help long term performance of the insulation batts in a timber frame wall, the correct thickness of batt should be used, they should fit snugly with the addition of external reflective wall wrap, the insulation batts can be held in their correct prime position. 

Brendon Wilkie

Director
DirectBuild Australia Pty Ltd