Many people are unaware of the problem of compression, which can severely reduce the effectiveness of bulk insulation in roofs, ceilings and walls. Fortunately, compression is avoidable, but only if you choose your insulation product carefully and your installer does the job properly.
What is bulk insulation?
Bulk insulation products are the various kinds of batts, blankets, loose fill insulation and rigid boards that go above ceilings, under roofs or into wall cavities.
They work because their physical mass contains millions of bubbles or pockets of air, which is a very poor conductor of heat.
What is compression?
It’s when something occurs that reduces the thickness of bulk insulation. Here are a few common scenarios.
- Blanket insulation that is squashed under metal roof sheeting.
- Battens under metal roofs that press against blanket insulation.
- Fixings that squash insulation. Sometimes, the insulation only retains its original thickness about halfway between each point of contact.
- Thick wall battswhich are compressed to fit into wall cavities.
With the product packed down, the little air spaces inside it become smaller or disappear altogether. As a result, its insulation properties degrade.
What are consequences of compression?
The direct consequence of compression is reduced R-value. An important point to remember is that published R-values for bulk insulation are always for products of a particular thickness. When a product is compressed, the R-value you may have seen on the specification sheet or the packaging no longer applies.
Worse still, if your insulation product is badly compressed, it can become a heat conductor rather than an insulator.
It’s easy to see why compression can lead to unnecessarily high energy bills or uncomfortable temperatures inside your building.
How to avoid compression
When installing glasswool insulation blanket under metal roof sheeting, use roof spacers to prop up the roof sheeting so the insulation doesn’t get compressed. Be aware that this can add costs in materials and labour though.
If installing batts in walls, make sure you use a thickness that fits in the wall cavity so it doesn’t need to be compressed.
Or use high-performance rigid board insulation products. Rigid insulation boards are relatively new in Australia but are a great way to get high performance in thin spaces without worrying about compression.