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Slab Insulation - What it is, why you do it, and why it seems so many home owners get told it’s to hard or not possible to do

Slab Insulation, its the hot topic right now across the industry.

Insulation around slabs comes in two basic forms;

  1. Slab Edge Insulation
  2. Underslab Insulation

Slab Edge insulation is the most commonly used. As a general rule it’s applied after the slab is poured and it achieves the following;

  • Reduces the thermal bridge created by the slab edge being in contact with the ground

That’s it…simple. With the thermal bridge somewhat protected (if you only do slab edge insulation you will still have a thermal bridge at the bottom of the slab) you can enjoy slab temperatures that are closer to the indoor ambient temperature, which minimises condensation and mould risk.


Important point - The building code requires slab edge insulation be installed for underfloor heating;

So if you’re building in Adelaide, you can buy pre-made panels of slab edge insulation with a rigid board fitted on the outside from Regen Building Solutions, this is a great product we developed with them as it provides the insulation required and protection from mechanical damage.

Underslab insulation is installed between the footings and slab. Not to be confused with a waffle pod slab which provides partial underslab insulation.

Underslab Insulation does require the pouring of footings to be done in two stages with a day of work inbetween to install the insulation and the reinforcement to connect the footings to the slab.

Generally, underslab insulation and slab edge insulation is XPS foam, although there are other products you can use, XPS foam represents the best balance between cost and R-Value.

Underslab insulation (in the case of Adelaide’s two climate zones) isn’t required for Building Code compliance. However, for a Certified Passive House its really the only way to get them to be certified.

So why do some builders show some resistance to installing it?

It’s about cost.

The extra insulation and the extra labour to install it all cost money, they also take more time and effort to organise a separate trade.

Sometimes it can also be a case of the builder not understanding the benefit, and therefore not seeing the point.

If you want to know more about what a builder who really knows their stuff is across in terms of energy efficiency, download our 5 key skills of an Energy Efficient builder to learn more!

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