If you look beneath many of the most sustainable homes in North America, you’ll often find foam-based insulations. Regardless of the amazing, innovative materials used elsewhere in buildings, we have all been very reliant on foam insulations below grade despite the fact that foam does not meet many of our sustainable building criteria.

We were able to use a remarkable new insulation that works below grade for Canada’s Greenest Home, and it is a real game-changer for our practice going into the future. The insulation is based on a product called Poraver, which are expanded glass balls made from 100% recycled glass here in Ontario. The glass balls share very similar properties with perlite, being a lightweight, mineral-based insulation. However, the Poraver balls are stronger and less dusty than perlite and don’t require the mining of virgin resources, as they are made from recycled glass.

Poraver makes this product largely as a lightweight aggregate for the concrete industry. Mixtures using portland cement and Poraver are not new, but we were not interested in trading the high environmental impacts of foam for the high impacts of cement.

For our project, the binder we used for the Poraver was a mixture of hydrated lime and a material called Metapor. Metapor is “metakaolin,” a kaolin clay that has been fired at high temperatures. This material is a by-product of the manufacture of Poraver. It is an excellent pozzalan, meaning that when mixed with lime and water the pozzolanic reaction is very similar to that of portland cement. Builders have used lime and pozzolans for centuries.

A sample block of Poraver showed us a lightweight, structurally sound insulation

What this means for sustainable builders is that we now have access to a material that has excellent insulative properties (R-value tests are still to come, but we expect results in the R 1.5-2 per inch range), excellent compressive strength (able to support foundation loads) and completely stable below grade (nothing to decompose, or be eaten as with foam and ants).

We used 8 inches of this material under our basement floor. It was easy to mix, easy to install and we were able to walk on the surface 24 hours after pouring.

In the future, we’d like to explore further uses for this material, including foundation walls and above-grade applications as well.

Working with Poraver has been one of the highlights of a project that has included many innovations.