My Best Build Decision

Jon Martin, who along with partner Noreen Jaafar built the awardwinning Treehouse, explains why his best build decision was the insulation that allowed him to sail towards Passivhaus certification

One homeowner explains how an interesting insulation product allowed him to achieve Passivhaus certification on his award-winning self-build

The Treehouse, the awardwinning home that my partner Noreen and I built, was a technically demanding build, especially as we decided from an early stage that we wanted to achieve Passivhaus certification. Of all the things we did and the many decisions we made, I think the best was to use Icynene spray foam insulation throughout the build (though we did end up using rigid insulation boards on the roof ).

It was that decision, having spoken to lots of people, that I think helped to achieve our airtightness figures. Once the foam had been sprayed, we tested the airtightness and had results of 0.57/h@50Pa (Pascals) even before we had taped the windows — which is below the Passivhaus standard of

0.6/h@50Pa. After taping, that rating came down to 0.32/h@50Pa.

The house is quite a tricky shape for installing insulation, but this method made all the difference; the spray foam got into all the areas we would have struggled to insulate neatly otherwise, and it saved us a vast amount of time. It seems like any extra expense for the insulation was effectively recouped by the speed with which the job was done. Yes, there were other ways of doing it, but it would have taken a massive amount of time and effort.

We chose the water-blown material, which is open-celled and breathable. We were glad we did when we realised one of the membranes had split and water had got in at one point. Ten days later it was bone dry. That’s the benefit of the open-celled stuff over the closed-cell: if you do get a failure somewhere it will dry out and dry out quickly. When you are working with 400mm of insulation like we were, that’s important.

I have to say that I hummed and hawed for a long time, but I spoke to the energy consultant, and my relatives in Canada where it’s far more common, and it just made sense for our project. We were looking to have just 500W of heating in the 210m2 home, so we knew getting the insulation right was integral to the project — and having gone through the recent harsh winter, we know we did.

An added bonus has been that it does seem to cut out more sound. It doesn’t take the low frequencies out, but seems to deaden road noise and other noises completely. H