paper igloo architecture and design

Airtightness workshop with Ecological Building Systems

September 27, 2013

Yesterday Martin and I spent the day attending the 'Better Building Fabric First' course at the 'Centre of Knowledge' of Ecological Building Systems Ltd in Athboy, in Ireland.

We had a great day with Niall Crosson and all of the team there. We had previously had a CPD on airtightness and vapour control in our home office back in Glasgow from Penny Randell, and she had mentioned the course to us. It was a really interesting day, and well worth the 5am start!

The morning was spent learning about thermal insulation, natural insulation products, the importance of the airtightness layer in any building, and intelligent moisture management within a construction, whether it be in a refurbishment context, a new build passivhaus or another low-energy building.

It was interesting to see again some of the thermographic images taken of constructions where taping of the airtightness layer had been missed or compromised, and the effects of the thermal bypass on the actual performance U-Value of the construction was easily visible. Most of the thrust of the improvements in the technical standards are aimed at lowering target U-Values and improving whole building airtightness to some degree, but the ventilation sections are still, in my opinion, a bit lacking. The importance of the phrase 'build tight, ventilate right' cannot be underestimated!

The day really drove home for us the importance of a whole envelope fabric first approach to low-energy design, passivhaus or otherwise. After all, there is little point in spending money increasing the amount of insulation within a wall if the actual performance of that wall is to be compromised by as much as 300 - 400% by not including, or finishing properly, an airtightness layer on the warm side of the construction, and a wind-tight layer on the outside of the construction to mitigate (or eliminate) thermal bypass! Especially when you consider that the cost of including the airtightness layer in a typical house can be as little as 0.5% of the construction costs, which is an achievable amount.

The majority of the afternoon was spent with airtightness expert Roman Szypura being shown how to apply a typical airtightness membrane, tapes and so on, all of which was demonstrated with pro clima products, which were certainly impressive.

The cut-away constructions in the Centre of Knowledge were also great - there is no substitute for seeing buildings (or parts of them) in the flesh so to speak!

A lot of tips and information was picked up, and I felt the day was a great complement to the passivhaus course I did last year at Strathclyde.

So, now we have to feed-back this information into our own design: we are re-visiting our external wall construction to see if we can get each layer within the wall to work harder and some to perform more than one function. For instance, if the airtighness layer can be achieved with a board material that can also function as the structural racking board then that saves on an additional membrane.... more on this later!

We also feel more certain that for us a service cavity will prove very useful. Not only is it invaluable in terms of helping various services trades (electricians, plumbers, etc.) to minimise the chances of the airtightness layer being damaged in some way, and in providing a space for a little more wall insulation, but the extra depth will allow us to create a good airtight seal with our polished concrete slab via a glued and taped connection, and still have a shadow gap detail at the floor with no skirting. One more tricky detail resolved!