04 How-to
Seal it Tight & Ventilate Right
One of the central dichotomies in sustainable design today - The goal: a comfortable, low-energy home, but how do we get there? – was discussed at Australia’s National Science Agency’s July webinar, attended by DMN Members. The CSIRO webinar explored two different approaches. Using the Passivhaus approach, the building is sealed, highly insulated and operates using heat recovery ventilation when needed. Passivhaus has proven results over 3 decades in Germany and now 60,000 certified homes globally. On the other hand, proponents of free-running buildings point out that it is possible to design buildings that need no heating or cooling in most Australian climates. Why live in a mechanically ventilated Esky when you could live in a free-running building, cooled by breezes and heated by the sun? Passions run hot enough to create an urban heat island on this topic. CSIRO’s moderator, Research Lead Anthony Wright, asked representatives from Passive House Association (Kylie Mills), Earth Building Association of Australia (Peter Hickson), a building scientist (Jesse Clarke) and a tropical free running architect (Phil Harris – Troppo Architecture) to discuss the issues: What is the best approach for Australia? How should regulators accommodate the two approaches? How should we be aiming to live in an altered climate?
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Here is a selection of the Q&A following the webinar: Q. Is painting the rear of plasterboard and effective way of preventing moisture laden air entering framing? • Jesse Clarke, Pro Clima, said: In an ideal world, adding vapour resistance as a paint coating to the internal face of the plasterboard can help to reduce water vapour from entering the structure. However, this assumes the plasterboard layer is completely sealed and airtight. Considering GPO outlets, light switches, light fixtures, etc., mounted to the gypsum, then it is never going to be an effective air barrier. Vapour control does not work well without air tightness. The more airtight the vapour control layer, the better it works. In addition, adding too much vapour resistance to the internal side can be catastrophic. Q. What about using alternate materials like Cross Laminated Timber (CLT)? Can a timber surface help with issues like internal moisture? • Jesse Clarke, Pro Clima, said: CLT is a great technology. There are various ways it is manufactured. The cross laminated pieces of timber may be edge glued or not depending on the manufacturer. The CLT itself also changes moisture content with the seasons, based on average surrounding humidity and the equilibrium moisture content in the timber. It potentially swells and contracts. This can make the CLT achieve different air-tightness levels in different seasons when the gaps open up or close up.
