I organised an afternoon of CPD talks last week entitled ‘Breathability and low energy retrofit’. The session, organised for ECAN and a joint event with CIBSE, was held at the RIAS, in Rutland Square Edinburgh and attended by about 30 architects, engineers and academics. It turned out to be a thought-provoking afternoon with some excellent speakers (see programme below).
For me, the strongest messages were that we don’t yet understand the complexities of the breathability of buildings – that is, how moisture moves through the fabric of the building and is absorbed and released into it. Valentina Marincioni of University College London & Natural Building Technologies provided some examples of the factors that affect breathability and the dire consequences of not understanding it. Therefore one needs not only to consider the water vapour permeability, the hygroscopicity and the capillarity of each material in the build-up of the structure but also various other contributing factors such as the local climate, the use of the space and ventilation. I was surprised to learn that the sun also has an effect in that direct sunlight on a wet surface can draw water on the external surface into the building.
A more worrying theme that emerged was the lack of understanding and research into the inter-relationship between air-tightness and ventilation. Are our homes sick? asked Paul Paul Farren of the University of Strathclyde & ASSIST Design Ltd. Paul’s research has shown that the vast majority of Britain’s bedrooms have an indoor air-quality that’s below the acceptable limit for much of the night, with bedroom air regularly becoming so stale it’s damaging to people’s health and affecting their brains, largely as a result of high levels of CO2 caused by our breathing. Air-tightness in new buildings have reached levels that have left ventilation behind – how do we change the air in our rooms without loosing the heat that we have just managed to keep in? Again this is a complex area that requires a holistic approach to the indoor environment in order to solve the problem.
The insulation of new homes is now at pretty good levels, both for the environment and our wallets. However I believe it’s now high time that the government and the UK’s building industry funded some serious research into breathability and air-tightness in relation to ventilation so that we can deliver buildings capable of performing in a fit way for the twenty-first century. We need to learn how we can ventilate our buildings without compromising on the air-tightness.