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I enrolled on the WUFI course with some trepidation. I regarded it as a privilege to have been sponsored by my employer, PDP London, and was determined to get to grips with the programme. WUFI’s reputation and that of the presenters loomed large. Gaining an understanding of the science behind building pathology (relating to harmful moisture) would allow me to make informed judgments when faced with the plethora of information out there about energy conservation and building health.

On the way to the pub (after an intense first day) Christian Bludau, the presenter from the Fraunhofer Institute looked up and down Kennington Road, and was staggered by so many brick buildings – unaware of our built heritage – but at the same time being completely comfortable with the idea of rigorous scientific process applied to building development. Between us Brits, we could identify at the most two buildings that would be visually improved by the application of external wall insulation and the inevitable render-wash.

The challenge is immense. Having the tools to understand the problem is a start. For the uninitiated, opening forays by the Fraunhofer institute and Joseph Little Architects into the science of moisture transport, as a result of differential vapour pressure, air gaps, capillary action; the effects of heat cycles and climatic conditions, all made some headway. Defining terms: vapour-open instead of “breathable,” staying close to the science – avoiding misconceptions and embracing counter intuitive concepts – prepared us for WUFI.

To reinforce the scientific nature of the programme, the presenters explained how vapour properties are measured and remained completely unfazed when asked how vapour variable membranes (the intelligentsia of sheet plastics) actually operate at the molecular level. It was shown, using the programme, how long it takes for buildings to dry out, if at all, and how retained moisture can have severe health consequences and lead to catastrophic building failure. WUFI can predict hygrothermal performance (the study of heat and moisture movement in buildings) long into the future.

It soon became apparent that the main focus of discussion was our own, humble, London stock brick. In running the WUFI programme, we were told of the paramount importance of accurate material input. Rubbish in, rubbish out. Great strides have been made in understanding roof hygrothermal performance but the analysis of wall performance, and appropriate solutions, lags behind. Material input for WUFI is available from a number of databases accessible from within the programme: the Fraunhofer database, the North American database, and generic material databases. Did I hear you ask UK database – the delegates did?

To cut a long story short, WUFI is an incredibly powerful hydrothermal modeling programme. To obtain meaningful results, the material inputs must be accurate, and the Fraunhofer Institute carry out rigorous empirical testing on as many materials as resources allow. Their testing of German products is extensive and experienced users are able to extrapolate non-tested material properties from similar tested materials but this process lacks precision when applied to the humble brick. When used as a facing material, the absorbency of brick (the most important factor in determining its hygrothermal performance) varies widely; without empirical tests the material property becomes unreliable.

I came away from the course with an understanding that computer modeling is of value when allied to reliable empirical data. Architect Joseph Little’s Building Life Consultancy is the leading UK and Ireland exponent of this and has undertaken significant work in Dublin and some privately funded work in the UK. What is needed are the resources to test individual buildings to accurately determine material properties (to run accurate thermal and hygrothermal modeling), and to develop more inclusive, publicly available data.

Accurate WUFI compatible data and accurate climate models must be developed and made available in the UK to allow widespread use and gain acceptance for the scientific approach. Brickwork is the predominant facing material for the vast majority of our housing stock and a better understanding of how walls, in particular solid walls, behave is vital in order to make the right decisions when improving the comfort levels and energy efficiency of our dwellings and other buildings. WUFI is integral to this scientific approach.

After completing the course, I made full use of the 6-week trial period and undertook in-house modeling of different types of internal wall insulation, and a project specific analysis of paints with different vapour permeability applied to a lime rendered, solid wall. I was guided in the use of the programme by Joseph Little and Matthew Wellesley Smith at NBT (Natural Building Technologies) and by reference to the NBT WUFI protocol.

PDP London is currently considering whether to bring WUFI, PsiTherm and other analytical tools in-house in addition to external project appointments. Where refurbishment projects require full compliance under Approved Document L1B and L2B 2013 of the Building Regulations, we are finding these tools invaluable. The experience gained will provide a good grounding for future step changes in energy efficiency.

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To attend a WUFI course in the UK this year, book your place now: 14th & 15th April: WUFI training course, London

Other related events from The Green Register:

  • 7th July: Iain McLellan and Michelle Sanchez from PDP London will be making a Green Register bite size presentation on PDP’s Park Crescent West project