The wood-whisperer

Julia Bachinger works in the building physics department at the Holzforschung Austria research institute. Her specialism is problems with moisture and heat. Most recently, the native Upper Austrian has been focusing on wind proofing — with illuminating results.

Ms Bachinger, how did you arrive at wood-construction research?
I originally studied architecture, but was always fascinated by building physics. After working in a building physics office in Vorarlberg, I deepened my focus through my dissertation and came across wooden flat roofs, which were a hot topic ten or fifteen years ago. That type of roof design is insulated between the rafters and therefore susceptible to humidity. As a building physicist, wood is probably one of the more exciting materials because you have to know how to use it properly. Having said that, I think that wood is one of the more exciting building materials generally, and not just from the point of view of building physics. 

I’m also convinced about the potential of wood from an architectural point of view, because it can do so much. Of course, there are always colleagues who think that concrete is better, because it allows us to create all shapes. But I can do this with wood too. You just need a better understanding of the material in order to use it properly. Facts such as these make working with wood more exciting. 

“Understanding the material” — this is a good description of your work at Holzforschung Austria. Which properties of wood are you trying to get to know even better?
I work in the field of building physics and mainly deal with humidity and heat problems. Other colleagues in our field 
are involved in fire and sound insulation, for example. Specifically, a small part of our work is building physics consultancy and expertise, the majority takes the form of research projects focusing on problems related to building physics. The latter is my main area of occupation. As part of these projects, we work with partners from industry and business, such as Isocell. Our activities range from simulations to laboratory and field trials. Above all, our goal is to generate output that actually helps in practice, i.e. on the building site and not just on paper. 

A major research project that you recently completed focused on a windproof connection to the eaves in timber construction. Why is this particular area of such importance? 
This project was funded by the Austrian research promotion agency (FFG) and involved many project partners — including Isocell, but also the guild of roofers and plumbers, the Austrian association of prefabricated housing (Fertighausverband) and many others. The point was that the eaves connection between the outside wall and the pitched roof is often neglected when it comes to wind proofing and is difficult to manufacture because the rafters pass through this area and form a canopy. There are always connections around these rafters that are difficult to seal against the wind. You might say that it comes down to a small detail that is nevertheless difficult to get right. We looked at what happens if this area is not properly sealed, and also asked the question: how can we make it more windproof? One reason why the whole project got off the ground was the wording of the Ö-Norm B 4119 standard for the “Planning and execution of sub-roofs and trussed beams”, which states that “minor leaks are permissible” for windproof connections. Of course this raises the question of what is minor — everyone interprets it differently. 

What insights could you draw from the research? 
Too many to list quickly in one question (laughs). No, of course it was a long process that produced many different insights. After all, we did research for more than two years and carried out laboratory experiments as well as a field trial. In the laboratory experiments, we first looked at whether the roof pitch has a major impact. We quickly realized that there is little difference between sloping and flat roofs. We used three different insulation materials — light mineral wool, heavy mineral wool and cellulose. We recognised that cellulose has more wind resistance than light mineral wool. Heavy mineral wool was within a similar range to cellulose. A fundamental insight was therefore that it is not always necessary to use foil for sealing, as other suitable insulation materials also provide good results. Also, different gap widths were an issue. The tests showed that it doesn’t really matter how big the gap is — as long as there is one, the amount of heat loss is pretty much the same. Another topic was the subroof membrane. Can this simply be glued in place? What happens if it is glued to the wrong form board? We realised that incorrect masking results in significant heat losses. 

You can read the whole interview in THE ISOCELLER 04