Smart vapor barrier - Germany IBP

The protective film, developed by Germany's Fraunhofer Institute, Holzkirchen, and commercialized by the country's largest insulation manufacturer, Grunzweig + Hartman (G+H), Ludwigshafen, is similar to that used in the food-packaging industry for casing sausages and other edibles.

Working with materials supplier BASF, Ludwigshafen, the partners' researchers came up with a 50-micron, transparent film made of a blend of nylon 6 and 66 without plasticizer. Polyethylene films currently used in construction tend to have densities high enough to cause a ``hot-house'' effect, which prevents the escape of condensate.

The nylon membrane, called Difunorm Variois, is said to have 10-fold higher permeability than PE films. Coming in widths measuring 6.6 by 197 ft., the web opens its ``pores'' in the direction of the room interior when summer heat draws moisture out of wood roofing beams and siding. This allows the water molecules to escape into the room and out through windows. In winter, when cold air holds less moisture, the nylon membrane prevents room moisture from seeping into the timber construction.

Conventional vapor barriers usually prevent moisture produced by building occupants from migrating into the insulating layers of the walls and roof where it can build up and freeze. But Hartwig Kunzel, director of the Fraunhofer project, says timber moisture left over during the building process or absorbed from rain or snow, cannot normally dry out fast enough. The new membrane helps to reduce building costs, since roof insulation does not need to be ventilated, he says.

Susanne Gehle, G+H product manager, says that the film is priced to compete against currently used PE sheet and paper barriers. It also allows builders to do without the chemical wood preservatives that are often used to prevent mildew or moisture buildup.

The initial launch of the system is in Germany. But the building products firm also sees potential for it in the U.S. and Canada, where wood housing is more prevalent than in Europe.

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