Construction technology Membrane keeps buildings dry
The Fraunhofer Institute for BuildingPhysics IBP has achieved a major successwith a nylon membrane, a product fromthe packaging industry. This material isnow used throughout the world for thethermal insulation of buildings. Timber-framed build- ing on the outdoor area at IBP. Fraunhofer IBP "Initially we did not understand much about polymer membrane," points out Dr Hartwig Künzel. "As specialists in building physics we are primarily interested in the transfer of moisture and heat in buildings." And yet the departmental head at the Fraunhofer Institute for Building Physics in Holzkirchen kept returning to the subject of lining material when just over 10 years ago he started to become involved in the renovation of old buildings: "At the time we were conducting work on a re- search contract for the restoration of tim- ber-framed buildings. Materials were being tested in outdoor conditions on the Insti- tute's premises and the first computations of moisture behavior were being made." The façades of historical timber-framed buildings are normally subject to preserva- tion orders, which means that the buildings can only be insulated from the inside.
In such cases thermal insulation has far-reaching consequences: rainwater pene-trates into the beams and the infilling
The misture barrier is qucikly and easily ap-
even gets into the insulating layers. If the
interior paneling is hermetically sealed e.g.
Künzel first sought a solution to this prob-
able polystyrene or plastic sheet, the damp-
on his thesis at university he developed the
the room – it is trapped and at some stage
the beams will start to rot. Inside the build-
'unsteady transfer of heat and moisture')
computer program to calculate the transfer
of heat and moisture. He explains: "The ad-
50 Fraunhofer magazine 2.2001
vantage of such computations is that things
moisture protection layer with the Patent
can be simulated which do not yet exist."
Computing with WUFI
Office – the Fraunhofer Institute for Build-
ing Physics now has the patent rights in al-
retrofitting timber-framed buildings a mois-
ture diffusion layer is required which in
brane. That was in 1995. The research sci-
walls to penetrate inwards. In winter, how-
Physics, is now used throughout the world
to calculate the transfer of heat and mois-
mid, the layer must do exactly the opposite.
is suitable for determining the drying time
side outwards, as condensation would form
and the risk of condensation, it can simu-
late various climatic zones and calculate
tests: The Fraunhofer engineers studied its
In order to find such a moisture diffusion
tion work. "With WUFI the relatively time-
moisture permeability in a building on the
layer, Künzel with his team firstly examined
institute's outdoor testing area: the roof
dozens of commercially available types of
restricted because data is now only need-
ed for checking the calculations," explains
metal roof was first insulated with mineral
fiber and then lined with nylon membrane.
For a whole year, temperature and humidity
sensors in the roof provided data. "The re-
used to make sausage skins or baking film.
WUFI is now deployed in various versions:
sults were excellent. The target values we
No one had realized that it could be used
had set for moisture transfer were exceed-
for insulating walls, let alone roofs.
Institute in Holzkirchen. The WUFI-2D pro-
An intelligent, Sales success in adaptive membrane numerous countries
na. Both versions can be installed on PC.
The engineers at Saint-Gobain-ISOVER test-
ed the material's fire protection and me-
moisture regulation in thermally insulated
At the Fraunhofer Institute in Holzkirchen
chanical properties, as well as its aging be-
roofs. The membrane adapts its permeabili-
havior. Their conclusion: "The membrane
the environment inside aircraft envelope.
selected for use as a humidity controlled
barrier passed both required fire protection
which shields the envelope from cabin hu-
tests without any fire-retardant chemicals
having to be added to the material." The
mechanical properties, too, proved highly
satisfactory: the membrane displays highimpact strength, and therefore does nottear so readily if someone inadvertentlysnags it with a roof batten. A four-weekweathering test showed that heat and cold
brane comes into contact with moisture it
positive characteristic of the membrane was
swells up, the polar water molecules pene-
the material becomes soft. As a result the
the roof structure or the timber framework,
plastic acquires pores through which fur-
The research scientists tested the function of
not penetrate the pores – unlike the polar
the moisture barrier
water molecules. As a final trial the mem-
on a building with a
ture penetrates through the pores into the
brane was used on a pilot construction site,
sheet metal roof.
building interior. Walls and roof dry out.
then in 1997 it was introduced to the mar-
ket under the brand name 'ISOVER-Vario'.
creases the pores close up again, and themembrane then acts as a barrier to mois-
ty to the ambient air humidity: in winter it
ture. In winter this barrier protects the walls
plies to several countries in Europe and sells
protects against condensation, in summer it
facilitates the drying out of roof and wall
membrane per year. "We are now in the
structures. The 'intelligence' of nylon re-
pleasant situation where we are receiving li-
sides in its structure: in dry condition the
Künzel immediately registered his idea of
cense income," Künzel comments happily.
material's plastic molecules form a tight im-
using a humidity controlled membrane as a
Monika Weiner Fraunhofer magazine 2.2001