Comparison of methods for the renovation of wooden beam ends

© Fraunhofer IBP

View of a half-lap joint to replace a rotten section of a wooden beam end.

© Fraunhofer IBP

Methods applied to renovate wooden beam ends using different support elements and types of insulation, together with the associated thermal and hygrometric features.

© Fraunhofer IBP

Curve showing the change in core humidity of beam ends in a north-facing wall.

The old cooperage that forms part of the outbuildings of Benediktbeuern Abbey dates from the second half of the 18th century – and is therefore subject to a preservation order. Its most remarkable features are its baroque hipped roof and distinctive king posts. But when part of the wooden ceiling was removed to gain access to the attic, it was discovered that almost all of the beam ends were severely infested with wood-destroying fungi.

The Fraunhofer IBP researchers saw this as an opportunity to test different renovation methods and measurement techniques in a single building. They restored a total of 24 damaged beam ends, using six renovation methods which differed mainly with respect to the type of insulation, the beam support brackets, and the hollow space in which the beam ends are inserted.

So, what is the best renovation method for wooden beam ends? Measurements of the renovated structure demonstrated that the water content of all beam ends lay within uncritical boundaries, and never exceeded 16 percent by mass during a whole year of testing. This seems to indicate that the composition of the beam supports – mortar, elastomers or nanogel – is a relatively insignificant factor, as are the insulation and the air gap. In other words, the water content curve is not sufficiently informative with respect to the choice of renovation method. Although it was observed that beam ends with a copper cap serving as a thermal bridging element demonstrated the highest surface temperatures, this did not result in lower humidity values compared with other wooden beam ends. Inhomogeneities in the structure of the wall appear to have a greater effect than the choice of renovation method. To test this hypothesis, the researchers calculated the water content curve for three renovation methods using the WUFI® 2D simulation program. The factors that entered into this calculation were changes in the outdoor climate measured using local environment sensors, and measurements of the indoor climate. These calculations confirmed the results of the sensor measurements, according to which the choice of renovation method is insignificant.

The tests proved that the choice of mechanisms to support the beam ends in the masonry are much less critical than expected. The damage repeatedly observed in beam ends is more likely to be a result of unexpected incidents occurring many years after the building was constructed, such as the displacement of roof tiles, blocked gutters or other sources of leaks. Consequently, few errors can be made when replacing or repairing damaged beam ends, as long as their outer surface is sufficiently protected against rain.

Contact us

Contact Press / Media

Prof. Dr. Martin Krus

Fraunhofer Institute for Building Physics IBP
Fraunhoferstr. 10
83626 Valley, Germany

Phone +49 8024 643-258

Fax +49 8024 643-366