Lessons from Switzerland reveal intriguing opportunities in timber construction

DBI’s recent study trip to Switzerland unveiled innovative solutions and more lenient regulations for timber construction compared to Denmark’s building code.

Like many other countries, Switzerland is increasingly focusing on timber construction. As in Denmark, Switzerland also has a system that categorizes buildings by fire classes and requires certified fire safety engineers for building approvals. However, significant differences exist in construction opportunities between the two countries.

“We were introduced to various types of timber construction in both Zurich and Basel, and we saw several solutions that are not currently possible in Denmark under the pre-accepted solutions,” says Lars Vædeled Roed, Fire Safety Engineer at DBI, elaborating:

“For instance, the possibilities for floor separations, load-bearing structures, cladding, and interior surfaces are much more limited in Denmark’s pre-accepted solutions compared to Switzerland.”

Extensive use of timber

According to Danish law, it is generally not allowed to use more than 20% timber cladding when constructing buildings higher than one story. This rule does not appear to apply in Switzerland. For example, the study group visited a multi-story office building where both the ceilings and walls were made of timber.

“The entire ceiling and parts of the walls consisted of CLT (Cross-Laminated Timber) elements. At the same time, the load-bearing structures were made of unprotected timber,” says Lars Vædeled Roed, and adds:

“In Denmark, we can construct timber buildings up to four stories under pre-accepted solutions, but load-bearing timber structures must be protected with materials such as gypsum unless supplemented with sprinkler systems. However, the Swiss timber buildings we visited did not use such measures. Instead, they relied on systems like fire alarm systems, warning systems, or emergency exit and panic lighting.”

As an example, one four-story office building featured unprotected timber for both load-bearing structures and interior surfaces. This was combined with facades and floor separations also constructed from CLT timber elements.

“In Switzerland, it is permissible to construct load-bearing structures in unprotected timber and use a high percentage of timber on interior surfaces for buildings up to 30 meters, which is their threshold for high-rise buildings. In Denmark, the equivalent threshold for timber construction is only 12 meters,” notes Lars Vædeled Roed.

Interesting solutions using clay

In Denmark, fire compartment separations must be constructed with non-combustible materials like gypsum or concrete. In Switzerland, however, these separations can be made using clay or timber structures.

“We saw several buildings where clay was used. In one case, floor separations were built with load-bearing timber structures and a separating layer of compacted clay. In another, walls were made from prefabricated clay elements, while the load-bearing structures were timber,” explains Lars Vædeled Roed, pointing out that these were office buildings, and Swiss regulations may differ for residential construction.

“Like Denmark, Switzerland also has categories defined by usage, meaning stricter rules likely apply to residential buildings. For example, we visited a rehabilitation center built for overnight patients. Here, alternative construction materials were compensated for with sprinkler systems and the argument that the nearest fire station was only a few minutes away,” he says.

Alternative elephant enclosure at the Zoo

Another highlight was the elephant enclosure at Zurich Zoo.

“The enclosure consisted of a very large timber dome with large openings to let light in. It was only a single story but was designed to accommodate large crowds. The only fire safety measure was a fire alarm system, with no additional installations,” says Lars Vædeled Roed, adding:

“This would not be acceptable in Denmark, where stricter regulations require specific fire safety installations based on occupancy levels and building size, such as sprinkler systems or fire ventilation systems.”