Kaifu-bad in Hamburg

Kaifu-bad – oldest spa in Hamburg

Location Hohe Weide 15, 20259 Hamburg Germany
Building Year 1895, renovation 2015
Architect MRLV Architekten, Markovic Ronai Voss
Structural Design WTM Engineers
Customer Bäderland Hamburg GmbH
Products Used Kerto LVL
Type Public Buildings

​​Saving a historical bath with Kerto® LVL

Kaifu-Bad is the oldest swimming pool complex - and the largest open air one in Hamburg. The entire complex is a protected monument built originally in 1895. The bath was closed for many years because the roof was in danger of collapsing. As part of the renovation project, one of the pools was converted into a salt-water bath, which poses unique challenges. How could Kaifu-Bad be renovated in a way that respects the protected design, meets modern sustainability standards, tolerates the challenge of salt water and stays within budget? This could only be done with Kerto® LVL (laminated veneer lumber).

Engineer Stefan Heidrich

​Stefan Heidrich obtained his diploma as a civil engineer in 1993 and has worked at WTM Engineers as a structural designer in building construction since 1996. He has many years of experience in project management of challenging buildings built as solid, steel or wood construction with special expertise in remodelling and renovation of existing buildings and the structural design of swimming pools.

Architect Manfred Voss

​Dipl. Ing Manfred Voss has been the partner and managing director of MRLV architects Markovic Ronai Voss since 1993. He studied architecture at the Technical University (TU) “Carolo-Wilhelmina zu Braunschweig”. The main focus areas of MRLV are building services, sustainability and energy optimisation without exaggeration. The fields of activity include: museum building, hotel building, sports and pool construction, residential construction, office- and school buildings.

In the Kaifu-Bad case, MRLV was in charge as general planner with the Service phases 1-8 (building equipment, structural engineering, building physics, building acoustics, room acoustics, fire protection, facade planning)  

History of Kaifu-Bad
​Kaifu was built in 1895 as a folk bathhouse. In 1905, another indoor swimming pool was added. The older pool hall has now been converted into a unique salt-water bath. After going for half a century without a major renovation, the bath had to be closed to the public as the roof was in danger of collapsing. In the future, people can swim and relax here enjoying the atmosphere of the historical bath.

Unique challenge

Standing extreme conditions

“What sounds simple presents unusual challenges for us as architects,” reports Manfred Voss, from the renowned architectural firm MRLV. ”The salt water bath has a salt content of 6%, which is good for humans but bad for steel. Consequently, the salt content will result in an enormous exposure to corrosion, in particular for any metal structures. We knew from the beginning that a conventional solution wasn’t an option. We have therefore chosen a wooden construction.”

     

Corrosion free wooden structure

Corrosion free wooden structure 
 

The solution by renowned architectural firm MRLV was to replace the old, ailing roof truss with a steel-free construction. The architect collaborated with the structural engineer Stefan Heidrich from WTM Engineers, and they developed a roof design without any load bearing metal supports or joints.

Any metal joints that can still be seen today only served as an assembly aid, and they remain there without static importance. According to Voss, ”Industrially manufactured, dimensionally stable Kerto® LVL (laminated veneer lumber) helped us to achieve an efficient solution. We were thus able to develop an object-specific design that meets both the static and the economic requirements.”

Load bearing

Minimal thickness, maximum bearing

”Since a traditional timber framework would be too expensive, we chose pre-fabricated cross-bonded Kerto-Q wooden trusses,” says Stefan Heidrich. They are constructed of two halves, which are a mirror image of each other. The halves are joined by a round metal bar, which works as a pin in the structure. These built-in metal parts are exposed in the temperature-controlled hall. In this air-conditioned area no condensation is to be expected. The entire roof truss is fully accessible in accordance with safety regulations to ensure the monitoring of the roof’s condition and the easy replacement of parts.
 
Open the full technical drawing (.jpg)

More information

Kaifu-Bad - load bearing wooden structures 
 

Despite the truss members length of 14 metres, they could be manufactured in a thickness of only 134 mm. This was possible as the Kerto-Q glued components have very high strength, stability and rigidity, and can thus take over this important part of the statics. In addition, the Kerto-Q LVL panels allowed an arched cut of the bottom of the trusses, restoring the historical shape of a barrel vault.

Bracing

Values guide Metsä Group's operations 
 

Roof bracing made simple with Kerto-Q LVL panels

Forged drawstrings that are based on historical models, give Kerto® LVL glued trusses in the necessary horizontal bracing. These metal parts add a touch of historical continuity as they are fully visible above the swimming pools. The roof frame covers a span of 27.5 metres. The Kerto roof panels together with the historic masonry walls brace the buildings against horizontal loads from wind and usual structural asymmetries. This was possible with the use of 69-millimetre-thick Kerto-Q LVL panels. The Kerto-Q LVL panels ensured high strength values at a relatively low thickness, with a very high load capacity and dimensional stability. 

Kerto purlins with wood joints

New way to preserve the old

Two rows of purlins, one for the roof and second for the ceiling, connect the main trusses with special wooden joints. The purlins were made of slender, high-strength Kerto-S LVL beams, which are ideally suited for this application. The main trusses were drilled for service access in a way that is not visible from the swimming pool due to the suspended ceiling required by the preservation order.

More information

Product: Kerto glued components

​Structural gluing of Kerto-Q panels allows large cross-sections that exceed standard product dimensions. Allows wide range of shapes to be machined.

Connection: Kerto hanger with a notch

​​The end of Kerto-S is notched to allow the Kerto hanger bottom "rail" to fit under the beam and at the same time keep the bottom on the same level as the arch.

Connection: Kerto hanger​

​Kerto hanger is structurally glued to Kerto-Q component. Steel angles add support during construction. The top end is machined so that it aligns with the top of the Kerto component.

Self-supported panel joints​
​The edge of the panel can be machined for self-supporting panel joints.

Usually, they form a half-lap joint where part of the panel thickness is machined to create matching pairs of the edges. The diameter, spacing and insertion depths of the fasteners should be according to the structural design.

Product: Kerto-S

​​Top or bottom edge machined to align with the arch. Positioned vertically for maximum capacity. Well suited for purlins.

Product: Kerto-Q

​​Thick panels give high bracing capacity and allow wider purlin spacing. Big panels allow fast assembly. Easy to fasten for load transfer.

Results

Images above Mr. Voss / MRLV

Fast installation of Kerto® LVL elements saves money

Thanks to the pre-fabricated Kerto® LVL (laminated veneer lumber) elements, the whole project was finished much faster than a conventional reconstruction. As all the wooden parts had already been finished at the factory, they were ready to install on site, which saved significant amounts of time – and money. Although the challenging roof structures and the moisture-proofing caused extra costs, these were covered with the savings from faster and more efficient installation. Use of pre-fabricated wooden elements on this scale is still a new and rare thing in Germany. 

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