Roof for the Mītava open-air concert hall in Jelgava, Latvia

The Mītava Open-Air Concert Hall is the largest wooden structure and largest open-air concert hall in Latvia. It has a roof span of 58 meters. We designed, manufactured, and built this building. 

  • Location
    Jelgava (Latvia)
  • Year of construction
  • Dimensions
    Building area 2770.7 m2, ridge height 15 m
  • Client
    Municipality of Jelgava
  • Architect
    Vents Grietēns, “Grietēns un Kagainis”

The role of ZAZA TIMBER Engineering (previously: Rodentia) in this project was:

- Structural design
- Detail drawings
- Shop drawings and assembly drawings
- Fire safety modelling and consultation
- Custom-made structural steel gutter solution to divert rainwater from the roof structure

The roof is made of curved glulam beams connected with steel ties on a ring beam level. The curved beam span is up to 57.8 m.
During the design process, we considered the open-air nature of the building, as well as its exposed location near water. In combination with the relatively light timber structures and the tensile membrane roof, there is a significant uplift load on the structure.

Steel dowels and bolts were used for the joints, and Rothoblaas fully threaded screws were used for high load bearing capacity moment connection.

As a non-standard solution, German custom-made spherical bridge bearings by Maurer were used for some of the connections between the ring beam and steel columns to provide rotation between these elements.

The project and calculations were developed in collaboration with the engineers of the Canobbio Textile Architecture roof membrane manufacturer, who calculated the roof membrane, as well as Project 3, who designed and calculated the building’s foundations. The use of a tensile membrane allowed for a roof structure without additional support elements between the curved roof beams (with a 5.5 m space between beams).

ZAZA TIMBER Production (previously: IKTK) manufactured the timber structures for building the stage.

We made 235 curved and straight details with a total volume of 521 m3. We mainly used 24 cm-wide boards. The strength class of the structures is GL28h. The structures were made of pine and spruce wood.
- The block glued ring beams around the perimeter of the build are 34 meters long, 2.1 m high and 48 cm thick (glued from two 24 cm beams).
- Roof beams: 2.1 m high, 24 cm thick with varying length, between 14 and 33 m.
- Other details we produced: purlins, acoustic details, beams for auxiliary buildings.

The factory provided all necessary cutting, drilling, sawing.

ZAZA TIMBER Construction (previously: Igate Būve) provided a full construction cycle: building the foundations and timber structures, roof membranes, wind mesh, electrics, lighting, rainwater plumbing and landscaping.

We built the roof structure over the existing open-air amphitheater.

Before assembling the timber structures, we built deep foundations: 106 drilled pipes to a depth of 6 m, concreting, assembly of steel columns.

We assembled the timber structures and large span beams (up to 57.8 m).

For the structures not exposed to direct weather, we used a clear varnish to protect the wood (Remmers HK-LASUR), while the structures exposed to direct weather were treated with a primer (Adler Pullex Imprägnier-Grund), a solution that prevents the capillary absorption of water via cross-cut wood (Adler Hirnholzversiegelung), universal timber lasur (Pullex Plus Lasur) and impregnating timber lasur (Adler Protector Plus).

We organized the special transportation of oversized structures.

We prepared the connectors (screws, steel parts, shear keys, ties). For assembly, we used a special screwdriver with computer-controlled torque.

We made acoustic panels and built acoustic solutions.

We built a tensile roof membrane (2770 m2), architectural visual quality, self-cleaning coating (delivered by Cannobio).

We paved and landscaped the grounds.

Construction time: 11 months.