Finnvedsbostäder, a public housing company, has developed five apartment buildings in the center of Värnamo (Sweden) that met passive house standards. The five buildings consists of 40 rental apartments were designed by BSV Värnamo architect and engineer firm, and constructed by NCC. Despite its first project with such high airtightness requirement, NCC has managed to succeed and finish the construction in June 2006.
The core load-bearing structure were made of concrete and cast on site. The base floor was constructed with quite good U value 0,09 W/m2.K. Below the concrete floor is 350mm of EPS with insulated plinth, which was done by having two L-shaped EPS elements on the outside of the plinth. The exterior walls were made of wooden frame packed with 285mm of mineral wools divided in 3 different layers and 150mm cellular plastic in the center of the mineral wool layers, all of which made a U-value of 0,095 W/m2.K. The roof has a pretty common passive house U value: 0,07 W/m2.K by having three layers of mineral wool insulation.
Windows were planned to be Dreh-Kipp windows with very good U values, however, it was not possible to produce such windows in Sweden at the time. Therefore, other windows with the mean U value of 0,94 W/m2.K were in use. To ensure overall good U value for the apartments, the number of fixed windows was increased (because its U value could be lower than operable windows). The apartment entry doors were designed by the general of Finnvedsbostäder himself, due to the difficulty of finding entry door with U value of 0,6 W/m2.k on the Swedish market.
Airtightness and moisture are the two very important aspect in these buildings. To keep the construction airtight and dry, plastic foil was mounted in between the mineral wool layer and cellular plastic insulation layer. The plastic foil in the walls was sealed for each apartment to be able to measure the specific airtightness. As to protect the wooden structure from the moisture in the concrete slab, a metal sheet and a plastic spacer block are placed on the concrete slab under the wooden beams to break the capillary suction.
All five buildings have solar collectors for domestic hot water production, one collector of 25m2 on each building. Additional heat is supplied from electric batteries in the water tank. Hot water is then distributed from the central room to individual apartments. Heatings in each apartment is provided by mechanical ventilation unit with heat recovery, efficiency 85%, with electric heating battery varying 0,9 – 1,8 kW depends on the apartment size.