Brogården Alingsås, Sweden
This case is about 8 blocks of flats which were built between 1971 and 1973. It belongs to AB Alingsåshem which is a municipal housing corporation in the municipality of Alingsås, Sweden. The town is situated in the western part of the country.
These buildings count on 144 apartments and 14860 m2 living area in total. They also have balconies and patios. Works began in August 2011 and finished in September 2014. The total cost is approximately € 36.5 million where there were some grant of € 0.68 million by European Union and € 0.4 million by local government, the rest was paid by a loan.
The aim of renovation was to reduce the very high use of energy, besides there were leaky pipes, lots thermal bridges, annoying air currents, poor soundproofing, and so on.
The envelopes of buildings (figure 74) were formed by gypsum boards on non-loadbearing wooden studs and facade bricks, as well as being
insulated by a thermal insulation of 95 mm of thickness. The basement was of concrete walls without any insulation while the roof had an insulation of 300 mm on roof slab. The types of insulations are unknown.
The buildings presented windows with single pane and supplementary aluminum sash and one additional pane, their U-Value were 3.0 W/m2K.
The air conditioning was composed for a mechanical ventilation system by air intake through window vents, and a district heating system by radiators. This heating system was renewable to 98 % as well as serving to warm up water too.
The common areas had lighting by incandescent light fittings. The building did not count on any renewable system in order to produce energy.
According to the preliminary studies, the energy consumption was approximately 177 kWh/m2, where the heating system was 115 kWh/m2, the hot water 42 kWh/m2 and the electricity of the building 20 kWh/m2.
It is important to stand out that Brogården is classified as an area of conservation value. Therefore the selected material had to be similar to the original buildings.
The envelope had to be demolished in its entirety. The previous wall was replaced by a new wall with several layers of insulation and slotted steel studs; it has 440 mm of insulation in total. Regarding basement a layer of 100 mm expanded polystyrene was installed at 1 meter below ground level as well as 100 mm drainage panels downwards to ground floor. On the roof, it placed 400 mm of a new mineral wool insulation.
Windows were changed for a triple pane system with insulated glass which counts on a U-Value of 0.85 W/m2K.
With regard to air conditioning, the ventilation system was balanced by a single heat recovery unit for entire building, which also combines with the heating system (district heating). The hot water system continues being the same although solar collectors were installed on the roof in order to support it, moreover water-saving faucets and shower heads have reduced energy used enormously.
As it is usual in these cases, lighting was changed to low energy fittings such as halogen and LED lighting in staircases.
The new energy consumption is 48 kWh/m2 in total, where only 19 kWh/m2 belongs to the heating system while the hot water system reduces its consumption to 18 kWh/m2 due to the new solar collectors. Finally the electricity of the building is 11 kWh/m2.
Due to cold and wet weather during the winter season, it is important to protect (if it is possible) the work in the external part of the building like the facade; in consequence it should cover the facade with a cape after the old brick facade and original balconies are removed.
After removing the façade, it assembles the outer wall with its four layers of insulation (figure 77) (mineral wool), finishing then with the facade tiles installation.
The same as with the facade, it installs the insulation on the roof . First, the roof structure has to be reinforced. For that, it rebuilds the wooden roof and connects the eaves with the exterior wall and its insulation.
Also, it is important to add an additional 100 mm of insulation in top in order to ensure moisture safety (keeping the relative humidity of the wood well below critical values) and prevent temperature of the wooden layer from dropping too low.
The work on the roof is especially important as the ventilation ducts will be situated in the attic; therefore it has to be insulated perfectly in order to prevent unwanted heat exchange between the air and the attic space.
As it can appreciate in the following figure 84, the attic insulation (300 mm of mineral wool) will fill up towards the sides of the box and the wooden shelves in the middle of the picture are built temporarily in order to enable the insulator to reach to fill every space between the ducts.
The holes for windows are made in the prefabricated elements, which will be protected by a plastic foil or a wind barrier from the outside, prior to window assembly. During the window assembling, a plastic foil sheet is mounted around the frame which the interior plastic foil of the air barrier later will be joint to.
The next steps of the windows are: raising and insulating the inner wooden frame of the wall. Around the window, the angled opening is shaped by wooden elements and then to be filled with insulation.
- Big reduction of energy consumption, around 60 %.
- The tenants had to relocate during the project; however Alingsåshem offered them apartments in the same area while the renovation was being carried out.
- After renovation, some tenants (approximately 25 %) did not get back due to the large rent increase (an average of 40 %)
- After refurbishment, electricity and hot water is no longer included in the rent.
- The inclusion of high energetic efficiency equipment in lighting and water achieved a marked reduction in energy consumption in these systems.
- In general, residents were satisfied with the apartments after the upgrade.
- The knowledge developed at Brogården has spread to other projects, through e.g. over 700 study visits and collaborations in national and international energy efficiency programs.