Apartment block - Oulu, Finland

Figure 67 & 68: Case 2. Before and after renovation

The Building is situated in Virkakatu 8, Oulu, Finland, this case was a pilot project and is owned by PSOAS Student Housing Foundation. The building was built in 1984 and possesses eight apartments, which are split in two floors. Its state before the renovation was not good and outdated, so it needed a complete refurbishment. There is approximately a floor area of 576 m2 available.

The renovation was accomplished by NCC Construction Finland (NCCFI), which took over of design, retrofitting and so on. The employed building method has replication potential for the retrofit of facades made from concrete sandwich elements.

The renovation began on site in August 2012 and finished in February 2013, so it lasted around 7 months with a cost by 1.4 million of euros. The construction was financed by PSOAS although also counted on Europe Union support.

The following figures 67 and 68 display the building before and after renovation.

Although the target has not a big impact, it is about a case with high replication potential due to its building technique and character, typical of standardized suburban construction in Finland.

Before renovation

As a result of a research done previously, PSOAS decided on realizing a building renovation, including a comprehensive refurbishment of indoor spaces and a facade renovation with the TES method based on using timber prefabricated elements for the renewal of the building envelope.

The structure of the building is based on standardized load bearings end and partition walls, with non-load-bearing sandwich elements on the long exterior walls and the upper floor constructed with long precast hollow core slab elements. The main concrete facade elements are faced with face brick. The building has concrete element balconies as free-standing towers, tied back to the facade concrete elements. In addition it had an air tightness of 3.3 l/h. The estimated existing external wall had a U-value of 0.28 W/m2K according to Finnish building regulations with 140mm of mineral wool.

The original ground slab, which had a U-Value of 2.1 W/m2K, consisted of 70 mm reinforced concrete slab insulated with 50 mm polystyrene, while the roof U-Value was 0.22 W/m2K. The windows presented a U-Value of 2.1 W/m2K.

The heating system was connected to the district heating system for the property, shared by all 5 houses and the heating level was estimated to be 148 kWh/m2 and the target value was set to 30 kWh/m2. The ventilation system was natural.

The total energy consumption was 115 MWh/year.

After renovation

The building underwent a complete retrofitting of the envelope. The outer facade layers of the existing prefabricated concrete sandwich elements were removed and only the inner concrete layer was left in place.

A new facade was retrofitted, by using prefabricated timber based elements. The old roof was replaced completely by a new timber truss roof and a new thermal insulation layer of 550 mm blown loose fill mineral wool resulting in a U-value of 0.08 W/m2K. Moreover the existing ground floor slab was replaced, with a new in-situ ground floor slab with 200 mm graphite-enhanced EPS insulation. Special effort was made to improve airtightness in the building envelope, and leaks in the concrete frame were grouted, passing from 3.3 l/h to 0.8 l/h.

The old windows were replaced for other new ones with a U-Value of 0.8 W/m2K. Besides, the lighting was changed to LED in stairwells and apartments.

It was installed, a new district heat circuit and domestic water pipes from the service building as well as a new real-time automatic valve control of the flow of space heating from the district heat exchanger, which had been replaced in 2006 by PSOAS. It was also added, a new thermostatic radiator control of indoor temperature.

The energy performance of the building was improved by adopting apartment-specific, balanced ventilation systems equipped with high efficiency heat recovery.

After renovation, the new consumption passed from 115 MWh/year to 48 MWh/year where only the heating system consumes 23 MWh/year (40 kWh/m2year). In the following figure 69 is the Finnish Energy Certificate for the building before and after the renovation represented.

Figur 69

Figure 69: Energy certificate (Before/After renovation)

Costs summary

Next, is shown a table with the different costs of the project, counting a lot of types of costs, such as: design costs, surveys costs or contract general costs, etc.

It is important to stand out that the table has been gathered from the final report of the project, which explains the following:

“NCCFI cost breakdown for Oulu demonstration project. Facade size: total area approximately 480 m2. Facade cost includes passive house compliant windows, but excludes new roof and balconies. The cost is divided by 576 m2 leasable floor area. As a result of the small size of the demonstration, the overhead site and contract costs were large. This overall cost level was considered comparable with new build market prices for passive house energy performance. As a result, the asset value of the property has been significantly improved for a renewed life expectancy of 50 years. (S. le Roux, 2012)”

Overall measures Cost % Cost/m² leasable floor area
Design 49 200€ 3% 85€
Surveys 12 300€ 1% 21€
Site costs 86 100€ 6% 149€
Contract general costs 84 200€ 6% 146€
Σ Overhead costs subtotal 232 000€ 16% 403€
TES energy façade 233 300€ 16% 405€
Roof replacement 84 400€ 6% 147€
Ground slab replacement 72 600€ 5% 126€
Building services 80 000€ 6% 139€
Monitoring and automation 27 300€ 2% 47€
ΣEnergy renovation measures 497 500€ 35% 864€
Interior renovation and balconies 700 500€ 49% 1 216€
ΣTotal 1 430 000€ 100% 2 483€

Renovation process

Building works began with the removal of the original in-situ ground floor slabs and the external layer of concrete and brickwork from the precast facade elements.

The old thermal insulation layer was stripped away. Additional foundation structures were added, widening the existing concrete footing to carry the load of the new facade elements.

The original facades consisted of prefabricated sandwich elements with 80-85 mm external brickwork, 130-140 mm of thermal wool insulation and an 80mm inner layer of concrete on the long facades and a 150 mm inner layer of concrete on the short end facades, which carried the upper floor slabs. Detailed measurements of the existing building were made for the manufacturing of the retrofit facade elements. New facades were manufactured 125 km away from the site, in a northern Finnish factory in Haapavesi, from prefabricated timber based elements. A thin thermal insulation layer was added to the elements on site as an adjustment layer between the elements and the uneven existing concrete surface.

Figur 71

Figure 71: Set of elements of facade

External cladding and windows were assembled on site. The total thickness of new thermal insulation in the completed facade is 300 mm. Inward opening wood aluminum passive house casement windows were installed. The TES Facade (figure 71) comprised of a prefabricated timber element system installed over an existing inner precast concrete shell:

  • 7mm corrugated fiber cement facade cladding, color black, and installed in-situ.
  • 44 mm air gap (22 + 22x100mm – c600mm sawn timber battens).
  • 9 mm gypsum wind barrier.
  • 50 + 200mm glass mineral wool thermal insulation (declared Lambda value 0,033 W/m2K).
  • 42x48mm c600mm sawn timber horizontal battens.
  • 42x198mm c600mm sawn pine vertical load bearing frame.
    Figur 72

    Figure 72: Renovation Facade steps

  • 9 mm plywood board.
  • 50 mm thermal insulation for adjustment layer, installed in-situ.
  • 80mm inner layer of existing precast concrete sandwich element.

The following figure 72 shows the completed process of facade renovation. From left: Original precast sandwich element, stripped concrete shell, adjustment layer to receive TES facade, prefabricated elements assembled on concrete shell, cladding applied in situ (M3 Architects, 2012).

Project highlights

  • The Finnish BES5 system with standardized precast elements and joint details was widely used for housing projects across Finland, and therefore the findings and solutions used for this demonstration project offers good possibilities for replication in modernization of Finnish housing projects from 1970’s onwards.
  • Compared to new building, a refurbishment project has good potential to be a safe and dry construction process, so long as the facade is well protected during the building site works.
  • Tenants valued the design and outcomes positively, but they were preoccupied with the disturbances that they suffered during the renovations. Despite of this, there were some positive comments.
  • Overall, a strong increase in perceived architectural qualities regarding public spaces within the building but also balcony design and bathroom.

Additional material:

Company: E2ReBuild 2014
Author: Simon le Roux

Company: E2ReBuild 2014-06-24
Author: Simon le Roux

Company: TES EnergyFacade 2011
Author: Dipl.-Ing. Frank Lattke