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Construction company Reponen – Energy-efficient construction with the support of VTT Expert Services


​When construction company ​Rakennusliike Reponen introduces new technologies or concepts, VTT Expert Services provides its support. The companies have 15 rewarding years of cooperation behind them.

In the early 2000s, Rakennusliike Reponen sought experts for energy-efficient construction.

"We saw that energy-efficiency was the future. VTT has been studying and developing energy-efficient construction for several decades. We wanted to tap into that expertise and use it for the construction of blocks of flats," says Mika Airaksela, CEO of Rakennusliike Reponen.

VTT, on the other hand, was pleased to have found a construction company that was genuinely interested in taking forward the concept they had developed. Still in the '90s, many construction companies built their projects according to the minimum requirements. Because energy-efficient construction requires wide-ranging expertise, VTT helped Reponen to put together a suitable group of companies. Five companies were invited to take part, and all but one are still involved. In the initial stages, not all technologies needed for energy-efficient construction had been fully completed. Rakennusliike Reponen built the first passive solution-level block of flats in 2005.

"VTT invests in research and expert services with longer-term goals, product development, experimental building, and follow-up of a new product or concept. We bring forward future needs, and companies can join us in developing them further," says  Senior Specialist Mikko Saari from VTT Expert Services.
In Airaksela's opinion, energy efficiency is worth investing in, because a major part of a building's carbon footprint is generated during use by heating, electricity and cooling, and energy prices are unlikely to drop in the foreseeable future. The energy efficiency can be best affected during the development stages of a construction project. With VTT's assistance, Reponen are able to reduce the carbon footprint of their construction projects to less than half of the level required by present regulations.

An energy-efficient house does not need radiators

"A house must be designed as an entity instead of trying to improve one single piece here and another one there. VTT Expert Services performs the thermography and airtightness studies on our building projects, which help us eliminate the biggest problem points and produce functional houses. When we started the tests, no one else was doing it yet," Airaksela notes.

A fully functional house is comfortably warm, draughtless and has fresh indoor air. Its energy consumption is low, the technology is kept simple, and the structures and building technology are fully functional in every respect. Reducing the amount of technology increases cost efficiency, which today makes it possible to build an energy-efficient house at the same price as a house built using older technology.

In a building implemented using Rakennusliike Reponen's MERA block of flats system (abbreviation from the Finnish concept for energy-efficient building, "Matala Energia Rakentaminen"), the walls, doors and building technology solutions create an external envelope with high thermal insulation capacity. Consumption is therefore virtually non-existent, and heating is needed only during one quarter of the year. If an "ordinary building" requires an average of 100 heating units a year, a MERA building needs no more than 20. 

"Thanks to a heating ventilation system developed by us, radiators and floor heating could be left out of a MERA blocks of flats, excluding bathrooms," Saari points out. "In fact, this is quite a radical innovation."

VTT Expert Services provides independent tests and measurements

The use of wood for building blocks of flats is still new and rare. Eight years ago, one per cent of all new blocks of flats were built of wood. Now the percentage has grown to six. For Rakennusliike Reponen, which has built more passive houses than any other construction company in Finland, using wood has not caused any problems. The largest wooden block of flats in Europe in the housing fair area of Kivistö, Vantaa, is one of the company's best known projects. Acting as an independent actor, VTT Expert Services has been responsible for studies such as settlement measurements, thermography, airtightness measurements, verification of plans made by designers, and interviews related to customer satisfaction in projects involving wooden blocks of flats.

"VTT Expert Services has been involved in all our development projects for the last 15 years. The collaboration has been good and constructive. We would hardly have continued it for so long if this was not the case," Airaksela says with a laugh.

In autumn 2016, Reponen launched a new building project in the new residential area of Kuninkaantammi in Helsinki, where two blocks of flats will be build of concrete and two of wood on adjacent plots.

"Since the buildings will be located in the same courtyard area, we can objectively compare the construction speed, the carbon footprint of the buildings, moisture performance and customer satisfaction. As far as I'm aware, no such comparisons have been made before" Airaksela says. The buidings are expected to be completed towards the end of 2017.

Tel.+358 20 722 7070
Fax+358 20 722 7001

Opening hours 9:00 - 11:00 and 12:00 - 15:00, GMT +2 time zone


P.O. Box 47, FI-02151 Espoo, Finland
Tel. exchange +358 20 722 111
Opening hours Mon - Fri 8:00 - 16:30,
GMT +2 time zone
Fax +358 20 722 7001
Contact us

Tel. +358 20 722 7070
Fax +358 20 722 7001
Opening hours 9:00 - 11:00 and
12:00 - 15:00,
GMT +2 time zone