According to measurements of tens of houses carried out in the City of Oulu, a wooden house uses 5–6 per cent less energy than a stone house. This is due to air-tightness.
A directive of the European Union requires each building to have an energy certificate showing its use of energy. This is due to the climate change and the drive to cut back energy use and carbon dioxide emissions, as well as the desire to improve the reliability of energy provision within the EU.
The certificate is obligatory for new detached houses and voluntary for old ones with less than six apartments. As yet there is no follow-up information about which category wooden houses fall into, though follow-up is being prepared, according to Motiva, a Finnish company promoting energy efficiency and the use of renewable energy.
In the City of Oulu, however, the air-tightness of detached houses has been measured for years. There is a link between air-tightness and energy efficiency, as air leaks also carry heat.
”We have measured the air-tightness of tens of detached houses in the Oulu area. According to the results, the air-tightness of wooden houses is one category above that of stone houses. This equals savings of 5–6 per cent in energy consumption,” says Mr Pekka Seppälä, Head of Quality at the Building Office of the City of Oulu.
According to Seppälä the superiority of wooden houses is due to the fact that most detached houses are made from wood, so that there is experience on how to build them well. On the other hand, an air-tight and energy-efficient house can be built from any material.
Quality of work determines air-tightness
Seppälä says that the quality of construction is the deciding factor in the air-tightness of a house. Air-tightness has to be taken into account in the plans, and the plans must also be implemented faithfully.
The most cost-efficient and simple way to improve the air-tightness of a house is to ensure that the air seal is intact. The air seal means that the fabric of the house includes a layer of special paper of plastic which stops air leaks. According to Seppälä, the most important issues are sealing all vents and the joints between structural elements.
Construction quality involves, among other things, that the seams in the plastic seal are not placed on the rock wool insulation between the wall uprights, so that the seams do not buckle. Placed on the uprights, the seams are flattened by the boards used to make up the inside wall.
“The cost of air-tightening is perhaps 300 euros. With an additional 2,000–6,000 euros you get a low-energy house. That’s not much, compared to the typical cost of 400,000 euros for buying a site and building a house.”
Savings worth power plant’s output of several years
Since 2004, the City of Oulu has offered free advice on quality for builders of detached houses and the craftspeople hired by them. This year the activity covers all ten municipalities in the Oulu sub-region.
”We arrange quality information events twice a year. They consist of 5 to 7 evening events plus one event during working hours. We discuss technical issues such as energy efficiency, environmental and cityscape issues and land use planning,” Seppälä says.
The aim is to improve the quality of detached houses built within the city. The results have been positive.
”We have compiled statistics on all detached houses which received a building permission in 2008. They use 32 per cent less energy for heating than the minimum given in the regulations.”
This means that the houses built in 2008 alone use over 600 gigawatt hours less energy than required. The savings equal 3.5 times the annual output of the nearby Merikoski hydroelectric power plant.
Air flow shows up in the heating bill
Energy-efficiency has not been the driver in developing building regulations, and it has only received attention in the past few years.
Building according to the minimum requirements of the Finnish building regulations results in getting a house with an air-tightness of four air changes per hour (ACH). The ACH figure means the number of times that the total volume of air in a space is exchanged in one hour.
In a low-energy house the ACH figure is 1–2, or even below 1. Decreasing the ACH from four to one equals a saving of roughly 20 per cent in the heating costs.
By Krista Kimmo
 The City of Oulu
The City of Oulu in pictures
Modern Finnish wooden towns
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