Image: Wingårdh Arkitektkontor AB
Constructing buildings with wood frameworks instead of concrete is good for the climate. This has been shown in a scientific comparison of the two building materials. Even economically, wood comes out best.
Välludden in Växjö is one of the building projects that has been started since, in 1994, in Sweden, the limitation of construction in wood to two stories was waived. This project entails, among other things, a four story building with 16 apartments. The net emission of carbon dioxide from the building has been analysed from the perspective of frameworks in wood or in concrete. The analysis is based on two buildings that are identical apart from the framework material and some consequential adaptations.
"With some given prerequisites, among others sustainable forestry with regeneration and good growth, the comparison shows that wood is clearly more beneficial than concrete in terms of the climate. The one or the other can result in a difference in emission of as much as 150 to 280 kg carbon dioxide per cubic metre of heated area," says Leif Gustavsson, professor in building technology at Linné University in Växjö.
The researchers examined four variables in the analysis:
- The difference in the use of energy in the production of the respective buildings (including material and products).
- The quantity of residual products (from felling, wood industry and demolition of the building) that can replace fossil fuel.
- The amount of carbon that is stored in the building's wood material.
- The emission of carbon dioxide in connection with cement production and rebinding when the concrete decomposes.
Wood is the better choice
The results of all the aspects of the study above show that wood is the better choice from the point of view of reducing the net emission of carbon dioxide. In the first place it takes less energy to produce a building in wood. Moreover, the production and the tree felling and demolition of the redundant building provide residual products that can replace coal, gas or oil.
"But it is important that the residual products are really used, for example, to produce electricity or heat. Otherwise a large part of the benefits of wood are lost," says Leif Gustavsson.
That the wood building is better at storing carbon is of no significance with respect to the complete life cycle since a demolished building no longer stores carbon. But as long as more wood is built into buildings than is released during their demolition, the carbon storage increases in the buildings, which benefits the climate. And, finally, cement production is a high energy consumption process. It has a net emission of carbon dioxide – even bearing in mind that the carbon dioxide will rebind with the atmosphere when the cement eventually decomposes.
Lower building costs with wood
Today about 15 per cent of newly constructed apartment blocks in Sweden have wood frameworks. There is a large potential for increasing this at home, and in Europe as a whole the potential is larger still. About a million new apartments are built every year in the EU countries. Leif Gustavsson, as a researcher, has no opinion on which building materials should be used. This is in the hands of the industry, customers and politicians. But he points out the possibilities that exist.
"Research implies that climate change is a problem we must overcome by reducing the quantity of greenhouse gases in the atmosphere. Wood buildings have a positive effect in this respect. And building in wood has a greater effect on carbon dioxide emission than using the same amount of wood to directly replace fossil fuels," says Leif Gustavsson.
Calculations in the Växjö study also show that, of the two project buildings in Välludden, the one with the wood framework cost less to build than that with the concrete framework, meaning that wood buildings and reduced emission do not necessarily entail more expensive housing.
The image shows the first eight story buildings in the Stockholm area entirely in wood, which will be built in Sundbyberg. Martinsons, one of Sveaskog's customers, has been chosen as the supplier and builder of the four spectacular high rises. The first of them is expected to be finished during the spring of 2013 and all four ready for tenancy in 2015. Image: Wingårdh Arkitektkontor AB.