Why wood beats concrete when it comes to building eco-friendly apartments

A wooden apartment building produces 5–11 percent fewer emissions during its lifetime than its concrete counterpart does, according to a new study.

The reduced emissions do depend on the building’s energy efficiency, but the research for Sitra found that the construction phase alone accounts for 29 percent of the difference – the equivalent of taking a car off the road for two years. The most crucial factor, however, remains the type and amount of energy used after residents move in.

Sitra’s Energy Programme commissioned consultants to investigate the carbon footprint of a recently finished wooden apartment building. The study conducted by Bionova Consulting adds more evidence to the ongoing debate on the matter.

Director Jukka Noponen, head of Sitra’s Energy Programme, points out how important it is to know more of the carbon footprints of buildings, regions and communities. ”Lower emissions should be a priority in all building and community development projects. All materials have potential,” he says.

According to the study, energy-efficient buildings and green energy solutions are the most commonly used methods for reducing emissions. Making the transition to passive houses reduces lifecycle emissions by 16–18 percent, while near-zero energy building reduces them by as much as 39 percent. As the energy consumption and emissions of buildings decrease, attention should also be turned to construction materials.

The case study carried out by Bionova Consulting examined a hybrid wooden apartment building for which detailed structure-specific data was available. The construction project involved Rakennusliike Reponen, Versowood Oy, Koskinen Oy and the city of Heinola.

The data from the project was compared to the data of a corresponding concrete building. According to the lifecycle survey, the difference – arising during the construction phase – between the emissions of wooden and concrete buildings is 5 – 11 percent in favour of the wooden structure, depending on the energy efficiency and the length of the lifecycle studied.

”The significance of the construction phase on a building’s lifecycle emissions has increased twofold in just a little over a decade,” says Leading Specialist Jarek Kurnitski of Sitra’s Energy Programme.

”For passive apartment buildings, emissions during the building’s use account for some 70% of its lifecycle emissions. Of course, for energy-hungry buildings, the significance of emissions during use is only more prominent.”

Kurnitski stresses that climate impact should be studied alongside energy efficiency in order to discover the most cost-effective means to decrease emissions. In the future, efficient use of materials should also be included in the search for further efficiency. Generally accepted standards and guidelines are needed to make carbon calculations a regular practice in the design and procurement of buildings.

The consultants’ work focused on duty cycles 30, 50 and 100 years long. The volume and quality of energy consumed during the use of the building constitute the single most important element in terms of carbon footprints when conducting investigations based on the entire lifecycle of a building.

The study revealed just how much the significance of construction materials as contributors to carbon footprints has increased. When emissions generated during the construction phase alone were considered and lifecycle calculations left out entirely, the emissions of an apartment building built of concrete were 29 percent higher than those of the hybrid wood building.

The construction phase emissions per square metre (heated net floor area) were 191 kg CO₂/nm² for the timber structure and 268 kg CO₂/nm² for the concrete structure. Thus the difference per square metre is 77 kg CO₂/nm² and, per each family living in the building, 6 tonnes of CO₂. This is the equivalent of two years car use.

Publication information

Passiivitason asuinkerrostalon elinkaaren hiilijalanjälki -Tapaustutkimus kerrostalon ilmastovaikutuksista
(Lifecycle carbon footprint of a passive block house – A case study about the climate effects of a housing block)

Panu Pasanen, Juho Korteniemi and Anastasia Sipari
Bionova Consulting
Sitra Studies 63 (in Finnish)
2011
ISBN 978-951-563-820-5
ISSN 1796-7112 (URL:  http://www.sitra.fi)

Further information

 Jukka Noponen, Director, phone + 358 40 587 4323
Jarek Kurnitski, Senior Lead, Built Environment, phone + 358 40 574 1870