Service life is a key factor in sustainable construction
Will a building material last for 50 years, or have to be replaced after 15? The answer will have a major bearing on the cost and environmental impact of your building.
It is therefore important to have a good grasp of life cycle costs (LCC) and life cycle assessment (LCA) in sustainable building. Especially if you want your building certified. Senior Researcher Harpa Birgisdottir offers her views on the life cycle of construction materials.
When you work with sustainable building, it is important to take a long-term view and choose building materials carefully. For example, is it better to choose materials that are slightly more expensive to buy, but that last significantly longer than cheaper alternatives? And which materials result in the lowest environmental impact over the life of the building?
Life cycle costs (LCC) and life cycle assessment (LCA) are two tools that can help you make the right decisions, according to Senior Researcher Harpa Birgisdottir from SBi, the Danish Building Research Institute.
“It’s usually the construction phase for a building that receives the most attention. But it’s important to know the life times for the various materials, and shift the focus to what is best based on the building’s total service life. This applies to major elements such as cladding and load-bearing walls, as well as floor and ceiling materials. People are often surprised to find that a material which is cheaper or has a lower environmental impact at the time of purchase turns out to be less eco-friendly in the longer term,” says Harpa Birgisdottir.
LCC: Life cycle cost
Using LCC (life cycle cost), it is possible to identify the total lifetime costs of constructing the building and maintaining it for a defined period, such as 50 years.
An LCC calculation includes not only capital expenditure, but also what it will cost in present value to maintain and possibly replace the various building elements. Water and energy costs are also included in the calculation – as are cleaning costs, typically a major item in the total cost picture.
LCA: Life cycle assessment
An LCA (life cycle assessment) examines the building’s total environmental impact and resource consumption.
It looks at raw material extraction and processing, transportation, production of the various building materials, operation and maintenance, and waste treatment and recycling when the building is one day demolished.
Highly weighted in certification and tenders
One of the areas where LCC and LCA play an important role is in relation to the certification of sustainable buildings – such as a DGNB certification. DGNB gives the environment and economics 22.5 per cent each of the total weighting. LCA accounts for 13 of the 22.5 percentage points in the environmental component.
Some tenders may also require LCA calculations for the various building components. For example, the City of Copenhagen requires LCA calculation in their own projects, beyond a certain size.
Short or long time frame
The service period is a key aspect in the calculation of LCC and LCA, i.e. the time frame used for the building’s life cycle. It can vary for different building types, and is typically defined in advance if the calculation is part of a certification process.
For example, for a DGNB certification the service period for LCC is 50 years, while LCA is calculated for both a short period of 50 years and a long period of 80-120 years, depending on the building type. There can also be good reasons to calculate using a longer period.
“The effect of the building’s service life on the overall assessment varies depending on the design and the materials chosen. Many building materials have a service life of well over 50 years. In such cases we need to look at a service period of something like 100 years in order to properly distinguish between materials with short and long life times,” says Harpa Birgisdottir.
Standard calculation tools
- The Danish Building Research Institute (SBi) at Aalborg University and the Danish Transport, Construction and Housing Authority have jointly developed the LCAbyg and LCCbyg tools, which can be used to calculate life cycle cost and life cycle assessment.
- The two tools use set standards for the calculations. As a supplement, SBi published a report specifying the average life times for various building elements in 2013.
- The LCAbyg calculations depend on environmental data for the building products being assessed. Ökobaudat – the German national database containing average data for various products – is used.
- Users can also add data sets composed of information from manufacturers’ Environmental Product Declarations (EPDs) and the like [insert link to EPD article]
Can map the environment potential
“When calculating LCC and LCA – for example for a DGNB certification – we have to stick to standardised data in order to be able to compare the calculations. Calculations are performed in accordance with standard rules and estimated life times, as specified in the SBi report from 2013,” says Harpa Birgisdottir.
“In other cases, we want to use LCA to investigate the environmental potential of various design solutions. Such as the environmental impact of using different techniques to protect a material so it lasts longer. Or the effect of reuse and recycling on a given construction project. The Danish Realdania organization did this in its project MiniCO2 houses in Nyborg. We were forced to adapt the standard calculation rules slightly in this case.”