For modelling existing buildings for adaptive-reuse purposes in eTool it’s important to launch into your LCA with full clarity on how to account for the existing building in a fair, reasonable, and repeatable manner. There are three main scenarios that our users encountered and we’ve provided some guidance below on how to attack these.
Foot Printing “As Built” or Existing Building
An “As Built’ audit of an existing building is essentially conducted in a similar fashion to a standard LCA except that the inventory collection will focus on the actual materials, processes, energy consumption, water consumption etcetera. At eTool, we also encourages users to put forward recommendations for improvement that can still be achieved by retrofitting the building.
Retrofit or Refurbishment of Existing Building
If the primary purpose of the LCA is to improve the environmental performance of the building for the remainder of it’s life, the study should be approached as per a normal LCA study. Care should be taken to assign appropriate design lives to the components in the building depending on whether they are new versus existing, and/or will recur during the remaining lifespan of the building.
Some strategies investigated in the study may ask the question “is it better to keep this existing component or replace it?”. For example, keeping the existing windows (poorly sealed, high conductivity) may have a lower embodied impact, but what is the trade off in terms of higher energy use for heating and cooling. In this instance, the best way to model this is to include the existing windows in your base case, and when modelling the improved case add the additional new windows. Set the design life of both components to accurately reflect the number of replacements you expect to occur over the whole building life. This could require a bit of a “hack”, for example, if the building is half way through it’s predicted 100 year life span, and you expect the old windows to never require replacement but the new ones to require replacement after 25 years use, you would set the service life of the windows as such:
- New windows: 50 years (will force eTool to count 2 x the windows)
- Old windows: 100 years (will force eTool to only count 1 x the windows)
Update your energy use with the simulated energy savings for each scenario. This should provide a relatively accurate life cycle picture of the net benefit (or impact) of the strategy.
When modelling existing buildings it can be tricky to comply with current standards when a very old building is being modeled (+50 years) as there would not be LCI data available for the materials and processes used in that building. That said, as long as the study authors (you) are transparent about this shortcoming it is better than exiting the study.
New Building that Retains Parts of Existing Building
The approach our users normally take for this scenario is:
- Business-As-Usual Design – Model the existing building along with all the new parts of the building i.e. assuming the whole building was a new construction. All parts of the building that are new/additions should be modeled as per normal although to facilitate the next step, it would be a good idea to keep the ‘existing’ parts of the building in a separate template.
- Proposed Design – delete all material elements of the existing building that are being preserved to demonstrate the ‘benefit’ of reusing those parts of the building. Do take into consideration of elements that will have recurring impacts that may occur during the life cycle of the ‘new’ building (i.e. wall/ceiling linings, internal & external finishes). For elements that will not be replaced in the remaining life time of the building, the product life for those elements should perhaps just be increased to cover the rest of the service life of the building.
Note that any demolition impacts of the existing building to facilitate the construction of the new building should not be included in the LCA study of the ‘new’ building as those impacts should be accounted for in the LCA study of the existing building’s own study. Including those end-of-life impacts would be double counting the impacts according to EN 15978 methodology.
The figure below demonstrates the boundaries for modeling existing buildings in eTool.
In this scenario, it would be somewhat pointless (or not be of significant impact) to try to model the benefit of retaining elements that have a very short service life (i.e. gets replaced quickly like internal finishes/linings) as you will still need to account for their recurring impacts that occur in the rest of the building’s service life. Retaining structural elements that will last for the rest of the building’s life (i.e. foundations, structural walls/floors etc) or will only be replaced once or twice over the life of the building would be of much bigger benefit to model.
Remember to record the removal of the existing building parts in the recommendation tab to document the benefits of the adaptive-reuse strategy. This will then quantify the benefit of retaining the existing building. In effect the study is quantifying the benefit of the avoided material use that was achieved by retaining the part/s of the existing building.