Why This Post?
Well, it turns out it’s REALLY important. My eyes opened to this on the first life cycle assessment we conducted four years ago now. I probably didn’t realise how important it was until more recently though. The crucial moment was when we did some back of the envelope, top-down carbon budgeting to understand how much greenhouse pollutions our buildings could push into the atmosphere and still enable a stable climate. And this is where it gets interesting. The workings to our rough carbon budget for buildings are here and they throw out a fairly large challenge. In fact, for residential buildings, we need to go net zero operational carbon, and then reduce the remaining embodied emissions by nearly 90%.
Often when you hear the term embodied energy, embodied carbon or embodied impacts, it’s associated with materials choices. Or at least that’s the normal approach to reducing embodied impacts. But there’s an elephant in the living room that’s not being addressed, and this post discusses that. If you don’t want to read about it, sit back and enjoy this video (apologies for the less than professional sound quality).
Some LCA Basics
Life Cycle Assessment isn’t just about measuring impacts. One of the key elements of ISO 14040 is to consider the “Functional Unit” of the object of your assessment. The functional unit enables comparisons between variations of the product or services. In the case of buildings, it would correct for things like design life and size. Inherently, it’s correcting for the function of the building. And the formula for the impacts of a building hence becomes:
As mentioned above, most people focus on reducing the impacts when trying to improve building environmental performance. In reality though, it’s the denominator that often has the most effect on the impact of a building. And this stands to reason. If your building houses more occupants, or lasts longer, it’s providing more benefit for the same initial and disposal impacts (construction and demolition). As mentioned in a related post here, we actually need to reduce our embodied emissions by nearly 90% to hit a sustainable level of GHG emissions. So we need every bit of help we can get, and some focus on functionality and design life presents us with some very low hanging fruit.
Extending design life is a brilliant way of improving the impacts per functional unit for a buildings. This is because most maintenance, energy and water inputs are pretty constant over the building’s life, where as the initial materials, construction, demolition and disposal impacts are quite independent of design life. For residential buildings in Australia, for example, these initial and end of life impacts total approximately 25% of the total life cycle impacts. So, by doubling design life without any change to energy efficiency, you can reduce the overall impacts of your building by over 12%.
How to Influence Design Life
In order to answer this question we really need to think about what is driving demolitions. There are two good surveys that answer this question quite well. One is from the US and the other Australia. They compliment each other in their answers. Here are the results:
US Study Conducted By Athena:
|Reason for Redevelopment||Proportion||Categorised Reason||Proportion|
|Area Redevelopment||35%||Not Related to Durability||61.3%|
|No Longer Suitable for Needs||22%|
|Code Compliance Too Expensive||2%|
|Socially Undesirable Use||1%|
|Maintenance Too Expensive||0%|
|Changing Land Values||0%|
|Out Dated Appearance||0.90%|
|Lack of Maintenance||23.80%||Lack of maintenance / neglect||26.4%|
|Other Physical Condition||2.60%|
|Structural or Material Problem||3.50%||Durability Issue||3.5%|
There seems to be a surprisingly large proportion of buildings that are being redeveloped for reasons other that structural integrity. So, building strength and durability seems to be only part of the design life story. It gets a lot more interesting when you read this study further, as it turns out the longest lasting buildings are actually timber. This was counter intuitive to me, I would have expected the steel and concrete buildings to be lasting longer than the timber ones. The other interesting thing was that there seems to be a hump that a building needs to get over at the 30-50 year mark, and once it’s over that, it’ll last a long time.
The Australian survey supports the theme that durability is only part of the story.
|Reason for Redevelopment||Proportion|
|Demolished for Site Redevelopment||58%|
|No Longer Suits Owners Needs||28%|
|Building Becomes Unserviceable||8%|
Dynamics of Carbon Stocks in Timber in Australian Residential Housing
These studies suggest that the durability of a building only plays a small role in predicting service life. Other factors, predominantly redevelopment pressure, are actually more important. The strategies to counter this are relatively simple. I’ve listed a few below:
- Increase density compared to surrounding suburb through:
– Building value : Land value ratio
– Maximise yield
- Diversify lot ownership, which increases difficulty for redevelopment in the future
- Design quality (create timeless character by ensuring house is designed for the site and surrounds)
- Enable retrofitting (enable occupant density to be increased or building use to be transformed easily without demolition)
Other strategies that assist in extending the service life of the building (or materials) include:
- Ensure appropriate materials are used to weather any likely natural disasters in a region (e.g. fire)
- Where redevelopment potential is very low, focus construction methods
- Design for deconstruction (extend materials service life beyond the building)
We should be thinking of buildings as permanent features, that may stand for many centuries. Whilst this would be a paradigm shift in Australia, there are countless examples of suburbs within the world’s major cities where average design life of existing structures would be well in excess of 100 years. These are cities like London, Paris and Rome where this resilience to redevelopment is in itself the appeal of these cities. There are still pockets of historical buildings in Australian cities also, and our aim should be to promote this approach to the extent that it become the norm.
Increasing functionality is perhaps slightly simpler. It does require buy-in from the owner. In the residential context it really comes down to increasing occupancy within the same space. This doesn’t necessarily mean sacrificing life-style. Very well considered design will yield efficiencies in ensuring that every square metre of floor space is well utilised. Integration of stairs, corridors, studies, entertainment areas etc into bedrooms or living rooms are examples of efficient design. It also pays to compare our current residential functional average to that of our past, and also other countries. The chart below shows that over the last 35 years, Australia has trended badly in terms of environmental sustainability in relation to functionality of residential buildings. During this period, the average size of new buildings has significantly increased, whist the occupancy per dwelling has dropped. It’s encouraging to see a recent reversal in this trend, and we hope it continues.
When we look at he space per person, it’s increased from 54 to 96 square metres. Compare this to the average space per occupant in the UK of 32 square metres and it’s clear that we have some wiggle room in this area.
In commercial buildings, there’s very good financial incentive for improving floor plate efficiency as it means greater rent. Small changes can yield big uplift in rental revenue. Intelligent strategies to improve floor plate efficiency include:
- Sharing services between floors
- Optimising lift size, speed and number
- Minimising services risers
- Minimising circulation ways
The common areas associated with large apartments or office buildings are also very worthy of attention. In Australia particularly, car parks often amount to 25% of total floor space or more. This is a huge burden on the useful floor area of the building, not only in terms of embodied impacts, but also operationally, due to lighting and ventilation requirements. Currently, car park efficiency is an area that doesn’t receive a lot of attention. We have yet to see a design brief where a developer has stipulated a target floor area per car park. Good practice internationally is 20 square meters per car space, and this is with a normal 90 degree layout. If the car park is large enough to accommodate loop, by moving to 45 degree angle parking the space requirements can be reduced even further. This is enabled by reducing the required space to pull in and out of the park to a single lane for 45 degrees nose-in parking, whereas 90 degree parking requires two lanes. It’s not uncommon to see car parks in Perth buildings requiring 30 square meters of space per car park, so there’s huge potential in this area for efficiency improvements and cost gains. Could that three level basement car park be optimised and reduced to two? Ask the question and refer to some international benchmarks on car park design, you might be pleasantly surprised.
The most frustrating thing about all these great opportunities to improve a building’s design life or functionality is that we rarely get to help people do it. The reason is, it’s usually been designed by the time we’re engaged. There’s a nice chart, a version of which is below, that explains how as a project progresses from brief to concept to construction and onwards, the ability to influence it’s environmental performance drops off sharply. This post effectively explains a bit part of the reason why. There are other design opportunities that also need early consideration to become feasible as well. We recognised this pretty early on at eTool and developed way of running ‘scoping study’ LCAs to help design teams identify and reduce environmental impact ‘hot spots’ in their concept designs. We’ve taken this a step further now by offering a target setting service. We can help a design team develop performance targets for their building before a concept design has even been dreamt up. All we really need is a draft brief and we can profile the life cycle impacts of a normal approach to delivering the intended function of the building. We then use this model to simulate improvements that the owner and design team want to target, these can include design life or functionality improvements. Early feedback on this service has been great, get in touch if you want more information.