Low Energy Buildings - Are we getting more for our money?

Eoin ONeill
Global climate action is influencing many industries across the world today. By 2030 all new buildings must operate at net zero to meet the climate change targets.

The demand for low energy construction has arrived in Scotland and it is a more significant change to the market than we have experienced in the recent past. For some in our industry I believe it has initially caused discomfort, however in the words of Rabbie Burns “Nae man can tether time or tide”. 

Like them I was uncertain in the deliverability, and of course the associated cost of this new standard in construction. At Faithful+Gould, we are striving to be at the forefront of this change. Not just because of the inevitability of the impact on our industry, but also because we inherently believe in the part we (and our construction industry colleagues) can play. We have set up our UK net zero group to cure ourselves of any concerns through education, gaining first-hand experience and diving into the details for the facts surrounding low energy construction.

There are many opinions on how best to deliver a low energy building. The leading methodology with over 1000 buildings underway in the UK, both residential and non-domestic, is Passivhaus. A key reason to build using the Passivhaus methodology is that there is not the same variable energy performance as we see in existing buildings. The methodology behind a Passivhaus building differs from a standard carbon neutral building, which combines energy efficiency and clean energy generation to offset any energy use. The building aims to use less energy in the first place by being effectively sealed against the elements.

The Passivhaus concept has five basic principles which are shown below:

Often when we talk about Passivhaus we rightly focus on the high quality, comfortable internal environments due to the air quality and the form factor that allows the building to work with, not against the environment. However, when cost comes into the conversation, we see clients and consultants alike becoming nervous and unsure of what it will mean for the project. Despite the Passivhaus standard having been around for 30+ years, the outturn costs for low energy buildings is a topic people are only now gaining more information on in Scotland. It is therefore important to understand the cost impacts and fluctuations by analysing physically how this building differs to that of a traditional build. 

For a traditional build, it is possible to place all the costs items of today against yesterday’s benchmarks and expect them to be proportionally similar. Yet for the likes of a Passivhaus methodology that is not the case. Accurate benchmarking is built-up from data gathering and data analysis. With the relatively small data pool to draw from at this time, we simply do not have the base information to allow our teams to undertake top-down analysis.

Therefore, our team are working from the bottom-up when analysing costs, and there is no doubt that upon comparison the knock-on effect of a low energy build is that there are cost movements from what we know as traditional cost breakdowns. To name some changes: the mechanical ventilation system is generally larger, the building is made airtight using specialist tapes and barriers, the building is thermal bridge free, the roof walls and floor are insulated to a higher standard. The capital cost of certain materials will be higher because they are simply of a higher standard, examples of this are windows, MVHR units and products associated with airtightness. The amounts of materials will both increase, such as insulation, and decrease, such as those associated with the heating system infrastructure. It can be a balance that needs to be carefully managed by an experienced and committed design and commercial team.

There is also a cost to the additional time taken to make sure the quality is high and for a Passivhaus a certification is needed. Upon consultation with Contractors in Scotland a typical build will have an additional programme time of circa 5 to 10%. Though we would challenge this going forward – as an industry we have the opportunity to normalise this type of construction and quality expectation, which should result in efficiencies in delivery.

Which brings up another point. Not all the additional cost items are contributed solely to methodologies such as Passivhaus. New demands have been set in quality standards following publications such as the Cole reports, and our industry must rise to the challenge.

Having undertaken several cost studies on low energy buildings there is no ‘one size fits all’ solution and each design will have its own associated cost. Cost impacts can vary depending on your approach and that is why the design and construction team must work together in a progressive fashion for a common goal to build a successful project.

All other factors aside, the main reason to build a Passivhaus purely from a cost perspective is because studies and live examples show that the building will cost less in the long term. This is mainly due to the decreased energy use costs. Therefore, with a higher quality building and resulting low energy use, we truly are building for the future.  The business case for such buildings should indeed reflect the fact that we are getting more value from the money we spend.

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