A Comparison of Residential Sustainability Evaluation Tools

I hear a lot of comments in my job about which method of sustainability assessment is best. There is a lot of support for one tool or another, and in the current situation where a review of housing standards is expected from the Coalition it seemed appropriate to carry out a short comparison of those methods that are used to evaluate the sustainability of housing in the UK. This is not a particularly in-depth review, but it is enough to highlight a few important issues that are obvious without any more in-depth study.

I have chosen to compare SAP, PassivHaus, Code for Sustainable Homes and LEED in this exercise. I am very familiar with three of the four, so it was interesting to include LEED for the sake of comparisons.

Bearing in mind that it is well understood that any attempt at understanding sustainability should consider the three main issues of environmental, social and financial sustainability, I divided the issues that all these tools consider into those three sections. I was forced to add a section called Process because LEED has a specific credit aimed at promoting the involvement of the same design team from beginning to end. This seemed to be a very sensible aim so I included a section for it, a section with only one item in it.

If you feel strongly about any of the evaluation, feel free to comment at the end of this piece and I will read it and respond.

Evaluation Methods

The two main outcomes of the exercise are:

– there are no attempts in any of the tools to include costs or relative costs, economics appears not to matter to the people who design such tools. This may be a result of the tools being mainly designed and applied by construction professionals in the environmental sphere, with the only attempt at cost evaluation happening after the event. It may also be symptomatic of the general unwillingness of the surveying sector to get involved in the proactive design and operation of such tools until the tools have become adopted, and then their work is reactive

-there is a lack of evaluation of sustainable design after buildings have been occupied, there is no attempt to consider whether any of the sustainable features actually work, or have been adopted/enjoyed/ignored by residents; apart from LEED where there is a specific credit aimed at ensuring that there is a proper handover to residents and that the systems have been explained to them. There is a credit in the Code for Sustainable Homes for the Home User Guide, but there is no guarantee that anyone will ever read it.

At a time when there is a lot of focus on the issue of the ‘Performance Gap’ it seems to me that it is essential that we routinely evaluate post occupancy satisfaction. It is not only buildings that suffer from a ‘Performance Gap’, components and features of buildings can fail to achieve the desired results even when the building as a whole appears to work. Occupants of buildings can suffer from a ‘performance Gap’ too when the features of the building are not explained to them in a way that they can understand and adopt.

It is important for the industry to check that the tools which go beyond Building Regulations towards higher levels of sustainability are actually working and that the features they recommend are actually being used and are working. This should not be an expensive exercise, a fairly simple and standardised questionnaire to every household in a ‘sustainable’ home should do the trick.


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