HPH277 : The importance of building performance evaluation – with Professor Fionn Stevenson
Professor Fionn Stevenson explains why building performance monitoring and post-occupancy evaluation should be mandatory on new homes.
Interview with Fionn Stevenson
Having spent eight years in practice as a chartered architect, Fionn was finding that the housing wasn't performing as well as she had designed it to do. This led to her interest in building performance and eventually she became a researcher and academic in the subject, as Professor at University of Sheffield – School of Architecture. She has now been involved in building performance for over 20 years.
Six simple action points in a light touch review
A light touch post-occupancy evaluation involves going into a home to check how well it's performing against its design intentions.
The first step is for the expert to spend around half a day studying the original drawings and specifications for the project, as these are what will be checked against during a tour of the home. They provide the baseline of what is supposed to have been done.
This is followed by a half day tour of the home with the occupants, plus the designer and contractor. The occupants will explain about living in the house for the evaluator to see what's going on and check that against the original design intentions.
The occupants will also complete a simple two-page survey which provides a lot of further information.
A half day thermographic imaging survey is then carried out to see how the fabric of the building is really working.
Next is looking at how the building is performing in terms of energy used and water consumption. This can be done at the simplest level of looking at utility bills, or recorded through smart metres.
And finally, there will be a spot check where, during the half day tour, the evaluator will use a hand-held 4-in-1 metre to check on the room temperatures, plus levels of light, sound and humidity.
UK housing doesn't perform as it should
Given the nature of unique sites and being very contextual, Fionn says UK housing does not perform as it is expected to do. She says that research shows that on average new homes in the UK use at least twice the amount of energy they're supposed to use. That can be down to the design but also the quality of construction.
Another concern is the indoor air quality results, with high levels of carbon dioxide build-up, low-level toxins from off-gassing of new materials, and air fresheners which are supposed to make the air quality better but can actually make it worse. New homes need to have good ventilation strategies, but often they have been poorly designed, constructed or commissioned.
Building evaluation should be mandatory
As well as post-occupancy evaluation, there can also be building performance evaluation. This involves starting the evaluation process from as early as developing the brief, and right through the complete cycle of the project.
Fionn says it's amazing that there is no mandatory requirement to carry out post-occupancy or building performance evaluations, and that is something she is lobbying to get changed. The RIBA is now producing new guidance and in the future is looking to mandate its practitioners to make it a part of their service. But there's no mandatory requirement to carry it out as currently it requires consent from the client.
“If it was mandatory there would be an automatic performance feedback loop because people would have to automatically report what is actually going on in the housing. That reporting would then go into databases and everyone could see what was going on.”
Fionn has worked with a number of volume housebuilders, and says that although they carry out extensive customer satisfaction surveys to see how well their buildings are performing, they are not asking the right questions. They don't drill down into why the house is or isn't working for them, and this is because they haven't had to be accountable for the performance in mandatory terms.
“What they’re interested in is selling the home. They’re not as interested in how well the home is performing once they’ve sold it. They just want to make sure the customer is happy, they want to make sure that they get their NHBC scorecard with the highest number of stars, and that’s all about reputation. And their reputation rests on the initial customer satisfaction survey, not the overall performance of their homes.”
There needs to be databases of results
Fionn mentions the Building Performance Network as being a group of organisations and experts who are spearheading the drive to make building performance evaluation and post-occupancy evaluation routine. They are collecting data and setting up a UK database.
And Fionn says that this is what needs to be happening. She says there should be two databases: one a private one where people can access their own data, and the other a public one with anonymised results to give a national picture of how everyone is doing and enable people to benchmark and compare against others.
A culture shift is required
Fionn explains that at the moment the process for architects and clients is “let's design a home.” In fact what it should be, is “let's design and evaluate the performance of a home.” The majority of architects don't go back to really evaluate how well their buildings are performing. Fionn says the key message she is trying to get across in her book is that this should be routine.
Be energy sufficient, not just energy efficient
Fionn is in the process of starting her own self build project. But rather than design it herself, as she has been out of practice working as an academic for so long now, she is using the networks she has built up to find the best team to deliver her project.
She has prepared her brief and will be looking for people that will champion her wants, needs and follow the details of the brief throughout.
A fabric first approach will be used to make sure the house is properly insulated, airtight and ventilated. With that is the importance of getting the size of the home right. She explains that it's not enough just to be energy efficient, but we need to think about whether we are being energy sufficient. In other words, having the house optimally sized and not any larger than it needs to be.
“There’s a bit of a misnomer about zero-carbon because of course you can make your home automatically zero-carbon if you go onto a renewable energy supplier. But that doesn’t mean your home is actually being very good for the environment. We’ve got very large self-built homes that are claiming to be exceptionally low energy or carbon zero but actually the embodied energy, the amount of materials that are being used in them is huge.”
Keep the buildings simple
Fionn says that there is a temptation with self build to have the house of your dreams and put in a lot of unnecessary kit. Her own research has found that often in homes that were using heat pumps together with PV and solar-thermal, often they were contradicting each other as they weren't designed to work together. Also, solar renewable energy installations hadn't been installed correctly or on the wrong orientation, meaning they weren't performing as they had been designed to do.
Another thing the post-occupancy evaluations have thrown up, is how important it is for any mechanical ventilation system to be well designed, brilliantly constructed and have the minimum duct runs possible. It must have vents perfectly positioned and be ergonomically designed in a way that is accessible for the occupant to interact with it.
There isn't enough data to help self-builders with decision-making
Fionn explains that we're still flying blind with a lot of modern building systems as there just isn't enough data from post-occupancy evaluations to see how well they perform. Being laboratory tested can only do so much.
“Who is going out there, outside of the laboratories, into the homes with the thermal imaging camera, doing the walkaround, seeing the little bits of mould that are appearing in the corners? If we move on to service systems, we’ve got loads of mechanical ventilation heat recovery systems. But who went out there and actually asked the occupants whether they can use them? That’s been the issue, that it is difficult for self-builders to choose systems and know that those systems have been not just rigorously tested in the laboratory where the products are developed but that they’d been systematically tested around the country in every city, in every town, as a routine part of post-occupancy evaluation which is then fed back into the industry. This is exactly why the housing industry performs so badly.”
An investment worth making
Fionn stresses that you should be alert throughout the whole design, build and occupancy process, but there are key points where attention particularly should be paid.
The first is at the outset of the project, where post-occupancy evaluation is included in the brief, and budget allocated for it. Typically it might cost around £5,000 for a light touch post-occupancy evaluation, but it could be saving you tens of thousands in identifying hidden risks and defects.
Other benefits are that you're also future-proofing for climate changes, ensuring there won't be overheating as UK summers continue to get hotter, and also improving health issues with better air quality.
The second critical stage is the commissioning of the home. When the services, heating and ventilation systems are commissioned is a crucial time for there to be an independent evaluator checking whether they have been set up properly, to avoid a lot of problems down the line.
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