Four key questions can reveal why your sustainably-designed housing isn’t performing as expected. Fionn Stevenson runs through six action points for a light touch POE
New housing routinely uses at least twice as much energy as was predicted and housing renovation projects often suffer the same fate. The underlying reasons for this significant performance gap are often unknown to the design team. Fortunately, a ‘light touch’ post occupancy evaluation (POE), held just before the end of the Defects Liability Period in a contract, can reveal what has happened and where to make immediate and long term improvements.
There are four key questions:
- Is the home (or homes) physically performing as expected?
- Are the inhabitants’ needs met in their home(s)?
- Are there any physical and/or social problems that need solving now?
- How can we improve our housing design for the future?
Six POE actions, undertaken in sequence, can answer these questions.
Review of key design, construction and specification documents related to the project intentions
Examine the outline brief and specification documents and compare these to the key drawings for a typical home in the project (1:100/1:50 layout plans, long and cross-sections, all elevations). Check key 1:5 details around openings, foundation and roof junctions, as built. Highlight any areas of potential concern compared to best practice and climate change predictions. Note any changes to the specifications or drawings. This should take no more than half a day (design team).
Basic energy and water use audit
Obtain permission from inhabitants to use their data anonymously using a written procedure. Gather energy and water meter data for individual homes via the client or service suppliers involved. Break down the annual figures (KWh and litres) in relation to the relevant net floor area to compare with your chosen benchmarks (KWh/m2/pa) (litres/home/pa). Where this is not possible, use annual water and energy bills and compare with benchmarks to see if these are excessive or not. If the results are worse than the benchmarks, use further POE methods to find out why (design team).
Obtain permission to carry out a brief survey of at least one home, inside and out, using a basic thermal imaging camera to identify any obvious heat-loss issues. The survey should take around half a day, and then a further half-day to analyse and report on. Highlight any areas of concern to the client. Use someone trained in thermography, as it is easy to get wrong. Use BS EN 13187:1999 Thermal performance of buildings. Qualitative detection of thermal irregularities in building envelopes. Infrared method.
Simple survey of the inhabitants
Use the domestic Building Use Studies (BUS) questionnaire or equivalent. Aim for a 50–100% return rate from all homes in the project, using either hand delivery and pick-up of the questionnaire or digital means. Hand delivery is usually more successful. It could take around a couple of days to deliver and input the data, depending on the number of homes involved. The initial analysis included in the cost of the BUS survey will highlight any issues. Do the survey around one year after initial inhabitation to capture seasonal variations. Pay close attention to the individual inhabitant comments as they may well highlight new areas of concern or even best practice. A completed questionnaire means the inhabitant has given permission to use their data anonymously (design team).
Short tour of one home
Obtain permission from the inhabitant to do a home tour, allowing one hour for the visit with another hour afterwards for team discussion. This should happen after the above surveys have been analysed, as this highlights issues for the home tour to focus on. The group should be no larger than five to seven people for the walkthrough, including the inhabitants, and a representative from the client, architect, engineer and contractor. Use a home tour guide to undertake this activity in sequence, which should cover all rooms and the exterior. Compare findings to the initial document review (design team).
Spot-check environmental conditions
Use a simple hand-held multi-function 4-in-1 environmental meter to correlate temperature, humidity, light and sound levels with any initial observations made during the walkthrough, and highlight any issues. Take readings in the main living room and the main bedroom as key areas. These meters are relatively cheap and worthwhile investing in for the practice (trained personnel).
The above results should be analysed, triangulated, discussed and presented in a short final report. If there are any areas of underperformance with an unidentifiable cause, advise the client to move to the next levels of diagnostic or, if necessary, forensic investigation, which may involve monitoring the fabric and indoor air quality, airtightness testing or other methods.