Loughborough DEFACTO English housing study
Longitudinal monitoring of temperature, humidity and energy across hundreds of English homes; the empirical basis for the 'one in five bedrooms overheats' figure.
Source
Summarised from Loughborough University DEFACTO overheating study, a Tier 2 source on Your Home Climate. We did not run this project; the figures below are reported by them. Click through to verify any of them at the original publication.
https://www.lboro.ac.uk/research/defacto/The problem, before any work started
Until DEFACTO, the official UK overheating numbers were largely modelled. Policymakers and homeowners were arguing about a problem that nobody had measured at scale. Loughborough went and measured it.
What actually happened
- 01Temperature and humidity loggers were deployed across a sample of English dwellings spanning every common archetype.
- 02Data was collected through multiple summers in occupied homes, not laboratories.
- 03Readings were assessed against CIBSE TM59 and Approved Document O overheating criteria.
- 04Findings were published and fed directly into the policy case for Part O on new homes.
What changed for the home
- Overheating in English bedrooms moved from anecdote to measurement: roughly one in five monitored bedrooms exceeded the TM59 threshold.
- The conversation shifted from south-facing living rooms (the popular assumption) to top-floor bedrooms under poorly insulated pitched roofs (the actual hotspot).
- Approved Document O for new homes followed shortly after.
What the source reports
- Bedrooms exceeding the TM59 overheating threshold~20% of monitored bedroomsmeasured
- Archetype with the highest overheating riskTop-floor flats and loft conversionsmeasured
Measured means monitored data from the site. Reported is the publisher's stated figure. Modelled is a target or design figure rather than an outcome.
What this case can, and can't, tell you
What it tells us
- Overheating is now a measurable feature of English housing in an ordinary summer, not a rare event.
- Top-floor bedrooms and loft conversions sit at the top of the risk list.
- Modelled overheating figures were broadly directionally correct, but the lived-experience data is the one to cite.
What it doesn't
- How much of the observed overheating is fixed by cheap shading and ventilation versus requiring structural change.
- Whether a given individual home in the sample's archetype will overheat to the same degree; site, orientation and occupancy vary widely.
- What happens to the figures as the climate continues to warm; the dataset is a snapshot, not a forecast.
Our take
We treat DEFACTO as the strongest empirical anchor for almost every overheating page on the site. Where we quote 'one in five bedrooms', this is the study behind it. Where we point readers at loft conversions before air conditioning, this is the study that earns us the right to do so.