the sealed room burns differently

Problem statement

New UK dwellings have had to meet an airtightness limit since 2002, the limit was tightened in 2022, and PAS 2030/2035 retrofit standards push existing homes in the same direction — so an ever-larger share of the housing stock is being sealed. A 2025 evidence review for the UK energy department screened 75 documents on the unintended consequences of airtight homes and concluded that condensation, damp, poor indoor air quality, radon build-up and overheating "can all be alleviated simply by ventilating appropriately"; but "a key unintended consequence that cannot be remedied with more ventilation is fire and smoke risk. There is a dearth of research on the subject and there is a significant gap in the literature relating to changing airtightness regulations and fire/smoke behaviour." The reviewers found that "the general knowledge of fire behaviour in confined building spaces is embryonic," that "there are few studies that specifically examine the impact of making buildings airtight and the behaviour of fire," and that "due to the limited science in this area, it is not possible to know how regulated practices relating to airtightness and ventilation affect such risk — meaning that some risks may remain or be exacerbated even when regulation is followed." The unsolved problem is that two regulatory programmes — energy efficiency and fire safety — have been changing the same rooms without anyone establishing how a low-rise domestic fire develops, spreads and is escaped in a dwelling built or retrofitted to modern airtightness.

Why this matters

Dwellings account for the large majority of fire deaths in the UK, and low-rise houses "represent the bulk of the housing stock." The review's synthesis of adjacent studies suggests airtight enclosures may see intensified air flow through remaining voids, fire developing within cavities, depressurisation that "may make doors and windows difficult to open," reversal of air movement in ducts that could defeat pressurised escape routes, and incomplete combustion in gas appliances where purpose-provided ventilation is inadequate (one cited government study found only 2 of 55 airtight homes met minimum ventilation provision). None of these has been quantified for the terraced and semi-detached houses now being retrofitted by the hundred thousand under UK schemes, or for the airtight new-build standards spreading across Europe and North America. If the effects are real, escape-time assumptions in domestic fire guidance, smoke-alarm siting and ventilation-system fail-safes may all be calibrated to leakier houses than the ones being built.

What’s been tried and why it hasn’t worked

The review's rapid evidence assessment found the topic essentially unresearched at the level of the whole dwelling. The nearest work is Littlewood and colleagues' UK studies, which used blower doors and smoke generators to show that construction defects and thermal-upgrade works can bypass air barriers and fire breaks, letting smoke pass "within and between buildings" — but that work "does not specifically address the impact of changes in airtightness and fire risk." Simulation studies of pressure and smoke movement exist for multistorey buildings and identified some risks, yet "although not specifically addressed by the research, it may be assumed that similar behaviours would be present in all enclosed spaces where airtightness is increased ... There is, however, a need to test any propositions and assumptions made here as the evidence is limited." Mainstream fire research is oriented elsewhere: "most fire and buildings research is concerned with the combustibility of materials, spread of fire and escape mechanisms in the event of fire," and energy-efficiency research treats airtightness as a performance metric with ventilation as the only trade-off. The gap has persisted because the two research and regulatory communities have different journals, test methods and departmental homes, and because under-ventilated fire dynamics is well understood as physics but has never been mapped onto the specific permeabilities, cavity constructions and ventilation systems that airtightness regulation produces.

What would unlock progress

The enabling move is to connect an existing body of knowledge — compartment-fire dynamics of ventilation-limited fires, backdraught and smoke pressurisation — to the specific building physics of airtight dwellings, producing quantitative statements regulators can act on: how fire growth, flashover timing, smoke pressure and tenability change between a 10 and a 3 m³/h·m² @ 50 Pa house of typical UK construction, and whether ventilation systems (MVHR, extract fans) should shut, run or reverse on alarm. Validated fire models (e.g., FDS-type CFD and zone models) plus reduced-scale compartment tests can produce this evidence far more cheaply than full-scale burns; the review's own list of observed phenomena is a ready hypothesis set. Adjacent precedent: the analogous work done for tunnels and for pressurised stairwells in tall buildings, where enclosure airtightness is a designed parameter of the fire strategy rather than an unexamined by-product of energy policy.

Entry points for student teams

A fire-engineering or building-physics team could run a matched set of domestic-fire simulations across a range of envelope permeabilities and ventilation strategies for one or two archetypal UK house types, reporting time to untenable conditions, peak compartment pressure and door-opening force — a research contribution the review explicitly asks for. A team with lab access could build a reduced-scale compartment with adjustable leakage area to test the depressurisation and door-force claims. A policy team could map, for the UK or another jurisdiction, where airtightness regulation, ventilation regulation and domestic fire guidance make incompatible assumptions, and draft the test protocol a regulator would need. Relevant skills: fire dynamics/CFD, building physics, experimental design, regulatory analysis.