The environmental case for a four-day week is real, but it is the easiest case to overstate. Fewer commutes and quieter offices save energy. Extra leisure can spend some of those savings on flights, drives, and heated homes. A credible consultancy should argue both sides in the same article — because your staff and your board will.
The savings are straightforward
Most people who gain a weekday off make one fewer return commute that week. In the US and Ireland pilots reported in December 2022, staff commuted about an hour less per week on average, and car commuting fell. Multiplied across a workforce, that is fuel, emissions, and congestion avoided on the day itself, plus a possible peak-spreading benefit if days off are staggered rather than concentrated on Friday.
Offices use less energy when they are closed or thinly occupied: lighting, heating and cooling, lifts, catering, and cleaning all fall, though rarely by a clean 20%, because buildings leak baseload energy even when empty. Firms that close fully one day a week save more than firms that keep a building open for a skeleton crew — an environmental argument, incidentally, for co-ordinating days off where service allows rather than scattering them.
Modelling studies scale these mechanisms up. A University of Reading and Henley Business School modelling exercise, widely reported in 2021, estimated that a UK-wide four-day week could cut weekly car mileage by hundreds of millions of miles in its scenario. Older cross-country OECD analysis associated shorter working hours with lower environmental footprints over decades. Treat both as directional: they show the mechanism is large enough to matter nationally, not what your firm will save next quarter.
The rebound is also real
Economists call it rebound: time and money saved in one place get spent in another. A fifth day used for a long weekend away by car or a short-haul flight can erase weeks of commute savings in a single trip. Homes occupied all day use more heating, cooling, and electricity than empty homes. Leisure consumption — deliveries, activities, retail — carries its own footprint.
This does not cancel the case; it changes its size and its distribution. Commute savings are near-certain and accrue weekly. Leisure emissions are choices, concentrated in higher-income staff who can afford to fly on a Friday. The net effect in most plausible scenarios remains favourable, especially where commutes are long and car-dependent, but any firm claiming a precise carbon figure from a pilot should show its method: commute distance by mode, office energy by occupancy, and an honest note on what it did not measure.
There is a subtler rebound inside the office. If four days become so meeting-dense that work spills into evenings at home, you have not saved energy or time; you have moved both off the books. Environmental reporting, like wellbeing reporting, should count actual hours and actual travel, not rostered intentions.
What to do in a pilot
Measure three things simply. First, commute: a short before-and-after survey of mode and distance by staff, multiplied by days actually taken off. Second, estate: metered energy for office days before and during the pilot, noting weather and occupancy changes. Third, business travel: flights and mileage in the pilot window versus a comparable period, so a sales team’s travel surge is not mistaken for a four-day effect.
Design helps. Staggering days off keeps a building half-open five days a week; closing fully on one day, where customers allow, is better for energy and simpler for staff norms. Encouraging rail over short-haul flights for the new long weekends is beyond an employer’s control — but travel policy for work trips is not, and it usually dwarfs the commute effect for frequent flyers.
Beware of claiming national modelling as your result. Say instead: our staff made roughly this many fewer commute trips, our office used this much less metered energy, and we did not measure leisure travel. That restraint is what makes the rest of your sustainability report believable.
The environmental argument should help close a case already made on people and performance; it should rarely lead it. Lead with burnout, retention, and service quality, where pilot measurement is strongest. Then add the planet, honestly, as a meaningful co-benefit with a rebound you are watching rather than a saving you have invented.
Sources
- 4 Day Week Global, US and Ireland pilot results (December 2022) — commuting time and car-use findings.
- University of Reading / Henley Business School, UK four-day-week commute modelling, reported by the World Economic Forum (2021).
- OECD cross-country analysis of working hours and environmental footprint (1970–2007), as summarised in working-time and environment reviews.
Day5Group is a consultancy that assists in the transition to a 4 day work week. More about Day5Group · All blog articles