The UK Health Security Agency has issued its first cold-health alert of winter 2026/27, a yellow alert covering the North West and West Midlands from 9am on Thursday 12 November to 12pm on Saturday 14 November 2026.
The alert, published on 10 November, concerns pressure on health services, not construction work, and no other English region was covered when it was issued. For sites, though, the first frosts of the season bring the same set of rules into play every year. They sit in three places: health and safety law, material standards and the building contract.
None of those rules is new, and none depends on an alert being in force. What changes on a cold morning is which of them a site manager has to apply before work starts.
Illustrative winter construction site scene showing frost-covered safety equipment and cold weather conditions. Image: London Construction Magazine
No legal minimum temperature for outdoor work
The Health and Safety Executive's guidance on outdoor working gives no temperature below which work must stop. The figures often quoted, 16°C or 13°C for rigorous physical work, come from HSE guidance on indoor workplaces.
On site the duty is framed differently. Regulation 34 of the Construction (Design and Management) Regulations 2015 requires an outdoor site to be arranged, so far as is reasonably practicable, to give protection from adverse weather where that is needed for health or safety. Schedule 2 of the same regulations sets the minimum welfare facilities, which include rest facilities kept at an appropriate temperature and somewhere to dry clothing.
Work at height has its own test. Regulation 4(3) of the Work at Height Regulations 2005 allows it only when weather conditions do not jeopardise the health or safety of the people doing it. HSE's advice for cold conditions is practical: suitable protective clothing, somewhere to warm up with hot drinks, more frequent breaks and, where it can be done safely, delaying the task.
Temperature limits for concrete and masonry
Material rules are more exact. The cold weather chapter of NHBC Standards, which applies to homes built under NHBC warranty, states that ready-mixed concrete should be at least 5°C when delivered, citing BS EN 206. Concrete should not be placed where the ground or contact surfaces are frozen, and once placed it should be covered to keep it above freezing, with heating if necessary.
Against slight overnight frost, NHBC advises 50mm of insulation held down firmly at the edges over oversite concrete. In very severe frost it says insulation alone is inadequate.
For masonry, the same chapter says brickwork and blockwork should not be built when the air temperature is below 3°C and falling. Work can resume at 1°C and rising where the temperature is expected to exceed 3°C. Frost protection may be needed for up to six days, depending on conditions.
Heidelberg Materials, in its guidance on cold weather placement, says concrete that has reached about 2 N/mm2 is likely to resist frost damage, and that most mixes get there within 48 hours if kept at or above 5°C.
Test cubes, striking times and delay claims
Cold also affects the evidence a site relies on. Concrete gains strength more slowly at low temperature, so striking times that hold in summer cannot be assumed in winter. Cubes cured in standard conditions show what the mix can achieve, not the strength of a cold slab. Heidelberg suggests cast-in maturity sensors to help decide when to strike.
The cubes themselves need care. The Get It Right Initiative's quality alert on concreting in cold weather, issued on 18 January 2023, advises storing moulded cubes indoors in moist conditions between 15°C and 25°C. Cubes left outside in frost can return low results that say little about the concrete supplied.
The contract decides who pays for lost days. Under JCT forms, exceptionally adverse weather conditions are a Relevant Event, which gives the contractor more time but no loss and expense. NEC4 clause 60.1(13) works on measurement: a compensation event arises only where the weather recorded in a month exceeds the one-in-ten-year value for the place named in the Contract Data.
An ordinary cold snap therefore stays at the contractor's risk under both families of contract. Daily temperature records, kept from the first frost, are what any later claim will stand on.