Clients are increasingly refusing to accept that extreme weather is an excuse for handing over a building late. At the same time, the weather is, as you may have noticed, becoming more extreme. Matthew Richards reports on a troubled outlook for Britain's contractors
Earthquake, volcanic eruption, the outbreak of war, radioactive fall-out, civil disorder and exceptionally adverse weather. All of these have been regarded in construction contracts as "force majeure" – meaning that their occurrence allows the contractor to hand over a building late without also having to hand over its profit on the job in the form of liquidated damages.

This rule, which has long been a source of comfort to the construction industry, is now being amended by an increasing number of clients, who are taking the position that contractors ought to be able to deal with adverse weather, no matter how exceptional it may be. Ann Minogue, partner in solicitor Linklaters, says: "A lot of clients don't use the clause any more, because there are effective means to deal with bad weather these days."

One of those clients is Stanhope, which is among Britain's biggest developers. "Inclement weather is excluded from our contracts," says Peter Rogers, a director at Stanhope. "As far as I'm concerned, the contractor should know that there's going to be bad weather. For a three-week job, weather can have a huge effect, but over a year, it averages out." As a result, Stanhope now insists that all of its contractors subscribe to forecasting services.

This trend is a worrying one for contractors for three reasons. First, the statistics are that, on average, one day in six is lost to rain, wind or cold, and crane operators' downtime in winter can be as much as 60% of the available man-hours. However, as we know, these figures are subject to considerable variance, which means that the contractor's price is partly a bet that the weather will co-operate with the build programme.

Second, the chances are that things are going to get worse. Global warming has already brought floods, a hurricane and the occasional tornado to the British Isles, and climate experts forecast even worse times ahead. Confident assertions are difficult to make about mathematically chaotic systems such as weather, but it seems that we are already experiencing the first consequences of climate change. A Meteorological Office survey of construction firms published last month found that one-quarter of them had had to change their working practices over the past few years to cope with deteriorating weather. According to the sample, 21% of contractors lose 11 to 20 working days a year to the weather, and a further 16% lose 21 to 50 days.

The third cause for concern is that contractors will no longer be able to rely on the weather to provide them with an excuse for their shortcomings. Thousands of construction firms use the Met Office's services, however most buy historical data such as "downtime summaries" and long-term averages, rather than forecasts. Downtime summaries, costing £95 per site per month, give the number of working hours between 7am and 5pm with adverse weather conditions. Long-term averages, which cost £120 per site, put the downtime into context by showing the average amount of downtime over previous years.

Andrew Hemsley, managing director of consulting at QS Cyril Sweett, says contractors buy this data to provide themselves with an alibi. "If you've run over your completion date, one of the easiest ways to avoid paying damages is to say it's because of bad weather." All you have to do is buy site-specific data from the Met Office that shows how bad the weather was on your site at a critical stage, and you can invoke that magic "exceptionally inclement weather" clause. "It's amazing how many extensions of projects are allowed because of bad weather that was never there in the first place."

As far as I’m concerned, a contractor should know if there is going to be bad weather

Peter Rogers, director, Stanhope

Shelter from the storm?
The good news is that contractors who are worried about the trend are not completely at the mercy of the weather.

The obvious move is to do what Stanhope's Rogers wants and sign up to a forecasting service. These are not, of course, entirely reliable, but there is good news on the way. The Met Office is developing state-of-the-art forecasting technology targeted at the construction industry. "We want to bring construction companies into the forecasting market," says Martin Rodgers, business manager at the Met Office. "If we can forecast bad weather, builders can plan for it." In other words, you can anticipate periods of high winds or heavy precipitation by concentrating on work that is not dependent on reasonable weather.

Prototypes of the new forecasting technology are being tested on site at the Met Office's own headquarters, which is being constructed in Exeter. "We're developing the products to be ready for this winter," says Rodgers. The testing is still top-secret – the Met Office is part of the Ministry of Defence – but the products are expected to involve site-specific forecasting using radar. For a fee, firms will be alerted to bad weather approaching their sites.

There are some caveats, however. For one thing, even short-term weather systems are almost impossible to predict accurately. The latest attempt to do so, by the Japanese, involves a £300m supercomputer the size of four tennis courts that performs 36 million million mathematical operations a second. And even if you know that there is trouble ahead, it may not help you if a job on the critical path is affected.

An equally obvious form of protection is to buy insurance. But that is expensive, and firms can find that they are still exposed – Simon Tolson, senior partner at lawyer Fenwick Elliott, says he is acting for two contractors who each lost between £200,000 and £300,000 in the November 2000 floods. They are pursuing insurance claims against an insurer, who, Tolson says, is "wriggling on the hook".

What the weather can do to a site

This costs contractors 5% of their turnover. As little as 5 mm will make a site too dangerous for scaffolders and steel fitters. After a downpour, groundwork will be delayed two or three days until the ground dries out. Rain can creep in and damage fittings, and in strong rain, tarmac or paving can’t be laid. Wind
Slating or tiling is unsafe in winds of more than 23 mph, as is crane work over 28 mph. Wind turbulence is dangerous around tall buildings. Cold
You need a minimum temperature of 2°C for concreting and 15°C for surface dressing roads with stone chippings. Ground frost means working at height is too dangerous, and makes moving earth impossible. Fresh paint cracks at low temperatures. Heat
After several hours of temperatures greater than 30°C, steel will expand. When it cools it contracts, cracking adjoining concrete. If the temperature is high and humidity is low, mortar dries out, making bricklaying difficult.

The shocking truth: what the Meteorological Office survey found

  • 60% of firms said the weather impacted quite seriously on their business but only 17% took weather into account as a vital part of planning. One-quarter didn't take it into account at all.
  • 58% of firms only use weather information during a project, not before.
  • 50% of firms allow time for weather-related delays, but most estimate or guess the time they should allow. Only 43% of those who estimate the time use weather information to do it.
  • 25% of firms experienced problems such as concrete being ruined by frost up to five times a year. One in 10 encountered problems up to 100 times a year, and one in 20 more than 100 times. The average across the industry is 26 weather-related problems a year.
  • 21% of firms lost 11-20 work days as a result of weather-related delays in the past 12 months, and a further 16% lost up to 50 days.
  • Only a quarter recognised the benefits of forecast information to help minimise the effect of weather on their business – and, despite the fact that they're worried that weather conditions will worsen, two-thirds of those questioned say their use of weather information will not change.