Growing Danger of Roof Collapse This Winter
By Brian Morris, Senior Account Consultant, XL Gaps and
Gregoire Mach, Senior Loss Prevention Consultant, XL Gaps
In the past 2 decades, heavy snows have covered Europe as far South as Greece, causing a rash of deadly and costly roof collapses. Business stops for months, legal prosecution lasts for years, and losses reach tens of millions. We offer crucial information and tips to keep snow from stopping your business this winter.
Crucial Information and Tips to Keep Snow from Stopping Your Business
Climate change has caused shifting, global weather patterns and increased volatility year round. Snowfall, like rainfall, is more unpredictable. Potentially dangerous snow storms are not only spreading to Southern and coastal regions. They now strike even snow-resilient countries like Russia, Denmark, Sweden, Belgium, Germany, Austria, and Poland with unexpected force.
Safety at High Altitudes?
For many years, structural codes assumed a direct correlation between altitude and snow loads (weight). According to the EU, at altitudes above 1500 m—primarily in the Alps—roofs are built to withstand heavy snow loads.
In 1997, however, 159 exceptional snow load events were reported below 1500 m, nearly all in Southern Europe and the UK. Greece, Italy, Portugal, and France all registered unusual snowfall. Spain reported 47 incidents, the UK reported 44.
In 2006, heavy European snowfall caused several high-profile tragedies in countries which should have been prepared for snow. In Poland, the Katowice International Fair collapsed under a snow load, killing 65 and severely injuring 170 more. In Germany, the Bad Reichenhall ice skating rink collapsed, killing 15, including 12 children. It took two days to evacuate victims trapped beneath the rubble. In Moscow, a market collapsed, killing 66 people.
In each case, professionals—architects, engineers, managers, or inspectors—were arrested and tried. Trials lasted years, many ending in indictments for manslaughter or for directly endangering lives through negligence or error.
Other headline collapses in recent years have each cost tens of millions in property damage, business interruption, client loss, delay penalties, and other damage.
Each new disaster underscores the growing danger of unpredictable snow loads. The EU is advocating higher roof and safety standards at altitudes below 1500 m. They have advised every country to reevaluate snow forecasting to include exceptional snowfall, and to revise building codes, monitoring, and emergency procedures accordingly.
Snow Load Danger Factors
The increased frequency of snow-induced roof collapses has also prompted deeper investigation into the relationship between altitude and snow loads. Scientists now confirm that it is inconsistent—strong in some areas, nonexistent in others. There are many other factors which influence snow loads.
First Factor: Snow!
As obvious as it seems, building managers should be on constant alert for snowfall in winter.
Numerous industrial collapses have occurred at night or over the weekend, when nobody was on site to realize that the snow was too heavy for the roof. Better planning, inspection and maintenance could easily have prevented the collapses.
TIP: At the end of every winter day, and before the weekend, building managers should check the local meteorological internet site for predicted snowfall, including the type of snow. Someone should be on site at all times during snow storms, to check for dangerous snow buildup and freezing damage.
Obvious Rooftop Snow Buildup
Snowflakes come in many varieties, from fluffy and light, to wet and heavy.
TIP: A common rooftop stick can measure the thickness of a fluffy rooftop buildup. Local or national snow codes will prescribe a thickness limit. When it reaches that limit, it is time to remove the snow for safety. Many of the recent roof collapses could have been averted, had building managers been vigilant about simple, physical rooftop inspections.
Wet Snow: Heavier Than It Looks
Especially in warmer countries or at the beginning and end of winter, snow is frequently wet and heavy. Because wet snow is dense, it can put a heavy strain on rooftops, without appearing to be thick. Rooftop stick measurements will not reveal how much extra pressure is on the roof, so other measuring methods are crucial.
A simple string hanging from the ceiling is an effective and inexpensive measuring tool. Roofs, like bridges, are made to be flexible. They bow, or deflect, beneath extra weight.
TIP: Paying careful attention to small changes in the distance from string to floor can reveal extra weight, before the roof is damaged. Some companies may wish to invest in new, wireless roof sensors. Sensors monitor the weight of snow, rain or ice in real time, giving building managers a chance to remove snow long before a collapse, or before the strain damages the roof. Early detection also offers managers the advantage of hiring snow removal services sooner, before regional snowfall increases demand, making them difficult to obtain.
More extreme roof deflection could indicate that damage or a collapse is imminent, and snow or ice removal is urgent. Those indicators are: lights hanging lower or flickering due to stretched wires, water leaks at roof-to-wall connections, creaking sounds, peeling paint, leaking pipes connected to the roof, bolts or screws found on the floor, and roof drains at a higher level than the roof itself.
Scientists have highlighted the influence that rooftop shapes have on snow drifts (accumulation).
Companies reduce material costs by building industrial roofs that are nearly flat, with shallow gradients angled just enough for rainwater to run off. Flat roofs are naturally more susceptible to snow buildup.
High-bay warehouses and other building add-ons also alter the rooftop shape. Snow collects in the corners between flat factory roofs and taller warehouses. These deep snow drifts exert much greater pressure on roofs than evenly distributed snow.
TIP: Structural engineers should always assess the impact of a building additions on existing premises, and reinforce roofs and other support elements accordingly.
Too Little Structural Support
Inexpensive temporary structures like tents are built to lower standards, on the assumption that they will be removed at the end of construction and other projects. The truth is that they can linger for years, until they collapse under snow loads or other weight.
Factory owners favor open spaces with minimal support columns. While this facilitates the workflow, it also increases the span between supports. If the roof is not reinforced to compensate for fewer vertical supports, a heavy snowfall could put excess stress on joints, causing the roof to sag or collapse.
One Swedish school collapsed after the caretaker removed supporting braces. Why did he do it?
The children were climbing on them!
Sweden offers other snow learning opportunities. From 2009 to 2010, Sweden reported 160 serious snow-induced collapses. Those spun off 3000 insurance claims for: property damage, business interruption, employer’s liability, subrogation (pursuing reimbursement from liable parties for claims paid), professional indemnity, and third-party liability. Had the loss of life exceeded the two recorded deaths, legal prosecution for negligence and manslaughter would have continued for years, as defense costs mounted.
Those bad years inspired researchers at the Lund University in Sweden to study snow-related collapses across Northern Europe. Evidence revealed that 50% of cases were attributable to faulty building design.
TIP: Review premises for sufficient structural support. Of course, removing building supports is never a good idea.
Nearly all of the large collapses can be traced back to a combination of design and construction errors, negligence, and unpredicted snow loads. When a roof does collapse, it can inflict stress equivalent to an earthquake, compromising the structural integrity of the entire building.
After a collapse, if everything goes well, rebuilding and recovery can take 6-9 months. When it doesn’t go well, recovery time averages 12-16 months. That is a lot of lost business. Building managers should do everything possible to prevent a roof collapse. Better construction, roof reinforcement, and improved inspection and maintenance cost very little compared to the consequences of a collapse.
TIP: Finally, buildings should be assessed and repaired every year, with extra attention after a hard winter. Even roofs that survive without collapsing suffer damage. Temperature variations, snow clearing, and ice removal can corrode or weaken the rooftop, leading to leaks or deeper structural weakness.
Prevent a Winter Business Collapse
Heavy snowfall is spreading across Europe. This 4-season snow safety checklist will help you save your business from a winter collapse.