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Property Precautions - Weight of Snow [Hardfacts]

Introduction

In the United Kingdom, extreme conditions of prolonged winter snow combined with sub-zero temperatures are fortunately quite rare. However, the potential exists with climate change to experience such conditions more frequently. It is, therefore, important that property owners and occupiers are prepared for such conditions and do not lose sight of the fact that significant weight loads introduced by snow on buildings have the potential to damage the structure resulting in significant property damage, damage to the contents and business interruption.

The most hazardous conditions are likely to arise in the UK when repeated snow falls, that can take place over several days, do not have sufficient time to melt from roofs consequently accumulate and exceed the design capability of the roof. Furthermore, conditions can be exacerbated when rain follows heavy snow falls as rain water will initially be absorbed by the snow layers which will further increase the weight of snow.

Snow and ice on a roof exerts vertical loads that can cause a roof to deflect or bow downwards. Also these extremes in weight load can transfer horizontal forces through the structure that can cause walls to deflect outward at either the top of or base of the wall. Where snow loads imposed on a roof are within the design limits for the roof then generally any minor sagging or deflection that may occur will usually be temporary and simply disappear after the load is removed.

In addition, melting snow combined with rainfall can overwhelm building drainage systems as well as local drainage systems in the area which can result in flooding and damage.

Any work on roofs and gutters will involve work at height and safe methods of working must be used at all times. Any work at height during adverse weather will have the added risk of snow, ice and cold weather. It is important that a full risk assessment is carried out and a safe method of work established. It may be that the work could be more safely carried out by qualified and competent contractors.

Whilst severe winter weather cannot be avoided, following these simple practical guidelines will help avoid or mitigate damage to property and prevent business interruption.

To protect against the likelihood of snow related damage to your property, it is important to develop a timely prevention and maintenance program before the winter weather commences, during and after the winter period. These simple practical measures should form part of your building maintenance program.

BUILDINGS AT GREATER RISK

• Geographical location and exposure to wind
• The age of the building can be a significant factor in the snow load risk. All properly designed and constructed roofs in this country are built to withstand a prescribed snow load which is determined by a number of factors including expected frequency and severity based on geographic location. Lack of correct design or design to standards that are lower than current building regulations is not uncommon as newer building regulations provide better guidance for estimating snow loads.
• Roof overhangs that project several feet beyond the horizontal support, particularly if there is a significant build-up of ice
• Buildings with extensions or modification to roofs without considering the original load design e.g. installation of a new roof using original structural framework, adding building services such as air conditioning plant to the roof
• Buildings with lightweight roofs such as profile steel, asbestos or cement sheeting can be vulnerable due to their limited inherent strength and as these are lightweight materials they might not necessarily benefit from substantial purlins, joists, rafters etc
• Roofs which have had their insulation properties improved allowing snow to accumulate for longer periods
• Large span roofs
• Low pitched roofs
• Some older structural steel framed roofs can suffer from corrosion
• Substantial snow drifts can accumulate in valleys, behind parapets and against neighbouring higher structures
• Staggered roof lines of differing levels can result in snow building up on the lower roofs from drifting or sliding snow that is deposited from adjacent roofs of higher levels
• Poor maintenance of gutters and drainage systems resulting in them becoming blocked, frozen, and melting snow and rain not being able to drain away from the roof

If in doubt, specialist advice from chartered structural engineers or other appropriately qualified persons should be sought about the loads acting on a building or how these loads can be safely accommodated by the structure to ensure your buildings are best prepared for the anticipated snow loadings they will experience.

HOW DO ROOF FAILURES DUE TO WEIGHT OF SNOW OCCUR

Roof collapses due to excessive weight of snow can happen for a number of reasons including:

• When snow load exceeds the design load for the roof
• Inadequate structural design
• Imbalance of snow load on a roof
• Failure of one key member of construction detail causing others to fail as a result of load transfer
• Inadequate roof drainage systems
• Roof drainage systems such as gutters, downspouts and drains that are blocked by debris prevent rain water, water from melting snow and ice from being able to freely drain away from roofs
• Introducing additional weight to roofs, such as fixed machinery or plant which may reduce the original load tolerances available for weight imposed by snow
• Poor workmanship and construction detail
• Critical bracing not installed or poorly installed
• Trusses, rafters and purlins installed at wider spacing than specified in original approved designs
• Materials of reduced quality or of smaller dimensions than specified in original approved designs

MAINTENANCE BEFORE THE WINTER WEATHER BEGINS

Regular and systematic building inspections are a key part of any maintenance programme in order to help identify problems promptly.

Early remedial action by a competent person is essential to reduce further, more costly, damage. It may be necessary to engage a competent person with the appropriate skills and equipment to carry out inspections in certain areas e.g. roofs.

Intervals between inspections may vary depending on such things as the location, age, construction, usage etc. of a building.

Log books are indispensable for keeping track of maintenance regimes, identified problems and actions taken.

Rainwater Removal - Gutters, Gulleys, Downspouts and Drains

Blocked or damaged rainwater removal systems will allow damage to the building fabric, water ingress and most importantly may prevent water being drained away from the property and in freezing temperatures this can result in ice dams forming during snow and prolonged cold conditions. Ice dams can form when heavy snow melts during the day, flows and cannot sufficiently drain away and then refreezes at night. After several melting-freezing cycles combined with further falls of snow the weight load on the roof will obviously increase.

There are a number of practical measures that should routinely be undertaken throughout the year as part of your overall building maintenance plan that can help prevent damage caused by heavy snow and ice dam formation which include:

• Inspect all gulleys, gutters, downspouts and drains and repair any damage
• Inspect and clean accumulated debris such as leaves, vegetation and silt from all roofs, roof drains, gutters, valleys and downspouts so that water will flow freely
• Inspect and clean accumulated debris such as leaves, vegetation and silt from the underground drainage system around the property to ensure that it will effectively remove water away from the building
• Inspect the structural elements of the building for accidental damage that may detrimentally affect the structural strength e.g. damage caused by impact from forklift trucks, high loaders etc

Again log books are indispensable for keeping track of maintenance regimes, identified problems and actions taken.

Roofs

Roofs generally need to be inspected at least twice a year or following particularly stormy weather during the the non-winter months - debris on the ground from broken slates and tiles indicates that there is a problem. In some cases roofs can be inspected using binoculars or vantage points from nearby higher buildings.

Ice can form when heavy snow melts during the day, flows under the roof tiles, and then refreezes at night. After several melting-freezing cycles tiles may be displaced, and water may often enter the roof space and damage insulation, ceilings, walls, contents and even the building itself.

Repair or replace:

• Missing , slipped or broken slates or tiles
• Damaged or rusty cladding
• Cracked flat roof coverings. A bitumen roofing felt may need to be completely renewed after 10 years.
• Corrosion to structural steel framework, bolts etc
• Leaking or damaged rooflights
• Damaged flashing
• Gaps and missing mortar between ridge tiles

In addition moss, which retains moisture, needs to be removed since it can cause slate to delaminate and can gradually erode all metals particularly lead work - a seasonal brushing down is often all that is required to prevent excessive build up.

Internal inspection of the roof and framework must also take place

STEPS THAT CAN BE TAKEN DURING WINTER WEATHER

By taking some simple practical steps during severe snow conditions it may be possible to reduce the likelihood of roof collapse. The following steps should be taken during such weather events:

• Try to keep roofs, gutters, downspouts and drains clear of ice so water can freely drain away - they may be covered in ice and allow water to pond under the snow and ice
• When clearing snow from yards, driveways and footpaths around the curtilage of your premises you should make sure that snow is not deposited against the foot of any downspouts as this may interfere with effective drainage
• Only where it is safe to do so, chip and channel any ice dams to ensure that water can flow freely
• Be watchful for signs of stress and deflection of the roof and wall structure such as deflection, cracking, splitting or twisting, particularly in trusses, purlins, joists, beams and girders
• Roof failures can occur at the exterior wall connections particularly in buildings with flat roofs so it is important to check the connections for signs of cracking, twisting or deflection
• Be alert to any unusual sounds emanating from the building such as cracking or creaking from the roof
• Specialist advice should be obtained if considering the removal of snow from roofs and this should only be undertaken if it is safe to do so and by a competent person following a risk assessment
• Keeping attics well ventilated can reduce the build up of snow and formation of ice dams
• If portable heaters are being considered you should first seek approval from your insurance company and comply with any additional requirements that may be required. In addition, heaters must be adequately maintained, staff must be trained to use them safely and ensure that fire risk assessments are updated to reflect the additional hazard.

BE ALERT FOR THE TELL TALE SIGNS

Often before a roof collapses due to the excessive weight of snow and ice the building will generally exhibit some signs that the roof is under excessive load including:

• Visual deformation of the roof steel
• Cracked or split wooden structural elements of the roof framework
• Doors and windows that suddenly become difficult to open or close
• Creaking or cracking noises
• Separation of ceiling joists and beams from wall plates
• Signs of new movement in flashing around chimneys, door trims, ceilings, staircases and other mastic type seals which are only designed to withstand very small amounts of movement
• Deformation to service or conduits to mains services
• Sprinkler heads being pushed down below ceiling levels

Safety of life is of utmost importance so if there is any doubt about the integrity of a roof in such extreme snow conditions then the building or area should be evacuated until professional advice can be sought.

HEALTH AND SAFETY

It is important that you are aware of the following risks:

• Any work at height must be subject to a Risk Assessment and development of safe working methods
• Safe means of access must be used - cherry pickers may be preferable to ladders
• Any person undertaking work at height on roofs, clearing gutters etc must be competent and suitably trained. The danger of going onto a roof for whatever reason should not be underestimated.
• Buildings which have been damaged are likely to be unstable and may present a serious health and safety risk. Unless damaged buildings have been verified as being in safe condition by a qualified and competent person it is sensible to keep out of the buildings to avoid the risk of injury through collapse of the structure.
• Seek professional advice to check that any roof is safe and suitable to stand on and has no fragile areas. You should always assume that any roofing surface is fragile until confirmed otherwise by a competent person.
• Seek professional advice to ensure that the roof is capable of supporting additional loads when it is already under load from snow and ice

SNOW AND ICE ROOF MELTING SYSTEMS

There are a range of snow and ice prevention systems available from specialist installers that can reduce the build up of ice, snow and the dangers posed by heavy snow building up on roofs which can lead to structural damage.

Typically these are electrically powered trace heating systems comprising of heated mats and cables which are routed and positioned in critical areas of the roof, eaves, valleys, gutters and downspouts etc. Such systems are designed to activate automatically by strategically located thermostatic and moisture detection that switches on the heat source whenever the ambient temperatures fall below a set point.

BUSINESS CONTINUITY

Being prepared for such events will increase your businesses resilience and enable your organisation to resume operations in the most effective and shortest possible time should disaster strike.

Although headline disasters capture the attention, businesses need to be aware that other more specific events are just as likely to threaten their organisation. Disasters can and do happen and will cause healthy businesses to fail. Disasters create missed opportunities, cash flow problems and can often result in bad publicity. All this can lead to a loss of client confidence and your competitors will take advantage.

Planning makes a substantial difference to the possibility of surviving an incident. While it may seem an extra burden to prepare a plan, challenging situations place severe pressure on individuals to make decisions and take action under stressful conditions. Experience proves that it is easier to consider all the issues surrounding a potential crisis objectively beforehand.

Insurance has a vital role to play in supporting your recovery, but it makes sense to have a plan as well. This should give you the opportunity to reduce the risk of some incidents occurring and to know what immediate measures to take to minimise the initial impact.
Business Continuity Plan doesn't need to be complicated and does not need to deal with every scenario. If your plan enables you to cope with the worst case scenario, it will also help you to deal more easily with less serious incidents.

The Business Continuity Planning process is designed to help you reduce the likelihood and impact of risk occurring and becoming a disastrous event, as well as putting in place suitable contingency plans that will enable your business to maintain its revenue and client base, assist with the continuity and recovery of your business and ensure its survival should the worst happen and disaster strike.

The Business Continuity Planning process is an on going business process that would normally consist of the following key elements:

• Identification of your businesses critical resources (people, machinery, data, suppliers etc.), departments and processes
• Identification of the minimum level of service that your business has to provide at all times, even if a disaster strikes
• Identification, assessment/impact analysis and prioritisation of risks that may affect your critical resources, departments and processes and ability to deliver the minimum level of service
• Where practical and cost effective to your business, the implementation of risk reduction measures for those risks that are unacceptable to your business
• Development of an Emergency Action Plan that will provide an immediate response the disaster and minimise the effects of disaster including timely removal of mobile equipment and stock, covering key machinery and plant with plastic sheeting
• Loss of operating systems and/or electronic data produced thereon is likely to have a serious and lasting effect on your company's ability to trade efficiently and effectively, in both the immediate and medium term future. Appropriate precautions need therefore to be taken on what data is perceived as being important and having an impact on the business, if lost so backing up computer systems is important.
• Development of a Business Recovery Plan that will assist you in maintaining your business and its client base should a disastrous event strike
• Procedures to test, maintain and update the Plan

Key Action Steps

• Do you know and understand the snow load designs for all the roof sections of your building/s?
• Does your building maintenance program include measures to ensure that your buildings are not compromised by snow events?
• Are you prepared for such events and is your business able to respond effectively to deal with such events?

Effective precautions are required for all work on roofing surfaces, no matter how short the duration, whether the work concerns construction, maintenance, repair, cleaning or demolition.

References

Building Regulations 2000, Approved Document A - Structure
The Building Standards (Scotland) Regulations - Technical Standards

Next Steps:

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• Call our Risk Helpline on 0345 366 66 66
•  Email us at riskadvice@aviva.com

Please Note
This document contains general information and guidance and is not and should not be relied on as specific advice. The document may not cover every risk, exposure or hazard that may arise and Aviva recommend that you obtain specific advice relevant to the circumstances. AVIVA accepts no responsibility or liability towards any person who may rely upon this document.