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During the winter periods in 2009/2010 and 2010/2011 a large number of roofs collapsed or were damaged in Sweden due to heavy snowfall. Also many farm buildings were damaged. In this publication an investigation carried out at the Department of Rural Buildings (LBT) is reported. The aim of the work was to clarify the extent of damages related to agricultural structures and the causes of them and to suggest measures to reduce the risks of future damages. The work has consisted of analyzing and compiling reports of occurred damages, interviewing affected house-owners and by coordinating the work with parallel projects dealing with roof damages outside agriculture which were carried out at the Technical Research Institute of Sweden (SP), at the Faculty of Engineering at Lund University (LTH), and at Skanska construction group.
During the winters in question the insurance companies got about 3000 reports concerning various types of roof damages in Sweden. It was estimated that about 60% were related to farm structures. Consequently this means that about 2000 farm buildings related to or of agricultural origin were affected. Included in this figure are also depreciated buildings and structures that have only been intended for temporary use but have been left behind and included in the insured building stock. Nothing could be found indicating that the number of collapses or damages would have been lower if building permit or building notification regarding farm buildings had been required. E.g. in Denmark where also farm buildings require building permits a great number of collapses and damages occurred due to snow loads during the winters in question. In Sweden also a large number of building permit duty buildings were affected by damages due to snow loads.
Additionally the following conclusions could be drawn concerning farm buildings:
• A majority of the damaged buildings had a wooden load-bearing structure.
• The normative snow load value on ground in the different snow zones was only exceeded in some isolated occasions where roof damage had occurred
• Unsymmetrical snow load, snow pockets, buildings connected to each other so that snow may slide down from higher situated roofs and from roofs with higher slope as well as faulty shoveling imply an increased risk of collapses and damages.
• A need to change and complete roof snow load coefficient should be investigated. The effects of roof size, geometric design and local lee giving structures probably have to be refined.
• No or defective constructional calculations could be observed in connection to many damaged objects.
• The roof shoveling must be done safely. Practical shoveling instructions must be worked out to avoid e.g. unsymmetrical snow loads on the roofs.
• Ignorance and/or negligence could be concluded as causing failures when building with own labour and organization as well as on general or all-in contract.
• It is important that the farmers who are going to build realize and acquire information about the responsibilities resting on them as a building employer. This knowledge must be conveyed at all education levels from agricultural schools to university. Such information must also be disseminated at courses and seminars for active farmers. Additionally information may be spread by magazine articles and information leaflets etc.
• When buying and building manure storage including a roof or grain silos the building employer must have information of what forces in terms of snow and wind it can stand. This is of particular importance when the building or part is imported or bought from places with other climatic conditions. Additionally, it is important to get confirmation from the insurance company of what stipulations that are applied for such roofs.
• The insurance companies should somehow make more clear demands on inspection and control of the buildings being insured. This would motivate the house-owner to higher degree of accuracy when designing and erecting new buildings as well as maintaining existing ones. Fulfilling requirements may also be reflected in a lower insurance premium level.