Snow load
Our qualified employees remove snow from your flat roofs. They are specially trained to avoid any kind of accidents and to protect your buildings from damage caused by snow loads.
Excerpts from the DGUV 212-002
In recent years, changing climatic conditions have led to exceptionally heavy snowfall. Although the expected snow depths were taken into account in the calculations when constructing roofs and snow removal was therefore generally not necessary, existing buildings are often undersized for such loads. In addition, in recent years, the carrying reserves for snow loads have been reduced by superstructures (e.g. photovoltaic systems). In addition, heavy equipment and redistribution of snow during spontaneous snow clearance in the event of an accident led to traffic loads that had not previously been taken into account. This resulted in serious accidents caused by collapsed roofs or falls. These must not be understood as misfortune, but must be avoided in the future.
Snow management
Snow management is the systematic identification and assessment of all dangers and risks associated with snow and the determination of necessary measures (e.g. planning, preparation and initiation/implementation of timely snow clearance) in order to reduce the relevant dangers and risks minimize.
Tasks and responsibilities of those involved
In the state regulations, the rules of the accident insurance institutions and the state of the art, there are clear specifications for safety and health protection. These requirements result in clear obligations for the addressees of this DGUV Information, the violation of which can have legal consequences in the event of damage (e.g. civil law, criminal law, administrative offenses law, labor law). Snow management should include the following measures in particular:
• Identification of potential hazards, e.g. B.
– insufficient suitability and qualification of the clearing personnel
– poor planning
– Crash inwards and outwards
– roof collapse – weather conditions (thunderstorm, cold, wind)
– Electric shock (e.g. through photovoltaics, house connection lines)
Assessment of possible consequences (e.g. interruption of operations if there is a risk of collapse)
• Provision of necessary capacity to carry out the snow clearance
• Derivation and implementation of necessary measures as part of a concept, e.g. B.
– Preparation of an emergency plan for the timely initiation of snow clearance
– Structural preparations on the building to enable safe snow clearance
• Accompaniment and supervision of snow clearing.
Liability of those involved
Liability risks in connection with critical snow loads can arise from both the planning and the implementation through action or omission. They result from personal injury and/or damage to property, e.g. B. can have the following causes:
• Proof of stability does not take into account any extraordinary snow loads or traffic loads caused by personnel and equipment during snow clearance
• Changes in the condition of the building (e.g. due to aging, conversions) are not taken into account in the expected loads
• Snow is not cleared, is carried out too late or is inadequate
• Mistakes in building planning (lack of fall protection, etc.)
• Missing/insufficient evacuation and security concept
• Inadequate qualification and instruction of those involved
• no routine work
• Working in exceptional situations
• special weather conditions
• lack of early warning system
• poor traffic safety.
Purpose of snow removal
Roof snow clearance is intended to ensure the stability of buildings. The building as well as the people located in the building and the systems and processes housed in it should be protected from the dangers caused by snow.
Snow removal planning
The following parameters are particularly important:
• Determination of the current condition of the building (requires: exact knowledge of the current statics of the building, availability of the documents/plans, knowledge of the critical snow load)
• Determination of actual snow/ice loads
• Determination of the decision criteria for the need for snow clearance or a structural change
• Determination of the procedure for snow removal, taking into account the following factors:
Weather forecast (announced snowfall)
– Weather conditions (cold, wind, snowfall)
– Available time slots (darkness, further snowfall)
– Available people
– Required work equipment and its transport to the roof area
– Type of snow transport on the roof
– Safe access to the roof surface
– Safe workplaces and traffic routes on the roof surface
– Safe drop off points
– Anti-fall and fall-through protection measures
– Protection against falling masses/objects at the dropping points and roof access points
– rescue measures.
In addition, general hazards such as B. Danger of stumbling through impact and lightning protection devices (Figures 2 and 3) as well as superstructures, risk of slipping on foil roofs, electric shock (e.g. through house connection lines, through damage to photovoltaic systems) and ergonomic aspects including the risk of dehydration of the clearing personnel in the clearing concept to include.
When planning new buildings, it makes sense to consider the aspect of snow clearance, including the building logistics (e.g. traffic routes, escape routes, delivery, parking lot).
Safety devices on the roof area are to be planned after or together with the determination of the snow clearance procedures. It should be noted that railings at a possible dropping point and anchorage devices can make snow clearance more difficult.
(Source: DGUV 212-002)
Assessment bases for snow clearance
The basis for the assessment of the necessity of snow clearance are the load assumptions within the framework of the stability calculation of the structure during planning. Later, however, the actual condition of the building can be decisive.
Stability of the building
The stability of buildings and the load-bearing capacity of roofs are verified by static calculations. The load assumptions required for this are regulated in standards. DIN EN 1991-1-3/NA applies to snow and ice loads: 2010-12 Euro-code 1: Actions on structures - Part 1-3: General actions - snow loads. This standard contains information about natural snow loads depending on the different roof shapes. Accumulations caused by snowdrifts are also taken into account. Furthermore, snow load zones are described depending on the geographic location within Germany. The values for these zones are average values determined over many years. They can be exceeded by actual snow events. In addition, additional loads resulting from snow clearance (snow accumulations due to redistribution, clearance equipment, etc.) are not taken into account. However, this should be taken into account when dimen-sioning future buildings.
The static calculations for the building are an essential basis for snow remo-val work on roofs. They document the static system and the target state at the time the building was erected. During the lifetime of a structure, the load assumptions can change due to newer findings, climate change, etc.
In addition, the building could have been erected differently from the plan or modified after completion.
Assessment procedure
Knowledge of the current state of stability of the structure is absolutely necessary in order to assess whether snow clearance is necessary. If this knowledge is not available, the stability can be determined in accordance with VDI guideline 6200. The maximum/permissible additional load that does not endanger the stability of the building can then be determined taking into account the current structural condition of the building. The additional load is the sum of the determined snow load and the estimated traffic loads. Traffic loads are, for example, machines, personnel and snow accumulations that can result from the clearance. However, the evaluation can also lead to the need to reinforce the roof construction if the expected additional load endangers the stability. If the permissible additional load is exceeded, stability is at risk. From this point on, the roof may no longer be entered. People are not allowed to stay in the building.
The determination of the current condition of the building and the static checks required for carrying out the snow clearance must be carried out by a competent person. In order to carry out snow clearing safely, a limit value must be determined which must be determined as part of the risk assessment for the safety concept. This results from the permissible additional load reduced by a safety factor. Snow removal is still permitted up to this limit.
Graphic: Source DGUV 212-002 / illustration assessment scheme
Determination methods for snow loads on flat roofs
Snow measuring tubes can be used for the direct, manual determination of the snow load. A quantity of snow is cut out with a pipe, weighed and converted into a distributed load.
The advantages of this method are the low investment costs and the option of selecting any number of measuring points. The disadvantage, however, is that to cut out the amount of snow, the roof surface and thus any danger areas must be entered. In addition, this method means a considerable effort for large roofs.
Alternatively, the level measurement can be used to measure the snow depth. The snow depth is read from the installed gauges. With a sensible arrangement of the gauges, stepping on the roof surface for the reading process can be avoided.
The direct, automated determination of the snow load is carried out by snow scales installed on the roof. This means that there is no need to inspect the roof and the measurement results can be viewed and evaluated with the help of a computer. Depending on the software, alerting procedures can be integrated, e.g. B. Information can be sent to the responsible persons by e-mail or SMS. A disadvantage of these methods are the selective measuring stations with the comparatively high costs and the high maintenance effort.
The roof and walls usually have to be penetrated for the power supply and the data line. In addition, depending on the design of the snow scale, there is a risk of icing and it should be noted that in the case of large roof areas, it may not be possible to make representative statements about the snow load.
The various types of snow differ significantly in terms of their density. Therefore, the snow depth alone is not sufficient to be able to make a decision as to when snow must be cleared. Rather, the snow load must be determined. The snow load can be determined directly or indirectly using manual or sensor-based measuring methods.
Graphics: Source DGUV 212-002 / Figure Determination methods for snow loads on flat roofs
Flow chart for snow management
Spontaneous clearance work on unsafe roofs is associated with high risks and is therefore not permitted. Therefore, an evacuation must be carefully planned.
In the following flow chart, the procedure for a subsequent creation of an object-related snow management is shown as an example. The object-related snow management consists of three stages:
Stage I : Object analysis
Stage II : Creation of a snow clearing concept
Stage III: Implementation
Stage I: Object analysis
Graphic: Source DGUV 212-002 / figure I of snow management
Stage II: Snow clearing concept
Graphic: Source DGUV 212-002 / figure II of snow management
Stage III: Implementation
Graphic: Source DGUV 212-002 / Figure III of snow management
Conclusion/final word
Conclusion for snow removal on roofs of existing buildings:
- The responsible building operators must determine in good time whether snow clearance is required (see Stage I).
- Before starting work, a clearance concept and risk assessment must be drawn up (see Stage II).
- The implementation (see level III) is to be supervised ba a person authorized to issue instructions (supervisors). This must monitor the snow clearing work. You must have sufficient knowledge to do this.
Snowfall is a regular event that can lead to exceptional situations on existing buildings.
There are two reasons for this:
- Changed climatic conditions lead to extreme snowfalls, for which roofs were not originally designed.
- The originally estimated traffic load of roofs has changed e.g. due to additional structures / e.g. PV systems) reduced.
In order to avoid the failure of roof constructions and accidents, the natural phenomenon of snowfall must be given special consideration in the object analysis/risk assessment.
The assessment of the snow loads is the basis for the planning and implementation of protective measures.
This DGUV information makes it clear that in order to reduce the risk potential for existing buildings and for new or conversion plans, snow clearance must be planned in detail in advance.
The complete DGUV 212-002 can be found at: https://publikationen.dguv.de/widgets/pdf/download/article/3098