When does snow on a roof actually become a safety risk? At what point should action be taken to prevent structural overload?
This article explains how to determine the right moment to remove snow from a roof in order to prevent structural overload.
How to assess snow load on a roof?
Assume that snow accumulation on the roof is monitored on an ongoing basis. This makes it possible to accurately track the current safety condition of the structure. Depending on the method used, measurement results may be expressed in weight units (kg/m²) or interpreted as structural deflection or deformation, expressed as a percentage of the maximum allowable value.
What factors should be analysed before deciding to remove snow?
The key question is:
How far in advance should roof snow removal be initiated to avoid exceeding 100% of the permissible load and compromising the building’s safety?
Answering this question requires analysing several factors:
- the current roof load,
- the rate of snow accumulation,
- forecasts of heavy snowfall,
- the time required to mobilise a snow removal crew,
- the time needed to remove snow from the entire roof.
Let us assume that up-to-date measurements are available and that the rate of snow accumulation is known – for example, how many kilograms per square metre are added per hour, or how the structural deflection changes over time. Comparing consecutive measurements makes it possible to determine:
- how quickly the load is increasing,
- how much time remains before reaching, for example, 50–70% of the permissible load,
- whether forecasted snowfall may lead to exceeding safe levels.
At this stage, the type of measurement system itself is not the most important factor. What matters is that the data are frequent, reliable, and allow trends to be clearly identified. If a structural monitoring system such as SENSE S-One is used, measurements are updated automatically every three minutes.
If weather forecasts indicate upcoming heavy snowfall, two key questions arise:
- Will we be able to remove the snow in time?
- Will the load exceed a level that requires immediate action?
These questions help determine whether there is still time to wait or whether a decision must be made immediately. Combining the rate of load increase, weather forecasts, and crew mobilisation time provides the most reliable picture of the situation.
When should snow be removed from a roof – what is the best moment?
Many studies indicate that snow removal should begin when the load reaches approximately 70–80% of the maximum permissible structural load. Before deciding to allow access to the roof, however, a building manager should verify two additional factors:
- the time required to mobilise the snow removal crew,
- the forecasted amount and intensity of snowfall.
The response time of a snow removal contractor is usually specified in the contract. In theory, this indicates how many hours will pass between placing an order and the crew’s arrival on site. In practice, during periods of heavy snowfall, contractors often have a large number of assignments. It is therefore worth making sure that the snow removal company:
- will not prioritise another, more profitable job,
- will arrive with a crew large enough to begin actual work.
It does happen that a contractor – despite contractual provisions – initially sends only one person. Such a person merely confirms presence on site but is not capable of clearing a roof area of several or even tens of thousands of square metres.
It is also important to carefully review contract provisions. Response time does not always mean the actual start of snow removal work. In some cases, it refers only to arrival on site for an inspection.
Assume that this parameter has been verified and that the contractor declares sending an adequate number of workers within 12 hours of notification. This can then be factored into planning.
The next step is analysing snowfall forecasts. Knowing the current snow cover alone is not sufficient. Equally important is the rate at which the load increases over time.
This is where Weather Alerts prove particularly useful. In this solution, snowfall is provided in units of kg/m² per day, allowing for quick assessment without complex or imprecise calculations.
A decision critical to safety
This brings us to the stage that is absolutely critical to the entire roof snow removal process.
Removing snow from a roof with an area of 10,000 m² costs approximately PLN 80,000–120,000. For large logistics parks with roof areas of several hundred thousand square metres, snow removal costs are counted in millions of zlotys. It is tempting to postpone the decision and “wait a little longer.” However, responsibility for building safety far outweighs the cost of snow removal itself. In the event of an accident:
- the costs of dealing with the consequences are enormous,
- there is a risk of losing operational continuity,
- responsibility for human health and life comes into play.
Ultimately, a decision has to be made:
do we save money and take the risk, or invest in snow removal and ensure peace of mind?
A responsible building manager understands that there are no compromises when it comes to safety. Therefore, the decision should be made:
- based on concrete measurement data,
- using a reliable risk assessment,
- taking into account load forecasts and contractor response times.
Summary: when should snow be removed from a roof?
To determine when snow should be removed from a roof, three groups of information are required:
- the current condition of the roof structure
– snow load preferably expressed as a percentage of the permissible load specified in kg/m² or kN/m², - forecasted load increase
– the rate of snow accumulation and a precise forecast of upcoming snowfall, - time required to mobilise the snow removal crew
– the actual time from notification to accessing the roof and starting work.
It should also be remembered that snow removal may take from several days to more than a dozen days. During this period, weather conditions may change significantly, further increasing risk.
How does SENSE Smart Roofs take care of roofs?
In our work with clients, we:
- define individual alarm thresholds for initiating snow removal,
- analyse roof load-bearing capacity as part of a technical assessment,
- monitor structural deflections using the SENSE S-One system,
- monitor water levels on the roof using SENSE DSW sensors,
- use Weather Alerts to link forecasts with roof loads,
- select the most optimal course of action that ensures safety and helps avoid unnecessary snow removal.
This entire process is described in an individual roof snow removal instruction, prepared by our structural engineering specialists.
👉 If you would like to apply these principles to a specific building, our engineers can prepare an induvidual roof snow removal instruction based on the actual structural parameters and monitoring data.
Contact us at sales@sense.com.pl or call +48 794 234 334.
