How much snow cover is actually dangerous? When should steps be taken to make a building safe? When removing snow is needed?
In the previous series of publications, I explained how to measure snow cover. Now I would like to draw your attention to another issue closely related to safety – i.e. starting to remove snow from the roof at the best moment for this. By the way, I would like to remind you that the Sense Monitoring team has prepared for you a new product – a manual of snow removal from the roof, which you order here.
KEY ROOF CONSTRUCTION PARAMETERS
Let’s assume that we measure the snow cover on the roof in real time. This allows us to accurately track the current operating status of the structure. Depending on the measurement method, we can give it in units of weight, deflection or deformation of the structure. For simplicity, let us enter a value expressed in percentage, where 100% means reaching the standard parameter SGU, SGN or load specified by the designer. In order for the roof structure to meet the assumed level of safety, it is not allowed to exceed the mentioned 100 per cent of the selected parameter.
The key question now is: how far in advance should you start removing snow so that this value is not exceeded and the safety level of your building does not decrease? This question requires the analysis of several factors. We have established that our measurements are up-to-date and that we know exactly how much snow is coming in every hour (thanks to the solution from Sense Monitoring, your measurement can be updated up to every 3 minutes). A comparison of the measurements shows the dynamics of the accumulation and the time it takes to reach 30-50-70% of the allowable load. The forecast says that heavy snowfall is coming. Will we be able to clear the snow in time? Will we not lead to a lower level of safety?
WHEN SHOULD SNOW BE REMOVED FROM THE ROOF – WHAT IS THE BEST TIME?
Many instructions for snow removal from the roof say to start removing at around 70-80% of the assumed maximum load of our structure. However, before we start this activity, as building managers, we should check two more factors: (a) the time for mobilisation of the snow removal team (b) the forecast amount of precipitation.
The response time of the snow clearing company is usually written down in the contract. However, these firms are very busy during heavy rainfall. It is therefore better to make sure that the team does not receive another, more lucrative order for snow clearance beforehand. Even knowing that they will pay contractual penalties for breaking the contract with us. Remember to check in the contract whether the response time defined there is the same as starting snow removal. Unfortunately, it is common practice to send one person per site and not to mobilise the entire crew necessary for clearing snow from an area of a dozen or several thousand square meters.
Let’s say we have checked this parameter, and we know that the contractor declares to send the appropriate number of people within 8 hours of the notification. Next, we check the dynamics of snow cover growth. For example, you can use the website www.meteo.pl, which gives values in units of kilograms per square meter per hour.
SAFETY CRITICAL DECISION
Now begins the absolutely crucial moment for the entire process of removing snow from the roof. Clearing snow from a 10,000 m2 roof costs approximately PLN 50-60,000. Who would not want to save such an amount? That’s right. On the other hand, the responsibility for the safety of the building and the consequences of not ensuring safety are much greater. And the costs in case of any accident are, to say the least, enormous.
Someone has to make a decision: do we save and risk, or do we spend but sleep well? A responsible building manager knows that there are no compromises when it comes to safety.
The decision must be based on facts and a precise, reliable risk assessment.
To sum up, in order to make the right choice and answer the question: when should snow be removed from the roof, it is necessary to know the current condition of the roof structure, projected load growth and time for mobilisation of the snow removal crew. It is also necessary to remember that snow clearance may last from several to over a dozen days, and during this time the weather may change dramatically.
HOW DOES SENSE MONITORING TAKE CARE OF THE ROOF?
We agree individually with our customers on the alert level to start snow removal, we choose the most optimal variant to ensure safety and at the same time to save on unnecessary snow removal. Feel free to contact me via email email@example.com or directly with me under this post.