Wind loading in roofing design

Wind loading in roofing design

 

To ensure that buildings are secure, roofs must be wind resistant. A roof is the single most important part to maintain a building’s integrity – if the roof blows off the building can be destroyed very quickly. When wind hits a building, it creates a suction effect, as suction of this nature can pull the roofing system up, you obviously want to make sure your roofing is pull-proof and able to survive every storm intact. As part of our Roof Consultation SOPREMA carries out wind uplift calculations to make sure our roofing systems are strong enough to withstand specified wind uplift forces.

Wind uplift calculations: unique for every building

Each project requires its own specific wind uplift calculations as every building is unique in this respect. The effects of storms depend on location, wind force and the dimensions of the building. Hence, SOPREMA takes the following factors into account for each wind uplift calculation:

  • GPS coordinates
  • height and shape of the building
  • surroundings

Combined, these factors determine how winds will hit the building.

Three primary zones

Wind loading in roof design is not the same for every part of the roof. At SOPREMA, we divide every roof into three areas, and we make detailed calculations for each:

  • field area
  • perimeter area
  • corner area

The wind pressure is low in the middle of the roof, and higher in the perimeter zones. But the highest pressures are typically found in the corner areas, where the wind flips up over the wall.

Mechanically fastened vs adhered with adhesive

Roofing materials can be mechanically fastened or adhered with adhesive. Our calculations will take your system of choice into account.

  • Adhesive
    When testing a glued system, you end up with a value – let’s call it ‘X’ – that indicates what wind pressure the system will be able to withstand. If your design pressure is also X, you are good to go. If the test approves of value X for the roofing system in question, and the pressure you worked with for your design is less than X, modifications will need to be made to bring both values in line./li>
  • When it comes to mechanical roof fixing by contrast, calculations need to be done for each of the three areas we mentioned earlier. The test will tell you: in the field area you need X fixings per square meter, in the perimeter area you need Y fixings per square meter and in the corners you need Z fixings per square meter. Each fixing has a value in newtons (for instance 450), so you can work towards a specific wind uplift by putting more fixings in.

Do not rely on the value of your fixings only

Let’s conclude by commenting on a common misunderstanding. As the value for each fixing is known, you might be tempted to rely on the values entirely when designing roofs. Yet the entire construction must be taken into account, as the following simple comparison makes abundantly clear. If you put a sheet of paper on a roof, the roof will obviously not be stable whether you use sufficient fixings or not. The screw might stay but the sheet is bound to blow off at the first strong breeze.