Your Guide to Wind Loads

In the last edition of the Window Geeks: Master Class, we covered the basics of wind loads and windows. This time, we’re diving deeper. What factors affect wind load calculations? Why is terrain so important? And how will these affect the window product choice for your project? Let’s find out!

Tested, or designed and constructed?

The BC Building Code requires windows to be “designed and constructed” in accordance with the NAFS standard. It does not, however, require windows to be tested per the NAFS standard. The building location is important to note when calculating the wind load for a window – as every town & city in Canada has different historical weather and wind speed data.

Summary of factors affecting wind load calculations:

• City
• Building Grade
• Published hourly wind velocity in the code (1/10, 1/50)
• Terrain
• Topography
• Building geometry (flat small, vs tall and slim)
• Location of window/door on face or corner of the building
• Building surface

Terrain consideration

One crucial question to ask when it comes to wind loads is… open terrain, or rough terrain? To answer this, we’ll look at how close our project is to open fields or water. Rough terrain is classified as a location where there is suburbs or forest density that can help partially slow the wind. For open terrain, a calculation is required as part of the BC Building Code (4.1.7.3 - 5.C) “in cases where the site is less than 1 km or 20 times the height of the building from a change in terrain conditions, whichever is greater, provided an appropriate interpolation method is used” (405_Division B-Section 4.1. Structural Loads and Procedures (Rev2) 2018 BC Building code). For example, if a building is 12 meters high (multiplied by 20 would equal 240 meters) and is 700 meters from a lake or ocean, we would interpolate the wind load between open and rough terrain using a logarithmic equation for our terrain calculation.

Design Impacts

Wind load impacts the following components of window & door design:

• Glass thickness (deflection and stress)
• Water rating (Driving Rain Wind Pressure (DRWP))
• Performance grade requirement for the window/door
• Reinforcement required in the window which in turn affects the thermal performance
• Attachment method to the building structure

If you have any further questions on wind load and its impact on your project, the Window Geeks are here for you. Be sure to join us next time when we’ll be looking at deflection limits!

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