Would You Like to Know How Weather Affects Trusses?

Originally published by the following source: SBC MagazineMarch 4, 2019
by Evan Protexter, EIT

   

Heavy rains, high humidity, and large temperature drops at night create a perfect place to store trusses if the goal is to potentially damage trusses from weather exposure. This was the thought process SBCRI followed in order to select locations for the weathering testing program. As previously mentioned, weathering locations were used to expose trusses to weather in an effort to cast a wide net and get as much weather data as possible.

For each of these locations, SBCRI worked with a component manufacturer (CM) from the area to manufacture and set trusses out in distinct exposure setups. The idea for these exposure setups was conceived by SBCRI and verified a meeting with the SBCA E&T committee with intent of closely imitating typical field storage conditions.  The locations chosen were:

  1. Baltimore, Maryland
  2. Meridian, Mississippi
  3. Madison, Wisconsin

As can be seen in the table above, these three locations typically experience high levels of rainfall throughout the summer and have high temperature swings between daytime and nightfall during the time trusses are set out to weather. Not to mention the fact that daytime humidity was typically 60% and nighttime humidity was around 100% for all these locations, giving the trusses a large humidity swing too.

Temperature is typically constant in an area and is easily monitored through any online weather service. The hurdle to overcome was the fact that most online weather reporting stations are at airports, or dedicated buildings in the nearest city. This means that there may not be a weather station within 10 miles of where the trusses are stored creating an issue for monitoring rainfall at the truss storage location.

To solve this issue, SBCRI sent each CM a weather station (pictured at right) that could be installed at the plant to collect weather data at the locations the trusses are stored. One example of this concept at work occurred in Madison, where the west side of the city experienced approximately 12” of rain over a 24-hour period in August of this year. Had we used the Madison weather data from an online source, we would have logged approximately twice as much rainfall as the trusses experienced which was closer to 6”. The additional benefit to having dedicated weather stations at each location is the ability to monitor weather conditions remotely (see image below) and collect data for future analysis.