Have you ever wondered what types of questions people “Ask a TRI Expert“? This series, brought to you by the Tile Roofing Institute, allows anyone to ask anything about tile roofing installation, maintenance, etc. The Tile Roofing Institute (TRI) is a non-profit association of producers and associates of concrete and clay tile and is considered one of the leading experts in the industry. Here’s a recent question from a home inspector, and the response from TRI President and Technical Director, Rick Olson.
The high wind tables in the Tile Roofing Institute’s Concrete & Clay Roof Tile Installation Guide can be intimidating at first glance. A recent “Ask the Expert” response by TRI President and Technical Director Rick Olson describes how to use the tables to determine fastening requirements.
“Oklahoma is considering changing to a 115mph wind zone. I need help to decipher the tables in the back of your TRI manual so to know how to use these on an install.”
Although they seem onerous at first glance, the wind tables are not too harrowing to navigate with a few clues.
If Oklahoma is considering the 115 MPH designation, we will assume they are going with the 2012 IBC/UBC and the tables in Appendix C would apply. Since most tiles are installed on Gable/Hip roofs we would be looking at Tables 9A (roof slopes 5.5:12< 6:12), Table 9B (roof rlopes 2.5:12<5.5:12, shown below) or Table 9C (roof Slopes 6:12< 12:12).
This will let us know what the wind uplift would be on the tiles. Since you are 115 MPH, you would use the 120 MPH column for exposure C (most commonly used outside of coastal areas).
*Example: 5:12 hip roof at 25-ft. mean roof height, exposure C is 13.4 ft-lb of resistance (from Table 9B).
Now we need to go to Table 7 on page 85 (since Table 2 on page 95 only has the very high wind options that are above your 120-mph cutoff).
Here we list all of the fastener options and their corresponding resistance. You need to select the tile profile. So let’s say a flat tile on a batten on a 15/32” sheathing.
We need an option that will exceed the 13.4 so we will be looking at the 1-#8 screw at as a minimum with 25.6 in Table 7.
If you were a direct deck application with a 15/32” sheathing, you could use the 2-10d smooth shank as a minimum with 20.2