If you're installing a large commercial roof for your warehouse, you've likely considered a number of different options. One thing you may not have considered, however, is the possibility of chattering in tile or slate roofs.
What Causes Chattering Tiles?
Commercial roofs are typically very large structures covering a significant amount of space. This means that, during windy weather, a significant proportion of the roof is exposed to high uplift forced caused by the wind blowing over the roof. Large, flat roofs are more prone to this due to the vortices shed by the wind as it passes over the structure.
Although the wind force may not be extreme enough to rip the slate clean from the roof, the tiles may be repeatedly lifted and dropped. This cyclic condition is known as 'chattering', which may cause the slate to break from fatigue if allowed to continue for a long period of time.
What is the Effect of Chattering Tiles?
On many commercial roofs, some tiles aren't nailed down to the overlapping row. This means that it is only the tile's dead weight that is holding the component down, and thus it is free to move if forced. If the uplift force generated from the wind is greater than the tile's dead weight, the tile will be pried clean from the roof.
Some commercial roofs have tiles that are head nailed, meaning it is joined to one other row of tiles at one end. In this situation, wind uplift causes the tile to pivot around the head nail, lifting the tile up and allowing it to drop again once the nail has taken up the restoring force. This effectively causes the tile to 'flap' similar to a cat flap installed on many doors. However, there will be a point where the wind uplift force exceeds the restoring ability of the head nail, causing the tile to pry loose of its fixity.
To prevent this, some companies may install interlocking tiles by clipping one of the bottom corners on the tile. The success of this approach depends on the tile clip used; clips come in many different materials and only the strongest will allow the tile to remain completely fixed. If there is any amount of slack in the clip, then there is a high chance that the tile will be able to 'chatter'. If the tile is allowed to lift even a few fractions of an inch, then the cyclic process of chattering can lead to significant wear on the roof.
How Should You Go About Fixing This?
Typically, roof chattering won't be noticeable until a year or two after the roof has been installed. This is because the resistance of the head nail or clipping will decrease over time, slowly allowing the amount of chattering to increase. Additionally, chattering doesn't usually occur over the entire roof; rather, it occurs over localized portions of the structure. As such, rigidly restraining each and every tile can be an arduous (and expensive) task.
With that said, there are a few ways that you can reduce the impact of chattering on your commercial roof:
- Use Heavy Tiles or Slates - The reason for this is fairly obvious; slates with a higher dead weight will provide more resistance against wind uplift. By opting for heavy tiles you are reducing the stress induced on any clippings, resulting in a much more robust roof.
- Use Mechanical Screws Rather Than Nails - Screws perform much better than nails, and by drilling in a number of screws to clip the tile you are effectively reducing the amount of slack in the system.
- Choose High Quality Clip Fixings - The greater the distance between the interlock and fixing, the higher the overturning moment (thus more movement). Choose a clip that has a straight pull down between interlock and fixing to maximize the restoring force on the tile.