Tiled roofs are built to be durable, but they do succumb to external factors that cause failure, such as wind pressure. As the air flows over the roofing, the movement creates a strong upward force that causes the tiles to rattle and loose. Over time, some tiles become so loose that a strong wind can remove them completely.
Tile roofing does not get “blown off” the roof. The upward force that the wind creates as it moves over the roof causes an upward suction force. This is a key fact you must keep in mind to understand the intricacies of building a secure tile roofing system. Getting tiles secured against the upward lift of the wind is important in ensuring that they stay on the roof.
When the wind blows over the roof surface, it causes a decrease in the air pressure on the tile roofing. When this happens, it simultaneously causes air pressure under the roof to increase. The increase in the air pressure within the loft space creates positive pressure on the tiles. The negative air pressure above causes the upward suction force that lifts the tile tail. This is why a low roofing pitch will cause forces to increase.
If the roofing tiles are sucked upwards but not blown, using the old method of fixing roofing tile will simply not work. Traditionally, roofing tiles are pegged or nailed at the top or head. This helps secure the tile against gravity but will have little or no effect on the upward lift. The one thing that secures the bottom portion of the tile is its own weight.
In the United Kingdom, tests showed that clipping or securing roofing tile at the bottom would help withstand five times the force that a roof tile nailed at the head has. Tiles can be wired or clipped to keep the tail secure against wind uplift. Securing tiles this way also helps stop any rattling or chattering that occurs when the wind is blowing over the rooftops. Chattering occurs when the wind lifts and drops the tiles. I recommend using a small amount of silicone between tile courses to secure the tiles and prevent chatter.
Note that today’s roofing tile clips have to be installed correctly to make sure that they do their job. Tile clips should be nailed close to interlocking channels. Many installers place the nail far from the interlock to avoid damaging the tile. To prevent the tile from coming loose, the roofing clip must be bedded securely. For me, the old method of wiring tiles at the bottom is the better option for modern clipping. Installing the wire helps fix the eyelet found on the bottom part of the tile and also between the tile courses to the supporting baton. Doing so will secure the tile. This is my preferred method because, from experience, I know it works. I have already re-installed wired roofs that are at least 50 years old and still found wires that remain clamped tight.
The roofing felt is the most critical component to preventing wind damage. Prior to fixing the tiles, sarking or roofing felt is installed under the batons. The roofing felt is meant to prevent wind damage. It is more important than waterproofing the paper because the roof has to act as a barrier against the wind. Sarking helps prevent air pressure from increasing inside the loft, thereby stopping any risk of wind uplift. Keep it securely fixed using 150mm overlaps. To secure it further, install an extra baton at the point of overlap to prevent the wind from entering between the sheets. The felt must be secured correctly so that wind force will not concentrate on the weak spot. If this happens, there will be more problems with the structure.
Hip and ridge tiles have to be fixed mechanically in areas that experience high winds. Do not rely on roofing mortar alone to keep these tiles secure. If the bond that holds the tile and mortar breaks, the tile can come loose. Instead, tiles must be nailed, clipped, or wired.
Watch out for areas that are frequently submitted to uplift. These are the eaves, ridges, and verges. It is important to be extra careful with these areas and ensure that they are fixed properly. To keep them secure, nail and clip every tile around the periphery.
Take time to inspect and secure roofing tiles during the installation stage so that they are not vulnerable to heavy weather. There will be some extra cost and time, but these will be offset by savings in terms of maintenance and your peace of mind.