One of the things that I learned early when working on and installing tile roofs in Southwest Florida is that the old way of installing the drip edge on top of the underlayment during installation was a poor idea. It is still required today by code to be installed over a piece of underlayment and not directly to the wood decking.
I understand the idea behind this in regards to uplift and direct wind, but on a tile roof, it is unnecessary. It also flies in the face of reason in regards to the water that flows under the tiles and over the underlayment on a tile roof. Tile roofs will shed over 90% of the water from rains over the tops of the tile. A small percentage of water passes though and gets under the tiles. This water travels down under the tile part of the roof. During a rain, water will pool at the eave of the roof under the tiles until it drains out.
The issue created by installing the drip edge over the underlayment was the standard when I started in roofing. The issue is that the top of the drip edge is lapped backwards toward the top of the roof. Meaning, the top of the drip edge is now a minor dam to water that will travel under the tile roof and will have to exit over the top of the drip edge at the eave of the roof. To counter act the backwards lap, we were required to install a band of roof cement over the backward lap with a trowel. This would seal the top of the drip edge and redirect water over the top of it. This basically kicks the can of the problem of the backward lap further down the road of time. At some point, some or most of the roof cement will deteriorate from heat and weather to the point that it will crack open and start allowing water to channel beneath the drip edge. Water sits under the drip edge and finally overcomes the underlayment, rotting out the edge of the roof and the fascia below it. This issue would manifest between 5-10 years after a roof was installed. I also had several occasions where some of the roof cement would leach out from under the tile roof and over the drip edge and fascia where it discolored or stained both.
In 2005, I was asked to look at a tile roof on a home for sale in Pelican Landing in Bonita Springs that had an issue with rotting fascia. I was to give an estimate on how much it would be to replace the rotted fascia. After looking closer at the issue, I found that not only was the fascia rotted out in many areas, but that the first 5-6” of decking was also rotted out. To resolve this issue, we would not only have to replace the fascia but the first 2’ of decking as well. Our estimate was to remove the first two rows of tiles all the way around the eave of each roof facet, remove the eave closure, drip edge, underlayment, and change out the rotted plywood decking and fascia. That was a big roof. It was only 10 years old and had to have major repairs.
We did not get the repair (thank goodness). I think that they found someone to replace the fascia only (or paint it really well) and left the real problem to the next owner.
I saw many roofs like this. This was the preferred way to install a tile roof backed by Florida Building Code. It wasn’t long after this roof that I had the crew install the drip edge under the underlayment. The crew nearly rioted. Installing tile roofs was something that they had been trained in doing and had many years of installation experience in. This was in complete contrast to what was the “correct way” to install tile roofs. However, once the drip edge had been moved under the underlayment, water flowing under the tiles no longer had this weak area on the roof to undermine and our roofs no longer had this type of long-term issue.
Today we install a small strip of underlayment, which is called a slip sheet, down on the edge of the roof first. The slip sheet is a little wider than the drip edge itself. We then will install the drip edge on top of the slip sheet. After this, the underlayment for the rest of the roof is installed over the top of the drip edge. This maintains the adherence to the Florida Building Code while correcting the issue created by installing the drip edge over the underlayment.
It was tough to break the crews of the original way to install the drip edge over the underlayment. Change can be hard. We not only mitigated the issue with the drip edge, but we eliminated several of these types of installations that would later lead to not only roof leaks but to other major issues. This and several other changes that we made to our tile installations changed our roofs to long term, low maintenance roofs.