Given that scenario, Silva has developed a number of practices that take into consideration the potential for ice damming while also managing water run-off. He installs an ice barrier (aka ice-and-water membrane), then drip edge, then the roofing—weaving in step-flashing between each course.
Steps for Installing Drip Edge and Step Flashing
Here is Tom Silva’s process:
1. Start with the ice barrier
In climate zones prone to ice damming, code requires that a self-adhering ice barrier membrane be applied directly to the sheathing so that it “extends from the lowest edges of all roof surfaces to a point not less than 24 inches inside the exterior wall line of the building”. That 24 inches is measured horizontally from the inside edge of the wall and so the overall dimension from the roof’s edge depends on your roof’s pitch and your eave depth. Silva likes to go beyond the 24 inch minimum to 36 inches from the inside wall. Due to the location of this roof, which will receive runoff and snow from adjacent roofs, Silva ran the ice and water membrane all the way up the roof (a belt-and-suspenders approach), lapping it up the sidewalls. He also carried the self-adhering membrane over the joint where the fascia meets the sheathing. This ensures that any backup that happens – like from ice bridging the fascia and gutter – won’t creep under the sheathing, which would cause rot. Note: In this video, Silva used a granulated ice and water membrane. In order to ensure that the lap over the fascia and sheathing remained intact (it can crack if folded over an outside corner), he used a non-granulated bituthene membrane to seal the joint.
2. Add the drip edge
While it may be a common practice to install drip edge tight to the fascia, Silva advocates for a better approach. He pulls the drip edge off the fascia so that a 3/8”-1/2” gap remains between the drip edge and fascia. Doing this allows the drip edge to fully serve its function, which is to direct the path of water away from the roof’s edge and away from the fascia. The common practice of installing drip edge tightly to the fascia creates a path for water to cling to the fascia and run down it, wearing the face of the fascia and shortening its lifespan.
Using drip edge with a nailing edge approx. 4” deep, nail the drip edge to the sheathing every 16” If installing multiple runs of drip edge, lap them by 1/4-1/2-inch keeping the nail back from the lapped joint. This will allow for expansion and contraction and prevent buckling.
- Install the starter course
The starter course is comprised of a shingle that’s roughly half the width of the field shingles. In this video, Silva installs a starter course comprised of shingle strips specifically designed for this purpose. Note that it includes a strip of tar along its edge. Be sure to run that edge so that it is facing up as it will soften in the sun, adhering to the course laid on top of it—minimizing the chance of uplift from wind.
Install the starter strip so that it overhangs the drip edge by 1/2-inch. Nail the starter strip about 3” up from the leading edge, using 4 nails evenly spaced for a full strip (approximately 10”-12-inches apart).
Note: Manufacturers offer specifications about nailing schedule and minimum strip sizing, so be sure to read the installation instructions that come with the shingles you’re using.
- Install the step flashing
Before running the first row of shingles, install a piece of step flashing along the sidewall so that it sits tightly against the roof. Align the step flashing with the leading edge of the starter course and nail it in place using one nail in the upper corner. There’s no need to nail more than this, and don’t nail through the flashing into the shingle as this will introduce a potential leak to the roof. Consecutive layers of asphalt shingles will cover the flashing, holding it in place.
When the siding is installed it should be tucked behind this piece, and then consecutive courses lapped over it. The remaining siding on the sidewall will overlap the step flashing and nail.
5. Install the first course of shingles
Here, Silva and the apprentices are installing architectural shingles. They extend the course 3/8-1/2-inch past the starter course, then nail in place, then install step flashing, then the next course, and so on up the roof. Be sure to follow the shingle manufacturers recommended lapping and nailing schedule.
