In this video, General Contractor Tom Silva teaches three apprentices from our GenNEXT program his method for roofing a section of the house that will receive significant snow loads.
by Chris Ermides Updated 08/08/2024Protecting your roof from water damage is crucial for maintaining the integrity of your home, as it prevents water damage and other costly problems. Two key components in this system are drip edge and step flashing.
In this guide, we’ll explore how to properly install these essential elements, drawing on expert advice from This Old House general contractor Tom Silva. Silva demonstrates his method for roofing a section of a house that will receive significant snow loads, taking into consideration the potential for ice damming while managing water runoff.
Proper installation of drip edge and step flashing is essential for several reasons:
Before beginning the installation process, gather the following materials:
Here is Silva’s process for installing flashing:
In climates prone to ice damming, the International Residential 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 the overall dimension from the roof’s edge depends on your roof’s pitch and eave depth. Silva likes to go beyond the minimum of 24 inches to 36 inches from the inside wall.
Due to its location, the roof featured in the video will receive runoff and snow from adjacent roofs. To address this runoff, Silva runs the ice and water membrane all the way up the roof (a belt-and-suspenders approach), lapping it up the sidewalls.
He also carries the self-adhering membrane over the joint where the fascia meets the sheathing. This application ensures that any backup that may occur from ice bridging the fascia and gutter won’t creep under the sheathing, which would cause rot.
Note: In this video, Silva uses a granulated ice and water membrane. Since membrane can crack when folded over an outside corner, he also uses a non-granulated BITUTHENE membrane to seal the joint specifically. Doing this helps protect the fascia and sheathing.
While it may be common practice to install the drip edge tight to the fascia, Silva advocates a better approach. He pulls the drip edge off the fascia so that a 3/8–1/2-inch gap remains between it and the fascia.
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 practice of installing drip edges tightly to the fascia creates a path for water to cling to the fascia and run down it, wearing down the face of the fascia and shortening its lifespan.
The starter course features 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 application. 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.
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.
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. Avoid nailing through the flashing into the shingle, as this will create potential leaks in 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.
Here, Silva and the apprentices are installing architectural shingles. They extend the course 3/8–1/2 inch past the starter course, nail it in place, and install the step flashing. Repeat these steps with the next courses until you achieve full coverage.
Be sure to follow the shingle manufacturer’s recommended lapping and nailing schedule.
While flashing and drip edge serve similar purposes, they are not interchangeable. Drip edge is specifically designed to direct water away from the fascia and into the gutters.
Conversely, flashing is used to prevent water intrusion at joints and transitions on the roof.
Step flashing should not be nailed to the wall. Instead, it should be nailed to the roof deck with a single nail in the upper corner. This allows for proper water drainage and prevents potential leaks that could occur from nailing through the flashing.
Proper installation of drip edge and step flashing is crucial for protecting your roof and home from water damage. Paying attention to detail in your roof’s protective system can significantly extend the life of your roof and prevent costly repairs down the line.
By following Silva’s expert techniques, you can make your roof ready to withstand heavy snow loads and prevent ice damming.