Proper practices for the installation of roof drip edge flashing.
Roofing drip edge or cap is the metal flashing that covers the wood decking at the edge of a roof and supports the roof shingles.
It is intended to prevent water from contacting and damaging the roof decking, prevent the roof shingles from drooping over the roof edge, and improve the appearance of the roof line.
Why do you need drip edge?
Rain water running down the roof will fall into the rain gutter and splash up and back against the roofing and gutter board. At the rake, or gable end of the roof, rain water can be blown by the wind against the edge of the roof decking.
In times gone by, wood trim or mouldings would protect the edge of the roof decking from getting wet. In those days the roof decking consisted of solid wood planking, and even if it did get wet, the wood was able to dry without damage and would last.
Modern building practice of using plywood or composite wood for the roof decking demands that the wood is thoroughly protected from the weather. If not, these materials, which tend to suck up water like a sponge, will quickly delaminate and rot away. The old practice of using solid wood trim to protect the roof edge has been replaced for the most part by aluminum and vinyl siding that is easily infiltrated by wind blown rain. Drip edge is installed to prevent this water intrusion.
Drip edge installation.
Drip edge is installed first at the eave or lower edge of the roof. After the ice shield or ice guard, if being used, is installed. This prevents water from ice dams from backing up under the drip edge and leaking into the soffit. The drip edge should fit flush against the gutter board and over the gutter.
On the rake, or gable edge, the drip edge is installed over the ice and water shield and the tar paper / underlayment. This creates a layered protection. If water blows under the edge of the shingles, the drip edge will direct the water over the tar paper and away from the roof decking.
If possible, have a roofer with the proper equipment bend your drip edge to the roof pitch angle before installation.
Unfortunately, most drip edge is bought pre-made from the factory. Meaning it comes in standard sizes with the downward flange fabricated at a 90 degree angle. As most roofs , other than flat roofs, have a pitch/slope, these pre-made drip edges don't fit very well at the eave. Many roofers will try to compensate by pushing the drip edge against the gutter board for a better fit. This usually results in bowing or curving edges, or the front lip of the drip edge raised above the roof line, which creates a small gully for water to sit. There is also less room to nail the flashing securely to the roof.
Nailing the drip edge flashing is somewhat dependent on the local weather conditions. If you live in an area with frequent high winds and storms, nails placed 4-6 inches apart is recommended . If your location is calmer, a nail at every rafter is sufficient to secure the flashing at the eaves, and every 12 inches along the rake. Fewer nails will be necessary with heavy gauge metal flashing.
Be sure the nails used are long enough to penetrate through the roof decking.
Use nails that are compatible with the flashing material used.
Copper nails with copper drip edge and galvanized nails with galvanized or painted steel, and aluminum.
Video: Drip Edge Flashing Installation
In this video we illustrate the proper procedure for installing roof drip edge when installing ice and water shield, or ice guard membrane.