How to Install Drip Edge Correctly

At the eave, drip edge goes on bare deck and the underlayment runs over its roof leg. At the rake, the underlayment goes down first and the metal caps it. Same material, opposite order, twelve feet apart.

The two edges do different jobs. Underlayment is a drainage plane — water past the shingles runs down it, and at the eave that water has to leave the building. Land it on top of the eave metal and the metal carries it past the fascia into the gutter. Put the metal underneath and it runs off the end of the sheet onto bare wood.

At the rake there is no downhill flow to catch. Water crossing a rake is wind-driven, moving sideways and often uphill, so what you protect is the cut edge of the underlayment. Bury the metal under it and a gust lifts that edge and drives water beneath the sheet. Cap it and there is no edge to lift.

Why the gutter apron argument is real

Water leaving a D-style drip edge above a gutter does not always fall. In a light rain, on a shallow pitch, or where the kick is short, surface tension wraps it around the bottom edge and down the back of the fascia — into the gap between fascia and gutter. That water never enters the trough. It runs behind the gutter, into the soffit and along the wall.

The symptom is a leak reported only in a soft, steady rain and never in a downpour, because heavy rain has enough momentum to jump the gap. The apron’s long leg extends over the back of the gutter, so there is nothing to wrap onto. If a fascia is stained behind a gutter that drains fine, this is usually why — work the rest of the roof leak diagnostic before you blame the shingles.

• ●Roof leg — commonly 2 to 4 inches, code minimum around 2 inches back onto the deck. Wider legs nail easier and give the eave membrane more to bond to.
• ●Face height — roughly 1½ to 5 inches; an apron’s leg runs longer because it has to reach the gutter. The face must cover the sheathing edge and project below it, not stop flush. A short face is why water finds the fascia.
• ●The hem — a folded-back outer edge, and not decorative. It stiffens the free edge so a long run stops fluttering, holds the profile straight over a wavy fascia, and stops the metal slicing hands.
• ●Material — painted steel is stiff, holds a line on a long run, and is the usual hail-country choice. Aluminum will not rust and bends on the tailgate, but it is soft and oil-cans on a tall face. Copper is for copper roofs and historic work.
• ●Galvanic pairing — never fasten copper with steel nails, and never let copper runoff land on an aluminum gutter. Aluminum against modern pressure-treated lumber corrodes, so on a treated sub-fascia use a barrier or switch to steel.

Roofing nails go through the roof leg on a stagger, alternating side to side so the metal cannot pivot. Spacing is typically 8 to 12 inches on center; the code minimum lands around 16 inches, and tighter is cheap insurance on an exposed elevation. Fastener length follows the deck the same way shingle nails do — through the sheathing, or a solid bite into a board deck.

1. 1

   Run the eave first, on bare deck

   Hold the roof leg tight and check the face clears the sheathing edge for the whole length. If the fascia is bowed, shim or plane it now — the metal telegraphs every hump.

2. 2

   Lap 2 to 4 inches, upslope piece over downslope

   On a rake the upper stick always laps over the lower, so runoff crosses the joint on top of the metal instead of diving into it. On a horizontal eave, lap toward the direction the water travels. Code minimum lap is about 2 inches; 3 or 4 costs nothing.

3. 3

   Dry in over the eave metal

   Roll the eave course to cover the roof leg completely, bonding the ice barrier to the metal. Leave the rake clean deck, or run the sheet long and cap it.

4. 4

   Run the rake bottom-up, over the underlayment

   Start at the eave corner and work toward the ridge, each stick lapping over the one below. Run it the other way and you have built a hundred small scoops facing uphill.

5. 5

   Build the corner: rake over eave, cut and fold

   The rake piece runs past the eave piece and laps on top of it. Cut the rake stick’s roof leg back so it sits flat, notch the face, and fold the tab down around the outside of the eave metal — a small wrap, seamed tight. A butt joint with sealant is what everybody does, and it is the first joint that leaks.

• ●Buckled run — face nailed into the fascia; thermal movement waves it and opens the laps. Visible from the street.
• ●Flutter — unhemmed L-metal on a long exposed rake. The free edge oscillates, works the nails loose, cracks the coating along the bend.
• ●Fascia tracking — face too short or kick missing, so surface tension carries runoff around the bottom edge and down the wood. Slow rot, no visible leak, and the homeowner blames the paint.
• ●Inverted eave — eave metal on top of finished underlayment, so everything draining down the sheet goes behind the metal. The most common order-of-operations error in the trade.
• ●Peeled rake — rake sticks lapped bottom-over-top, free edges facing the wind. Uplift gets under the lap and unzips the run.