By The Roofing Brief Team. Last reviewed: October 2026.
Gutter flashing is the L-shaped metal strip, usually sold as a gutter apron, that carries roof water off the eave and into the gutter instead of behind it. One leg tucks under the shingles on the roof deck, the other bends down over the fascia and drops inside the back of the gutter. A stock aluminum apron from Gutter Supply is 2 in by 3 in, 10 ft long, bent at 35 degrees and .019 in thick, and HomeGuide (November 7, 2025) puts gutter apron installation at $2 to $5 per linear foot.
Gutter flashing at a glance: which piece goes where
| Your situation | Use this flashing | Rule or threshold | Source |
|---|---|---|---|
| Shingle eave with a gutter, roof being replaced | Gutter apron (eave drip edge) under the underlayment | Lap joints 2 in, nail 12 in on center, extend 1/4 in below the sheathing | 2021 IRC R905.2.8.5 |
| Shingle eave with a gutter, roof staying | Slip-in apron under the first course, or wait for the reroof | Retrofit drip edge runs $5 to $9 per ft vs $1.50 to $3 during a reroof | HomeGuide, Nov 2025 |
| Rake edge or gutterless eave | Standard drip edge, over the underlayment at rakes | Underlayment goes over the drip edge at eaves, under it at rakes | 2021 IRC R905.2.8.5 |
| Eave ends against a sidewall above the gutter | Kickout flashing | Required where the eave of a sloped roof meets a vertical sidewall | 2021 IRC R903.2.1 |
| Roof slope runs up a wall beside the gutter (side flashing) | Step or continuous sidewall base flashing | At least 4 in high and 4 in wide, directing water onto the roof or into the gutter | 2021 IRC R905.2.8.3 |
| Copper gutters | 16 oz copper apron | Match the gutter metal; 16 oz copper aprons come in 8 and 10 ft lengths | Gutter Supply copper flashing listing |
| Fascia already soft or stained | Replace fascia first, then apron | Fascia and soffit replacement runs $9 to $34 per ft | HomeGuide, Nov 2025 |
What is gutter flashing?
Gutter flashing is a thin, formed metal strip installed at the roof edge to carry water from the shingles into the gutter and shield the fascia board behind it. It is bent into an L, with the top leg sitting on the roof deck under the shingles and the vertical leg hanging behind the gutter’s rear wall; HomeGuide puts the typical overhang at 2 to 6 in and the common piece length at 10 ft. Without it, water sheeting off the shingle edge can wick behind the gutter and soak the fascia.
The most common form of gutter flashing is the gutter apron. On a shingle roof it does the eave job of the drip edge that IRC R905.2.8.5 requires at eaves and rakes, with a longer face that drops into the gutter.
Gutter flashing vs drip edge vs gutter apron
Gutter apron and drip edge are both gutter flashing, but they are shaped differently and go in different places. A gutter apron is a long L whose face leg reaches down into the gutter (3 in on Gutter Supply’s 2 x 3 in piece). A drip edge is a T-shaped or angled profile with a small lower flange that flings water off the edge, and under IRC R905.2.8.5 it must extend at least 1/4 in below the sheathing and 2 in back onto the deck. Aprons belong at eaves with gutters; drip edge belongs at rake edges and eaves without gutters.
| Feature | Gutter apron | Drip edge |
|---|---|---|
| Shape | Wide L (Gutter Supply bends it at 35 degrees) | T or angled with lower kick flange |
| Vertical leg | Reaches into gutter; 3 in face on a 2 x 3 in apron | At least 1/4 in below the sheathing (IRC R905.2.8.5) |
| Best location | Eaves with a gutter | Rake edges, eaves without gutters |
| Main job | Push water into the gutter, cover fascia | Throw water off the deck edge |
| Fascia coverage | Full | Partial |
| Installed cost | $2.00 to $5.00 per ft (HomeGuide) | $1.50 to $3.00 per ft during a reroof (HomeGuide) |
Many roofs use both: apron at the gutter eaves, standard drip edge at the rakes, which together meet the IRC R905.2.8.5 requirement for drip edge at eaves and rakes. For the full side-by-side, see gutter apron vs drip edge. If your existing gutter sits too far off the fascia for either to work, read the gap between drip edge and gutter.
The flashings that make up a gutter system
A gutter does not rely on one flashing. Water reaches the trough from eaves, rakes, walls and valleys, and the 2021 IRC assigns each junction its own rule in Chapter 9. Getting one wrong sends water behind the gutter or into the wall.
| Flashing | Where it goes | What it stops | Code (2021 IRC) |
|---|---|---|---|
| Gutter apron | Eave edge, above the gutter | Water wicking behind the gutter and rotting fascia | R905.2.8.5 (eave drip edge) |
| Drip edge | Rake edges, gutterless eaves | Water curling under the deck edge | R905.2.8.5 |
| Kickout flashing | Where a roof eave meets a wall at the gutter’s end | A concentrated stream of water dumping into the wall cavity | R903.2.1 |
| Step / sidewall flashing | Where the roof slope runs up against a wall above a gutter | Water tracking down the wall behind the gutter run | R905.2.8.3 (4 in by 4 in minimum) |
| Valley flashing | Where two slopes meet and feed one gutter | Concentrated valley flow overshooting the trough | R905.2.8.2 (open metal valley lining at least 24 in wide) |
The most skipped piece is kickout flashing at the lower end of a gutter that terminates against a wall. IRC R903.2.1 requires a flashing that diverts water where the eave of a sloped roof meets a vertical sidewall; without it, every storm sends the gutter’s end stream into the siding and framing. Code text: 2021 IRC Chapter 9, Roof Assemblies.
What gutter flashing is made of, and the widths and gauge that matter
Gutter flashing is formed from aluminum, galvanized steel, or copper. IRC R903.2.1 sets the floor for metal flashing at 0.019 in (No. 26 galvanized sheet), and that is exactly what stock aprons ship in: Gutter Supply’s aluminum apron is .019 in and its galvanized apron is 26 gauge. Aluminum does not rust and bends by hand; galvanized steel is stiffer; copper matches copper gutters.
| Material | Typical thickness | 10 ft piece price (2 x 3 in) | Source |
|---|---|---|---|
| Aluminum | .019 in | $8.56 (about $0.86 per ft) | Gutter Supply aluminum gutter flashing, Oct 2026 |
| Galvanized steel | 26 gauge (0.019 in minimum per IRC R903.2.1) | $27.55 (about $2.76 per ft) | Gutter Supply galvanized gutter flashing, Oct 2026 |
| Copper | 16 oz (about 0.0216 in) | $70.68 (about $7.07 per ft) | Gutter Supply copper gutter flashing, Oct 2026 |
Pick a width by measuring from the roof deck edge down the fascia to a point at least 1 in inside the gutter’s back wall; the apron’s face leg must be at least that long. A 3 in face (Gutter Supply’s 2 x 3 in) suits a gutter hung tight under the roof edge; a gutter hung lower on a taller fascia needs a longer face or a custom-bent apron from coil stock.
How much does gutter flashing cost?
Gutter apron flashing costs $2.00 to $5.00 per linear foot installed, or $200 to $1,000 for 100 to 200 linear feet, per HomeGuide’s drip edge cost guide (November 7, 2025). Material alone runs $0.86 per foot for .019 in aluminum, $2.76 for 26 gauge galvanized and $7.07 for 16 oz copper at Gutter Supply’s October 2026 prices. Timing moves labor the most: HomeGuide lists drip edge labor at $1 to $2 per foot during a reroof versus $3 to $7 per foot to retrofit on an existing roof.
| Item | Cost | Source |
|---|---|---|
| Gutter apron, installed | $2.00 to $5.00 per ft ($200 to $1,000 for 100 to 200 ft) | HomeGuide, Nov 2025 |
| Drip edge installed during a reroof | $1.50 to $3.00 per ft | HomeGuide, Nov 2025 |
| Drip edge added to an existing roof | $5.00 to $9.00 per ft | HomeGuide, Nov 2025 |
| Aluminum apron, material | $8.56 per 10 ft piece | Gutter Supply, Oct 2026 |
| Galvanized apron, material | $27.55 per 10 ft piece | Gutter Supply, Oct 2026 |
| Copper apron, material | $70.68 per 10 ft piece | Gutter Supply, Oct 2026 |
Worked example for 120 ft of guttered eave: add 10 percent for laps and waste (HomeGuide’s allowance) to get 132 ft, or 14 ten-foot pieces once each 2 in lap is counted. In aluminum that is 14 x $8.56 = $119.84 of material; installed, HomeGuide’s $2 to $5 per foot puts the job at $240 to $600 before any fascia repair.
How to install gutter flashing at the eave
Gutter flashing at a shingle eave goes on before the gutter, sequenced so water always laps onto the piece below it. The lap, fastener and overlap rules come from IRC R905.2.8.5 and R905.2.5. On a re-roof the apron goes down over the deck, the underlayment laps over it at the eave, then the shingles cover the top leg. Our drip edge installation detail covers the same lap order at both eaves and rakes.
- Set the apron on the eave with the top leg at least 2 in onto the roof deck and the vertical leg over the fascia, extending at least 1/4 in below the sheathing and dropping behind where the gutter will hang.
- Lap adjacent pieces at least 2 inches in the direction water flows so no joint faces uphill.
- Fasten to the deck with roofing nails (12 gauge shank, 3/8 in head minimum, long enough to penetrate the sheathing or 3/4 in into it, per IRC R905.2.5) at the 12 inch on-center maximum that IRC R905.2.8.5 sets.
- Run the underlayment over the top leg at the eave (IRC R905.2.8.5: over the apron at eaves, under the drip edge at rakes).
- Install shingles over the covered top leg, then hang the gutter so its back wall sits behind the apron’s vertical leg.
On an existing roof where you cannot lift shingles, a slip-style apron can tuck under the first course, but HomeGuide prices retrofit drip edge at $5 to $9 per foot, about three times the $1.50 to $3 reroof price, so a re-roof is the cheapest time to do it. Where the eave dead-ends into a wall, add kickout flashing (IRC R903.2.1) at that corner before the gutter goes up.
What happens without gutter flashing?
Without gutter flashing, water running off the shingle edge slips behind the gutter and soaks the fascia and the wood behind it. The fascia holds the gutter hangers, so once it softens the gutter starts to pull loose and sag, which spills more water and speeds the rot. HomeGuide prices fascia and soffit replacement at $9 to $34 per linear foot and repairs at $500 to $2,600, against $2 to $5 per foot for the apron that prevents it.
Once rot starts, the fascia must be cut out and replaced; see fascia rot from gutters and our roof flashing guide.
Frequently asked questions
Is gutter flashing the same as a gutter apron?
In everyday use, yes. Gutter apron is the specific L-shaped flashing, sold in 10 ft pieces such as a 2 x 3 in aluminum apron, that most people mean when they say gutter flashing. Strictly, gutter flashing is the broader term that also covers drip edge, kickout flashing, and sidewall flashing that keep water inside a gutter system. Every gutter apron is gutter flashing, but not all gutter flashing is a gutter apron.
Do you need flashing behind gutters?
On a shingle roof, yes: IRC R905.2.8.5 requires drip edge at eaves, and at a guttered eave a gutter apron does that job while its longer face drops behind the gutter’s back wall. Without it, wind-driven and surface-tension water tracks behind the gutter and rots the fascia and soffit. HomeGuide prices the apron at $2 to $5 per linear foot installed.
Does gutter flashing go under or over the underlayment?
At the eave it goes under the underlayment: the apron is fastened to the deck first, then the underlayment laps over its top leg. At rake edges the order flips and the underlayment goes under the flashing. IRC R905.2.8.5 spells this out, and getting it backward at the eave lets water run under the flashing.
How wide should gutter apron flashing be?
Wide enough for the vertical leg to reach inside the gutter’s back wall and cover the fascia. A stock 2 x 3 in apron (2 in on the deck, 3 in face) suits a gutter hung tight under the roof edge; a tall fascia board or a gutter hung lower needs a longer face or an apron bent from coil stock. HomeGuide puts typical overhang at 2 to 6 in.
How much does gutter apron flashing cost?
Aluminum gutter apron costs $8.56 per 10 ft piece (.019 in, 2 x 3 in) at Gutter Supply in October 2026, galvanized $27.55 and 16 oz copper $70.68. Installed, HomeGuide puts gutter apron at $2 to $5 per linear foot, or $200 to $1,000 for 100 to 200 feet.
What is side flashing at a gutter?
Side flashing is the step or continuous base flashing where a roof slope runs up a sidewall. IRC R905.2.8.3 requires it to be at least 4 in high and 4 in wide and to direct water onto the roof or into the gutter, and IRC R903.2.1 adds a kickout where the eave meets the wall so the gutter’s end stream does not run into the siding.