Roof Drip Edge Calculator: Eave and Rake Linear Feet

Drip edge is a metal flashing, typically aluminum or galvanized steel, installed at the edges of a roof to direct water away from the fascia board and into the gutter system. Without drip edge, water running off the edge of the roof sheathing and shingles follows the bottom face of the sheathing by surface tension and wicks back against the fascia board. Over time, this causes fascia rot, paint peeling, and eventually decay of the roof structure at the eave.

IRC Section R905.2.8 requires drip edge on all roof edges. The requirement applies to new construction and re-roofing work in all jurisdictions that have adopted the IRC, which includes 49 US states. Drip edge is not optional or discretionary on any permitted roofing project. Inspectors check for its presence and correct installation sequence before signing off on the final inspection.

It depends on which edge you are talking about. At the eave (bottom edge), drip edge goes on the bare deck before the underlayment. The felt or synthetic underlayment is then installed over the top of the eave drip edge, overlapping it by at least 2 inches. This directs water from the underlayment surface onto the drip edge face and into the gutter.

At the rake (gable-end edge), the sequence is reversed. Install the underlayment first, then install the rake drip edge on top of the underlayment. This keeps the rake drip edge on top of the felt so that wind-driven rain hitting the edge cannot get behind the underlayment. This two-sequence rule is specified in IRC R905.2.8 and is the most commonly violated sequencing requirement on residential re-roofing jobs.

IRC R905.2.8 requires a minimum 2-inch overlap where two pieces of drip edge lap at a joint. Most experienced roofers use 3 to 4 inches as their working standard, particularly at eave joints in cold climates where ice can form under the drip edge and lift it. The critical rule is that the upper piece must lap over the lower piece, not the other way around. Reversed laps create pockets where water can pool and enter the joint from below.

At inside corners, where two drip edge pieces meet at an angle rather than a straight run, the overlap approach does not apply. Inside corners require a miter cut at each piece so the two meet cleanly at the angle. Some installers use a single bent piece for inside corners to eliminate the joint entirely, which is the cleanest solution where the metal gauge is flexible enough to bend without creasing.

Standard residential drip edge in the US market is sold in 10.5-foot (126-inch) lengths. This is the industry standard length from most roofing supply distributors, including ABC Supply, Beacon Roofing Supply, and regional distributors. Some suppliers also offer 12-foot lengths, particularly for commercial-grade galvanized products. Always verify the exact piece length with your specific supplier before ordering, because a calculation based on 10.5-foot pieces and fulfilled in 12-foot pieces will result in over-ordering.

This calculator defaults to 10.5-foot pieces, which is correct for the vast majority of US residential roofing supply sources. If your supplier stocks 12-foot pieces, simply enter 12 in the piece length field. The piece count and waste calculation adjust automatically. Note that 10.5 feet is not arbitrary; it is a length that fits in a standard pickup truck bed and allows a single person to handle without mechanical assistance, which is why it became the residential standard.

Yes, the same profile can be used on both eave and rake edges, and this is the standard practice on most residential re-roofing jobs. Using the same profile simplifies ordering because you are buying identical material for both locations. The material is the same product; the only difference is where it goes on the roof and the sequence in which it is installed relative to the underlayment.

Some projects do use different profiles on eave and rake. A common example is using F-style (wider face) at the eave to better direct water into the gutters on a low-pitch roof, while using D-style at the rake because the rake edge does not have gutter water management concerns and the narrower profile is sufficient. On commercial-grade steep-slope applications, T-style is sometimes used on all edges for its larger face leg and wind resistance. In practice, using the same profile everywhere simplifies field installation because there is no chance of mixing the two profiles.

IRC R905.2.8 applies to both new construction and re-roofing projects in jurisdictions that have adopted the IRC. A re-roofing project that strips the existing shingles back to the deck, which is required whenever more than one layer of shingles exists or when the existing shingles are too degraded for an overlay, must include drip edge installation before new underlayment goes on. In this context, the sequence follows the same rule as new construction.

On a shingle overlay (second layer installed over existing shingles), the drip edge question is more complex. If existing drip edge is present and in acceptable condition, some jurisdictions allow the overlay to proceed without replacing the drip edge. Others require new drip edge on any permitted re-roofing. Check your local building department’s re-roofing requirements before determining whether drip edge is part of the scope on an overlay job.

Rake length is the actual sloped length from the eave to the ridge along the gable end, not the horizontal measurement from the wall plate to the ridge. For a 7/12 pitch roof on a building with a 20-foot horizontal run from wall to ridge, the actual sloped rake length is: sqrt(20 squared + (20 x 7/12) squared) = sqrt(400 + 136) = sqrt(536) = approximately 23.2 feet. The slope factor for a 7/12 pitch is 1.158, so you can also multiply the horizontal run by 1.158 to get the sloped length.

In the field, the easiest way to measure rake length is to measure directly along the edge of the roof sheathing from the bottom corner of the gable to the ridge, using a tape measure held against the edge of the deck. This direct measurement is always more accurate than calculating from pitch and run, because it accounts for any irregular framing that differs from the nominal pitch. Measure both rake edges separately on complex roofs, since the two sides of a gable are not always perfectly equal in practice.

Drip edge in the US residential market is produced in three primary materials: aluminum, galvanized steel, and galvannealed (G-90 coated) steel. Aluminum is the most common for standard residential work. It does not rust, comes pre-painted in a wide range of colors, and is lightweight and easy to cut and bend in the field. The standard gauge is 0.019 inch (26-gauge equivalent in aluminum). Pre-painted aluminum drip edge is the dominant product in most US markets outside of the immediate coastal zone.

Galvanized and galvannealed steel drip edge is used in high-wind zone applications where the heavier weight and stiffness of steel provides better resistance to wind uplift at the roof edge. It is also required by some coastal and hurricane-zone building codes that specify minimum metal thickness for wind-exposed flashings. Stainless steel drip edge is used in severe marine environments, such as on oceanfront properties within 1 mile of saltwater, where standard aluminum corrodes within a few years. The cost increase for stainless is significant, so it is typically reserved for genuine marine exposure situations rather than used generally.

Ice and water shield is a self-adhering, rubberized asphalt membrane applied to the eave area of a roof in cold climates to prevent ice dam leaks. Its relationship to drip edge follows the same sequence as standard underlayment: the eave drip edge goes on the deck first, then the ice and water shield is installed on top of the drip edge and overlaps it. In most cold-climate applications, ice and water shield covers the first 24 to 36 inches from the eave edge (the area at risk from ice dam backup), and standard underlayment covers the rest of the deck above that zone.

The critical detail is that the ice and water shield must seal to the drip edge properly. Self-adhering ice and water shield bonds to the drip edge metal when the adhesive backing is pressed firmly against it. This creates a watertight seal at the eave that prevents ice dam water from getting behind the drip edge and entering the structure even when water is backed up several feet up the slope under the shingles. IRC Table R905.2.7 specifies where ice protection is required based on the design freezing index for different climate regions.

In practice, drip edge is almost never reused from an existing roof. The material cost of new drip edge is low relative to the total cost of a re-roofing project, and the labor cost of carefully removing and saving the old drip edge without bending it is higher than simply installing new. Removing shingles and underlayment also typically bends or damages the existing drip edge in the process, making it unusable without straightening.

From a code perspective, there is no prohibition on reusing undamaged drip edge, but inspectors may question whether previously installed material meets current code requirements for gauge, profile, and minimum dimensions. New drip edge installed as part of a permitted re-roofing project is always the simpler path to a clean inspection sign-off. The cost of drip edge for an average-sized roof is typically $100 to $250 in material, which is a trivial line item on a $5,000 to $15,000 re-roofing project.

The IRC does not specify a minimum dimension for drip edge overhang into the gutter, but the NRCA and standard installation practice call for the drip edge to extend at minimum to the inner face of the gutter. The goal is to ensure that water running off the shingle surface and over the drip edge face falls into the gutter rather than behind the gutter or onto the fascia board. For K-style gutters, the drip edge should reach at least to the back wall of the gutter, and the gutter front lip should be at or slightly below the drip edge to prevent water from catching at the joint.

A drip edge that is cut too short and does not reach the gutter interior will route water onto the fascia face even with the gutter present, because surface tension pulls the water back along the underside of the drip edge rather than releasing it cleanly into the gutter. When a homeowner reports that water is going behind their gutters despite recently replaced gutters, a short-cut or incorrectly positioned drip edge is the most common cause.

For complex roofs with dormers, wings, or L-shaped plans, calculate the drip edge in sections. Walk the perimeter of the building and identify each exterior eave edge and each exposed rake edge. Measure each separately and add them up for the totals. Interior valleys, where two roof sections meet and water runs down the joint, do not get drip edge. Valleys get valley flashing, either open metal or closed woven shingle, which is a different product.

The only additional consideration on complex roofs is inside corners, which this calculator accounts for with the inside corners input. At an inside corner, where the eave edge of one roof section meets the rake or eave of another section at an inward-facing angle, a mitered cut is required that wastes approximately 9 inches from each piece. Count each inside corner junction in your roof plan and enter that number in the calculator. Outside corners, where two eave edges meet at an outward-facing angle, use a standard lapped joint with no additional waste beyond the 2-inch minimum lap.

Drip edge is partially visible below the bottom course of shingles at the eave and along the edge at the rake. The face of the drip edge at the eave is typically visible from ground level as a thin horizontal band below the shingles and above the gutter. Rake drip edge is visible as a narrow vertical band at the gable end. On most homes with gutters installed, the eave drip edge face is hidden behind the gutter front lip and is not visible at all.

Pre-painted aluminum drip edge comes in standard colors, most commonly white, brown, black, and gray. Matching the drip edge color to the trim color or gutter color is the standard practice for a finished appearance. On homes where the drip edge face will be visible (no gutters, or gutters set lower than the drip edge face), choosing a color that complements the fascia paint color makes a meaningful difference in the finished appearance. If the drip edge will be completely hidden by gutters, color matching matters less and white (the default stocking color at most suppliers) is acceptable regardless of the fascia color.

Yes. These are three completely separate products serving different functions. Drip edge is the metal flashing at the perimeter of the roof (eave and rake edges) that directs water off the edge and into the gutter or clear of the fascia. It is installed before the shingles go on.

Starter strip is a narrow strip of shingle material (either a purpose-made starter product or a shingle with the tabs removed) installed along the eave edge at the bottom of the shingled area, above the drip edge and underlayment. Starter strip provides wind sealing and adhesive at the eave course of shingles to prevent wind uplift. It is an asphalt product, not metal.

Valley flashing is the metal or synthetic flashing installed in the valleys (the V-shaped intersections where two roof sections meet). Valley flashing channels water down and out the valley rather than allowing it to infiltrate at the joint between the two roof sections. These three products are all required on most complex rooflines but are specified and ordered separately as they serve distinct functions at different locations on the roof.

This calculator defaults to 10%, which is the standard waste factor for drip edge on a moderate-complexity gable or hip roof. This accounts for end cuts at corners, the minimum 2-inch overlap at each piece joint, and one or two pieces lost to field damage or defects. For a simple rectangular roof with no inside corners, 10% is typically sufficient and will leave you with one to two extra pieces.

Increase to 15% for roofs with multiple dormers, L-shaped or complex plans, or steep pitches where longer pieces are harder to handle without bending. Increase to 20% for very complex rooflines or when working with T-style commercial drip edge, which is less forgiving of adjustment cuts and requires precise mitering at corners. It is almost always better to have two extra pieces of drip edge on site than to run short at the end of the rake edges when the supply house delivery is two days away.

Standard 26-gauge aluminum D-style drip edge is not rated for high-wind zone applications in locations with design wind speeds above 110 miles per hour. In Florida, coastal Texas, Gulf Coast markets, and other FEMA-designated high-wind regions, the building code typically requires heavier gauge metal (24-gauge or thicker), wider profiles that provide more surface area for fastening, and closer nail spacing (often 6 inches on center rather than 12 inches) at both eave and rake edges.

FEMA Building Science publications for high-wind roofing, available at the FEMA website, provide specific requirements for roof edge flashings in wind zones. Some hurricane-zone jurisdictions require sealed drip edge installations where the joint between the drip edge and the underlayment is treated with roofing mastic or tape to prevent wind-driven rain infiltration. If your project is located in a wind zone or is on an oceanfront or exposed hilltop site, verify the local wind speed requirements and drip edge specifications before purchasing materials based on standard residential specs.