Roof Flashing Types + Installation Reference

Overview

Flashing is metal (or sometimes membrane) installed at penetrations, walls, + transitions to direct water away from vulnerable points in the roof system. Flashing failures cause 60-70% of all roof leaks; correct flashing selection + installation determines the long-term integrity of every roof.

Flashing materials

• Aluminum (most common residential): rust-proof, easy to work, \(-$\)
• Galvanized steel: stronger, harder to bend, can rust at cuts, $
• Stainless steel: premium, never rusts, \(\)
• Copper: high-end residential, patinas naturally, \($\)
• Lead (older homes, chimneys): traditional, soft + workable, expensive, regulated
• Membrane / rubber: pipe boots, EPDM, neoprene

Match material to roof + climate. Salt-air coastal: aluminum or stainless ONLY (steel rusts fast).

Types of flashing

Step flashing

L-shaped pieces (typically 4-5" × 7-8") woven into shingle courses where roof meets a vertical wall.

• One step per shingle course
• 4-8 inches up the wall
• 2-3 inches under the next shingle course up
• Counter-flashing covers + seals the top edge

Best for: roof-to-wall transitions (sidewall, chimney sides).

Common mistake: continuous "ladder flashing" instead of step flashing. Single long piece leaks at every course separation. Must be discrete steps woven into shingles.

Counter-flashing

Covers the top edge of step flashing. Often cut into mortar joint of brick or stone wall, or surface-mounted to siding.

• Bent into J-shape: top embedded, bottom hangs down over step flashing
• Sealed with non-hardening caulk in mortar joint
• Replaceable when re-roofing without disturbing wall

Common mistake: omitting counter-flashing. Step flashing alone exposes top edges to water + wind.

Apron flashing

Wide piece bent over the top of a chimney or transition where roof meets a vertical face.

• Typically 8-10 inches wide
• Extends down roof 4-6 inches
• Up the wall 6-8 inches
• Used at front face of chimney or skylight

Cricket / saddle

Small peaked structure built behind chimney to deflect water around it.

• Required by code for chimneys > 30" wide
• Built up of decking + flashed like a mini roof
• Prevents water dam behind chimney

Pipe boots / vent collars

Flexible neoprene or EPDM boots that seal around plumbing vent pipes, gas vents, etc.

• Sized for pipe diameter (1.5", 2", 3", 4")
• Slides over pipe
• Base flashes into shingle courses
• Lifespan: 5-10 years (cracks at the rubber seal); ALWAYS replace at reroof
• Newer "lead boots" with rubber gasket: 15-25 year life

Drip edge

L-shaped flashing installed at eaves + rake edges of roof.

• 1.5-2 inch leg on roof
• 1.5-2 inch leg over fascia
• Directs water into gutter; prevents wicking under shingles
• Required by code in most jurisdictions for new + reroofs

Code typical:

• At eaves: install BEFORE underlayment (water sheds onto drip edge)
• At rakes: install OVER underlayment

Headwall flashing

Used where a vertical wall meets the high end of a roof slope.

• Combined function with step + apron flashing
• Often L-shaped with extended horizontal leg
• Counter-flashed at top of vertical surface

Skylight flashing

Combines apron + step + counter-flashing into a kit specific to the skylight model.

• Aprons: top (head) + bottom (sill)
• Step flashing: sides
• Counter-flashing/secondary flashing: top edge sealed
• Each manufacturer specifies their flashing kit; use their kit, not generic

Valley flashing

Two configurations:

• Open valley: visible metal in valley; water flows in channel; durable + cleanable
• Closed-cut valley: shingles from one slope laid across; other slope cut to centerline; less metal cost, more shingle work
• Woven valley: shingles from both slopes interwoven (older method, not preferred today)

Open valleys typical in higher-end + steeper-slope applications. Closed-cut acceptable on most residential.

Always install ice + water shield under valley (36" wide centered) before flashing.

Plumbing vent flashing

Specific configuration:

• Aluminum base + rubber boot (or all-lead with rubber gasket on premium)
• Pipe slips through boot
• Base flashes into shingles
• Caulk boot-to-pipe annually

Chimney flashing (multi-piece)

A chimney needs four flashing components together:

1. Step flashing (sides)
2. Apron flashing (front, lower side)
3. Cricket (back, high side, > 30" wide chimneys)
4. Counter-flashing (cut into mortar) all around

Chimney flashing is the most failure-prone area on residential roofs. Repair = often replace the entire system.

Installation principles

1. Shingle behind flashing on the high side; flashing behind shingle on the low side - water sheds OFF flashing onto the shingle below
2. Step flashing: woven, one per course
3. Always counter-flash step flashing
4. Sealant is supplemental, not primary - flashing geometry sheds water; sealant is a backup
5. Replace, don't repair, old/rusted flashing at reroof
6. Material match: don't mix aluminum + copper or galvanized (galvanic corrosion)

Common mistakes

• Continuous flashing instead of step: leaks at first wind-driven rain
• No counter-flashing: top edge exposed
• Sealing instead of flashing: caulk fails in 2-3 years; flashing lasts decades
• Reusing old pipe boots: cracking is internal; "looks ok" is wrong
• Mixed metals touching: galvanic corrosion
• Drip edge wrong order: eaves drip edge should be UNDER underlayment

Code references

• IRC R905 (residential roof coverings): flashing requirements
• IRC R903: weather protection
• NRCA Roofing Manual: industry-standard installation details
• Local amendments: many jurisdictions have additional flashing requirements

When flashing repair is enough vs full replacement

• Repair: 1-2 isolated failures, surrounding flashing in good shape
• Replace at section: multiple failures, age > 15 years, rust on metal
• Full system: complete reroof; never reuse flashing

Maintenance

For customers wanting long-life roofs:

• Annual flashing inspection (visual)
• Reseal counter-flashing at mortar joints every 5 years
• Replace pipe boots every 8-10 years (proactive)
• Watch for ice damming (compromises eave flashing)

References

• NRCA Roofing Manual (flashing chapter is industry standard)
• IRC R905 (residential code)
• Manufacturer flashing detail libraries (GAF, CertainTeed, Owens Corning)
• Manuall internal: Asphalt Shingle Roof Replacement SOP, Diagnose + Repair a Roof Leak