Chimney Flashing
Purpose: Waterproofs the base of a chimney where it meets the roof.
How It Works: Chimney flashing is made up of numerous types of roof flashing to ensure there's no leaks around or inside the chimney.
Components:
- Step flashing (along sides)
- Apron flashing (front/base)
- Cricket flashing (on uphill side)
- Counter flashing (embedded into chimney)
Key Benefit: Handles water flow around a large vertical structure.
Vent Pipe Flashing
Purpose: Like chimney flashing, this one is pretty self explanatory in the name. Vent pipe flashing seals around plumbing vent pipes that penetrate the roof.
How It Works: A metal or rubber collar is fitting snugly around the pipe, and an integrated flange sits under shingles.
Common Materials:
Skylight Flashing
Purpose: Seals around skylights to prevent leaks.
How It Works: Skylight flashing uses a combination of step flashing, head flashing and sill flashing. It often comes as a manufacturer-specific kit.
Key Benefit: It's designed for complex water flow around openings.
Counter Flashing
Purpose: Protects and covers the top edge of base flashing.
How It Works: Counter flashing is installed into a wall or chimney, often embedded into mortar joints. It overlaps base flashing to prevent water entry behind it.
Common Locations: It's designed for complex water flow around openings.
Key Benefit: Creates a two-layer system for extra waterproofing where it's needed most.
Continuous Flashing (Gutter Apron Flashing)
Purpose: Provides a long, continuous waterproof barrier along vertical surfaces.
How It Works: A single long piece of metal runs along the joint, often where the roof meets a wall.
Common Locations:
- Along sidewalls
- At the base of vertical walls
Key Issue: It's less flexible than step flashing, so it can crack or fail if the structure moves.
Valley Flashing
Purpose: Protects roof valleys where two roof planes meet.
How It Works: A metal channel is installed in the valley in order to direct large volumes of water safely down the roof.
Types of Valley Flashing:
- Open valley (visible metal)
- Closed valley (covered by shingles)
- Woven valley (shingles interlaced)
Key Benefit: It's designed to handle heavy water flow areas.
Step Flashing
Purpose: Protects the joint where a roof meets a vertical wall, like siding or a chimney.
How It Works: Side flashing is installed in small, overlapping L-shaped pieces. Each piece is layered with each course of shingles so that water is directed down the roof rather than into the wall seam.
Common Locations:
- Roof-to-wall intersections
- Dormers
- Woven valley (shingles interlaced)
Key Benefit: Allows independent movement between roof and wall, reducing leaks.
Kickout Flashing
Purpose: Directs water away from a wall into a gutter.
How It Works: Kickout flashing is installed where roof edge meets a vertical wall to “kick” water outward instead of letting it run down the siding.
Key Benefit: Prevents siding rot and foundation water damage.
Base Flashing
Purpose: Works with counter flashing to seal roof-to-wall transitions.
How It Works: This type of flashing is installed at the base of a vertical surface and moves with the roof while counter flashing remains fixed.
Common Locations:
- Chimneys
- Skylights
- Woven valley (shingles interlaced)
Headwall Flashing
Purpose: Protects the top edge where a roof meets a vertical wall.
How It Works: It's installed horizontally at the intersection of the roof and vertical wall to direct water away from the wall.
Common Locations:
- Roof terminations against walls
Saddle or Cricket Flashing
Purpose: Diverts water around large obstructions.
How It Works: It's a small peaked structure installed behind chimneys or skylights to split water flow and prevent pooling.
Key Benefit: Reduces debris buildup and leaks.
Roof Flashing Side-by-Side Comparison
| Flashing Type |
Primary Purpose |
Common Locations |
Roof Flashing Materials |
Installation Style |
Key Advantages |
Potential Issues |
| Step Flashing |
Seals roof-to-wall joints while allowing movement |
Sidewalls, dormers, chimneys |
Galvanized steel, aluminum, copper |
Installed in individual overlapping pieces with each shingle course |
Excellent leak protection; accommodates expansion and contraction |
Improper layering can cause leaks |
| Continuous (Apron) Flashing |
Creates a long waterproof barrier at roof-to-wall intersections |
Sidewalls, lower wall intersections |
Aluminum, steel |
Single continuous strip |
Faster installation; fewer seams |
Can fail if building shifts; prone to cracking |
| Counter Flashing |
Covers and protects top edge of base flashing |
Chimneys, masonry walls |
Aluminum, copper, steel |
Embedded into mortar joints or attached to wall |
Adds secondary waterproof layer |
Poor sealing can allow water behind flashing |
| Base Flashing |
Works with counter flashing to seal vertical transitions |
Chimneys, skylights |
Metal (steel, aluminum) |
Installed at base of vertical surface |
Allows independent movement between roof and wall |
Must be paired with counter flashing for effectiveness |
| Valley Flashing |
Channels water where two roof slopes meet |
Roof valleys |
Steel, aluminum, copper |
Installed as open or covered valley system |
Handles high water volume |
Debris buildup; improper install leads to leaks |
| Drip Edge Flashing |
Directs water away from fascia and into gutters |
Roof edges (eaves and rakes) |
Aluminum, steel |
Installed along roof perimeter |
Prevents wood rot; improves drainage |
Improper overlap can allow water intrusion |
| Vent Pipe (Boot) Flashing |
Seals around plumbing vent penetrations |
Roof pipes, vents |
Rubber, neoprene, silicone with metal base |
Integrated flange under shingles |
Easy installation; flexible seal |
Rubber can crack or degrade over time |
| Skylight Flashing |
Waterproofs skylight openings |
Around skylights |
Aluminum, steel, manufacturer kits |
Multi-part system (step, head, sill flashing) |
Designed for complex drainage |
Improper installation leads to leaks |
| Chimney Flashing |
Protects chimney-roof intersection |
Around chimneys |
Steel, copper, aluminum |
Combination of step, apron, and counter flashing |
Comprehensive water protection |
Complex install; failure at multiple points |
| Kickout Flashing |
Directs water from wall into gutter |
Roof-to-wall edge transitions |
Aluminum, steel |
Angled piece at roof edge |
Prevents siding rot and water damage |
Often missing in older homes |
| Headwall Flashing |
Protects top edge where roof meets wall |
Roof terminations |
Aluminum, steel |
Horizontal installation under siding |
Prevents water intrusion at top seams |
Needs proper overlap with siding |
| Cricket (Saddle) Flashing |
Diverts water around large obstacles |
Behind chimneys, skylights |
Metal, shingles over framing |
Small peaked structure |
Prevents pooling and debris buildup |
Adds complexity and cost |
| Edge Flashing |
Reinforces and protects roof perimeter |
Roof edges |
Aluminum, steel |
Installed along edges |
Improves durability and drainage |
Often confused with drip edge; improper install reduces effectiveness |
Key Roof Flashing Considerations
- Most critical flashing types: Step flashing, valley flashing, and chimney flashing (highest leak risk areas)
- Most commonly overlooked: Kickout flashing (major cause of siding and wall damage)
- Most prone to failure: Vent pipe flashing (due to rubber deterioration)
- Most complex systems: Chimney and skylight flashing (multiple components required)
Want to know what type of flashing your roof needs? Property owners in the Austin area can give LOA a call for a free roof inspection that will evaluate your flashing.
