Flashings, Drainage, and Roof Penetrations

Why Flashings and Drainage Matter

Water follows the path of least resistance. On a roof, every transition—where a slope meets a wall, where a pipe punches through sheathing, where two slopes converge—creates an opportunity for water to enter the building envelope. Flashings are the sheet-metal or flexible-membrane components installed at those transitions to redirect water back onto the roof surface and away from vulnerable joints. A home inspector's job is to trace that water path, identify every location where flashing is required, and evaluate whether each flashing is correctly installed and in serviceable condition.

Types of Flashings and Where They Go

Drip edge is a metal strip installed at the eaves and rakes (gable edges) to direct water off the deck and into the gutter rather than letting it wick back under shingles. At eaves it goes under the underlayment; at rakes it goes over the underlayment. Reversed installation is a common defect.

Step flashing is used where a sloped roof meets a vertical wall—alongside a dormer, chimney, or skylight curb. It consists of individual L-shaped pieces installed one per shingle course, woven into the shingle layers so each piece laps the one below. Each piece diverts water laterally, preventing it from traveling behind the wall cladding.

Counter flashing (also called cap flashing) overlaps the top edge of step flashing or base flashing and is embedded into mortar joints or wall substrates. It seals the upper edge and allows slight independent movement between roof and wall.

Valley flashing protects the concave intersection of two roof planes. Open valleys use exposed metal (aluminum, galvanized steel, or copper); closed-cut and woven valleys rely on shingles with metal or membrane underneath. Inspect open valleys for open seams, rust, holes, and adequate width.

Chimney flashing is the most complex assembly: base flashing wraps the upslope and sides, step flashing runs along the sides, counter flashing caps the step flashing, and a saddle (cricket) is built behind chimneys wider than a code-referenced minimum to divert water around the chimney rather than letting it pond against the upslope face. A missing or improperly sloped saddle is a significant defect.

Pipe boot (plumber's boot) seals around plumbing vent stacks. It consists of a metal base flange nailed to the deck and a rubber or lead collar that compresses around the pipe. Common defects include cracked or torn rubber collars, separated seams, and missing sealant at the collar-to-pipe interface.

Skylight flashing may be a factory-integrated kit or field-fabricated. Inspect the head (upslope) flashing, side step flashing, sill (downslope) flashing, and the integrity of the glazing seals and curb.

Inspecting Drainage Components

Gutters and downspouts are the terminal components of roof drainage. Inspect gutters for: adequate slope toward downspout outlets (no visible ponding or staining at the wrong end), secure fastening, open joints or holes, and proper clearance to allow water off the roof. Downspouts should discharge away from the foundation—extensions, splash blocks, or underground drains. Missing downspout extensions adjacent to the foundation are a routinely cited deficiency.

Flat or low-slope roofs rely on interior drains and scuppers. Confirm that scupper openings are clear and that strainer baskets on interior drains are present and unobstructed.

Systematic Inspection Sequence

Follow a consistent order so nothing is missed:

1. Ground observation — scan the entire roof perimeter with binoculars before climbing. Note ridge, hips, valleys, penetrations, and gutter condition.

2. Eave and rake — confirm drip-edge installation and gutter attachment.

3. Field of roof — check for missing or damaged shingles and any penetrations visible in the field.

4. Valleys — walk toward each valley and examine metal condition, lap, and shingle alignment.

5. Penetrations — chimney, all vents, skylights, exhaust fans. For each, inspect all four sides of the flashing assembly.

6. Walls and dormers — confirm step and counter flashing at every roof-to-wall junction.

7. Attic interior (from below) — look for daylight, staining, or moisture on sheathing at every penetration and flashing location identified above. This cross-check catches hidden leaks.

Safety on the Roof

Never access a roof that is wet, icy, or frost-covered—slips cause serious falls. Wear rubber-soled shoes with good traction. On steep slopes (typically above 6:12 pitch) use appropriate fall protection; many inspectors decline to walk steep roofs and inspect from the eave edge or from a ladder at the perimeter plus drone imagery. Inspect the attic and use binoculars from the ground to supplement when roof access is unsafe. Document in your report why the roof was not walked, per InterNACHI and ASHI SOP allowances. Never probe suspect areas with bare hands—metal flashing edges are sharp; wear gloves when handling flashing samples.

Reporting Language

As an inspector you observe and report; you do not diagnose causation or perform repairs. Use measured, consistent language: "Evidence of moisture intrusion was observed at the left-side chimney step flashing. Recommend evaluation and repair by a qualified roofing contractor." Avoid absolute statements like "this will leak" or "this is fine." Your report is a professional document reviewed by buyers, sellers, attorneys, and licensing boards.