Underlayment and Flashing Installation Verification

Purpose

This procedure puts a hold point between dry-in and the first covering course, so that every lap, every edge order and every flashing dimension is measured by a second person while it is still visible. After the starter course goes down, none of it can be seen again without tearing the roof apart, and the only evidence the shop will ever have is what somebody measured and photographed on this pass.

Most leaks a shop is called back for come from this layer rather than from the shingle. The shingle sheds water; the underlayment and the flashing handle what gets past it, which on a real roof is all of it eventually.

Scope

Covers pre-cover verification of underlayment, ice barrier, drip edge, valley liner, wall flashing and penetration flashing on residential and small commercial steep-slope roofs, on the dried-in deck, before any covering course starts.

Does not cover the installation sequence itself, owned by the tear-off and dry-in SOP. Does not cover inspection of flashing on a roof already covered, owned by the flashing and penetration detail inspection SOP. Does not cover low-slope membrane seams, owned by the seam weld inspection SOP. Does not cover deck condition, signed off before underlayment.

Roles and responsibilities

The hold point

A hold point means the next operation does not begin until someone other than the person who did the work signs it. One person verifying their own laps is not verification, because the same reading that produced the error produces the check.

Two things keep it from becoming a bottleneck. Verify plane by plane rather than roof by roof, so the covering crew is never idle long. And verify against the roll and the printed instruction on site, never against a number remembered from the last job.

Procedure

1. Put the product instruction and the roll in your hand before you measure anything. Read the required head lap, end lap, fastener type and fastener pattern off the printed instruction for the exact product installed, and write those four values at the top of the verification entry. The roll marking counts too: the adopted IRC references the material standards, so a felt reads ASTM D226 Type I or II or D4869, a synthetic its own listing. Acceptance: four values written down before the first measurement, matching a product that is physically on site. Wrong looks like a verifier working from the lap number for a different synthetic. Stop rule: no instruction on site and no legible roll printing means the office pulls it before verification continues. Hazard: none, this is reading done at the truck.

2. Verify underlayment laps, fastening and lay-flat across the whole plane. Measure head lap at three separated points per course run and end laps wherever a roll ended, then look down-slope across the plane for wrinkles, fishmouths and lifted edges. Acceptance: every measured lap at or above the printed number from step 1, cap fasteners at the printed pattern, no fishmouth and no unfastened edge anywhere on the plane. Wrong looks like staples in synthetic underlayment, which tear out in wind and leave a crew standing on a sheet that is no longer attached. Stop rule: any lap under the printed number is re-run rather than sealed, and any lifted edge is re-fastened before the next step. Hazard: dry synthetic underlayment is slick and dusty synthetic is slicker, so this walk happens tied off with clean soles, and never on frost or on damp material.

3. Measure the ice barrier from the interior face of the exterior wall, not from the eave. Where the adopted IRC requires an ice barrier for your area, the membrane is a self-adhered sheet meeting ASTM D1970 as that code references it, and it runs from the lowest roof edge to a point at least 24 in inside the exterior wall line, measured horizontally. Convert that to distance along the slope before you compare it against what is installed. Acceptance: the along-slope run of installed membrane, converted back to horizontal, lands 24 in or more inside the wall line, on every eave the requirement covers. Wrong looks like a single 36 in course called good on a deep overhang. Stop rule: short by any amount means another course before shingles, lapped to the membrane manufacturer's stated overlap. Hazard: this measurement is taken at the eave edge, so it is taken from a connected position with the tape, not by leaning out over the edge to hook it.

4. Verify drip edge presence and, more importantly, order. At the eave the drip edge goes on the deck first and the underlayment or ice barrier laps over it. At the rake the underlayment goes down first and the drip edge over it. Acceptance: correct order at both edges on every plane, end laps at the overlap the adopted IRC requires for asphalt shingle drip edge, and fasteners at the required spacing. Wrong looks like drip edge run over the eave underlayment, which delivers water behind the fascia and rots it from the inside while the roof looks perfect. Stop rule: wrong order at the eave is corrected, not sealed over. Hazard: cut drip edge has a live edge the length of your forearm, so it is handled with cut-resistant gloves and offcuts go straight in the bucket rather than on the plane.

5. Verify the valley liner and the valley type actually specified. Confirm the liner width and centering, the type of valley the contract calls for (open metal, closed-cut or woven), and that nothing is fastened within the drainage path. Acceptance: liner centered on the valley line at the width the underlayment or metal manufacturer specifies, no fastener inside the clear width either manufacturer states, and metal laps running down-slope. Wrong looks like a metal valley lapped up-slope, which turns every lap into a scoop. Stop rule: a fastener inside the drainage path is pulled, the hole patched to the membrane manufacturer's instruction, and the patch recorded. Hazard: a valley is where two planes send water and both send a falling body, so it is crossed tied off rather than walked down.

6. Verify wall flashing: step, headwall and kickout. Confirm step flashing is one piece per course rather than a continuous strip, that headwall or apron flashing runs up the wall and under the water-resistive barrier, and that a kickout is present and open at every lower end of a roof-to-wall intersection. Acceptance: step pieces at the height and width the adopted IRC requires for asphalt shingles, each lapping the one below, and a kickout that visibly throws water clear of the cladding and into the gutter. Wrong looks like a continuous L strip caulked to the wall, which fails at the first course that lifts. Stop rule: a missing kickout stops the plane, because the wall behind it is what rots. Hazard: this reaches into an intersection where cladding and flashing edges are both sharp and a lifted siding course can be under spring load.

7. Verify penetration flashing and boot detail before anything covers it. Check that each pipe, vent, skylight and chimney has its underlayment cut and lapped so upper material laps over lower, that the base flange sits flat, and that no detail relies on sealant for the primary seal. Acceptance: shingling order correct at every penetration on the plane, flanges flat with no bridging, sealant only where the instruction calls for it. Wrong looks like a boot bedded in a ring of roof cement with the underlayment cut square around it. Stop rule: a detail that works only because of sealant is redone. Hazard: asphalt roof cement meeting ASTM D4586 carries solvent, so it is used with nitrile gloves and eye protection, kept off skin, and never inside an attic or a closed space; read the product SDS before opening the pail.

8. Close what you opened, sign the release and photograph it. Re-fasten and re-seal every lap you lifted to measure, walk the plane once for loose fasteners and debris, then release it to the covering crew in writing. Acceptance: no lifted lap left lifted, every correction from steps 2 to 7 confirmed complete by the verifier who called it, and a release time with the verifier's name on the ticket. Wrong looks like a release given by radio while the verifier is on another plane. Stop rule: an open correction means the plane stays closed, and the covering crew moves rather than waits. Hazard: the covering crew will now walk this plane fast carrying bundles, so anything that rolls comes off before they arrive.

The record this produces

One verification entry per plane: date, plane identifier, product names for underlayment and ice barrier, the four values from step 1, measured head and end laps, the ice barrier along-slope and horizontal figures with the slope used, drip edge order at eave and rake, valley type and liner width, step and kickout confirmation, penetration count checked, every correction called with its measured shortfall, the release time and the verifier's name.

The photographs sit with it: each plane wide, each valley, each wall intersection, each penetration, and a tape in frame on the ice barrier. The office reads the entry when a leak is reported, and the warranty desk reads it when a manufacturer asks whether the assembly was installed to instruction, which is what most material warranties turn on.

Worked pass: 1-1/2 story gable, 6:12 pitch, north eave

Eave overhang measures 18 in horizontally from the exterior wall face to the roof edge. Pitch is 6:12, so the along-slope distance per unit of horizontal run is the square root of 1 plus 0.5 squared, or 1.118.

Step 3 requirement: 18 in of overhang plus 24 in inside the wall line is 42 in horizontal, which at 1.118 is 47.0 in along the slope.

Step 3 fails. Installed is one 36 in course of self-adhered membrane run from the eave edge, so 36 in along the slope. Converting back, 36 divided by 1.118 is 32.2 in horizontal, and 32.2 minus the 18 in overhang leaves 14.2 in inside the wall line against the 24 in required. Short by 24 minus 14.2, or 9.8 in horizontal. The stop rule fires and the plane stays closed.

Correction: a second 36 in course lapped 4 in over the first adds 32 in along the slope, for 68 in total. 68 divided by 1.118 is 60.8 in horizontal, and 60.8 minus 18 leaves 42.8 in inside the wall line. Passes with margin, and the margin is real rather than lucky, because the second course was full width.

The rest of the plane: step 1 recorded 6 in head lap, 6 in end lap, cap nails and the printed field pattern for that synthetic. Step 2 read head lap at three points per run, 6-1/2, 6 and 7 in, all at or above 6. Step 4 found both edges in the correct order. Step 5 found the liner centered with no fastener in the clear width. Step 6 found step flashing per course and a kickout at the porch-roof-to-wall intersection. Step 7 checked 4 penetrations: two plumbing vents, one bath fan and one range vent, shingling order correct on each.

The lead's note is worth more than the correction. The takeoff assumed one course of ice barrier per eave; on this pitch and overhang it is two on every eave, and the material list should carry that before the truck loads.

References

• International Residential Code, Chapter 9, in the edition your jurisdiction has adopted, for ice barrier extent, drip edge, step flashing and flashing at wall and roof intersections
• The underlayment, ice barrier and shingle manufacturers' installation instructions, which set laps, fastener type and pattern and are the condition of the material warranty
• ASTM D226 and D4869 for asphalt-saturated felt, ASTM D1970 for self-adhered ice barrier, and ASTM D4586 for asbestos-free asphalt roof cement
• See related: the tear-off and dry-in SOP, which owns the installation sequence this pass verifies, and the flashing and penetration detail inspection SOP, which covers a roof already finished