Flashing and Water Management Detail

Purpose

Every layer in a window flashing detail is covered by the layer above it. That means each layer can be verified exactly once, in the minute before it disappears, and after that the only verification left is a water test that either passes or sends someone back into a finished wall.

The failure this prevents is not a leak on handover. It is the leak that shows up in the second or third year as a stain on the drywall below the sill, by which time the sheathing has been wet through a dozen storms. The customer has a new window and a rotting wall, and the shop has no record of what the layers looked like because nobody photographed them.

Scope

Covers the water-management detail from the prepared opening to the point the exterior cladding or trim returns, for flanged and non-flanged replacement units on a drainage wall with a water-resistive barrier.

Does not cover: opening preparation and rot repair, which must be complete before this starts; interior air sealing and trim, which the trim and finish procedure owns; face-sealed assemblies, stucco reglets and masonry through-wall flashing, which are their own details; and the sill flashing theory itself, which the sill flashing detail reference card owns.

Roles and responsibilities

The handoff that fails is the first row. An installer working alone under time pressure covers a layer and photographs the outside of it, which proves nothing about the lap underneath.

Procedure

1. Read the day's conditions against the tape's data sheet before the first roll opens. Take the ambient and substrate surface temperature, then read the flashing tape's published minimum application temperature, minimum lap and primer requirement off its data sheet, and write all three on the job sheet. Acceptance: substrate temperature at or above the tape's stated minimum, and the minimum lap written down. Wrong looks like a lap taken from habit; 2 in is common on self-adhered flashing tape and some butyl products call for more, so the sheet governs. Stop rule: below the tape's minimum temperature, either switch to a tape rated for the conditions or warm and dry the substrate; a cold-set tape releases in the first summer, under the cladding where nobody sees it. Where a primer is required it is a solvent vapor, so apply it with the area open to outside air and follow the respiratory protection its safety data sheet calls for.

2. Cut and fold the water-resistive barrier head flap out of the way before anything is applied. Cut the barrier so the head flap lifts clear and tapes back temporarily, leaving the jamb and sill barrier laps undisturbed. Acceptance: a head flap that can be laid back down over the head flashing at the end, and no barrier tear running past the opening. Wrong looks like the barrier cut flush at the head, which removes the ability to shingle the head flashing under it and cannot be undone. Stop rule: a torn barrier is patched with a shingled repair before the pan goes in, not taped over from the outside. Cut with the blade drawn away from the body and retract it between cuts.

3. Form the sill pan with end dams and a back dam, then water-test it before anything covers it. Install the pan, preformed or site-formed, with both ends dammed, a back dam at the interior edge at the height the pan or flashing manufacturer specifies, and positive slope to the exterior. Then pour water into the pan at each end and at the center. Acceptance: the water leaves the pan to the exterior within 30 seconds and none stands behind the back dam; tune the time to your own pans but keep it a stated number. Wrong looks like water pooling at one end, which is a pan with no slope there and a reservoir sitting under the unit. Stop rule: a pan that ponds comes back out and gets re-formed; it does not get a bead of sealant in the low spot, because sealant in a drainage path is the defect this detail exists to avoid.

4. Roll every self-adhered layer over its full area at the pressure the sheet calls for. Work from the center out, press out every fishmouth, and give the laps a second pass. Acceptance: full contact with no visible air channel, no wrinkle crossing a lap, no lifted edge on the pan or its dams. Wrong looks like a tape smoothed with a gloved hand, which wets out the adhesive over maybe half its area and leaves capillary channels along the wrinkles. Stop rule: a fishmouth that will not roll out is cut, overlapped with a fresh patch and re-rolled; it is never left with sealant over it.

5. Set, shim and fasten the unit per the manufacturer's instructions, then operate it before flashing over the flange. Shim at the points the instructions name, fasten to the schedule they give, then open, close and lock every operating sash. Acceptance: the unit operates and locks with no binding, the reveal is even, and the installed frame's diagonals match within the manufacturer's tolerance. Wrong looks like a unit fastened first and operated after the head tape is on. Stop rule: a sash that binds is corrected before any tape covers a flange, because the fix is a shim adjustment and every layer after this has to come off to reach it.

6. Run the jamb flashing over the flange and over the pan legs, bottom lapped by top. Apply jamb tape from the sill upward, covering the flange and lapping over the turned-up pan legs by at least the sheet's minimum, and stop it above the head flange. Acceptance: a measurable lap over the pan leg at or above the written minimum, photographed with a tape in frame, and the jamb tape running past the head flange height. Wrong looks like jamb tape run under the pan leg, a reverse lap that channels water into the wall and looks identical from three feet away. Stop rule: any reverse lap is cut out and redone; no repair leaves a reverse lap in place.

7. Run the head flashing, then lay the barrier head flap back down over it. Apply head tape over the head flange, extending past both jamb tapes by the written minimum, then fold the head flap down over it and seal the diagonal cuts. Acceptance: the barrier lies over the head flashing, the head flashing lies over the jamb tapes, and the jamb tapes lie over the pan legs, all in one photograph before any trim goes on. Wrong looks like the head flap taped on top of the barrier rather than under it. Stop rule: if the flap was cut off at step 2 and cannot be laid back, a shingled barrier patch goes over the head flashing and under the barrier above before work continues.

   5 barrier head flap folded down last
   ------------------------------------
   4 head tape over flange and jamb tape
   ------------------------------------
   3 jamb   |  flanged unit  |   3 jamb
     tape   |                |     tape
   ------------------------------------
   2 pan legs turned up both jambs
   1 sill pan, back dam in, sloped out

Every layer sheds onto the one below it and nothing sheds inward. Photograph it here; after step 8 it is behind cladding.

1. Water-test the installed unit with the correct test for the unit type. For an operable window use a calibrated spray rack under AAMA 502, in the edition the specification or the manufacturer names, at a static pressure differential of two-thirds the specified design test pressure and not more than 6.24 psf. Acceptance: no water on the interior at sill, jambs, head or surrounding wall over the test duration, with a second tech watching the interior throughout. Wrong looks like using the AAMA 501.2 hose nozzle test on an operable window; 501.2 is written for permanently closed, non-operable joints and on an operable sash it produces a failure that tells you nothing. Stop rule: any interior water stops that opening and the layers come off in reverse order until the path is found. Before an interior observer stands at a wall being sprayed, de-energize the branch circuit serving that wall at the panel, lock and tag it, and verify the receptacle dead with a tester; a replacement crew is doing construction work, so 29 CFR 1926.417 controls rather than the general-industry 1910.333(b)(2), and 1910.147 excludes electrical utilization work at its own (a)(1)(ii)(C).

The record this produces

A per-opening flashing photo set and a test record, filed to the job.

Fields: the ambient and substrate temperatures, the tape product and its data-sheet minimum temperature, lap and primer requirement, the pan water test result with its drain time, one photograph per layer taken before it was covered with a tape measure in frame at the governing lap, the head flap condition, the fastener schedule used, the water test standard and edition, the differential applied, the duration, the interior observation result, and the names of installer and observer.

Who reads them later: the warranty desk reads the layer photographs the first time a stain appears, and whether a lap dimension is in frame decides whether the wall opens. The manufacturer's warranty administrator reads the fastener schedule and the pan detail, because an installation outside the published instructions is the standard reason a unit warranty is declined. The crew lead reads the temperature line across a winter and learns which tape to stock in January.

Worked pass: 34 in by 62 in flanged vinyl unit, north elevation, February

Step 1 failed. Substrate surface temperature read 36 F at 7:30 against the acrylic flashing tape's published 40 F minimum. The stop rule offers two paths and the crew took the material one: the acrylic went back in the truck and a butyl tape rated to 20 F came out, with its own minimum lap read off its own sheet and written on the job sheet. Waiting for a north wall to reach 40 F in February costs the day; applying the acrylic anyway buys a release under the cladding in July.

Step 3 failed on the first attempt. The pan was site-formed. Water poured at the center and the right end drained clear in under 20 seconds. At the left end about 1/8 in stood behind the back dam and was still there after 60 seconds, against a 30 second acceptance. The pan came out, a beveled shim went under the back edge at that end to restore positive slope, and the pan was re-formed and re-tested. Second test: all three pour points drained clear within 20 seconds, no standing water. Both results went in the record, the fail as well as the pass.

That failing pour is the reason the test exists. A pond that shallow is invisible once the unit sits on the pan, and it is not a slow leak, it is a standing reservoir against the back dam that finds the first pinhole in the seam.

Steps 4 through 7 passed with photographs at each layer. Jamb tape lapped the pan legs by 2 in against the butyl sheet's stated minimum, measured with a tape in frame. Head tape ran past both jamb tapes. The head flap folded at step 2 laid back down over the head tape and the diagonals were sealed.

Step 8 passed. Spray rack per AAMA 502 in the edition the manufacturer's instructions name, differential set at two-thirds of the specified design test pressure, which on this unit fell below the standard's 6.24 psf cap so the two-thirds figure governed. The branch circuit serving that wall was off, locked, tagged and proven dead at the receptacle before the observer took position. Fifteen minutes, no interior water at sill, jambs, head or wall.

References

• ASTM E2112, Standard Practice for Installation of Exterior Windows, Doors and Skylights, in the edition your supplier's installation instructions reference, for flashing method and sequence.
• AAMA 502 for field testing of newly installed fenestration, and AAMA 501.2 for permanently closed non-operable joints, each in the edition the specification or the manufacturer names. Neither is a regulation; they reach you through the specification or the warranty.
• AAMA 711, self-adhering flashing for exterior wall fenestration, plus the specific tape's own data sheet, which governs temperature, lap and primer.
• 29 CFR 1926.417, Lockout and Tagging of Circuits, for de-energizing a branch circuit during a water test on construction work.
• See related: the sill flashing detail reference card; the opening preparation and rot assessment SOP.