Water finds every mistake. It doesn't care whose scope the flashing was in, whether the sub was a day behind, or that the cladding crew showed up early and buttoned up a wall before anyone stepped back the transition. Two winters later, when a tenant on the third floor calls about a stain spreading across the ceiling, the leak is always somewhere you can't get to without pulling finishes. Flashing is the cheapest work on the job to install correctly and the most expensive work on the job to fix wrong.
The hard part about flashing isn't the flashing itself. It's that flashing lives in the seams between trades, and the seams between trades are exactly where a schedule falls apart. Nobody's contract says "own the window head flashing lap over the WRB and under the sill pan of the unit above." It's implied, it's assumed, and on a bad job it's nobody's. A four-week look-ahead won't install the metal for you, but used right it forces those handoffs into the open before a wall gets closed on top of a defect.
Why Flashing Is a Scheduling Problem, Not a Trade
Ask a PM who installs the flashing on a job and you'll get a shrug, because there's no single answer. The roofer flashes the roof-to-wall. The glazier flashes the window perimeter, or the framer does the pan, or the waterproofer does, depending on how the scope got carved up. The mason installs through-wall flashing. The metal panel sub laps their own head and jamb trims. The plumber and the HVAC sub create penetrations that somebody — usually not them — has to flash and boot.
So flashing is really a coordination problem wearing a trade's clothes. Every flashing detail is a sequence: something has to be dry-in and lapped correctly, the metal goes in next in the right shingle-fashion order (always lap upper over lower so water sheds out, never in), and then the concealing trade covers it. Get the order wrong and you've reverse-lapped a joint that will wick water for the life of the building. The look-ahead's whole job is to protect that order across three or four different companies who don't talk to each other.
The Four-Week Window Is the Right Horizon
People argue about whether a look-ahead should be three, four, or six weeks. For envelope and flashing work, four is usually the sweet spot, and here's the practical reason. Most flashing materials and transition accessories — self-adhered flashing tape, pan flashing, through-wall membrane, prefab corner boots, custom-bent coping — have a lead time somewhere between "in stock at the supply house" and "shop has to fabricate it." Four weeks out is far enough to catch the fabricated items before they become the reason the wall stops, and near enough that your weekly work plan reflects reality rather than wishful thinking.
The move is to run the four-week look-ahead as a rolling window, and every week when you pull the next week into the weekly work plan, you scrub it for flashing handoffs specifically. Not "window installation — 4 days." That line hides three separate flashing operations and two trade handoffs inside it. Break it down.
Read Every Wall as a Series of Transitions
The way experienced supers keep flashing from slipping is to stop thinking in trades and start thinking in transitions. Water doesn't leak through the field of a wall or the middle of a roof. It leaks at changes — where two materials, two planes, or two trades meet. Walk any elevation and the transitions are where all the risk lives:
- Window and door openings — sill pan first, then jambs, then head flashing lapping over the jambs and shingled under the WRB above. The single most common defect in the field is a head flashing tucked behind nothing, or a sill pan that got skipped because the glazier "doesn't do pans."
- Roof-to-wall — step flashing and counterflashing, and the eternal fight over who owns the counter. The roofer wants the wall dried in; the cladding sub wants the roof done. Somebody has to go first, and the answer is the roofing base and step flashing lead, with the wall's WRB or cladding lapping over the vertical leg after.
- Through-wall flashing in masonry and at floor lines — installed with the mason as the wall goes up, with weeps and end dams. You cannot add this later. Miss the course and the wall comes down.
- Penetrations — every pipe, conduit, hood, hose bib, and light box that punches the envelope. These trail the MEP rough by days or weeks and are the easiest thing on the whole job to forget until final.
- Parapet and coping — the roof membrane turns up the parapet, the through-wall or coping caps it, and the two systems have to marry. An open coping joint dumps water straight into the wall cavity where nobody sees it for a year.
- Base of wall and grade — where the WRB, the foundation waterproofing, and the flashing at the sill plate all have to lap correctly before backfill hides the whole thing forever.
When you build your look-ahead, these transitions are your real activities. A trade-flow view — the kind of location-based sequencing LookAheadWall is built around — makes this concrete, because you can see the roofer's line and the cladding line converging on the same wall in the same week and know a coordination conversation has to happen before then, not during.
The Handoffs That Actually Bite
A few sequencing rules earn their keep because the failure mode is expensive and invisible:
Nobody closes a wall until the flashing behind it is signed off. This is the whole game. The concealing trade — cladding, drywall over a rated assembly, backfill, roofing over a base flashing — is your last chance to catch a reverse lap or a missing pan. Build a hold point into the weekly work plan: cladding does not start on an elevation until flashing on that elevation is walked and initialed. It costs an hour. The alternative costs a mobilization to tear cladding off later.
Sill pans before the window, not after. The number of leaks that trace back to a window set into a bare rough opening with no pan is staggering. If the pan is the glazier's scope, it's in their line. If it's the framer's or the waterproofer's, that trade has to be complete and inspected on that opening before the glazier is scheduled to set glass there. Sequence it, don't hope for it.
Roof base and step flashing lead the wall. The vertical leg of the roof-to-wall flashing has to be in place so the wall's weather barrier and cladding lap over it. If the wall gets clad first, the field crew has to either cut the cladding back later or, worse, caulk the joint and call it done. Caulk is not flashing. Sequence the roofer's turn-up ahead of the adjacent wall cladding.
Through-wall flashing rides with the mason. There is no coming back for this one. It goes in as the course is laid, with proper end dams and weeps left open. Your look-ahead has to flag the flashing course a week before the mason reaches it so the material and the detail are on site and confirmed.
Penetration flashings trail the rough — put a placeholder in every week. Because they come days or weeks after the MEP sub creates the hole, penetration boots and collars are the classic orphan activity. The discipline that works is a recurring line in the weekly work plan — "walk penetrations, flash open ones" — so they never fall off the radar between rough and dry-in.
Build in Real Buffers
Flashing gets rushed because it sits at the end of one trade's work and the front of the next, and both trades are behind. Give it room. A day or two of buffer between the flashing operation and the concealing trade is not slack you're wasting — it's the window for the walk, for the inspector, and for the inevitable "the corner boot didn't show up, we're one short." When a schedule has zero buffer at the transitions, the buffer gets taken out of the flashing, because the flashing is the quiet task nobody's watching. Protect it on paper and it survives contact with the field.
Respect the Weather Window
Half of flashing is self-adhered membrane, sealant, and primer, and every one of those has a temperature and moisture range printed on the roll that people ignore under pressure. Self-adhered flashing tape won't bond to a damp or dusty substrate and won't tack below its rated minimum temperature. Sealant applied to a wet joint fails. If you schedule critical flashing against a forecast that's 38 degrees and raining, you're scheduling a callback.
This is where a short-interval look-ahead beats a bar chart drawn six months ago. You're pulling next week's plan against an actual seven-day forecast. Move the temperature- and moisture-sensitive flashing to the dry, warm days and slide the demo or interior work into the wet ones. Note it on the plan so the foreman knows why the sequence flexed — otherwise he'll swap it back to keep a crew busy.
Verify Before You Bury It
The single highest-leverage habit in envelope work is the pre-cover walk. Before any flashing gets concealed — clad over, backfilled, roofed over, drywalled — someone who knows the details walks it and confirms the laps shed water, the corners have real transitions and not just a smear of sealant, the end dams are there, the pan's back leg is upturned. Take photos. Not for a binder nobody reads, but because when a stain shows up later, the photo of that exact wall before it was closed tells you in five minutes whether the flashing was the problem or something else, and whether it's your defect or the sub's.
Bake that walk into the plan as a hold point, tie it to the concealing activity, and make it non-negotiable. Sharing the weekly work plan with your subs — so the glazier, the roofer, and the cladding crew all see the same hold point and the same sequence — is what turns "I assumed you flashed it" into a coordinated handoff. A super with 30 walls to run can't personally remember every pan and penetration; the plan has to carry that memory, and the subs have to be looking at the same plan you are.
The Bottom Line
Flashing coordination isn't complicated. It's just relentless. The details are simple — lap high over low, shed water out, don't bury it until someone's checked it. What makes it hard is that the work is spread across half a dozen subs, buried inside line items that hide the real handoffs, and always under time pressure at the exact moment it matters most. A four-week look-ahead used with discipline drags every transition into daylight a month before the wall closes, forces the "who owns this lap" conversation while there's still time to have it, and gives you the hold points to make sure nobody buries a defect. Do that consistently, and the third-floor tenant never has to make that phone call.