The Right Way to Install Flashing Around Windows and Doors
(Yes, There’s a Wrong Way—And It Involves Leaks and Regrets)
If you've ever stood on a construction site watching a general contractor yell at a construction worker while waving a piece of bent metal flashing around like a lightsaber—congrats, you’ve witnessed one of the most overlooked (and underappreciated) steps in building construction: flashing installation.
Let’s be real—flashing isn’t sexy. It doesn’t sparkle like new countertops or impress clients like a beautifully poured ready mix concrete foundation. But if you ignore it? You might be designing a new indoor waterfall you didn’t plan for on the floor plan.
What is Flashing and Why Should You Care?
Flashing is that thin layer of waterproofing—usually metal or tape—installed around openings like windows and doors to prevent water from creeping in. Think of it as the unsung hero of your custom home build—right up there with frieze board (bird block) and felt (underlayment).
If you want to keep your blueprints from becoming soggy regrets, you gotta flash it right.
Step 1: Start From the Bottom (Footer Up)
Water flows downhill (shocking, we know). That’s why flashings should always be layered shingle-style—bottom first, then sides, then top. Just like you wouldn’t install fascia before framing, don’t slap on head flashing before sealing the sill.
And for the love of your future change orders, don’t rely on caulking alone.
Step 2: Pan Flashing is Your Best Friend
Think of pan flashing as the cozy bathtub your window sits in. Use formable flashing tape or pre-molded pans to line the bottom of the rough opening. Add a little slope (called "positive drainage") so water flows out—not in.
Bonus points if your crew remembers to wrap the felt (underlayment) over the pan edge like a sandwich. Extra bonus if your daily report notes it.
Step 3: Side Flashing Goes Vertical
Up next: sides. Tuck them under the felt or green board (pressure-treated lumber, FYI). Overlap each piece by a few inches, smooth out wrinkles like you’re ironing your Sunday best, and keep the corners tight.
A sloppy flash job here is like hiring a backhoe operator to do finish carpentry—wrong tool, wrong result.
Step 4: Cap It Off Right
Top it off with head flashing, usually metal. It should extend past the sides by at least an inch, with drip edges bent outward. Then layer your house wrap (or whatever fire-resistive wrap your builders are using) over the head flashing.
Remember, when water runs down the wall, you want it to shed over—not sneak behind like it’s in a spy movie.
Tips From the Trenches
Use a BIM (building information modeling) or CAD (computer-aided design) system to plan complex openings.
Double-check that your grade doesn’t slope back toward the wall.
Keep a roll of formable tape and a heat gun handy when working in cold weather.
Review your cost codes to ensure flashing is tracked—it’s often forgotten in cost-plus contracts.
Check every install with a spray test before the siding goes up.
Why Flashing Matters for Green and Passive Homes
Green building? Passive house? You better believe moisture control is key. Energy efficiency tanks when your forced air heating/cooling system has to battle mold and mildew caused by leaks. Damp proofing the walls is one thing—but stopping water at the window is where it starts.
In Conclusion: Flashing is the Unsung Hero
Whether you're a seasoned contractor, a fresh-faced home builder, or just browsing construction blogs because your girder truss is giving you grief—remember: when done right, flashing is invisible. But when done wrong? You’ll be floating drywall in a new indoor swimming pool.
So flash it right. Stay dry. And may your expansive soils be stable and your GFCIs never trip.
Want us to do a walkthrough of your site and check for flashing fails? Contact our construction company—we’ve got the tools, the know-how, and the bid form ready.