What order do I flash a flanged window in a house-wrapped wall so water can't get behind it?

Here's the correct flashing order for a flanged window in a house-wrapped wall:

1. Install window with flanges flat against the sheathing.

1. Apply flashing tape over the bottom flange first, extending onto the house wrap. This creates the primary drainage plane.

1. Wrap sides: Apply house wrap or flashing tape over the side flanges, lapping over the bottom tape. If using house wrap, cut slits to fold over the flange.

1. Top it off: Apply flashing tape or self-adhered membrane over the top flange, lapping over the side flashing. This is your final weather barrier.

1. Install siding over the flashing, ensuring it laps over the window flange.

Key points:

• Always work bottom-up to ensure proper water shedding
• Use self-adhered flashing tape (minimum 3" wide) for best seal
• House wrap goes under the window flanges on the sides and top, but over the bottom flange tape
• Ensure all laps are minimum 2"

Per IRC R703.1, windows must be flashed to prevent water infiltration. The drainage plane (house wrap) should be continuous and properly lapped at all joints.

Pro tip: Use a utility knife to cut precise slits in house wrap rather than tearing it, and press all flashing firmly to ensure adhesion.

Flashing Sequence (Bottom-Up Principle):

1. Sill Pan (Critical): Apply self-adhered flashing tape on the rough sill extending 6" up jambs. Code: IRC R703.4 / R703.8. Slope sill or use back dam. Do not seal the bottom flange to the sill pan (drainage escape).
2. Jamb Flashing: Apply tape up jambs, overlapping sill pan tape (shingle fashion). Extend above head.
3. Set Window: Bed flange in sealant (per mfr). Nail per schedule. Leave bottom flange nails loose/out (drainage).
4. Head Flashing: Apply tape over head flange, overlapping jamb tapes.
5. House Wrap (WRB) Integration: Cut WRB head flap above window. Tape WRB head flap down over head flashing tape (shingle lap). Tape WRB jambs over jamb flashing tape. Sill WRB: Tape bottom WRB flap up onto sill pan flashing (or leave loose over sill pan for drainage).
6. Head Drip Cap (Metal/Plastic): Install over head flashing/WRB lap. Seal top leg to sheathing.

Key Rules:

• Shingle Lap: Everything laps down and out. Upper layers lap over lower layers.
• No Reverse Laps: Never tape bottom over top.
• Drainage Path: Water hitting flange → jamb/sill flashing → out bottom (not into wall).
• Sealant: Back of flange (setting bed) + top of head drip cap. Never caulk bottom flange to sill pan.

Common Fail: Taping WRB sill under sill pan flashing (traps water). WRB must lap over sill pan or drain freely onto it.

Verify window mfr instructions for specific flange sealing details.