What type of window flashing tape should I use?

Self-adhered flashing tapes like DuPont FlexWrap NF, Henry Blueskin TWF, or 3M All Weather Flashing Tape are the most widely used. Choose a product compatible with your housewrap manufacturer — Tyvek FlexWrap for Tyvek housewrap, for example. For sill pans and corners, use a flexible (stretch) tape that conforms to 90-degree angles.

How much window flashing tape do I need?

Calculate the total perimeter of all windows and doors (add the width plus height times two for each opening). A standard 3x4 ft window has about 14 feet of perimeter. For 8 windows, that is 112 linear feet of tape. Add 20% for overlaps and waste, and buy the appropriate number of 75-foot rolls.

What is the correct order for installing window flashing?

Always install in this exact sequence: (1) sill flashing across the bottom with a back-dam fold, (2) jamb flashing on both sides overlapping the sill tape, (3) set the window, (4) lap the housewrap head flap over the top of the window flange. Never tape the bottom flange of the window — leave it open for drainage.

Do I need window flashing tape with a flanged window?

Yes. Even nailing-flange windows need proper flashing tape to seal the gap between the window flange and the housewrap or sheathing. The flange alone does not create a waterproof seal — flashing tape is required to integrate the window into the wall's water management system.

What causes window leaks in new construction?

The number one cause of window leaks is improper flashing installation — specifically, incorrect layering sequence that traps water behind the WRB instead of directing it outward. Other common causes include missing sill pan flashing, failing to use a back-dam at the sill, and sealing the bottom window flange (which prevents drainage).

Can I use caulk instead of flashing tape around windows?

Caulk alone is not an acceptable substitute for proper window flashing. Caulk can crack, shrink, or fail within a few years, while quality flashing tape maintains its seal for decades. Use flashing tape as the primary waterproofing method and supplement with a compatible sealant at specific joints if recommended by the window manufacturer.

Window Flashing Calculator

Window flashing tape calculator: Estimate linear metres for all openings. Free tool for self-adhesive flashing tape.

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Enter Your Measurements

How to Use This Calculator

1Count total number of windows.
2Enter average window perimeter (typical 3×4 window = ~14 ft).
3Click Calculate.

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About This Material

Window flashing tape is a self-adhered flexible membrane used to seal the rough opening around windows and doors, creating a waterproof connection between the window frame and the housewrap or WRB. Common products include DuPont FlexWrap NF (flexible, follows corners), Henry Blueskin TWF (straight runs), 3M All Weather Flashing Tape, and ZIP System stretch tape. Flashing tape comes in widths of 4, 6, and 9 inches, with 4-inch being standard for most window installations and 6-inch or 9-inch for sill pans and wider applications. Rolls are typically 75 feet long and cost $25 to $60 depending on width and brand. The installation sequence is critical: sill flashing is applied first (with a back-dam fold), then jamb flashing overlapping the sill tape, and finally the housewrap head flap is lapped over the top to create a shingle-lap drainage system. Improper flashing is the leading cause of window leaks and wall rot in residential construction.

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