House Wrap / WRB Calculator
House wrap is the water-resistive barrier (WRB) behind your siding — the drainage plane that keeps wind-driven rain out of the wall. It is sold by the roll, but the 6-inch shingle lap between courses means a 900 sq ft roll only covers about 850 sq ft of actual wall.
Unlike cladding, you do NOT deduct windows and doors — the wrap is cut and folded into every opening and integrated with flashing, so you buy for the full wall area including gables.
Free, no signup. Behind stucco and adhered masonry veneer, code often requires two layers of WRB — double the roll count for those walls.
House Wrap Calculator
Estimate rolls of house wrap (WRB) for your walls — accounting for the 6" overlap that reduces coverage — plus seam tape and cap fasteners.
Wall area
Gross exterior wall area — house wrap is not deducted for openings
Don't subtract windows and doors — the wrap is cut and folded into every opening, so you cover the full wall.
Roll & overlap
Roll size and the horizontal lap between courses
DuPont specifies a 6" minimum horizontal lap. The lap reduces effective coverage — a 900 sq ft roll covers about 850 sq ft of wall at a 6" lap.
Calculation Formulas
House wrap covers the full wall including gable triangles; openings are generally NOT deducted because the wrap is cut and folded into them.
Example:
2,000 sq ft walls + 200 sq ft gables = 2,200 sq ft.
Courses run horizontally, so the roll width is the course height and the horizontal lap subtracts from it.
Example:
9 ft × 100 ft (900 sq ft) with a 6" lap → 900 × (9 − 0.5) ÷ 9 = 850 sq ft.
Waste-adjusted wall area divided by the effective (lapped) coverage, rounded up to whole rolls.
Example:
2,200 × 1.10 ÷ 850 = 2.85 → 3 rolls.
Total horizontal seam length equals area divided by course height; add ~15% for vertical roll-end seams.
Example:
2,200 ÷ 9 × 1.15 ≈ 281 LF → 2 rolls of 165-ft tape.
Plastic-cap nails or staples on a ~12–18" grid work out to roughly 0.55 per square foot.
Example:
2,200 × 0.55 ≈ 1,210 cap fasteners.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| Tyvek HomeWrap roll sizes | 300 / 495 / 900 / 1,000 / 1,350 sq ft | Nominal coverage of the common DuPont Tyvek HomeWrap rolls (3'×100', 3'×165', 9'×100', 5'×200'/10'×100', 9'×150'). |
| Horizontal overlap | 6 in | DuPont-specified minimum horizontal lap between courses. |
| Vertical (end) overlap | 6–12 in | Minimum lap at roll ends / inside corners. |
| Seam tape roll | 165 ft | Standard 1.88" WRB seam-tape roll length. |
| Default waste | 10% | Baseline for cuts, corners, and opening returns. |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
DuPont Tyvek Installation Guidelines(Tyvek HomeWrap)
View StandardManufacturer instructions defining roll sizes, the 6" horizontal overlap, seam taping, and window/opening integration.
Key Requirements:
- •Minimum 6" horizontal overlap, shingle-lapped
- •Tape all seams with compatible WRB tape
- •Integrate with flashing at all rough openings
IRC — Water-Resistive Barrier(IRC R703.2)
View StandardRequires at least one layer of an approved water-resistive barrier behind the exterior wall covering, lapped to drain water outward.
Key Requirements:
- •One layer of WRB (No. 15 felt or equivalent) minimum
- •Shingle-lapped to drain to the exterior
WRB Performance Standard(ASTM E2556)
View StandardSpecification for Type I and Type II housewraps, defining water-penetration resistance and water-vapor transmission.
Key Requirements:
- •Type I/II water-resistance and vapor-permeance thresholds
- •Air-resistance for products marketed as air barriers
Flashing Integration(IRC R703.4 / ASTM E2112)
View StandardFlashing must be integrated with the WRB in the correct shingle sequence at openings, penetrations, and terminations.
Key Requirements:
- •Sill pan → jamb → head flashing sequence
- •WRB laps over head flashing, under sill
Rainscreen (best practice)(Building-science guidance)
View StandardA ventilated gap between the WRB and the cladding improves drainage and dry-down, extending wall and cladding life.
Key Requirements:
- •Furring or drainage mat between wrap and cladding
- •Especially recommended behind wood and fiber cement
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
Cold climates
Zones 5–8
Air-tightness matters most here; taped housewrap or a dedicated air barrier reduces heat loss and interior moisture drive.
Regional Examples:
Hot-humid
Southeast, Gulf
Inward vapor drive makes a vapor-permeable WRB and a drainage gap important to avoid trapping moisture in the wall.
Regional Examples:
High-wind / coastal
Hurricane zones
Wind-driven rain and uplift demand more cap fasteners and meticulous seam and opening taping.
Regional Examples:
Wildfire / WUI
California, mountain West
Assembly-level fire requirements may affect WRB and cladding choices in Wildland-Urban Interface zones.
Regional Examples:
Stucco / masonry veneer
Southwest, nationwide
Behind stucco and adhered veneer, code often requires two layers of WRB (a bond break) — double the coverage.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
Plan disposal before you start
Smaller jobs still produce more debris than a few trash bags can hold. Check what's allowed in a dumpster and which disposal option fits the scope.
See disposal options →
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How to Use This Calculator
- Enter your gross exterior wall area in square feet (do not deduct openings).
- Add the gable / triangle area on top.
- Pick your roll size — 3-ft rolls for tight jobs, 9-ft or 10-ft rolls for open walls with less lapping.
- Set the horizontal overlap (6 inches is the DuPont minimum).
- Calculate for rolls, seam tape, and cap fasteners.
Overlap, Openings & Rainscreen
The horizontal lap is why coverage math matters: a wider roll wastes less to overlap, so 9-ft and 10-ft rolls cover more wall per square foot than 3-ft rolls. Do not subtract openings — the wrap wraps into them. Tape every seam with compatible WRB tape (untaped seams are the top leak path), and consider a vented rainscreen gap between the wrap and the cladding to boost dry-down, especially behind wood and fiber cement.
Frequently Asked Questions
How many rolls of house wrap do I need?
Divide your gross wall area (including gables, without deducting openings) by the effective coverage of your roll, then add ~10% waste and round up. Effective coverage is less than the roll's nominal size because of the 6-inch horizontal overlap: a 9-ft × 100-ft roll is 900 sq ft nominal but covers about 850 sq ft of wall. So a 2,200 sq ft house needs about three 900 sq ft rolls.
Do I subtract windows and doors from house wrap?
No — this is the opposite of siding. You cover the entire wall, including where the windows and doors are, because the wrap is cut and folded into each rough opening and integrated with the flashing. Subtracting openings would leave you short. Buy for the full gross wall area plus gables.
Why doesn't a 900 sq ft roll cover 900 sq ft of wall?
Because house wrap is installed in horizontal courses that overlap each other by 6 inches (the DuPont minimum) so water sheds outward. On a 9-ft-wide roll, that 6-inch lap turns 9 feet of roll into 8.5 feet of exposed wall — about 94% — so 900 nominal square feet covers roughly 850. Wider rolls waste less to overlap, which is why 9-ft and 10-ft rolls are more efficient than 3-ft rolls on open walls.
What size house wrap roll should I buy?
Wide rolls (9 or 10 feet) cover open walls fast with fewer laps and less seaming, so they're the most efficient for a whole house. Narrow 3-ft rolls are handy for gables, dormers, and tight retrofit work where a big roll is unwieldy. Common Tyvek HomeWrap sizes are 3'×100' (300 sq ft), 3'×165' (495), 9'×100' (900), 5'×200' or 10'×100' (1,000), and 9'×150' (1,350).
Do I need house wrap behind stucco or stone veneer?
Yes, and usually two layers. IRC R703.7.3 requires a water-resistive barrier behind cement stucco, and code and best practice call for two layers (a bond break) behind stucco and adhered masonry veneer so the cladding doesn't bond to and wick through a single WRB. Double the roll count for any walls getting stucco or adhered stone.
How much seam tape do I need?
Tape every horizontal and vertical seam — untaped seams are the number-one path for wind-driven rain. The total horizontal seam length is roughly your wall area divided by the roll width (a 9-ft roll on 2,200 sq ft ≈ 245 feet of horizontal seams), plus about 15% for vertical roll-end seams. A standard 1.88-inch WRB tape roll is 165 feet, so plan on one to a few rolls depending on house size.