House wrap course overlap — why a 900 sq ft roll covers only about 850 sq ft of wall
The 6-inch horizontal lap is hidden, so a 900 sq ft roll covers ~850 sq ft of wall. Don’t deduct openings — the wrap folds into them.
What this diagram shows
An elevation of three horizontal house-wrap courses, each lapping the one below by six inches shingle-style so water drains outward. Because the lap is hidden, the effective coverage per roll equals the nominal coverage times the roll width minus the lap, divided by the roll width. A 9-foot roll rated 900 square feet covers about 850 square feet of wall. Openings are not deducted because the wrap folds into them.
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House Wrap Calculator
Free house wrap calculator — how many rolls of Tyvek / WRB you need, allowing for the 6-inch overlap that cuts coverage, plus seam tape and cap fasteners.
