House Wrap: What It Does, Tears, Laps and Siding Leaks

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House wrap is the thin white, gray or printed sheet visible on new homes before the siding goes on. It is easy to dismiss as a branding billboard for whoever made it, but it does important work: it is the backup layer that catches water that gets past siding, and it helps keep wind from blowing through the wall. Brand names like Tyvek house wrap have become shorthand for the whole category, which also includes other spunbonded, perforated and coated products, building paper and fluid-applied membranes. This guide explains what a weather-resistive barrier does, how it differs from vapor and air barriers, why the way it is lapped and taped matters as much as the product, how it ties into window and door flashing, what sun exposure and tears do to it, and what a home inspector can and cannot see once siding covers it.

Part of our Structure & Exterior guide — start there for the full picture →

What Does Tyvek House Wrap Actually Do?

Tyvek house wrap and similar products are weather-resistive barriers, often shortened to WRBs. Their primary job is to shed liquid water that gets behind the cladding while still letting water vapor pass through so the wall can dry. No siding is perfectly watertight. Wind-driven rain gets past lap siding, through joints in fiber cement, around trim and through hairline cracks in stucco. The WRB is the drainage plane behind the cladding that directs that water down and out, rather than letting it soak the sheathing and framing.

A good WRB has three basic properties:

• Water resistance. It holds back liquid water that runs down its face.
• Vapor permeability. It lets water vapor move through it, so moisture that gets into the wall from inside or during construction can dry outward. Different products have different permeability ratings.
• Durability during construction. It survives installation, wind and some sun exposure until the siding goes on.

Most house wraps also reduce air movement through the wall when seams are taped and edges are sealed. Whether the wrap counts as the home’s main air barrier depends on how carefully it was detailed.

WRB vs Vapor Barrier vs Air Barrier

These three terms get mixed up constantly, and the confusion leads to real problems in walls.

Weather-Resistive Barrier

A WRB stops liquid water from outside. It sits behind the cladding, and it is meant to be vapor open in most climates so walls can dry to the exterior.

Vapor Retarder or Vapor Barrier

A vapor retarder slows the diffusion of water vapor through a material. In cold climates, vapor retarders are traditionally placed on the warm, interior side of the insulation, such as kraft-faced batts or a specified paint or membrane, to limit indoor moisture from reaching cold sheathing in winter. Placing a highly vapor-tight layer on the outside of a wall in a cold climate can trap moisture inside the wall, which is one reason most house wraps are designed to be vapor permeable. Colorado’s dry climate changes the risks compared with humid regions, but wall design still matters, especially in bathrooms and other high-moisture rooms.

Air Barrier

An air barrier stops air leakage. Air carries far more moisture into a wall than vapor diffusion does, and air leaks waste energy. An air barrier can be on the interior (drywall with sealed edges), on the exterior (taped sheathing or taped house wrap), or both. Its continuity matters more than its material: one gap at a rim joist or around a window can defeat an otherwise tight layer.

One product can serve more than one role. A taped house wrap can be both the WRB and the exterior air barrier. Some sheathing products have an integrated WRB facing with taped seams. The key is that each function is accounted for somewhere in the wall.

Installation Details That Make or Break House Wrap

House wrap only works if water that runs down its face stays on the outside of every lap, seam and penetration. Most failures come from installation, not the product.

Shingle-Style Laps

Like roof shingles, each upper course of wrap should overlap the course below it, so water running down always flows onto the outer face of the next sheet. A reverse lap, where a lower sheet is tucked over an upper one, directs water behind the wrap. Manufacturers specify minimum horizontal and vertical overlaps, and installation typically starts at the bottom of the wall and works upward.

Taping Seams

Vertical and horizontal seams are typically taped with the manufacturer’s recommended tape. Taping helps with air sealing and keeps wind from lifting laps. Generic duct tape or packing tape usually fails quickly outdoors.

Fasteners

Wrap is commonly fastened with cap nails or cap staples at the spacing the manufacturer specifies. Plain staples can tear through in wind.

Bottom Edge and Top Edge

The wrap should lap over the top of the foundation or over a flashing at the base of the wall so water exits rather than running behind the sill. At the top, it should tuck under roof-wall flashing where the wall meets a roof below.

Window and Door Flashing Integration

The most leak-prone points in most walls are the openings. A window or door is a hole through the WRB, and water that runs down the wall will find any path around it. Typical sequencing, in very general terms, looks like this:

1. The sill of the rough opening gets a flexible flashing that turns up the sides and laps out over the house wrap below, so water that reaches the sill drains outward.
2. The window is installed, usually with its nailing flange sealed or taped at the sides.
3. Side flashing laps over the window flange and over the sill flashing.
4. The house wrap above the window is cut and folded up so the head flashing can tuck under it, then lapped back down over the head flashing.

The details differ by window type and manufacturer, and many windows come with specific instructions that installers must follow. A common error is laying house wrap over the head flange instead of under it, which funnels water into the top of the window. Our guides to exterior window trim and window sill replacement show where these leaks usually surface, and the guide to roof flashing covers step and kick-out flashing where walls meet roofs, another frequent leak point.

Doors follow similar logic, with extra attention to the threshold, which sits close to the deck or landing where water and snow collect.

Tears, Sun Exposure and Construction Damage

House wrap is designed to be covered. Manufacturers typically state a maximum period of UV exposure before the siding should go on, and that period varies by product. Sun breaks down many polymer wraps over time, and Colorado’s high-altitude sunlight is intense. A wall left exposed through a long construction delay may need its wrap inspected or replaced before cladding goes on.

Other common damage includes:

• Tears from wind, ladders, scaffolding and other trades.
• Unsealed cuts where plumbers, electricians and HVAC installers ran pipes, wires and vents through the wall.
• Missing sections behind trim boards, corner boards or band boards.
• Wrap that was removed and not replaced during window or siding repairs.

Small tears are typically repaired with manufacturer tape or by lapping a patch shingle-style under the course above. Every penetration, from dryer vents to hose bibbs to light fixtures, should be flashed or sealed in a way that keeps water on the outside.

House Wrap Behind Stucco and Fiber Cement

Different claddings place different demands on the WRB.

Stucco

Traditional three-coat stucco absorbs water and holds it, so it needs a robust drainage path behind it. Many stucco assemblies use two layers of building paper or WRB, sometimes with a drainage mat, so water can drain between the stucco and the sheathing. Stucco that was applied over a single layer, or over wrap that bonded to the stucco and lost its drainage gap, can trap water against the sheathing. Our guide to stucco repair explains cracking, staining and when hidden moisture testing makes sense.

Fiber Cement

Fiber cement siding sheds most water, but joints, cut ends and nail penetrations still let some through. Manufacturers generally require a WRB behind it and specify details such as joint flashing and clearances from roofs and grade. Our Hardie board siding guide covers those details and what installation errors look like.

Vinyl and Wood Lap Siding

Vinyl siding hangs loosely and is not watertight, so the WRB behind it does much of the water management. Wood lap siding benefits from a small gap or drainage space to let the back of the boards dry.

Signs That a Weather-Resistive Barrier Has Failed

Because the WRB is hidden, failures usually show up as symptoms elsewhere:

• Interior water stains below windows or at the corners of window trim, especially after wind-driven rain.
• Swelling or soft spots in siding or trim, particularly below windows and at the bottom courses.
• Rot in sills, trim and sheathing found during window or siding replacement. Our wood rot repair guide covers evaluation and repair.
• Stucco staining streaking down from window corners.
• Peeling paint that recurs on the same section of siding.
• Musty odors or mold on interior surfaces of exterior walls.

EPA’s brief guide to mold and moisture states that the key to mold control is moisture control, and recommends fixing water problems promptly and drying water-damaged areas within 24 to 48 hours to prevent mold growth in most cases. Water that repeatedly enters a wall through a failed WRB often cannot dry that quickly, which is why hidden wall leaks can lead to mold and decay before anything shows inside.

What an Inspector Can and Can’t See

A home inspector looks at the exterior wall coverings, flashing and trim. The American Society of Home Inspectors (ASHI) Standard of Practice lists wall coverings, flashing and trim among the exterior items an inspector inspects. The same standard notes that inspections are not technically exhaustive and are not required to identify concealed conditions or latent defects, and that inspectors are not required to determine the condition of components that are not readily accessible.

Once siding is installed, the WRB is concealed. An inspector may see wrap at the edges of trim, below the bottom siding course or in an unfinished garage or attic gable, and may note missing kick-out flashing, poorly flashed penetrations, siding too close to grade or roofs, and staining that suggests water entry. Confirming WRB condition throughout a wall generally requires invasive investigation, moisture probing or removal of siding, which is beyond a standard inspection. On stucco homes, some buyers order specialized moisture testing for that reason.

For buyers of newer homes, asking the builder or seller for photos of the walls before cladding can be useful. Our guide to hiring a home inspector explains what the inspection covers and how to request further evaluation, and the structure and exterior hub links related siding, window and roofing guides.

Energy and Air Sealing Benefits

When seams, edges and penetrations are taped and sealed, house wrap can reduce air leakage through walls. Air sealing is one of the more cost-effective efficiency improvements in many homes. ENERGY STAR says that sealing air leaks and adding insulation can help a home be more comfortable and energy efficient, and its savings methodology estimates that homeowners can save an average of 15 percent on heating and cooling costs by air sealing their homes and adding insulation in attics, floors over crawl spaces and accessible basement rim joists. Those estimates apply to whole-house sealing and insulation projects, not to house wrap alone. For an existing home, most air sealing happens from the inside and the attic, since replacing wrap requires removing siding. Wrap replacement usually makes sense only as part of a re-siding or major window project.

Questions to Ask During a Re-Siding Project

Re-siding is the one time most homeowners get to see, and influence, the weather-resistive barrier on an existing house. When siding comes off, a few questions help make sure the new wall performs better than the old one:

1. What barrier will be used, and is it approved for the new cladding? Fiber cement, vinyl, wood and stucco manufacturers may each specify compatible WRB types.
2. Will the old wrap or building paper be removed? Damaged or degraded layers are often replaced rather than patched.
3. How will windows and doors be flashed? Ask whether sill pans or flexible sill flashing will be added and how the head flashing will lap under the wrap.
4. What about kick-out flashing? Where a roof edge dies into a wall, a kick-out diverter helps keep roof runoff out of the wall.
5. Will sheathing be inspected? Agree in advance on how soft or stained sheathing will be handled and priced, since it is often found only after siding comes off.
6. Is a rainscreen gap planned? Some assemblies add furring strips or a drainage mat to create a small air space behind the siding, which helps walls dry.

Photos of the wall after the WRB and flashing are installed, and before siding goes on, are worth keeping with the home’s records for future owners and inspectors.

House Wrap Costs

For a new build or re-siding project, house wrap materials are a small share of the total. Rolls of common residential wrap often cost a few hundred dollars each and cover a large area, and installed costs for wrap and tape on a re-siding job are commonly folded into the siding bid at somewhere around a dollar or less per square foot of wall, varying by product and region. Fluid-applied barriers and integrated sheathing systems cost more. Window flashing, tape and labor for careful detailing add to the total. Repairing water damage from a failed WRB, by contrast, can run into thousands of dollars once siding, sheathing and framing are involved. These are general 2026 ranges rather than quotes.

References

• ASHI Standard of Practice for Home Inspections — American Society of Home Inspectors
• A Brief Guide to Mold, Moisture and Your Home — U.S. Environmental Protection Agency
• Seal and Insulate with ENERGY STAR — ENERGY STAR
• Methodology for Estimated Energy Savings from Air Sealing and Insulating — ENERGY STAR

Seeing stains under a window or streaks down the stucco on a home you are considering? Contact us for a referral to a Front Range inspector who can look for the clues of hidden wall leaks.