Siding is the visible exterior finish, but it is not the wall’s only protection against water. A properly integrated water-resistive barrier and flashing system helps direct moisture away from the sheathing while supporting a flatter, better-looking finished exterior.

Exterior Wall and Siding Guide

The Wall Behind the Siding: Why the Water-Resistive Barrier Matters

Gentek shakes and scallops create the visible beauty of an exterior, but the finished panels are only one part of the wall. Behind them, a properly detailed water-resistive barrier and flashing system helps direct water away from the structure.

Homeowners naturally focus on siding color, texture and profile. Those choices determine how the exterior presents itself to the neighborhood and how well it complements the architecture.

A knowledgeable contractor must look deeper. The success of a siding project also depends on the layers underneath the visible finish. If the drainage plane is incomplete, poorly integrated or damaged, an attractive exterior can conceal a vulnerable wall.

This is why a re-siding project should be approached as work on the complete wall assembly—not simply as replacement of the outermost surface.

What Is a Water-Resistive Barrier?

A water-resistive barrier, commonly abbreviated as WRB, is a layer installed behind exterior cladding to help protect the wall assembly from liquid water. Housewrap and certain building papers are familiar examples, although the appropriate product and detailing depend on the wall design and applicable requirements.

The National Association of Home Builders describes the WRB as a drainage plane that helps protect the assembly from water that gets behind the exterior veneer, including wind-driven rain.

The key word is system. A roll of housewrap attached to a wall is not automatically a complete drainage system. Seams, openings, penetrations, transitions and flashing must work together so water is directed outward.

Siding and the WRB Have Different Jobs

Wall component	Primary role	What it should not be expected to do alone
Exterior siding	Sheds much of the weather, protects underlying layers and creates the visible architectural finish	Provide the wall’s only defense against liquid water
Water-resistive barrier	Provides a drainage plane behind the cladding	Replace exterior cladding or correct improperly detailed openings
Flashing	Directs water around openings, intersections and vulnerable transitions	Work effectively when isolated from the surrounding drainage plane
Sealant	Seals selected joints where specified as part of a complete detail	Substitute for proper flashing, lapping and drainage

Why Water Can Get Behind Siding

An exterior wall contains many joints and interruptions. These are normal parts of construction, but each one must be considered in the water-management plan.

Panel joints and overlaps
Outside and inside corners
Windows and doors
Roof-to-wall intersections
Light fixtures and electrical receptacles
Exhaust vents, plumbing penetrations and utility connections
Transitions between siding, masonry and other cladding materials

Wind can push rain against these locations and into small openings. A well-planned assembly accepts that incidental water may pass the cladding and provides a path for it to move back toward the exterior.

How the WRB Relates to the Finished Appearance

Water management may sound separate from exterior design, but the two are closely connected. Moisture-related damage behind siding can affect the flatness and stability of the surface supporting the finished panels.

A straight, sound substrate helps shake courses remain level and allows trim to sit cleanly around windows, doors and corners. Damaged or uneven sheathing can contribute to waves, irregular shadows and poorly aligned transitions.

The visual quality of a shake installation therefore begins before the first visible panel is fastened. Careful work behind the siding helps protect both the building and the intended design.

Why Proper Lapping Matters

Water-management layers should generally be arranged so upper materials direct water over the face of lower materials. This is often described as shingle-fashion installation.

The concept is similar to roof shingles: water flowing downward should continue onto the next outward-facing layer. An incorrectly reversed lap can direct water behind the drainage plane instead.

Project-specific sequencing must follow the applicable manufacturer instructions and construction details. The basic principle, however, is easy for homeowners to understand: gravity should help the wall drain rather than carry water deeper into the assembly.

Windows and Doors Require Special Attention

Windows and doors interrupt the drainage plane and create multiple horizontal and vertical joints. Flashing should collect and redirect water while connecting properly to the surrounding WRB.

NAHB guidance notes that window and door flashing should be installed in shingle fashion and extend appropriately to the exterior finish or the water-resistive barrier, depending on the wall assembly.

Attractive window trim cannot compensate for deficient flashing. The visible surround and the concealed water-management details should be planned together so the opening looks finished and performs as part of the wall.

Do Not Depend on Caulk Alone

Sealants are commonly used around exterior openings and accessories, but a bead of caulk should not be mistaken for a complete flashing strategy.

Exposed sealants can age, lose adhesion or separate as materials move. A durable wall detail should still manage water if an exterior sealant joint requires future maintenance.

When reviewing a proposed siding project, ask how water will be directed away from an opening—not simply whether the contractor intends to caulk around it.

What Should Happen During a Re-Siding Project?

The exact scope depends on the existing wall and whether the old cladding is removed. When the wall becomes accessible, the project team should evaluate conditions before covering them again.

Inspect the substrate. Look for damaged, soft, uneven or visibly deteriorated areas.
Identify previous water paths. Staining and deterioration may point to a roof, flashing or penetration problem that should be corrected.
Review the existing WRB. Determine whether it is present, continuous and suitable for integration with new work.
Plan openings and transitions. Windows, doors, roof intersections, masonry and fixtures should not be treated as afterthoughts.
Complete the drainage details. Install and integrate the specified WRB, flashing, tapes and accessories according to the approved design.
Install the exterior cladding. Follow Gentek’s current requirements for the selected profile and accessories.

Warning Signs That Deserve Investigation

These conditions do not prove that the WRB has failed, but they justify a closer inspection before new siding is installed:

Soft or deteriorated material beneath removed siding
Repeated staining below windows or roof intersections
Interior staining near exterior openings
Loose or visibly distorted sheathing
Missing or reversed flashing
Housewrap that is torn, incomplete or poorly integrated with openings
Exterior fixtures attached without clear mounting and drainage details

Questions to Ask Your Siding Contractor

Will the wall sheathing be visible and inspected during the project?
What type of water-resistive barrier is specified?
How will WRB seams, tears and penetrations be treated?
How will window and door flashing connect to the WRB?
What is the plan at roof-to-wall intersections?
How will lights, vents, outlets and utility penetrations be mounted and flashed?
What happens if concealed water damage is discovered?
Which current Gentek instructions and local code requirements apply?

Housewrap, Air Sealing and Insulation Are Not Interchangeable

Homeowners sometimes assume that any layer installed beneath siding must be insulation. That is not correct. A water-resistive barrier, air-control layer and thermal-insulation layer perform different functions, even when one product or assembly contributes to more than one objective.

Gentek Fairhaven Sound shakes should not be assigned an insulation value unless product-specific documentation provides one. If insulation or air-sealing improvements are being considered during re-siding, they should be designed and documented separately as parts of the complete wall assembly.

Protect What the Finished Siding Will Hide

Gentek shakes and scallops can create a warm, dimensional exterior, but their appearance is only the visible conclusion of the project. The work behind the panels determines whether the new finish is being installed over a sound, properly managed wall.

A good project respects both sides of the exterior: the color, texture and proportions people see, and the drainage, flashing and preparation they do not.

Suburban Wholesale & Supply helps exterior professionals identify Gentek siding, trim and accessory materials for Quad Cities projects. Visit us at 3602 North Harrison Street in Davenport, Iowa, to discuss current product options.

This article provides general educational information. Water-management details must be selected and installed for the actual building, manufacturer requirements and governing jurisdiction.

Sources and Technical References

Gentek Building Products: Fairhaven Sound Single Select Shakes & Scallops
Gentek 2026 Product Directory
National Association of Home Builders: Rain and Groundwater Management
National Association of Home Builders: Window and Door Flashing
U.S. Department of Energy Building Science Education: Continuous Rigid Insulation Sheathing and Siding
Installation and code requirements vary with the wall assembly and project location. Verify current manufacturer instructions and local requirements before construction.

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