Warranty-Backed Composite Siding Installation in Greater Seattle

What Is Composite Siding?

Composite siding is a broad category that encompasses any engineered siding product that combines multiple materials — typically wood fiber, resins, polymers, and additives — to produce a product with characteristics superior to natural wood in key performance areas. The most common composite siding types include:

• Fiber cement siding — a blend of Portland cement, sand, and cellulose fiber (see our dedicated fiber cement and Hardie Board pages for full coverage of these products)
• Engineered wood siding — wood fiber and wax or resin binders, producing a product that looks like natural wood with improved moisture resistance (LP SmartSide is the leading brand — see our dedicated LP SmartSide page for full coverage)
• Polymer/PVC composite siding — fully synthetic products with no wood fiber content, offering maximum moisture resistance and zero rot risk
• Wood-plastic composite siding — a blend of wood fiber and plastic resins, positioned between engineered wood and PVC composites in terms of composition and performance

This page covers the composite siding category broadly, with specific attention to polymer and wood-plastic composite systems. Fiber cement (including Hardie Board) and LP SmartSide engineered wood are covered in their own dedicated pages.

Why Composite Siding Performs Well in Greater Seattle

Greater Seattle’s combination of sustained rainfall, moderate temperatures, and high humidity creates specific demands for siding materials. Composite siding addresses the most common failure modes of natural wood siding in this climate:

• Reduced moisture absorption — composite products absorb significantly less water than natural wood, reducing the swelling, shrinking, and eventual rot that affects untreated or poorly maintained wood siding
• Dimensional stability — composite materials maintain their shape through Greater Seattle’s wet-dry seasonal cycles better than natural wood, reducing paint cracking and joint separation
• Rot resistance — composite siding does not rot, regardless of moisture exposure, making it suitable for the consistently damp conditions of the Pacific Northwest
• Insect resistance — composite materials do not provide a food source or harborage for carpenter ants, termites, or other wood-boring insects common in Greater Seattle’s wooded environment

Composite Siding Installation Details That Matter in Greater Seattle

Weather-Resistive Barrier

The weather-resistive barrier (WRB) — house wrap or building paper installed behind the siding — is the critical moisture management layer in any siding system. In Greater Seattle’s wet climate, the WRB must be properly lapped, taped at seams, and integrated with window and door flashings to create a continuous plane of water resistance behind the siding. We install WRBs to the detail level required by the climate, not the minimum required by code.

Proper Clearances and Drainage

Composite siding must be installed with proper clearances from horizontal surfaces — decks, roof planes, and grade — to prevent moisture wicking at the bottom edge of the siding system. Inadequate clearance is one of the most common sources of premature composite siding failure. We assess existing conditions and ensure clearances meet manufacturer requirements before installation begins.

Joint and Seam Management

Butt joints, corner treatments, and window and door trim integration are the most vulnerable points in any siding system. We use appropriate joint treatments — caulking, flashing tape, or trim components specified by the siding manufacturer — at every seam and transition to prevent water infiltration.

Fastening to Manufacturer Specifications

Composite siding products have specific fastener requirements — size, spacing, penetration depth, and fastener material — that differ by product. Incorrect fastening causes siding to buckle, pull away from the substrate, or void the manufacturer’s warranty. We follow manufacturer fastening specifications on every installation.

Common Composite Siding Problems in Greater Seattle — and How We Address Them

Moisture Infiltration at Penetrations

Even composite siding that performs well across its field area can allow water infiltration at utility penetrations, light fixtures, hose bibs, and electrical boxes that weren’t properly sealed at installation. We assess all penetrations and apply appropriate flashing and sealant at every opening in the siding system.

Paint and Finish Adhesion Failure

Most composite siding products require paint or a factory-applied finish system to provide the final barrier against moisture. Paint that peels or fails on composite siding is most commonly caused by surface contamination at installation, inadequate primer, or the use of paint products not rated for the specific composite substrate. We prepare composite surfaces per manufacturer specifications and apply appropriate coatings.

Bottom-Edge Deterioration

The bottom edge of composite siding panels, particularly if installed too close to a horizontal surface or with inadequate clearance from grade, can absorb capillary moisture from wicking, leading to delamination or swelling at the butt. Proper clearances and a correctly installed bottom-edge starter strip prevent this failure mode.