Product Application
Window Sill
BELCO XT® Sill Stock
Reliable Materials for a Vulnerable Location
FORM MEETS FUNCTION
Beveled and Relief Cut for Additional Protection
INSTALLATION BEST PRACTICES
Application & Installation Information
COMMON SIZES
Sill Stock Size
- 2x3
COMMON MATERIALS
Window Sill Material Options
Selecting the right window sill material is important for both functional benefits and aesthetic continuity. Some common material options like cedar and pressure-treated wood each come with drawbacks. Cedar, while naturally resistant to moisture and insects, tends to bleed extractives that can cause staining. It has also become increasingly expensive, prompting many to seek alternatives. Pressure-treated wood, on the other hand, offers resistance to decay but often suffers from warping, splitting, and instability over time. Some pressure-treated varieties can also leach chemicals, making them less appealing for environmentally conscious builders and homeowners.
Belco XT sill stock is made from preservative-treated wood, and provides a superior alternative. It combines the beauty of real wood with enhanced durability, thanks to a non-toxic preservative treatment that resists rot and insect damage without harmful chemical leaching. Factory primed and ready for installation, Belco XT ensures a high-quality, low-maintenance solution that integrates perfectly with timeless real wood window trim designs.
THE BELCO DIFFERENCE
Built to Last
Belco XT sill stock offers long-lasting performance thanks to our proprietary 2-step treatment process. First, Belco’s non-metallic, EPA-approved wood preservative treatment (Wolman® AG) penetrates the wood fibers and is then properly dried before priming. This key distinction is what sets us apart, ensuring our wood is fortified from within. Our proprietary, industry-leading water-based primer protects the surface and resists water penetration. The end result? Window sill products with unmatched durability that exceed the highest industry standards for coating consistency and wood substrate quality.
PROTECT YOUR INVESTMENT
Belco XT® Window Sill Stock is Backed by an Industry-Leading Warranty
We wholeheartedly stand behind the quality of our products. We go the extra mile when it comes to ensuring the longevity of our products. Belco XT sill stock is a durable one and done anti-rot solution that undergoes a proprietary two-step treatment process to protect the wood against damage from moisture, decay, and insects. Our products are so durable and long-lasting that they come with an industry-leading, non-prorated 20-year warranty. Protect your investment by registering your products with us after purchase.
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FAQs
Window sills sit at one of the highest-exposure points on the exterior envelope. They take the brunt of rain, snow, and wind-driven moisture, as well as splash-back from below. Because the sill projects outward, water naturally collects or slows across the surface, making it prone to swelling, end-grain saturation, and eventual rot if the material or installation is not properly engineered. This combination of exposure, geometry, and gravity makes the window sill one of the most moisture-sensitive components in an exterior trim system.
Belco XT window sill is engineered with a 15-degree beveled top that promotes rapid water shedding rather than allowing moisture to sit or puddle. The underside includes a relief cut (drip kerf) designed to prevent water from wicking back toward the wall or into adjoining trim components. Each sill is preservative-treated with Wolman® AG, kiln-dried, and factory-primed on all six sides, creating a triple-protection system that resists rot, insects, and moisture intrusion far more effectively than untreated or field-primed wood.
For best performance, Belco XT sills should be installed with the beveled face oriented outward, ensuring proper drainage away from the window. Maintain recommended clearances from siding and other horizontal elements, and always incorporate flashing above the sill to redirect water. All field cuts must be sealed with 100% acrylic latex primer, and the installed sill must be finished with two coats of high-quality exterior acrylic latex paint within 60 days of installation. Using corrosion-resistant fasteners and ensuring solid backing at all fastening points helps maintain long-term stability and prevents twisting or cupping. For more information, refer to the Belco Installation Guide.
Compared to cedar, Belco XT sill stock offers greater consistency, fewer defects, and enhanced resistance to moisture due to preservative treatment and full-coverage factory priming. Unlike pressure-treated wood, which is often wet, heavy, and difficult to finish cleanly, Belco XT products are dimensionally stable and ready for paint upon arrival. Builders gain a cleaner installation, better paint adhesion, and fewer callbacks for movement or premature surface failure. Dealers benefit from reduced cull rates and a product line that delivers reliable, repeatable performance.
