Casement windows come in two main styles: flush and lipped (also called stormproof). Both are variations on the classic outward-opening window, but they differ in appearance and performance. Understanding these differences helps you choose the right timber casement windows for your property, whether you’re replicating a historic look or seeking maximum weather protection.
Defining the Two Styles
Flush Casement Windows:
In a flush casement, the sash sits level with the outer face of the frame when closed, creating a flat, seamless look. This is the traditional style used in many period homes. It’s especially appropriate for conservation areas or listed buildings where authenticity is paramount.
Lipped (Stormproof) Casement Windows:
Here, the sash slightly overlaps the frame. This creates a visible “lip” and enhances weather resistance. The overlapping design is a more modern innovation aimed at improving sealing against wind and rain.
Visual and Aesthetic Differences
Flush casements have a clean, elegant appearance with slim sightlines. They’re ideal for traditional wooden windows in historic settings, maintaining the delicate proportions of original joinery. Lipped casements look slightly chunkier but can suit modern properties or those in exposed locations.
Weather Resistance and Sealing
Both types can be highly weather-tight when built correctly, but lipped casements inherently offer better protection against driving rain. Compression seals combined with the overlapping design create a robust barrier. That said, modern flush casements with advanced seals can also achieve excellent performance while preserving the traditional look.
Energy Performance Implications
The difference in thermal performance between flush and lipped designs is marginal when using high-quality materials and glazing. Timber casement windows with double or triple glazing and good seals will deliver strong energy efficiency regardless of style. The choice is more about aesthetics and site exposure than raw insulation values.
Maintenance Demands
Maintenance is similar for both styles. Keep frames clean, check seals, lubricate hinges and refinish timber as needed. Because flush casements have slightly slimmer profiles, they may require a little more care in exposed climates. However, engineered timber and factory finishes mitigate this.
Cost Comparisons
Lipped casement windows may cost slightly more due to extra material and hardware, but the difference is usually minor. Bespoke design, glazing type and finish have a bigger impact on price than the basic style.
What Contexts Suit Each Best
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Flush Casement Windows: Best for period homes, conservation areas, or anyone seeking a traditional look. Ideal when authenticity and slender sightlines are priorities.
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Lipped (Stormproof) Casement Windows: Great for modern homes, properties in exposed or coastal locations, or homeowners prioritising maximum weatherproofing.
Combining Styles
Some homeowners mix styles—for example, using flush casements on the front façade for a heritage appearance and lipped casements at the back for added protection. Because both can be made from the same timber and finish, the overall look remains cohesive.
Both flush and lipped timber casement windows have their merits. Flush designs offer traditional beauty and slim sightlines, while lipped casements provide extra weather defence. By considering your property’s style, location and performance needs, you can select the traditional wooden windows that best meet your goals.