20 8 月, 2025
When it comes to the long-term performance of UPVC windows and doors, one detail makes a huge difference: how the bottom frame is secured. It might sound technical, but getting this right is what separates high-performing installations from ones that eventually leak, draft, or fail.
The golden rule? Fix the bottom frame from the inside with one-sided fixing brackets. Why inside? Because this method significantly improves watertightness—the ability to keep rain and moisture out. The bottom frame seam is the most critical area when it comes to preventing water infiltration.
Here’s what happens in real-world conditions: UPVC profile expands and contracts with temperature changes. When the bottom frame is firmly fixed from the interior, it remains stable and resists moving perpendicular to the window plane. This allows the top and sides to absorb most of the thermal movement instead. A loosely fixed or elastic fixing design at the bottom would be a weak point—it could lead to micro-movements, gradually breaking the seal.
That’s why the goal is to keep the bottom frame as stable as possible. Any flex or bounce here directly threatens the silicone sealant along the frame. Once this seal is compromised, water seeps in—often hidden from view—leading to potential damage to the structure and insulation.
Therefore, a rigid, one-sided interior fixing isn’t just a recommendation; it’s a best practice for protecting the integrity of the sealant over decades. By locking the bottom frame in place, we ensure the silicone stays intact, doing its job year after year, through summer heat and winter cold.
In short: Stable bottom frame = lasting seal = dry and efficient windows. It’s a small design choice with a giant impact on performance.