Flagship guide · 7 min read
U-Values and Thermal Performance Explained
The single figure most quoted in glazing brochures, and the one most often misunderstood. Here is what a U-value actually measures, and what to do with it.
Structural Glazing and Large Spans Explained
Slim sightlines on a large sliding door or frameless corner window are a structural engineering outcome, not just an aesthetic choice.
3 min read
Contemporary Lake District extensions increasingly ask for very large expanses of glass — multi-metre sliding doors, structural corner glazing with no visible post, and tall picture windows framing a view. Achieving this without excessive framing or unacceptable deflection is a genuine structural engineering question, not simply a matter of ordering a bigger pane.
This guide explains, in accessible terms, what governs the maximum size of a glazed opening and how corner glazing without a visible post is actually supported.
What limits the size of a single glazed panel
Three factors typically govern maximum panel size: the structural capacity of the frame to resist wind load and its own weight without excessive deflection, the maximum size the glass manufacturer can produce and safely transport as a sealed unit, and the weight the track, hinges or running gear can support in the case of sliding and bifold configurations.
- Typical max single glazed unit size
- Around 3.5m x 2.5m, system dependent
- Max panel weight, sliding door track
- Commonly 100–400kg per panel depending on system
- Wind load
- Calculated to BS EN 1991-1-4 for the specific site exposure
How frameless corner glazing is actually supported
A corner window that appears to have no supporting post at the junction of two glass panels is not, in truth, unsupported. The load is typically carried by a structural steel post concealed within the glazing bar or set back from the glass line, by toughened or laminated structural glass fins bonded at the corner, or by the glazing being bonded with structural silicone to a concealed steel subframe. Each approach has different implications for maximum span, cost and lead time.
- Concealed steel post within a slim glazing bar — most common, most cost-effective
- Structural glass fin at the corner — genuinely frameless appearance, higher cost
- Structurally bonded silicone glazing to a hidden subframe — used on the largest architectural spans
Deflection, wind load and why a survey matters here
Large glazed elements must be calculated to resist wind load without deflecting beyond limits that would compromise the seals or, in the worst case, the glass itself. This calculation depends on the specific site's wind exposure category, which is why a genuinely large glazing project on an exposed Cumbrian hillside needs a proper structural assessment rather than a standard catalogue configuration.
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