Cantilevered Glass Guard on a Residential Stair
A homeowner is finishing a basement stair in a single-family house. The stair opening is guarded by a glass guard 1100 mm high above the finished floor. The design uses 12 mm fully tempered glass panels, 1200 mm wide, cantilevered from a continuous aluminum base shoe anchored to the floor. There is no top rail. The panels are separated by 20 mm vertical joints, and the bottom edge of the glass sits 150 mm above the floor because the base shoe is mounted on a raised curb. The homeowner wants an “open” look and asks the glazier to omit the top rail and to use the glass as the only guard. The local inspector has flagged the installation, citing the gap at the bottom and the lack of engineering for the glass. The glazier has a copy of the manufacturer's base-shoe test report for 12 mm tempered glass, but the report is for a 1000 mm guard height with a top rail.
1. Identify the code-related and structural concerns with this guard.
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The guard has several problems. The 150 mm gap at the bottom is a code concern because guard openings must not permit passage of a 100 mm sphere; a 150 mm gap can allow a small child to slip or become trapped. The 20 mm vertical joints are not the main issue, but all openings must be checked against the sphere rule. The guard height of 1100 mm is generally acceptable for a residential guard, but the structural system is not proven. A cantilevered glass guard with no top rail relies entirely on the base shoe and glass bending strength. The manufacturer's report covers a 1000 mm guard with a top rail, which is a different condition: the top rail distributes load and reduces glass deflection. Using that report for a 1100 mm cantilevered guard is an extrapolation beyond the tested configuration. The glass thickness, panel width, anchor spacing, and base-shoe stiffness must be engineered for the required guard load and deflection limit. The inspector is correct to require project-specific engineering or a tested system.
2. What does the manufacturer's test report cover, and can the glazier rely on it for this installation?
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The report covers a specific tested assembly: 12 mm tempered glass, a 1000 mm guard height, and a top rail. Test reports are limited to the tested configuration, including glass type and thickness, panel size, base-shoe design, anchor type and spacing, substrate, and the presence of the top rail. The proposed installation differs in at least three ways: the guard is 1100 mm high, there is no top rail, and the panel width and curb detail may differ. The glazier cannot rely on the report unless the manufacturer confirms in writing that the proposed configuration is within the tested scope or provides a new engineering evaluation. A generic statement that “12 mm tempered glass is strong enough” is not a substitute. The glazier should request a project-specific engineered design with load calculations, deflection criteria, anchor design, and installation details, or install a tested system that matches the report.
3. Propose acceptable solutions that preserve as much of the open look as possible.
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Several options can satisfy the code and structural requirements while keeping the guard visually light:
- Add a top rail: A slim metal top rail tied to the glass or to the structure can distribute loads and may bring the assembly closer to the tested report, but the height and panel size still need confirmation.
- Reduce the bottom gap: Lower the base shoe or add a solid infill at the bottom so no opening exceeds the 100 mm sphere limit. The guard must still be structurally independent of the stair treads.
- Use a tested cantilever system: Select a base-shoe and glass system specifically listed for the required guard height without a top rail, and install it per the manufacturer's instructions.
- Increase glass thickness or use laminated glass: If engineering shows that 12 mm tempered is insufficient, a thicker or laminated glass may be required. Laminated glass also provides retention after breakage.
- Obtain engineering: The glazier should not proceed on verbal approval. A sealed design should confirm glass stress, deflection, anchor pull-out, and edge clearance.
The best solution is usually a tested system with a minimal top rail or a specifically engineered cantilever base, plus correction of the bottom gap.