Door Glazing Calculator

Under Approved Document K (2013 edition, for use in England) Section 5 Diagram 5.1, safety glass must be used in (a) any glazing in a door that is wholly or partially within 1500 mm of floor level, (b) any glazing in a side panel within 300 mm of the door edge that is within 1500 mm of floor level, and (c) other wall, partition or window glazing within 800 mm of floor level. Door and side-panel glazing uses the 1500 mm rule, not the 800 mm low-level rule — this is a common source of non-compliance. Safety glass means toughened to BS EN 12150 or laminated to BS EN 14449. Per AD K para 5.4 it must satisfy Class 3 of BS EN 12600 (equivalent to Class C of the now-withdrawn BS 6206); for a door or side-panel pane wider than 900 mm the lesser Class 2 of BS EN 12600 (Class B of BS 6206) is permitted. Note that the letters A, B and C are BS 6206 grades — under BS EN 12600 they correspond to numeric Classes 1, 2 and 3 respectively.

Toughened glass is 4-5 times stronger than annealed glass and breaks into small, relatively harmless fragments. Laminated glass has a PVB interlayer that holds fragments together when broken, providing better security and sound insulation. For front doors, laminated is preferred for security. For internal doors, toughened is common due to lower cost. BS 6262-4 gives guidance on glass selection.

Measure the aperture (rebate to rebate) and deduct the beading overlap on each side, typically 8-12mm per side. For a 500mm aperture with 10mm beading overlap, the glass size would be 480mm. Always measure at three points and use the smallest dimension. Allow 2-3mm clearance for thermal expansion in dark-coloured doors.

As an indicative glazier rule of thumb for typical domestic door panels: small panels (under 0.5m²) often use 4mm toughened; medium panels (0.5-1.5m²) 6mm toughened or 6.4mm laminated; large panels (1.5-2.5m²) 8mm toughened or 8.8mm laminated; full-height glass doors 10mm toughened or 11.5mm laminated. These bands are a conservative starting point, not a code requirement — Approved Document K and BS 6262-4 cover the impact CLASS the glass must achieve, not a fixed thickness, because the actual thickness needed depends on the wind or barrier loading and the unsupported span rather than area alone. Always confirm the thickness with your glass supplier for the real loadings.

Yes, but it must still be safety glass in critical locations. Decorative obscure glass is available in toughened form that satisfies Class 3 of BS EN 12600 (equivalent to Class C of the older BS 6206). Popular patterns include Cotswold, Flemish, Autumn, and Contora. For composite doors, decorative cassettes with internal Georgian bars and an obscure outer pane are common. Ensure any decorative glass meets the BS EN 12600 class required by Approved Document K for its location.