6.7.5 Glazing
The method of glazing shall ensure adequate in-service performance. Issues to be considered include:
- standards
- performance requirements
- insulating glass units
- glazing systems
- condition before installation
- site glazing.
Standards#
Glazing and materials should conform to relevant British Standards as shown in Table 2.
Table 2: Relevant British Standards for glazing
| Standard/ Specification Number | Standard/ Specification Name |
|---|---|
| BS EN 1279-5 | Glass in buildings - Insulating glass units - Part 5: Product standard |
| BS EN 572-9 | Glass in buildings – Basic soda lime silicate glass products – Part 9: Product standard |
| BS EN 14449 | Glass in building – Laminated glass and laminated safety glass – Product standard |
| BS EN 12150-2 | Glass in building – Thermally toughened soda lime silicate safety glass – Part 2: Evaluation of conformity/ Product standard |
| BS EN 1096-4 | Glass in building – Coated glass – Part 4: Evaluation of conformity/ Product standard |
Performance requirements#
Glazing should be selected to meet applicable design and performance requirements in accordance with BS 6262-1.
The type, thickness and size of glass should be selected to provide an appropriate degree of safety, considering the intended use.
Safety glass for use in critical locations (including glazed shower/bath screens) should be marked as follows:
- manufacturers trademark or name
- the standard number for the type of glass eg BS EN 14449 laminated glass
- the impact performance classification eg 1,2,3 to BS EN 12600.
Notes
Further guidance on safety marking of glass is provided in technical guidance note TGN 6.7/17.
The design loads acting upon the glazed area should be determined in accordance with BS EN 199111, BS EN 199113 and BS EN 199114. The type, thickness and size of glass should be specified to suit the design wind loads.
To improve thermal performance and minimise condensation formation around the perimeter zone of glass, glazed units with spacer bars of low thermal conductivity should be specified.
Insulating glass units#
Insulating glass units should:
- be CE/UKCA marked in accordance with BS EN 1279
- hold appropriate third-party certification eg BSI Kitemark
- be checked to ensure they comply with the design, including glass type, gas filling, edge seal type and dimensions
- have a dual seal or a single seal of hot melt butyl and desiccant in at least one long and one short section of the spacer bar.
Notes
Further guidance on third-party certification schemes and marking of insulating glass units is provided in technical guidance note 6.7/16.
Glazing systems#
Drained and vented systems
Drained and vented systems should be used for site fixed insulating glass units (IGUs) and where units greater than 1m2 are used. These systems allow moisture that enters the glazing channel between the frame and the edge seal of the insulating glass unit to drain away and prevent long-term moisture contact with the edge seal.
To achieve the optimum service life of IGUs, the following basic principles should be adopted in the design of drained and vented systems:
- Removal of moisture: Frames should have adequate drainage and ventilation through holes, slots, or channels for the rapid removal of any water that may enter the glazing rebate
- Clearance: A minimum 5mm edge clearance should be provided between the glass edge and frame to prevent frame-to-glass contact, ensure drainage, and allow for differential thermal expansion of the IGU and frame. For very well drained and ventilated frames, the clearance can be reduced for the side and top rebates, to a minimum of 3mm in the case of glass lengths up to 2m
- Edge cover: A minimum edge cover of 12mm should be provided to keep the spacer below the sight line and to protect the edge seal from sunlight
- Rebates: The rebate height should allow for tolerances in both the frame size and IGU size to ensure the minimum edge clearance and minimum edge cover requirements are met. The width of the rebate platform should provide the required front, back clearances, and ensure sufficient contact of the glazing beads onto the platform. The width of the rebate platform should be equal to the sum of the front and back clearances, the nominal thickness of the IGU, the width of the bead, and an allowance for the tolerances on IGU and bead thicknesses
- Beads: Beads should have an installed height equal to the rebate height. Timber beads for timber frames should have a width in contact with the rebate platform greater than the height, to enable firm fixing of the bead to be achieved. The bottom bead should project slightly past the rebate edge. Screw fixings for timber beads should be located a minimum of 75mm from each corner and spaced at no more than 200mm centres. If pins are used, they should be twice the height of the beads and located a minimum of 50mm from each corner and spaced at no more than 150mm centres. Beads for metal and plastic frames should be fixed in accordance with manufacturers recommendations to securely retain the IGU and the glazing seals
- Compatibility: Glazing material should be compatible with frame finishes and glazing unit seals in accordance with manufacturers recommendations. Linseed oil-based putty should not be used in the installation of laminated glass or insulating glass units.
Fully bedded systems
Fully bedded systems are acceptable for factory glazing only where the insulated unit is less than 1m2, and should:
- comply with the relevant parts of BS 8000, BS 6262 and BRE Digest 453
- not have gaps around the perimeter of the insulating glass unit.
Condition before installation
When insulating glass units are stored prior to being installed they should be:
- protected from direct sunlight to avoid thermal stress
- stored in dry conditions
- provided with adequate support to prevent distortion or bowing.
A visual inspection of glass and insulating glass units should be undertaken for signs of defects which could lead to premature failure. Signs of defects include:
- water accumulation between sheets
- edge damage or scratching.
Site glazing
Site glazing should be in accordance with the frame design and undertaken by installers who are appropriately trained and conversant with good glazing practice.
The following features should be checked before glazing:
- drainage and ventilation holes or slots are present, are of a suitable size, and are free from obstructions such as fabrication swarf, etc
- ventilation and the free flow of water to holes and slots are not impeded by setting and location blocks, external bead retention lips, or glazing materials
- as water can be present in the glazing rebate, screw fixing holes and frame joints are adequately sealed against water ingress
- a minimum 5mm edge clearance is provided around the permitter of the insulating glass unit to prevent glass to frame contact, to ensure drainage and allow for differential thermal expansion
- gaskets or strip materials supplied cut to size are the correct length to ensure that there are no gaps at the corners.
Notes
Further guidance on system design and glazing considerations for insulating glass units is provided by the Glass and Glazing Federation.
Last updated: 2nd January 2024