Misted double glazing and replacement glass specifications

Is the condensation inside, outside or between the panes?

Moisture that can be wiped from the room-side surface is different from mist trapped between panes. External condensation can occur on well-insulating glazing. Persistent misting inside a sealed unit can indicate failure of its edge seal and needs investigation.

Before asking for a replacement, photograph the condensation and record where it appears and whether it clears. A leaking frame, blocked drainage route or failed perimeter detail can require a different repair from a failed insulating glass unit. Replacing glass alone will not necessarily resolve water entering around the opening.

References: Pilkington guidance on window condensation

IGU, DGU and glass build-up: what the numbers mean

IGU means insulating glass unit; DGU means double-glazed unit. A build-up written as 6 / 16 / 6 describes two 6 mm panes separated by a 16 mm cavity, giving a nominal overall thickness of 28 mm. This is an example of notation, not a recommended specification for a particular opening.

Thickness alone does not identify the glass. Two units with the same overall thickness can have different heat treatment, laminates, coatings, gas fill, spacer bars and edge-seal materials. A replacement needs the original specification or a properly assessed alternative.

• Overall dimensions, pane thicknesses and cavity width.
• Toughened, heat-strengthened or laminated glass where specified.
• Coating product and surface position; colour and reflected appearance.
• Spacer type, gas fill and edge-seal compatibility.
• Weight, support, edge cover, frame capacity and access for replacement.

Low-E, solar control, U-values and acoustic glazing

Low-emissivity (low-E) coatings reduce heat transfer. Solar-control glass manages incoming solar energy. Ug describes the thermal transmittance of the glass, while Uw describes the complete window; the two values should not be used interchangeably.

Acoustic performance depends on the whole glazing and frame arrangement, not simply on choosing a thicker pane. A replacement specification may need to preserve acoustic, thermal and solar performance as well as appearance. Ask for the existing glass schedule, O&M information or product identification before comparing options.

References: Pilkington low-E glass information

Toughened, laminated and specialist glass

Toughened glass and laminated glass describe different constructions. Laminated glass contains an interlayer between glass plies; toughening is a heat-treatment process. Some specifications combine both. A safety mark or a familiar appearance is not enough to reproduce a structural, overhead, guarding or fire-resistant glazing specification.

For high-rise glass replacement, record the installed unit weight, support details, access route and lifting constraints. Structural silicone glazing, overhead glazing and fire-resistant assemblies need system-specific assessment. Do not substitute a different glass build-up solely because it fits the frame.

What to send for a glass replacement enquiry

Send the building location, photographs of the whole opening and the defect, any visible glass marking or spacer-bar text, and the approximate size. Include the floor level and whether the area below is occupied. Measurements supplied by the client are useful for planning; final manufacture dimensions and specification need verification.

Our enquiry process can cover a single failed unit or a planned programme of façade glass replacements. The repair proposal should separate the glass specification, frame or drainage defects, access, installation and handover records so the scope is clear.