We always ensure we follow the Glass and Glazing Federation (GGF) Code of Good Practice, which sets out standards covering the sales process, materials, aftercare and more.
As you would expect, glass manufacturing is a complex and specialised process. We believe there needs to be more awareness of industry standards and the allowances they make for certain characteristics within the glass itself.
Glass is effectively for looking through, not at, so it should be inspected in that way, as the guidelines outline. End users should be advised about these standards where possible, as well as the nature of the glass manufacturing process, through which very small blemishes can occur.
We have outlined some of the key points from the Code of Good Practice below.
Sealed units
The glass used to produce sealed units is the same as the glass used in single glazing.
Viewing sealed units for scratches on the outer faces of the panes must be carried out before any rendering, plastering or other works adjacent to the glazing takes place, and as early as reasonably practicable following installation.
Glass and Glazing Federation Code of Good Practice
How to carry out a professional inspection
To carry out a professional-standard inspection, stand inside the room no less than 3 metres away from the sealed unit and look directly through it. When inspecting toughened, laminated or coated glass, you should also stand no less than 3 metres away.
The guidelines allow you to stand as far away as possible if the room does not permit the full inspection distance.
Inspections should be carried out in natural daylight, but not while looking directly towards the sun. There should be no visible moisture on the surface of the glass. View the glass at an angle of 90 degrees and exclude a 50mm-wide band around its edge. Glass should not be inspected using artificial light or torchlight.
Professional inspection explained
- View the glass from inside the room, standing a minimum of 3 metres away and facing the glass. In normal everyday situations, people usually look through windows from a distance rather than from close up, such as within 6 inches of the glass.
- Look through the glass, not at it. The glass is there to provide a view beyond the window rather than to be examined as a surface.
- Do not inspect it in direct sunlight. Direct sunlight can be refracted by a coating or tiny imperfections in the glass surface, highlighting things that cannot be seen under normal conditions.
- Ensure the glass is clean and dry inside and out. Rain, dust or condensation can be confused with potential problems and make the glass impossible to assess properly.
- Ignore the 50mm perimeter of the glass. When looking through windows, the eye is normally drawn to the central area rather than the edge of the glazing. Large, obtrusive marks within the perimeter are, of course, not acceptable.
What to expect when carrying out an inspection
GGF guidelines specify that flat, transparent glass, such as laminated, toughened or coated glass, is acceptable if the following are neither obtrusive nor bunched:
- Bubbles or blisters
- Fine scratches no more than 25mm long
- Minute particles
An important point is that the obtrusiveness of a blemish should be judged while looking through the glass under natural light, not at it. Users should understand that the glass in a sealed unit is a processed product and, as a consequence, small blemishes can be expected.
The guidelines confirm that smears, fingerprints or other dirt on the faces of the glass, or extraneous material within the cavity, are unacceptable if they are visually disturbing. More information is available in the GGF’s visual quality guidance and its information about insulating glass units.
Special glasses
A natural characteristic of toughened glass is that it may show visual distortions, which can be accentuated by reflections in sealed units. This is not a fault as such, but it can occur.
Laminated glass can have a few more blemishes because it is made up of several layers. Low-emissivity coatings can produce temporary visual effects. A coating may look like a transparent film or produce a haze in some lighting conditions. When lightly coloured objects, such as net curtains, are placed next to the glazing, the glass can look slightly darker.
Condensation
Sealed units will generally reduce the incidence of condensation, but users should be aware that it may still occur under certain conditions, such as high internal humidity or moisture levels within a room. Our guide to internal window condensation explains this in more detail.
Brewster’s fringes: the rainbow effect
Occasionally, small rainbow effects are produced by the refraction of light through the glass. This is caused by high-quality flat sheets of glass being placed parallel to each other.
Multiple reflections
Multiple reflections can occur in certain lighting conditions. They are caused by reflections from the multiple surfaces within sealed units and can vary from pane to pane.
If your glass was supplied or installed by us and you have a concern after carrying out the inspection above, please contact Clyde Windows. You can also learn more about our uPVC window installation service. For a disputed or complex case, the GGF offers an independent glass and glazing inspection service.
