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The consensus that ‘glass is perfect’ is untrue, no piece of glass will be completely perfect, however, Glazing Vision rooflights are of higher quality than others on the market as we examine to The Hadamar Standard as opposed to the GGF Standard, which many of our competitors use.

Glazing Vision places its customers at the heart of everything it does, therefore customer satisfaction is of utmost importance.

We want you to love your rooflight for its entire lifecycle, so we carry out multiple tests on every Glazing Vision off-the-shelf rooflight to ensure that your end product is of the highest standard possible. 

One of the very first tests that we undertake is the Glass Quality inspection, when we receive the glass for your rooflight from our carefully-vetted suppliers, our team undertakes many visual tests adhering to the Hadamar Standard as opposed to the GGF Standard that most other rooflight manufacturers adhere to.

What is the Hadamar Glass Standard?

Hadamar releases the ‘Guideline to Assess the Visual Quality of Glass in Buildings’ technical manual which outlines the acceptable visual qualities of glass used in rooflights and windows.

The technical guidelines released by Hadamar are evidently more stringent than those released by GGF, Hadamar allows less visual discrepancies and requires the inspection to take place at a closer distance.

Why do we use Hadamar?

Glazing Vision always operates to the highest possible standard and aims to exceed customer expectations, therefore we operate to Hadamar as opposed to Glass & Glazing Federation (GGF) as it is more stringent and allows fewer defects in the glass.

The GGF Standard dictates that visual inspections are carried out from a distance of three meters, whereas Hadamar requires the distance to be only one meter, being two meters closer allows our well-trained team to identify any defects and not miss them from being too far away.

Due to the nature of the rooflights that we produce, we are required to adhere to much stricter standards as the sleek design of our products means that the perimeter edges are visible due to not having caps on the corners, unlike many of our competitors.

This is what makes us a cut above the rest, we have the customer in mind at every stage of the process.

The allowable glass defects of GGF and Hadamar 

The visual inspection of the glass is required to be completed in natural daylight conditions (But not in direct sunlight) and the rooflights need to not have any visible moisture on the surface.

When comparing the two standards, it is evident that Hadamar is more stringent in terms of the visible defects that it deems as a ‘pass’ which in turn, results in a rooflight of higher quality.

Firstly, GGF does not require testing to take place on the first 50 mm of glass, however, this is required to be tested by Hadamar, therefore any faults in that area are identified, if the faults in this area are mechanical faults, the glass is rejected, which may not happen under GGF as the area is disregarded.

The GGF Standard allows more sizable defects to be passed whereas the Hadamar Standard requires these defects to be much smaller. For example, a spot with a diameter of 2 millimeters (mm) is not allowed under Hadamar, whereas GGF allows up to 3 of these spots.

Similarly, for spots that are less than 1 mm in diameter, Hadamar allows three in each 20 cm diameter area whereas GGF enforces no limitation of how many there can be in a 20 cm diameter. 


The consensus that ‘glass is perfect’ is untrue, no piece of glass will be completely perfect as visual discrepancies will always be present. However, Glazing Vision operating to The Hadamar Standard as opposed to the GGF Standard means that your Glazing Vision rooflight will be of higher quality and a considerable amount less visual imperfections, due to the Hadamar Standard allowing much less sizeable scratches, spots and residues.

The quality control of our glass is much more rigorous than our competitors who use the GGF standard, therefore you can rest assured that your rooflight has been checked and held against the highest industry standard.

“No piece of glass is perfect but Glazing Vision demand glass quality that is over and above the industry standard in the UK and work tirelessly with our chosen glass suppliers to maintain that standard. Regular manufacturer visits give us extra insight and knowledge to inspect glass with confidence and our vertical glass inspection stands allow each piece to be individually inspected to our exacting criteria in diffuse daylight conditions. There are no computers or cameras doing our inspections, just our well-trained, meticulous and dedicated staff” – Michelle Rolph, QSHE Manager