Builder fitted a used Skylight

[TopFuel]

Hi All

We have a contractor building a kitchen extension at my late Mother's house. Included in the works is a skylight measuring approx. 40 x 100cms that has been fitted in the ceiling. Prior to this, my neighbour happened to notice that the sealed glass unit for the skylight had been used before as there was remains of silicon sealant around the edges. The thickness of the glass was only about 15mm so does anyone know what the current building regulations are that cover this?
Many thanks

 

[jeds]

Usual overall thickness of a modern sealed unit is 24mm. It may be slightly more or less but defo not 15mm.

 

[^woody^]

Some current Velux units are 16mm thick