Installation guide

Through the years we have seen mistakes and poor practices in Skylight installations, which lead to many issues in the following months and years.

We feel obligated to share our experience and knowledge with you to avoid these issues. That’s why we have prepared a detailed “Step-by-Step Installation Guide” for a professional Skylight installation.

We can, and do guarantee the quality of the glazing unit itself, but we can’t take responsibility for the installation, it falls on the builder/fitter’s shoulders.

You are not required to fully comply with our guidance below, however we recommend you to follow it as fully as possible.



Structural opening – provided By builder

Bear in mind our Skylights sizes are the sizes of the bottom (internal) glass panel. The top panel is stepped by 100mm on each side, and the overall externally visible size is 200mm bigger in both directions:

For example only in this guide we will present installation sketches for a Skylight 600mm x 600 mm. For all other sizes we provide installation sketch in the gallery of each size separately.

DOUBLE/TRIPLE GLAZED SKYLIGHT 600x600mm has the following sizes:

The upstand should protrude min 150mm above the roof level.

A minimum pitch of 8-10 degrees relative to the horizon must be provided to avoid water pooling in the middle of the glass panel. It is worth to spend a few extra minutes before applying the silicone to run a water test to ensure the water is not pooling.

Upstand opening should allow for 5mm tolerance on each side:

Skylight Support – provided By builder

The Skylight support is a 25x50mm (2”x1”) timber:

Install the support in such a way that the top of support to be as follows:

-Double Glazed Skylight          – 28mm below the top of upstand;

-Triple Glazed Skylight            – 42mm below the top of upstand

Weather the upstand

Apply the roof covering material to cover the external face and top of upstand:

Once you finish weathering the upstand, you are ready to install the Skylight.

Make sure all surfaces where silicone will be applied are clean of dirt, dust, moisture etc.

  1. Place the Skylight on place. Apply Black structural silicone* as per supplier’s data sheet to fill in the gap between the top of Skylight Support you have prepared earlier and the bottom glass panel. Setting blocks should be used to achieve sealant thickness required (usually 6mm is enough);

  1. Place an appropriate size foam rope in the gap between top of upstand and overhanging top glass panel at a distance of 25mm from external edge of upstand and fill in the gap between top of upstand and overhanging top glass panel with Black weather silicone*

* With regards to the silicones we recommend the following products:

  • Black structural silicone – DOWSIL 895 Structural Glazing Sealant
  • Black weather silicone – DOWSIL 791 Weatherproofing Sealant


Be careful what silicones you are using to install and weather tight your Skylight. We recommend the above products as fully compatible with our glazing unit silicones.

A chemical incompatibility between silicones used in manufacturing the glazing unit and installing it can lead to discolouration and/or loss of adhesion to the substrate. Which means possible depressurization of the glazing unit (allowing moisture to penetrate inside the glazing unit and internal condense), not sufficient bonding to the support structure and poor weather tightness (possible leaks).