Installation guide

How to Install our Skylights on Pitched Roof

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

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

The upstand should protrude a minimum of 150mm above the roof level.

A minimum pitch of 6 degrees relative to the horizon must be provided to avoid water pooling in the middle of the glass panel (for every meter of Skylight a 10cm fall is required). It is worth spending a few extra minutes before applying the silicone to run a water test to ensure the water is not pooling (even though you are installing glass it will still bend in the middle)

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

The internal distance upstand to upstand needs to be 10mm bigger than the quoted skylight size (in our example: 610mm by 610mm)

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 is as follows:

-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 the upstand:

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

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

  1. Apply the foam rope on top of the 2”x1” timber support to level off any discrepancies which will prevent any pressure and stop cracking on the bottom glass laminated pane. THE WARRANTY WILL BE VOID IF A FOAM ROPE IS NOT USED.
  2. Apply, generously, on top of the upstand weatherproof sealant, usually, 1 tube is enough for 6 linear meters.
  3. Lower the skylight with suction cups, and make sure you check the load on each cup.
  4. Apply waterproof sealant on the underside of the overhang and smooth it over once more to make sure it is watertight.

For a pitched roof please follow the technical diagram below:

Skylight installation on pitched roof

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

  • 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 discoloration and/or loss of adhesion to the substrate. This 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).

Lead Flashing Textured 450mm x 5m Roll Grey – Easy-Trim

£88.99 inc. VAT

In stock

Lead Flashing Smooth 450mm x 5m Roll Grey – Easy-Trim

£88.99 inc. VAT

In stock

Foam Rope – Structural Glazing Tape – 9mm Thick (7.5m Rolls)

£16.99 inc. VAT

In stock

Weatherproofing Sealant ( Sillicon ) – DOWSIL™ 791

£13.99 inc. VAT

In stock