Fitting & Installation

Double / Triple Glazed Frameless Rooflight
Your rooflight is designed for straightforward installation by competent roofers and builders. This installation guide outlines the recommended process from measuring the opening through to sealing and finishing.
Important sizing note
All sizes listed on the website refer to the INTERNAL BOTTOM GLASS PANE
1. Measuring & Preparing the Structural Opening
1.1 Measure the Opening
  • Measure the tight structural opening where the rooflight will sit
  • Allow 5mm tolerance on all four sides so the bottom pane can drop in smoothly
Example
Opening: 1010mm × 1010mm → Order bottom pane: 1000mm × 1000mm
1.2 Understanding the Rooflight Overhang
  • Standard rooflights include a 100mm black stepped overhang beyond the visible glass.
  • A 1000 × 1000mm bottom pane typically results in a 1200 × 1200mm top pane.
  • If your upstand is wider, we can manufacture a larger stepped overhang (on request prior to purchase)
2. Suitable Timber Upstand
2.1 Upstand Requirements
Height
150mm above finished roof deck
Width
70mm (to suit standard 100mm overhang, see Image 2)
Pitch
5° minimum
  • Supports water run-off
  • If pooling occurs during testing, increase the pitch
2.2 What the Roofer Must Build
  • A structural insulated timber upstand with roofing material dressed up the sides
  • A 25mm timber rooflight support batten fixed around the full perimeter underneath the glass
2.3 Purpose of the Support Batten
  • Supports the underside panel of the stepped IGU
  • Helps prevent sagging and uneven loading.
  • Must be lined with structural glazing tape to cushion the glass and distribute load
3. Preparing the Roof Surface
3.1 Apply Roofing Material
  • Dress the roofing membrane up to the side of the upstand
  • Ensure surfaces are clean and free of:
  • Sharp edges
  • Debris
  • High spots / unevenness
3.2 Apply Structural Glazing Tape
  • Apply glazing tape to the support batten on all four sides.
  • Maintain a 5mm air tolerance between the glass and internal plasterboard edges
4. Installing the Rooflight (Main Steps)
Step 1 — Apply Low Modulus Silicone
  • Use a compatible low modulus weatherproof silicone (e.g., Dow 791).
  • Apply a continuous bead around the full perimeter on top of the upstand.
  • Ensure silicone depth is sufficient to bond to the underside of the rooflight.
Step 2 — Position the Rooflight
  • Use at least two installers to safely lower the unit onto the upstand.
  • Confirm the 100mm black border overlaps evenly on all sides
  • The top pane must protrude the upstand by ≥20mm
Important
  • Apply firm, even pressure to help the silicone spread and push out any air bubbles
  • Ensure full perimeter contact between silicone and glass
Step 3 — Structural Bonding
Once the initial silicone bead has skinned:
  • Use a compatible structural silicone (e.g., Dow 895 or equivalent)
  • Apply structural silicone to the outer underside circumference of the rooflight
  • Seal the outside underside surface where the border and upstand meet, ensuring a continuous full-circumference application.
  • Tool and wipe away excess for a neat finish
Step 4 — Final Support & Finishing
Bottom and top panes must remain fully supported. Check the following:
  • Silicone compatibility with glass + upstand
  • Correct use of setting blocks (if required)
  • No unsupported glass edges
  • A clean, continuous external silicone seal
Internal Finish
Plasterboard can be:
  • Installed after fitting the support batten (recommended), or
  • Installed first, with the batten fitted afterwards.
5. Important Notes
Ensure the installer checks and confirms:
  • Dimensions
  • Roof pitch
  • Upstand height
  • Siliconing method
  • Compatibility of sealants (glass + upstand)
Technical support: If you require any further assistance, please contact us before installation - info@rightglaze.co.uk