Specification Guide
& Non-fragility

What to look for in a quality rooflight

Great aesthetics and high performance are the basic checklist of any rooflight product. However, it’s important to understand the specification of the product, including the glass. Testing for impact-resistance, durability, environmental and thermal performance, and security are essential criteria.

Glass Specification & Safety
The first, and safest, choice for the inner pane of a rooflight should be laminated glass.  Laminated glass is constructed of two sheets of glass which are bonded together with interlayers to form a permanent bond. If the glass is damaged, these interlayers act like a ‘glue’ to hold the fragments in  place ensuring the glass does not break up into large jagged shards or  hundreds of little pieces, protecting occupants below.
Non-Fragility & Testing
Non-fragile rooflights are designed to be strong enough to prevent  a person from falling through the glass should they slip or trip whilst  carrying out maintenance, cleaning or other activities on the rooftop  (subject to risk assessment).Several testing procedures are undertaken by the Advisory Committee for Roof Safety and the Centre for Window & Cladding Technology. CWCT TN66 & 67 deals specifically in glass rooflights and sloped glazing.Class 1 refers to rooflights that can be trafficked infrequently for maintenance but are not designed for everyday foot traffic. Class 2 is the minimum non-fragility classification, designed to prevent a person from falling through the glazing if they were to fall onto the rooflight.

Frequently asked.

View all FAQ’s

For glass rooflights and roof windows, what is the safest choice?
What is laminated glass?
Where can I find more information?
Thermal Performance – and ‘True’ Thermal Break Design
The thermal performance of a rooflight must be considered for the whole assembly, because while glazing may be compliant, poor frame design can affect thermal performance. It’s important to look for the  ‘whole product’ U-values to ensure thermal performance in compliance with Part L Building Regulations. ‘Centre pane’ U-values do not take into account edge spacers and frame construction. Whole unit values are represented as Ud-value.

A ‘true’ thermal break is achieved when a frame design incorporates specific features to achieve the thermal break. The use of foam strips cannot be considered as a true thermal break as these strips may deteriorate over time and therefore their efficacy will be affected.
Design Details
Where a rooflight frame has been poorly designed, or the unit has been installed without sufficient pitch to allow water run-off, the result can be water building up on the glazing and eventually penetrating edge seals. Look for a glass unit that has been factory bonded into the frame, and specific design details that ensure the unit is fully watertight. Poorly designed frames can lead to water tracking back on the underside of the glass. Flat glass rooflights should always be installed at a slight pitch to avoid ponding – typically a minimum 5 degree pitch.
Any requests?
If you have any specific requests, do not hesitate to contact us.

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