Façade Engineering and Analysis Services Limited
Façade Engineering and Analysis Services Limited

Rooflight fragility testing and specification. CWCT Technical Notes 66 and 67.

Historically rooflight glazing has been described as either “fragile” or “non-fragile”. These descriptions were aimed to differentiate between glazing type but they had very little actual meaning as they took no account of factors such as roof location, maintenance strategy or loads likely to act on the glass.


To move towards clarifying what may be an appropriate solution for a specific rooflight CWCT have produced various documents that have touched on this subject.


  • Technical Update No.10 (replaced TU 4) “Use of glass overhead” dealt with slope and overhead glazing in general and discussed the use of laminated glass in the lower pane which is generally accepted as being required for the majority of rooflights.
  • Technical Note No.68 “Overhead glazing”. This supersedes TU 10 and was extended to additionally cover vertical glazing. The advice with regard to overhead glazing and particularly the lower pane remained generally unaltered with more clarity given to the use of differing glass types. In the location of rooflights a laminated inner is still recommended.
  • Technical Note No.42 “SAFETY AND FRAGILITY OF GLAZED ROOFING - guidance on specification and testing” considered rooflights more specifically and discussed the load categories that may be applied to classify roof glazing. This was replaced by TN Nos. 66 and 67 in February 2010.
  • Technical Note No.66 “SAFETY AND FRAGILITY OF GLAZED ROOFING - guidance on specification.”
  • Technical Note No.67 “SAFETY AND FRAGILITY OF GLAZED ROOFING – testing and assessment.”
  • Technical Note No.92 “Simplified method for assessing glazing in Class 2 roofs”


In the absence of any suitable other standards (EN or BS) Technical Note Nos. 66 and 67 should be cited in project specifications and compliance with these will be required.


In TN66 glazed roofs are classified into 4 classes.


Class 0

Roofs which are designed for unrestricted access by building occupants.


Class 1

Roofs which will be walked on for occasional cleaning/maintenance activities and which will therefore need to support both the weight of people on the glass and their equipment. Such roofs could be subject to impact from a person, and/or any object carried, falling onto its surface.


Class 2

Roofs where people are not intended to walk on the glass, but which are required to be non-fragile to protect people in the following circumstances:

• Where maintenance personnel walking adjacent to the glass roof could trip or fall onto the glass surface.

• Where maintenance personnel working on the glass roof could fall onto the glass surface from crawler boards or other access equipment.


Class 3

Roofs which are fragile.


FEASL can assist in reviewing location and maintenance strategy for each particular rooflight and help all parties to ensure that an appropriate classification is applied within the project specifications.


Although TN66 goes a long way to seeking to make the selection of systems and glass appropriate to the actual requirements of the project it has a practical drawback in that it leads to solutions having to be tested to TN67.


Commonly Class 2 becomes a suitable performance category and an alternative route compliance other than testing is given in Technical Note No. 92.


TN92 lists criteria, based on historical testing and understanding that, if satisfied by the proposed solution, can be accepted as demonstrating a Class 2 compliance and thus negate the need to project test.


FEASL can assist in reviewing proposed solutions in conjunction with project performance specifications with a view to allowing the specialist subcontractor to follow this route.


If the conclusion is that testing cannot be avoided then FEASL can act for the client, architect or main contractor to witness off-site testing if required.


Sub-contractors however may benefit as FEASL can advise and manage the testing process on their behalf, thus allowing the project design team to concentrate on the progression of the project works.


FEASL will;

  • Review the project specification and advise on appropriateness of the proposed regime.

  • Liaise with test house to create Method Statements for technical submittal.

  • Liaise with test house to ascertain availability and program testing works.

  • Coordinate test drawings with designers.

  • Upon completion of test sample drawings, coordinate rig support structure design with the test house.

  • In conjunction with the sub-contractors fixing team manage the installation of the test sample at the test house ensuring compliance with the detail design drawings and system supplier recommendations as applicable.

  • Witness testing.

  • Provide written reports and photographic evidence throughout the process.


TN 67 testing

Please contact Façade Engineering and Analysis Services Limited to discuss your requirements and how we may assist towards arriving at an appropriate performance specification and cost effective solution that benefits all parties.


In summary, FEASL can offer to:

  • Review rooflight location, access and maintenance strategies with the project design team and building owner.

  • Review the resulting project specification and resultant performance category.

  • Liaise with the specialist subcontractor to propose a suitable solution.

  • If testing is required: liaise between all parties and witness the process.

Contact details

Façade Engineering and Analysis Services Limited.




Tel: 01543 898150

Tel: 07404 447212

Alternatively, please use our contact form. 

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Change of Address

Please note we have moved offices into Suite 8 at Tradmark House.

All other details remian unchanged.

Luke Norton


We are pleased to welcome Luke to the company in a full-time role. He has previously assisted us with CAD and thermal modelling in a part time basis whilst completing his BTEC college course.

Luke has now accepted the offer of an apprenticeship with us and will be combining with Digital Engineering studies at Dudley College of Technology.

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