CROSS Safety Report
PV panels blown off roof
This report is over 2 years old
Concerns are raised about the adequacy of fixings for PV panels after panels were blown off of a flat roof.
Key Learning Outcomes
For structural design engineers:
Structural fixing systems should be designed for the required factors of safety, robustness, and redundancy, to cope with real conditions
Consider specifying tethers for non-structural items on roofs to ensure they do not present a hazard to the public should they become detached from their fixings
All roofs should be appraised for the suitability of accommodating PV panels
Evidence of structural competence should be provided prior to installation
Inspection by a competent person should be carried out to ensure the works are installed in accordance with the design intent
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This report is from a structural engineer who has been investigating PV panels being blown off a flat roof. Luckily nobody was hurt. The fixing method is simple however it relies on it being perfectly installed 100% of the time. This does not consider human error meaning that if one component fails, then entire module is not working at optimum design and becomes potentially dangerous.
The reporter is curious to know if this kind of incident has been identified to CROSS before? Their firm is looking into adding a secondary safety system which will allow the panel to come from the mount but prevent it from being able to fall from the roof. Any information CROSS may have would be gratefully received.
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As a practising Building Control Surveyor, I would appreciate an authoritative guidance note on the fixings for these panels. However, from my point of view, it still leaves us with a problem when carrying out an inspection on this type of work, as on many occasions, by the time we are called out to do an inspection, the panels have been fixed and the contractor has left the site, so access to inspect the fixings up a sloped roof is virtually impossible!
Expert Panel Comments
Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.
Fixings make up a significant proportion of reports to CROSS and those for PV panels have been queried before. As with all structural fixing systems there have to be factors of safety, robustness, and redundancy, to cope with real conditions. Nothing can be designed to be 100% perfect.
In the comments for report 498 (which discussed a cladding panel that had blown off), the importance of assessing local wind loads, and particularly of not underestimating the loads is vital. Also, in many cases it is not possible to define forces with any accuracy on small objects subject to wind. Items can vibrate with their fixings coming loose and then fall.
In leisure rides, for example, where items might fall onto the track and where there is potential mechanical vibration to cause object to fall, it is standard practice to add secondary restraint cables.
The Guide to the Installation of Photovoltaic Systems from the Microgeneration Certification Scheme deals mainly with the electrical side of installing PV panels. Structural calculations should be carried out.