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CROSS Safety Report

PV panels on domestic roof

Report ID: 528 Published: 1 October 2015 Region: CROSS-UK

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Overview

A reporter raises concerns as they suspect PV panels are being erected on domestic (and commercial) roofs across the UK without adequate engineering analysis and design.

Key Learning Outcomes

For PV panel suppliers, installers and homeowners:

  • 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

  • Guidance is provided in the Guide to the Installation of Photovoltaic Systems from the Microgeneration Certification Scheme.

Full Report

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This reporter is the client for construction of a residential home. The building is traditional, domestic in scale and execution. The duo-pitched roof is concrete tiles on battens on membrane on factory trusses. The roof supports a large area of PV panels whose attachments are supported on every third truss. The reporter asked the design and build (D&B) roof contractor if this was sufficient to support wind and snow loads.

The contractor responded that using every fifth truss for support was usual and this construction was very safe. Eventually calculations were produced purporting to prove the safety of the scheme but these did not cater for all load cases. Eventually a more complete (but still inadequate) calculation report was received showing the inadequacy of the executed work.

The number of support fixings has now been substantially increased. The reporter suspects PV panels are being erected on domestic (and commercial) roofs across the UK (the world?) without adequate engineering analysis and design.

Expert Panel Comments

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PV panel installation is normally subject to building regulations approval, which should pick up structural design deficiencies of the sort the reporter raises. Some guidance is available, as noted for report 519, in the Guide to the Installation of Photovoltaic Systems from the Microgeneration Certification Scheme.

The Scottish Government published Low carbon equipment and building regulations; A guide to safe and sustainable construction - Photovoltaics in 2012 which also contains advice on installation. It may be that recommendations are not being followed and building regulation requirements are not being enforced.

Some engineers recommend that for most roofs PV rails have to be fixed to every rafter. Another concern is the durability of the fixings being used. With the increase in the use of these panels, often retrofitted to existing roofs, it may be that an authoritative guidance note is required.

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