Improving your building safety with glass rooflights

The standards of performance that glass should achieve, centre upon preventing anybody from accidentally falling through a rooflight, but what about if someone sets about deliberately trying to gain entry to a building through one?

Following the 2015 introduction of Part Q, with its single requirement, to Schedule 1 of the Building Regulations in England, security and the vulnerability of glass have become buzzwords. The Welsh government consulted on the inclusion of requirement Q1 in their own building regulations, with it coming into effect from November 2018. Section 4 of the Scottish technical handbooks includes ‘4.13 Security’. The requirements in all three countries relate only to dwellings.

Making easily accessible glass secure

For now we’ll focus on Part Q in England and Wales, which requires an easily accessible window to be robust and fitted with appropriate hardware to resist physical attack. ‘Easily accessible’ is defined as being within 2m vertically of an accessible level surface (such as the ground or a balcony), or within 2m vertically of a flat or sloping roof no more than 3.5m above ground level. A secure window meets the requirements of one of the following standards:

PAS 24:2012

STS 204 Issue 3:2012

LPS 1175 Issue 7:2010, security rating 1

LPS 2081 Issue 1:2014, security rating A

Glazing Vision offer products tested to LPS 2081: the Secure and the Secure+. LPS 2081 tests replicate physical attack and assess the complete unit of glass, frame and hardware. Of course, this guide specifically concerns glass and, in the test, rooflight glass is allowed to break but should remain sufficiently intact to prevent an intruder gaining entry into the building.

The use of a laminated interlayer in the glass maintains the integrity of the unit long enough for the roof light to withstand an attack for the required period of time. Although the toughened outer pane may break relatively quickly when using the right tools and applying some knowledge of how best to attack the glass, the interlayer is much more difficult to penetrate.

It is the complete unit that is tested, of course, so use of laminated glass alone does not guarantee a particular rating. There is a lot more detail on Part Q and security in Glazing Vision’s Part Q white paper. Design guidance specific to other building types sets out security expectations for non-domestic applications.

Safety inside your building

Keeping people from entering a building through a rooflight – whether deliberately or accidentally – is one thing, but there is also a need to protect the people already in there. Where building users are concerned, the aim is to prevent falling debris from causing injury.

Just as a laminated inner pane should provide the last line of defence to anyone coming through the glass, it is also the ideal choice for minimising the risk of glass falling into the space below if the pane is broken.

The National Association of Rooflight Manufacturers (NARM) recommends that inner panes always be laminated. Subject to them not affecting the non-fragility classification, toughened or heat strengthened laminates should be considered over annealed laminates, which are prone to thermal stress failure.

Fire performance

National building regulations address fire spread across both internal and external surfaces.

The performance of external roof coverings dictates how close those coverings may be used to boundaries and other buildings. A covering rated as BROOF(t4) can generally be used without restriction; in Scotland, this is also called a covering of ‘low vulnerability’, a category which includes glass at least 4mm thick.

The definition of an internal ceiling lining includes glass, but typically doesn’t include the frame into which the glass is fitted. The performance required depends on the location of the glazing and the building type, but a rating of class D-s3,d2, C-s3,d2 or B-s3,d2 could be expected. Class B-s3,d2 is the most onerous, and glass is capable of achieving it.

European ratings and classifications should be the norm, but it’s not uncommon to still see national classifications referred to. Regulations give guidance on how national and European classifications relate, but it is important to bear in mind that the two are not equivalent.

Regulatory requirements for means of escape are generally unlikely to encompass roof glass, with one notable exception. Where an escape route is provided over a flat roof, the roof should have a fire resistance according to the use of the building (as given in the guidance to the regulations). Should a walk-on roof light form part of the escape route, then it would have to meet the same requirement.

Part B of the building regulations in England and Wales deals with fire safety. In Scotland it is section 2 of the technical handbooks, and in Northern Ireland it is technical booklet E.

A note on cost

It’s a rare building project where cost doesn’t enter the equation at some point. Whether it’s avoiding going over-budget or eking out a few pounds of profit somewhere, the price of materials and services is bound to come up at some point. In an ideal world, everything would be lifecycle costed to establish the best long-term value for money, but the price at time of purchase is usually king.

As with most products and materials, quality comes at something of a premium – especially when moving away from a standard range of products.

Requesting a bespoke product that needs testing to prove it meets certain performance criteria incurs costs that may not be immediately obvious. Multiple examples have to undergo testing to corroborate the results observed. In some cases, such as testing to CWCT standards, at least three versions of the product need to be produced. Then there are the service-related costs, including longer lead times, transport and handling, and storage if the new product cannot be stored on site, or the site is not ready to receive it.

For more information about the design, specification and construction process of glass to get the best results, download our guide to specifying glass in rooflights whitepaper.