Clear answers to glass questions

Phil Brown, European regulatory marketing manager at Pilkington UK, answers some of the questions he gets asked most frequently by glass and glazing traders.

I have a project near a busy road – what glass should I use to reduce noise levels inside?

The most common way in which the sound insulation of glass is quantified is with the weighted sound reduction Rw, which takes into account a correction for human hearing.

However, as urban road traffic is dominated by low-frequency noise, it is more relevant to consider acoustic performance in terms of Rw + Ctr – the latter being the decibel reduction figure weighted for the frequencies typical of traffic noise. The larger the value of Rw + Ctr, the less the airborne noise will be transmitted through the glass.

To maximise acoustic performance, the general rules to follow include making the glass as thick as possible, using laminated glass and, in a double glazed unit, installing different glass of different thicknesses to offset resonance effects. Sound insulation can be enhanced by specifying an acoustic laminated glass such as Pilkington Optiphon.

Our range of products can achieve sound reduction of more than 50 decibels, making them suitable for even the noisiest environments.

A customer’s glass has broken in their conservatory roof – why has this happened?

Glass can break for several reasons, from edge damage to poor installation or thermal stress.

To find out what caused the breakage, find the point where the breakage originated. In annealed glass, following the cracks in the glass should lead you to it.

Around the point of origin there is usually a ‘mirror’ zone – an area of highly polished-looking glass, and the size of this can be used to estimate the level of stress the glass was under when it broke. The smaller the mirror is, the higher the stress at the time of fracture. If the glass was under very high stress at the time it broke, it could indicate it was overloaded.

Damaged or poor-quality edges are another key reason for failures, so inspect the edge closely.

A common cause of breakage is excess pressure exerted on a point in the glass by the framing system. Protruding screw heads, non-flat rebates and excessive fixing pressure can all lead to fracture.

A further potential cause is thermal fracture, where excessive temperature differentials across the glazing can lead to overstressing. Thermal factures tend to be more prevalent in spring and autumn, when the central area of the glass is heated up from the sun while the edge is still cold from the night before. Thermal fractures are recognisable as they typically run perpendicularly from the edge of the glass. Specifying a thermally toughened glass will eliminate the risk of thermal fracture from solar radiation.

It’s not always easy to determine the cause of a fracture. If in doubt as to what’s behind a breakage in a pane of Pilkington-branded glass, take photographs of the damage – especially at the origin – and our technical team will be happy to give an opinion on the cause of the breakage. In some cases, the glass may need to be subsequently analysed.

I’m installing glass in a place that calls for fire resistance – what product do I need to use?

In the UK, fire resistance is within the scope of Building Regulations and detailed guidance on compliance is set out in supporting technical documents, for example Approved Document B (ADB) in England.

The purpose of these minimum requirements is to ensure that fire is contained within the room or space of origin, and that the spread of smoke and flames is inhibited by compartmentation. This will ensure that occupants, and the emergency services, have time to evacuate safely.

Minimum times for fire resistance are specified in AD B and usually classified in terms of integrity (keeping back the fire) and insulation (minimising the passage of heat).

The Pilkington Pytostop range offers fire-resistant glazing that can deliver insulation and integrity for up to three hours. Refer to AD B to determine the requirements for the application in which you are installing the glass and check that the product you buy has been tested to deliver the appropriate levels of protection. Always ask to see relevant test evidence and certification.

If in doubt, our team of fire glazing experts will be happy to advise on the best solution.