Installing recessed luminaires in ceilings - are fire hoods always required?

Showing a typical fire hood installation.

The ceilings in modern homes are fire rated to provide a certain amount of time before a fire beneath it spreads to the floor above. Many such premises today have fire-rated ceilings - typically 60 minutes or 30 minutes, depending on types and age of dwelling. In a fire, therefore, the floor above will not collapse for at least 30 minutes, giving occupants a reasonable chance of getting out safely.

However, with the increasing fashion for fitting recessed downlighters into ceilings old and new (often plasterboard), there is a considerably increased fire risk because of the necessary holes cut into the ceiling. Modern steel or aluminium recessed downlighters generally have a diameter of 50mm. This means that, effectively, the holes cut into the ceiling will be around 55 - 60mm. The inevitable gaps within the light fitting, or between fitting and ceiling, instantly compromises the ceiling's fire rating. Ignoring possible problems caused by heat from the fitting itself, if there is a fire in the room below, flames and smoke will find any gap, so spreading the fire to the floor above.

So, while the recessed light fitting itself more or less occupies the hole, it will not fill it with the degree of integrity required, no matter how well installed, so the ceiling's fire rating will be greatly compromised. It may help to minimise the number of downlighters and to space them as far apart as practicable. This, however, may not be practical for lighting considerations.

The question as to how much fire resistance is needed depends, to a degree, on the nature of the building itself. For the purposes of the regulations, buildings are divided into compartments separated by fire-resistant walls and floors. The idea is to prevent rapid fire spread that might trap the occupants, so as to reduce the chance of fires becoming large. Large fires become a danger to people nearby (such as fire fighters and those in adjacent buildings).

For example, in terms of fire compartment walls, semi-detached houses and terraced houses are considered to be separate buildings, and the walls and ceilings inside are not fire compartment types. Flats or maisonettes have all floors as fire compartment floors - but there be exceptions depending on the exact nature of the dwellings themselves and the walls within them. Downlighters are often installed in non-fire compartment ceilings. Even so, the minimum 30 minutes before ceiling collapse should still apply.

In order to maintain a ceiling's fire resistance after recessed downlighters have been fitted, it may be necessary to make a plasterboard boxes around luminaires (steel versions are available), or to fit fire hoods.

Steel insulation support boxes allow free air circulation around each downlighter. Insulation can be safely laid over them. It is good building practise for insulation material to be laid unbroken over the whole floor area. This contradicts the requirement that a minimum amount of free air is left around recessed downlighters to allow lamp heat to be dissipated. Such steel insulation support boxes meet, it is claimed, both of these requirements.

Various types of fire protection covers (hoods) are available. These include fully intumescent caps that minimise heat transmission and flame propagation. There is also the woven cloth type. Their use can even - in some circumstances - reduce transmitted acoustic noise, so have an incidental benefit.

Fire protection covers of whatever type should prevent flames and heat being transmitted through the fitting into the ceiling void. Usually these will have a 60-minute rating, though some may last up to two hours.

Are fire hoods and boxes necessary?

Is it, however, actually necessary to restore the fire resistance capability of ceilings after recessed downlighters have been fitted? The (now defunct) UK IEE Wiring Regulations 16th Edition BS 7671: 2001 Section 527-02-01 stated: 'Where a wiring system passes through elements of building construction such as floors, walls, roofs, ceilings, partitions or cavity barriers, the openings remaining after passage of the wiring system shall be sealed according to the degree of fire resistance required of the element concerned (if any)'. The recently implemented UK 17th Edition has a similar requirement, but check Ireland's new 4th Edition National Wiring Rules. So, the answer would seem to be 'yes'.

In Scotland and Northern Ireland, The Building Standards (Scotland) Regulations 1990, Amendment 5, 1999, Technical Standard Part D or The Building Regulations (Northern Ireland) 2000, Technical Booklet E respectively apply. The recent introduction of the revised Part P of the Building Regulations also has a bearing.

However, previous tests (by TRADA Technology Limited - TTL), to determine the effect of recessed downlighters on the fire resistance of plasterboard ceilings with conventional joists had showed that downlighters in such ceilings, even without being boxed-in and with no fire hoods, have little significant effect on fire resistance ratings up to 30 minutes. Therefore, fitting fire hoods or boxes should be unnecessary under these circumstances. This seems, at first sight at least, to be a contradiction.

In other situations, especially where recessed downlighters have been installed in ceilings under roof spaces, this could be a fire problem because thermal insulation and other debris often builds up on top of the fittings. Here, there may be a better case for installing fire hoods or plasterboard / metal boxes.

Suspended ceilings in flats and maisonettes can usually accept recessed downlighters without fireproofing measures but, in Scotland (for example), the rules are different again because there is a noise transmission requirement and other factors.

As can be seen, although at first sight, the regulations seem clear enough (and it might be thought that it is always safer to fit fire hoods etc), in practise, things are slightly more complicated.

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Contact: James Hunt Managing Editor Voltimum UK Tel: +44 (0) 1273 732125 Email: james.hunt@voltimum.co.uk Web: www.voltimum.co.uk

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Source: James Hunt