In this article about Building Regulations Approved Document B (Part B), which is concerned with fire spread in buildings, James Hunt looks at the potential risk of fire spreading through use of recessed lighting luminaires in dwellinghouses. He also looks at what can be done to mitigate any risk:

In 2007 over 60% of all accidental house fires were caused by electrical equipment so the Fire Kills campaign (http://firekills.direct.gov.uk), local fire and rescue services and the Electrical Safety Council (www.esc.org.uk) have all combined forces in the recent past to spread the fire safety message. This is the background to Part B of the Building Regulations with regard to dwellings.
A fire risk:
An issue that always seems to cause controversy and confusion is that concerning the use of heat hoods (for example) to prevent hot ceiling-mounted halogen downlighters setting fire to ceilings and ceiling voids. The luminaires' position within the ceiling voids can lead a reduction in the fire resistance of any ceiling, since the size of any hole can be up to 140mm. Also a build-up of heat can occur because of the confined volume within the floor void in which the luminaires are fitted - this can cause the surrounding floor joists to scorch, smoulder and in extreme cases, ignite.
Building Regulations B3 Internal Fire Spread (Structure) stipulates a fire resistance of 30 minutes for a domestic upper floor in a two-storey dwelling.
This is refined by including references to three criteria:
- Loadbearing capacity - 30 minutes from underside.
- Integrity - 15 minutes from underside.
- Insulation - 15 minutes from underside.
Full-scale fire tests have shown that where downlighters are installed and a fire occurs within the room, smoke spread into the floor void via a downlighter is almost immediate. The fire load within the room may determine the smoke temperature, which at first ignition may be low but will quickly rise to above 500oC. Smoke will pass quite quickly into the void and may eventually cause ignition of the surrounding floor joists, which may, or may not, last the required 30 minutes. This could threaten safe exit from the dwelling.
Ceiling fitted recessed downlights are extremely widely used in business premises, public buildings, retail spaces and homes. The downlighters are usually made of steel or aluminium and usually have a diameter of approximately 50mm (the holes themselves being about 60mm) - though some are larger. Such recessed downlights come in a wide range of shapes and use a variety of lamp types, including halogen, compact fluorescent (CFL) and LED lighting. They all have one thing in common, however, and that is the need to mount through the ceiling from below. Necessarily, this means cutting a hole in the (usually plasterboard) ceiling for each downlight, which may compromise the fire resistance capability. A snug fit is not sufficient to plug the gap.
Most premises (and all new ones) have fire rated ceilings. This provides time for a ceiling to hold back flames before it spreads to the next floor.
Installing recessed lighting means cutting into the ceiling, which can compromise the ceiling's fire rating. This has to be made good, for example, using intumescent materials or boxing in with plasterboard boxes or fire hoods - although such hoods are not always required.
Where downlighters are installed in ceilings under roof spaces, or where debris or thermal insulation may accumulate on top of the luminaire, building a plasterboard or metal box around the luminaire or installing a fire hood is likely to be necessary. If an insulation layer traps the heat, lamp life can be seriously reduced. Lampholder failure could also occur, as could discolouration of the ceiling and the downlight itself. In addition, plasterboard ceilings can dehydrate, possibly resulting in ceiling collapse, though this is rare. When boxing in a luminaire, unless otherwise stated, a gap of about 100mm around the luminaire and 75mm above is recommended for adequate heat dissipation.
Consult if unsure:
But first, remember that halogen downlighters for such applications have to comply with BSEN 60598 and they need sufficient space around or behind them not to overheat in use. Fire rated downlights protect against fire spread but are also designed so they stop air leakage and are moisture resistant. A common view is that additional protection is required. This may take the form of the already mentioned fire hoods or boxing in of the luminaires. Alternatively, specially designed downlighters are available that have been independently tested and assessed as suitable for installation without hoods or boxing in systems.
Before choosing a downlighter, the manufacturer's literature should be read carefully to ensure that it has been properly tested to ensure that it will not compromise the fire resistance capability. If this assurance is not obtained, the downlighters should not be fitted.
Building Regulations may also require both acoustic and thermal insulation, and fire barriers are not needed in every case, so the topic can indeed be confusing. If in doubt, always contact the lighting scheme designers, contractors and installers involved, or speak to the luminaire and light source manufacturer. Also check with the local authority building control what the required fire and acoustic performance is for the floor and ceiling concerned. Finally, downlighters must always be fitted in accordance with the manufacturer's instructions.
Heat losses through recessed luminaires:
There is another important aspect that can have an effect on downlight choice and fitting. Until recently, recessed downlights were installed in homes and workplaces with little or no thought to heat losses, or the effect they might have to ceiling voids or loft spaces. However, the global focus on climate change, energy efficiency, CO2 emissions and high energy prices has resulted in a requirement that modern recessed downlights have to comply, not only with Part B, but also Part C for air flow, heat and moisture losses, and Part E for acoustics (the transmission of sound). Cutting holes in ceilings also creates compliance issues with these, and there may also be issues with National House Building Council (NHBC - www.nhbc.co.uk) requirements.
As well as fire rating degradation, such issues include an increase in heat loss and moisture transfer (according to Building Regulations Part L1A and L1B Criterion 4 (Continuity of Insulation), which states: 'The building fabric should be constructed so that there is no reasonably avoidable thermal bridges in the insulation layers caused by gaps within the various elements'. Just such a scenario is likely to happen if holes are made in ceilings.
However, available now are recessed downlighters that meet all these requirements using an integrated intumescent material to seal the downlight if a fire occurs. As a result, the ceiling concerned will meet its required test times with the downlights fitted and exposed to flame (for 30, 60 or 90 minutes), so meeting Part B requirements. Some of the latest designs also incorporate an integrated heatsink, which allows the downlight to be covered with thermal insulation without risk - so no fire hoods are necessary.
In at least one case, such a heatsink also obviates the cold bridging effect of conventional recessed downlights, stopping heat transfer to the loft of ceiling void, which reduces energy costs. Full insulation helps maintain resistance to sound. Such recessed downlighters enable the requirements of Parts B, C and E to be met simultaneously, though there are more traditional ways of achieving the same effect.
Finally, remember that - for installers - installation time is usually quicker if the downlights can be final-fixed after the insulation has been laid.
Installation tips:
The following are recommendations for installing recessed downlights in the ceilings of dwellinghouses (please note - again, always first check with Part B, Building Control and the manufacturer if unsure, and ALWAYS install using the manufacturer's instructions):
1) Recommendations for 240V downlights - Where installed on a ground floor ceiling of a two-storey house, a maximum of four units can be provided at a minimum of 1.2m centres, fixed centrally between floor joists without fire resistant units or covers. Where installed within the first floor ceiling of a two-storey house, the insulation should be pulled back to allow ventilation. For any other circumstances, fire resistant units or covers should be provided - or a recessed downlighter used that meets the requirements of Parts B, C and E, as mentioned above.
2) Recommendations for low voltage lighting (non-FR rated) - Where installed on a ground floor ceiling with first floor above the unit should be surrounded by 12.5mm plasterboard with a minimum distance of 100mm maintained between the unit and the boxing. The box should be sealed with intumescent mastic at all joints. The transformer should ideally be located so to be easily reachable - note that the manufacturer's instruction MUST be consulted with regard to derating of cabling where one transformer is to be used to supply a number of units. Where installed within a roof void, any insulation should be kept away from the box.
To read more about Part B of the Building Regulations, see other parts of this VoltiTECH.