Fire rated or not? Separate fire hood or not? Insulation over downlights?
Fire hoods are fire resistant covers which char and expand when exposed to the heat of a fire. Their purpose is to slow the spread of fire, by blocking the hole in the ceiling where a downlight is fitted.
Fire hoods do NOT prevent the light itself overheating, and they are NOT suitable for keeping loft insulation away from the downlight.
Fire rated downlights are the downlight and fire hood combined into one item. The light will typically have a metal can on the back, and have intumescent material inside which will expand and block the hole in the same way that a separate fire hood will.
As with the separate fire hood, these are NOT suitable for situations where loft insulation is being placed over the lights.
These are devices with a single function - to provide a space around and above the downlight to avoid overheating. Normally used where loft insulation needs to be installed over the top of the downlights.
Various types are available, including metal frames and domes of compressed mineral fibre. Other materials such as plasterboard or ceramic pots could also be used - the primary function is just to ensure a suitable space is maintained around the light to prevent overheating and failure.
These items are not generally fire rated, and normally don't need to be anyway.
Separate fire hoods are expensive and very difficult to install properly from below. If fire rated items are required, the easiest solution is to buy fire rated downlights which do not require a separate hood.
Where insulation is to be placed above, then some form of spacer or support is necessary to avoid the light overheating in normal use. Placing insulation directly over most downlights will cause the light to overheat and fail.
Some downlights already include a suitable spacing device as part of the light itself - but check the manufacturer's instructions to confirm exactly what is permitted when installing them.
Fire rated lights are only needed if the ceiling they are being installed in forms part of a fire compartment - a room or part of a house which is intended to contain a fire and prevent it spreading to another part of the building for a defined amount of time.
In most domestic properties, few or no ceilings form fire compartments and fire rated lights are not required. However there is nothing wrong with installing them even if not needed, and there are other considerations such as sound transmission and moisture resistance.