How to fit spotlights, recessed lights and downlights in insulation

Fitting lights into insulation

This post is about how to fit lights, downlighters, recessed lights or spotlights into insulation safely and securely.

Kingspan Insulation is such a high performing insulation that if you place a downlight or spotlight directly into it without taking appropriate precautions, then there will be little chance for heat generated by the lighting to dissipate. The insulation is thermoset, which means it will not melt under the heat from the lights.

In the first instance you should contact the manufacturer of the lighting unit who will offer specific guidance for their spotlights and downlighters as excessive heat may affect the performance of that light. It may also be worth consulting the building warranty providers to check if they have any additional requirements which need to be complied with.

In the absence of this guidance, then there are a number of other options:

  1.  In order to prevent penetrating the insulation to recess light fittings, you can create a ‘service void’ or a false ceiling in effect below the insulation. The depth of this services void and the necessary clear space will have to be determined by the lighting manufacturer. The benefit of this is twofold – you will not penetrate the insulation or the inbuilt vapour control layer and secondly you may get a benefit as the void could be deemed as a low emissivity air space – potentially meaning less insulation is needed.
  2. If you are placing the lighting unit into the insulation, a rule of thumb is to cut a hole in the insulation twice the diameter of the light fitting. Mount the light fitting to the plasterboard as you would normally. Maintain a clear air space around the light fitting, according to the manufacturer’s instructions. To avoid warm, moist air being drawn into the roof space and potentially risking rot as well as clearly losing energy, an intumescent or fireproof ‘hat’ needs to be place over the light fitting – taking care to maintain the clear space required (Google ‘Downlight Covers’ for manufacturers of these). Insulation can then be placed over this to avoid the heat loss. Many lighting manufacturers will have their own products to solve this problem.

You should also be aware of the implications of electrical cables

As the cables to supply recessed fittings will often be either fully or partially buried within insulation some extra care needs to be taken. The effect is that the insulation could reduce the load-carrying capacity of that cable which may have to be increased in size to safely carry the load. The effect is as follows:

  • Circuits run within thermal insulation must be protected with cartridge fuses or mini circuit-breakers (MCBs). Rewirable fuses are not suitable.
  • Cable fully enclosed by insulation may need to be increased in size above the standard recommended size by as much as 20% if they pass at right angles through an insulating layer, and as much as 50% if they are enclosed along their length for more than 500 mm.
  • For cables enclosed by insulation but in contact with a thermally conductive surface on one side, the larger of the standard recommended sizes will generally need to be used.

For more information refer to BR 262 or BS 7671.

NHBC Technical Guidance document on recessed light fittings.

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Kingspan Insulation is a market leading manufacturer of optimum, premium and high performance rigid insulation products and insulated systems for building fabric and building services applications.

0 comments on “How to fit spotlights, recessed lights and downlights in insulation
  1. In a ceiling fitted with 100 mm foil back insulation ,would it be enough to drill up in with a 4inch cutter, not the whole way through, remove this then fit a downlite after it is plasterboarded

    • Hi Ronnie,

      Thanks for your question.

      If you are placing your downlights into the insulation we suggest following the instructions as set out in point number 2 above. Note the requirement for an intumescent or fireproof ‘hat’ to be placed over the light fitting, taking care to maintain a clear air space around the fitting as per the manufacturer’s instructions. The insulation can then be placed over this to avoid heat loss.

      In any case, we would always recommend contacting the manufacturer of the downlights for guidance.

      Hope this helps.

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