I’m not sure whether these are still in fashion, but with the recent amendments to NZS 4246: Energy Efficiency – Installing Insulation in Residential Buildings, I thought it would be an idea to touch on the subject of downlights and their effect on insulation.

To reduce the risk of fire a clearance is required around recessed light fittings when installing insulation. PinkBatts products are non-combustible and the risk of fire is much lower than other forms of insulation, however the clearances are still required to ensure lights fitting don't over heat and result in a fire.

The clearances required are:

• 50mm for Incandescent lamps
• 200mm for Halogen lamps
• 200mm for unknown lamp types
• Manufacturer specified clearance (e.g: CA rated lamps require no clearance).

Unfortunately this clearance also reduces the effectiveness of ceiling insulation.

The simplest way to account for this is to use the tables provided in NZS 4246: Energy Efficiency – Installing Insulation in Residential Buildings: Appendix C

Alternatively the effect of this is simple to calculate if you assume the R-value of the clearances are R0.25 and then use the ratio of the area to work out the reduction in R-value.

For example in a 100m² home you have:

1. Specified Pink Batts Classic R3.2 Ceiling.
2. The thermal bridging and the construction of your roof means the actual construction R-value is R3.0.
3. If you have 4 Halogen (100mm Ø) downlights  per 10m² therefore a total of 40 Halogen lights, and a total clearance area of 7.9m² (πr² x 40, r = 0.25m).
4. The average construction R-value of the ceiling is now only R2.78 ( [0.25 x 7.9 ]+ [3.0 x 92.1])/100.
5. Because the R2.78 no longer meets code, a higher R-value insulation product must be specified to compensate.
6. New specified product Pink Batts Ultra R4.0 Ceiling.
7. The construction R-value is now R 3.5.
8. Clearance area remains the same and new average construction R-value is R3.2 ([0.25 x 7.9 ]+ [3.5 x 92.1])/100.

Hopefully this simple calculation is of some use.  If you have any questions regarding the calculation feel free to drop me a line.