The use of downlights in ceilings reduces the effectiveness of ceiling insulation and needs to be accounted for when meeting NZBC H1.
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. Pink Batts 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.
T
he 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:
- Specified Pink Batts Classic R3.2 Ceiling
- Because of the thermal bridging and the construction of your roof, the actual construction R-value is R3.0.
- 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)
- The average construction R-value of the ceiling is now only R2.78 ( [0.25 x 7.9 ]+ [3.0 x 92.1])/100
- Because the R2.78 no longer meets code, a higher R-value insulation product must be specified to compensate.
- New specified product Pink Batts Ultra R4.0 Ceiling
- The construction R-value is now R 3.5
- 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. I will be away until the 5th of July but will endeavour to reply to any comments once I am back in the office.
June 24, 2010 at 5:06 pm
Hi Bhavna
I liked the article very informative.
My question is if you come in after the house is completed eg an electrician and install extra downlights can you restore the R value in some way. I am aware that it does not matter as far as building regs go but if you came in and changed from 10 hanging lights to 10 down lights what could you do to reinstate the R value or atleast reduce the losses.
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bhavna prentice:
August 6th, 2010 at 3:54 pm
Hi Gary,
Adding another layer of insulation to increase the overall R-value of the roof system would help. However the clearances would still need to be maintained.
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David Curl:
August 29th, 2010 at 7:23 pm
Giday Gary
Installing electrical lights is building work, and as such comes under the Building code and more importantly the Building Act 2004. Section 112 requires the building to have the same level of compliance after any building work as before for most of the building code clauses. The lights do not need a Building Consent, but all building work must comply with the building code (Section 17) If you do not install extra insulation then in effect you are in breach of the Building Act.
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July 7, 2010 at 10:58 am
Hi Bhavna,
In an ideal world, there would be regular sized spaces between studs and dwangs to fit the fibreglass insulation. Inevitably though, we are left with very small gaps (eg 20mm wide by 2.4m high) which, if left, can dramatically reduce the effectiveness of the insulation. What would be your solution to covering off these areas in order to provide a complete thermal blanket?
[Reply]
August 6, 2010 at 3:59 pm
Hi Geoff,
With our installers and under the Insulation installation standard NZS4246, gaps are not permitted. Generally all the product must be cut to fit the space or two pieces butted together to fit, to ensure there are no gaps.
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August 29, 2010 at 7:30 pm
Even with perfectly fitted insulation, recessed downlights are like throwing money down the drain. The code allows 1 every 5 square metres, but 1 chimney every 5 square metres loses a lot of heat, which you paid for. However, the irony is, since our houses have lost the eternal venting of a open fire chimney, moisture build up within the dwelling has caused serious problems. Maybe the downlights are providing greater protection to the health of both the residents as well as the house itself than what is lost through energy inefficiency. Makes you think…and how could you quantify it.
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