Ceiling insulation
Research indicates that around 375,000 New Zealand homes have inadequate ceiling insulation. [1] Good ceiling insulation is probably the most important to have. Whether it’s blanket or segment insulation, this needs to be well installed and thick enough for your situation.
On this page:
Safe installation around downlights, chimneys and flues
Blanket insulation or segments?
Energy savings
Ceiling insulation is the first step in making your house easier and cheaper to heat. Hot air rises. So the air near the ceiling is always warmest in rooms you’re heating. The ceiling is also where the heat loss in a house is the greatest.
If your house is multi-story, you only need to insulate the main upper ceiling. It isn’t necessary to insulate the ceiling between floors, it’s more important to insulate the outer envelope of your house. You may however want to insulate ceilings between floors if the ground floor is a separate flat. This can also be done with sound proofing insulation to control noise.
Take action in your ceiling
The easiest way to check if you need ceiling insulation is to have a quick look in your roof space. See how well the insulation covers the top of the ceiling, and measure its average depth.
Insulation should be evenly spread across the entire top of the ceiling. There should be no gaps, folds, creases or areas that are tucked in. To work as well as possible, insulation needs to cover the top of the joists that hold up the ceiling. This works better than sitting between the joists. See the information below on segments and blanket insulation.
To comply with the New Zealand Building Code, houses in the North Island need thermal resistance in the ceiling of no less than R2.9. The only exception in the North Island is the Central Plateau. There, and in the South Island, houses need a minimum of R3.3.
You may be eligible for ENERGYWISE™ funding to get insulation installed in your home. For this funding, in practice anything less than 75mm insulation in the ceiling gets treated as if there was no insulation at all. Anything less than 120mm of insulation gets a top up.
Safe installation around downlights, chimneys and flues
Downlights, chimneys and flues can produce a lot of heat, so special care needs to be taken with them to ensure safe insulation installation. EECA recommends having your insulation installed by a professional, but there are some things to consider if you are doing it yourself or want to check your insulation is installed correctly.
Downlights
If you've got recessed downlights there are some things to consider when it comes to insulation.
Large numbers of downlights are common in modern or recently renovated houses, and most are simply a hole in your ceiling. Because the traditional incandescent or halogen bulbs most people use run very hot, there must be a gap between the insulation and standard downlights.
These are your options when it comes to safe installation of insulation with downlights.
- The simple option - keep your standard downlight fittings and leave the required safety gap. Leave a gap of 150 mm between your old, open downlight fittings and your insulation, and never place insulation over the top of the light or any transformers. This will ensure the rising heat from the downlights is not a fire hazard.
- The better option - replace standard downlight fittings with fully enclosed fittings. Because the necessary safety clearances will reduce effectiveness of insulation, a better solution is to replace standard downlight fittings with ‘closed abutted' (CA-rated) type fittings. These have a fully enclosed canister to stop the insulation being exposed to the heat from the bulb, so insulation can be fitted right up to them (but not over the top). There is a range of CA-rated downlights available on the market. If you are not sure of the type you need, check with a registered electrical contractor.
- The best option - replace standard downlights with non-downlight fittings. Even with a good downlight, you will still lose heat through the ceiling of your house. Therefore, the best solution is to remove recessed downlights altogether or not put them in when renovating. They can be replaced with other types of lighting that don't require a hole in both the ceiling and insulation, but look just as good and can provide a better light distribution.
Chimneys and flues
Chimneys and flues can also get very hot. Leave a gap of 50 mm between the outer face of a brick or concrete chimney and the insulation, or a 150 mm gap for metal chimneys and flues.
What type of insulation?
Ceiling insulation can be made from polyester, wool, fibreglass and a range of other materials. Not all insulation is created equal though, and some products do have definite drawbacks.
If you are comparing different types of insulation, remember to check:
- What sort of performance guarantees the insulation manufacturers offer on their products
- That the insulation you are looking at has been tested to the AS/NZS 4859.1 Standard. Look for a AS/NZS 4859.1 compliance statement on the insulation packaging
- What's involved in safely installing the insulation if you are thinking of doing it yourself.
Once you know these things, make sure you are comparing products with similar R-values.
Blanket insulation or segments?
Insulation is available as either:
- Segments, which fit between the joists above your ceiling, or
- Blankets, designed to be rolled out across the top of the ceiling and the joists.
If you use segments, you need to put in higher R-value insulation to make up for the heat that gets lost through the timber joists. Modelling suggests that in order to achieve R2.9 or R3.3 with well installed segment insulation you need to use R3.4 or R4.0 products respectively.
Blanket insulation that covers ceiling joists prevents extra heat loss through the timber joists. This allows slightly lower R-value products to be used. To achieve R2.9 or R3.3 in ceilings with well installed blanket insulation you need to use R2.8 or R3.2 products respectively.
Installing ceiling insulation
Insulation can usually be installed by two to three people. Access is often through a manhole in the roof. If you are unsure of how to access and safely work in a roof space, EECA suggests that you get your insulation professionally installed.
Standards New Zealand has published a standard on installing insulation. It covers a variety of products and provides detailed instructions on how they should be installed.
Download Standard NZS 4246:2006 - The NZ Standard in Energy efficiency - Installing insulation in residential buildings.
Follow safe work practices when working around electrical wiring. See the Energy Safety website for more information about safety.
More information
- Home heating and energy options for New Zealanders can be found on the Consumer website - Consumer online.
Insulation
- For comprehensive information on insulation, download the Department of Building and Housing booklet Your guide to smarter insulation.
- For a comprehensive discussion on choosing insulation products, see the Smarter Homes website.
Product certification
- For a background to how products are certified, go to the Consumer Build website.
Building code
- Check with the Department of Building and Housing website for changes to the Building code.
- Visit the Department of Building and Housing website for a copy of ‘The Building Code Compliance Document Clause H1 Energy.'
Building Resources
Independent and unbiased research, testing, consultancy and information resource for the building and construction industry is available at:
Notes:
[1] Clark, S.J., Jones, M. & Page, I.C. 2005. New Zealand 2005 House Condition Survey. Wellington: BRANZ
