Insulation
Insulation is essential to keep your home warm in winter and cool in summer.
A well-insulated home will provide year-round comfort, and cost less to cool and heat. Insulation also helps to reduce noise levels and condensation.
Many New Zealand homes are cold and damp. These homes aren't just uncomfortable to live in, they can also have negative impacts on your health. Research has found that installing insulation will lead to health benefits such as reduced incidence of asthma.
There are legal minimum requirements for insulation in new homes and additions to existing homes. If you can, it's worth spending a little more to exceed these requirements and get an even warmer, more comfortable home with lower power bills. For existing homes, even though there are no specific requirements, installing or upgrading your insulation is one of the best investments you can make.
Find out more about the new insulation requirements in 'Your Guide to $marter Insulation' (PDF document, 3Mb).
Types of insulation
Bulk insulation
- Bulk insulation traps air in still layers. Pic: yourhome.gov.au
Bulk insulation materials use small, trapped air pockets to reduce or prevent heat flow. The air does the insulating - the material simply traps it.
Bulk insulation comes in a variety of formats - blankets, segments, rigid sheets or loose fill.
Reflective insulation
- Reflective insulation reflects radiant heat. Pic: yourhome.gov.au
Reflective insulation works by letting through only a small percentage of the radiant heat it receives (e.g. sunshine) and reflecting the rest using a shiny surface. A gap next to the reflective surface creates a still layer of air, which is important for reducing heat flow.
Reflective insulation comes as flexible metallic foils with either one or both sides reflective, as single or multiple layers. It should be perforated to improve movement of moisture away from surfaces.
Combination insulation
Combination insulation has reflective material bonded to a bulk material in both flexible and rigid formats.
Insulation materials
There are many insulation materials available including wool, polystyrene, glass wool, mineral wool, paper-based insulation and polyester. See insulation materials for a more detailed explanation of your options.
Straw bale construction or insulated concrete formwork construction methods also provide high levels of insulation and glass bricks have a high insulation value.
When should you install insulation?
The most economical time to install insulation is during construction of new buildings and during renovations before walls, floors and ceiling spaces are closed in. However, it's also common (and cost-effective) to install insulation or upgrade insulation in existing homes.
Where should you install insulation?
Most heat is lost through the ceiling and roof, so that should be your top priority for insulation.
The design and construction of your home will affect the specific types of insulation you can use, and where the insulation can be placed.
With some construction systems - such as aerated concrete blocks, glass blocks and straw bales - little or no additional insulation may be required.
- Sources of heat loss in an average uninsulated home
Roof and ceiling insulation
Roofs and ceilings work most effectively if they are insulated together. About 42% of heat loss from an average uninsulated home occurs through this area (up to 60% in older houses).
Use reflective insulation under the roof and bulk insulation in the ceiling. Rolling bulk blanket insulation across ceiling joists is the most effective way to insulate the ceiling.
Reflective insulation can be hard to fit to the roof of an existing home unless you're replacing the roof.
Wall insulation
About 24% of heat from an average uninsulated home is lost through the walls. Wall insulation can double as a moisture barrier.
If you're using a framed construction system, insulation should be placed within the wall framing. Insulation can also be installed outside the framing (but the insulation must be weatherproof to be effective).
Note that the amount of insulation you can install may depend on the thickness of the walls and the size of the framing. If you're building a new home or renovation, consider increasing the framing size to fit in more insulation.
If you're using a solid construction system such as concrete, insulation should be placed on the outside of the solid wall. The inside of the wall can also be insulated.
Wall insulation can be fitted to existing homes by:
- removing wall claddings and installing blanket or biscuit insulation - this is the best option for timber frames
- pumping or 'blowing’ bulk loose-fill or foam insulation into the top of the wall cavity, or through holes in the top of an external wall - this can be done for timber frames, but is labour-intensive and difficult to get a consistent fill
- fixing solid or blanket insulation to the outside of solid walls - this will include external cladding as part of the system.
Floor insulation
Up to 20% of heat loss occurs through the floor of uninsulated houses. Insulation should be used:
- on the underside of suspended timber or concrete floors
- on the edge and underside of concrete floor slabs.
In existing homes, depending on access, you can fit:
- foil and/or bulk insulation beneath suspended timber or concrete floors
- insulation around the edge of a concrete slab.
WARNING: Installing underfloor foil insulation can be risky. Be careful not to pierce electrical cabling with staples. Existing foil insulation, if improperly installed, can be live. If you are unsure about anything, hire a professional installer or get an electrician to check things out.
How much insulation is enough?
Insulation ratings
The ability of a material to resist heat flow is measured according to R values. The higher the R value, the better the insulation.
For bulk insulation, R values are provided for a specific thickness and density of material. The thicker the insulation, the higher the R value for that product.
For reflective insulation, the R values generally represent the combination of foil, construction material and air gap, depending on the situation the foil is used in. R values for reflective insulation differ depending on the direction of the heat flow - which is related to where the insulation is being used and whether you want to prevent heat loss or heat gain (from heat transferring through a metal roof).
How much do you need?
Under the Building Code, new homes and additions to existing homes must be insulated to a minimum standard (see tables below). If you can, it's well worthwhile spending a little extra and exceeding the requirements to ensure your home is as warm and comfortable as it can be (with the added bonus of lower power bills).
R values for light timber-framed homes | |||||
| Building Code minimum
| Better Practice
| Best Practice
| ||
Zone 1 & 2 North Island excluding the Central Plateau | Roof | R1.9 | R2.6 | R3.3 | |
Walls | R1.5 | R2.1 | R2.6 | ||
Floor | R1.3 | R1.9 | R3.1 | ||
Zone 3 South Island including the North Island Central Plateau | Roof | R3.3 | R3.1 | R3.5 | |
Walls | R2.0 | R2.1 | R2.6 | ||
Floor | R1.3 | R1.9 | R3.1 | ||
Source: New Zealand Standards 4218:1996 and 4244:2003 | |||||
R values for solid construction homes
| |||||
| Building Code minimum
| Better Practice
| Best Practice
| ||
Zone 1 & 2 North Island excluding the Central Plateau | Roof | R3.0 | R3.5 | R4.6 | |
Walls | R0.6 | R1.6 | R1.9 | ||
Floor | R1.3 | R1.9 | R3.1 | ||
Zone 3 South Island including the North Island Central Plateau | Roof | R3.5 | R3.5 | R4.6 | |
Walls | R1.2 | R1.6 | R1.9 | ||
Floor | R1.5 | R1.9 | R3.1 | ||
Source: New Zealand Standards 4218:1996 and 4244:2003 | |||||
Use these R values to specify how much insulation you need. For example, if you want to have walls with a rating of R2.6, then make sure the insulation you buy has at least this R value.
Different insulation products have different R values - some materials insulate better than others and some need to be thicker than others to get the R value you need. The type of construction and the materials used also contribute to the completed R value, but their contribution is not as great as the insulation. Your builder or architect should be able to advise on exactly how much insulation you will need.
Installation
Proper installation is critical for making sure insulation works properly. Most importantly, gaps and spaces must be avoided, as they will allow warm air to bypass the insulation and escape.
You can fit some types of insulation, such as blanket insulation, yourself. Others, such as loose fill, will need a professional installer.
The Energy Efficiency and Conservation Authority's Installing Insulation in Residential Buildings (PDF 2.49MB) has information about installing insulation. You can also talk to your insulation supplier or call a professional installer - they are easy to find in the Yellow Pages (www.yellowpages.co.nz).
More information
From Smarter Homes
From consumer.org.nz
Note: you may have to be a subscriber to access some of this content.
From other sites
The Energywise website has web pages on insulation and insulation design.
The Ministry for the Environment’s Warm Homes Project web page has information about efficient home heating and health effects from cold homes.
An Introduction to Designing Comfortable Homes (PDF, 377KB) is a booklet about energy efficient design, produced by the Energy Efficiency and Conservation Authority and the Cement and Concrete Association of New Zealand.
You can obtain copies of New Zealand Standards for insulation and energy efficiency from the Standards New Zealand website. For most new homes and additions, Building Code requirements are met by complying with New Zealand Standard NZS 4218:2004 Energy Efficiency - Small Building Envelope. SNZ/PAS 4244:2003 Insulation of Lightweight-Framed and Solid Timber Houses contains guidance on insulating beyond Building Code requirements. NZS 4246:2006 Energy Efficiency - installing insulation provides practical information on placing insulation.
You can buy BRANZ bulletins relating to insulation from the BRANZ website (click on the link to the BRANZ bookshop).
Handling Fibreglass - Health and Safety Guidelines is published by The Occupational Safety and Health Service.
Insulation case studies can also be found on the residential section of the Energy Efficiency and Conservation Authority's website.
