INSULATION
Insulated House as per Current NZBC regulations
Source: House Insulation Guide - BRANZ
Regulatory Requirements
Building Code Requirement
Clause G5—Interior environment
Habitable spaces with sufficient space for activity, accessible facilities and controlled internal temperature.
This clause has particular applications for early childhood centres, old people’s homes and communal non-residential places of assembly. It requires there to be adequate and accessible habitable space for activities (furniture and sanitary or mobility aids) according to the building’s intended use, and for certain buildings to be provided with listening systems and controlled internal temperature.
G5 is an example of how antiquated the building code is. Designing a building with a minimum temperature of 16 degrees ‘shall apply only to old people’s homes and early childhood centres,’ it is not ok.
The World Health Organization recommends a minimum indoor temperature of 18°C, and ideally 21°C if babies or elderly people live in the house.
We believe that ALL buildings shall be designed for healthy, comfortable internal temperatures.
Clause H1 Energy Efficiency
Provides for the efficient use of energy and sets physical conditions for energy performance.
This clause requires housing to meet a building performance index (BPI) not exceeding 1.55 (this is defined in the Verification Method and Acceptable Solution).
It requires enclosed spaces where temperature or humidity are modified to provide adequate thermal resistance and to limit uncontrollable airflow in certain buildings. It also sets out physical conditions likely to affect energy performance, and requirements for hot water systems, artificial lighting and HVAC systems.
Compliance with the thermal performance requirements of H1 can be achieved via three methods, summarised in the table below.
The most common method used is the Schedule Method and it specifies that building elements that are part of the thermal envelope shall have construction R-values no less than those mentioned in table 2
Table 2: Construction R-values for buildings with any wall type.
NZS 4218:2009 Table 2 https://www.standards.govt.nz/assets/Publication-files/BSP/NZS4218-2009.pdf
As discussed in the Background Section, insulation requirements are much lower than similar climates elsewhere in the world.
E3/AS1
E3/AS1, the Acceptable Solution for compliance with E3, states that occupants should determine their own methods and levels of heating to prevent indoor moisture problems. For condensation control in the colder months, the internal surface temperature should be maintained above the dew point temperature of the internal air by a reasonable margin. This varies with moisture load in the building but, in general, should be around two-thirds of the internal air temperature.
Even with above NZ Building Code construction R-values and an airtight exterior envelope, effective supplementary heating may still be required to maintain temperatures at a suitable level for a healthy indoor environment. Energy modelling can help identify the need for any additional heating (or cooling) during the design stages, and once a target heating input is known, an energy efficient heating system can be sized accordingly.
NZS 4218:2009 Thermal insulation – housing and small buildings
This Standard helps establish the levels of thermal insulation for houses and small buildings. When read in conjunction with Acceptable Solution H1/AS1, it provides a way of complying with the New Zealand Building Code in relation to the thermal insulation of houses for energy efficiency.
Residential Tenancies (Healthy Homes Standards) Regulations 2019
Where feasible, ceiling and underfloor insulation has been compulsory in all rental homes since 1 July 2019. The healthy homes insulation standard builds on the current regulations and some existing insulation will need to be topped up or replaced. https://www.tenancy.govt.nz/healthy-homes/insulation-standard/
The Role of Insulation
Insulation slows the flow of heat, either in or out by trapping millions of tiny pockets of air. Still air is an extremely good insulator, and trapped pockets of air are what give most types of insulation their varying performance of thermal resistance. Sounds like a simple enough concept, but in practice there are a few other considerations in regards to the overall construction and we need to consider how a number of elements work together to effect the insulation. Careful detailing is required to reduce thermal bridging as much as possible. Like the windproof shell of your puffer jacket, creating a wind tight and airtight envelope is also key to achieving the greatest possible performance from your insulation.
Thermal Bridges
A thermal bridge, also called a cold bridge or heat bridge, is an area which has higher thermal conductivity than the surrounding materials,
1. Creating a path of least resistance for heat transfer.
2. Thermal bridges in buildings may impact the amount of energy required to heat and cool a space, cause condensation (moisture) within the building envelope.
3. Result in thermal discomfort or worse.
There are strategies to minimise thermal bridging, such as limiting the number of building members for example, a common strategy is to remove unnecessary timber framing like dwangs or nogs (horizontal members).
Current research by Beacon Pathway has proven that NZ homes can have very high timber frame to insulation ratio and there are strategies at design stage that will help to minimise thermal bridging:
1. Remove unnecessary timber framing like dwangs or nogs (horizontal members), this will limit the number of building elements.
2. Create a ‘criss-cross’ style timber wall construction, where an insulated cavity is formed to the interior face of framing, constructed from horizontal battens. This reduces thermal bridging to the small areas where the horizontal battens cross the studs.
3. Apply continuous insulation materials to create thermal breaks.
4. Install external insulation to the outside face of the wall.
5. Use SIPs panels, which are discussed in detail elsewhere in this document.
Thermal bridges are worse than you think; a timber framed wall is a classic example.
Let’s say 80% of a wall is insulated with a material that has an R-value of R2.5, while framing makes up 20% of the wall with an R-value of just R0.75. A simple approach has been to calculate the construction R-value of the wall as (80% x R2.5) + (20% x R0.75) = R2.15. This doesn’t take full account of current knowledge in this area, however.
A more accurate way to determine the total R-value of the wall from BRANZ is:
BRANZ offers a thermal bridging calculation tool that determines the thermal performance of cavity insulated timber-framed walls. https://www.branz.co.nz/thermal-bridging-calculation-tool/
It may also be used to determine the steady state R-value (U-value) and compare results with a simple one-dimensional isothermal plane calculation for the same relative framing ratio.
The tool may be used to investigate:
● Changing overall window/door areas.
● Changing the size of individual windows and doors.
● The benefits of increasing insulation R-value.
● Changing glazing type.
● Eliminating unnecessary framing elements.
The tool also produces a visual representation of the heat flow like what is seen with a thermal imaging camera.
For further detailed information on diagnosing and remedying thermal bridges take a look here http://www.thermalbridges.org
Types of Insulation
There are a number of products on the market commonly used to thermally insulate homes.
These are categorised as follows:
Internal InsulationFor further detailed information on diagnosing and remedying thermal bridges take a look here http://www.thermalbridges.org
Between framing members (e.g between studs and dwangs)
● Fibrous insulation, either segments or blanket (rolls). Commonly made of glass wool, mineral wool, plastic fibres (e.g polyester), natural fibres such as sheep’s wool or a combination of these materials.
● Rigid Foam sheets. Made from either polystyrene (e.g XPS or EPS), polyurethane or polyisocyanurate preformed sheets (e.g PIR insulation).
● Loose fill. Made from various fibres such as glass wool, wool, cellulose or polystyrene beads.
● Spray in-place closed cell polyurethane foam.
Other
● SIPS Panels are two layers of engineered board, usually oriented strand board (OSB), but could be plywood or similar, fused or glued to an insulation core of either polystyrene or polyurethane foam.
● Strawbale construction. Used as insulation in post and beam construction. The straw bales are plastered over for exterior cladding and interior lining.
External Insulation
External insulation (installed to the outer face of a structural wall rather than between framing elements)
An alternative to insulating between framing members, and is used widely around the world, is using external insulation that sits outside the primary structure. The benefits of this is that the entire wall assembly can be quicker to construct and because the insulation is not broken by the studs, is far more efficient. This means that less thickness of insulation required and there is less thermal bridging. The type of insulation used can also limit the potential for sagging and settling, reducing the risk of poor performance. Options include:
● Rigid Foam sheets.
● Rigid wood fibre insulation sheathing.
● Rockwool.
Note that bulk thermal insulation will not sag/settle if the insulation is tight to the frame and it is the same thickness as the frame.
Supplier Information
Fibrous Insulation
Terra Lana https://www.terralana.co.nz/ produce a range of wool blend insulation products.
Terra Lana insulation is made from wool and polyester that both have a fibre diameter of around 30-35 microns. Glass wool is around 6 microns and can achieve more small air pockets between the fibres and subsequently a higher theoretical thermal rating (R-Value). All insulation products are tested in bone dry laboratories at elevated temperatures. Keeping in mind these are theoretical tests under optimum conditions, once moisture in the building, durability of product and installation quality are considered, Terra Lana often becomes the product of choice.
A guide to specifying Terra Lana Insulation can be found here:
https://www.terralana.co.nz/architect-info/how-to-specify/
Pink® Batts® Insulation
Pink® Batts® insulation is made from over 80% of NZ recycled window glass which will be otherwise sent to landfill. It is classified as “non-combustible” insulation (will not burn in the event of fire) tested as per AS 1530.
Tasman Insulation is confident about the long term performance of the Pink® Batts® product. All the BRANZ Appraised ceiling, wall and blankets products hold the Lifetime Warranty
Currently the Pink® Batts® range holds two independently assessed credentials:
● Environmental Choice New Zealand (ECNZ) – The only NZ Type 1 ecolabel. The ECNZ licence was first issued in June 2004.
● Environmental Product Declaration (EPD). Tasman Insulation holds an EPD for all Pink® Batts® glass wool insulation segments, blankets and boards.
Rigid Insulation
NZ Foam https://nzfoam.co.nz/ provide an orange range of premium polyurethane spray foams that:
● Use recycled plastic bottles and renewable content makes up over 22% of the total volume of the finished foam.
● Our foam has zero ozone depleting potential and zero greenhouse effect on the environment.
● No formaldehyde is used to make these products.
● Due to the low energy production, the recycled content, the zero lifecycle and the superior thermal effectiveness, polyurethane spray foam is well known around the world as having one of the lowest carbon footprints of any insulation product available.
Specifying Insulation
After considerable discussion the Superhome Movement has decided not to specify insulation in terms of R values but in terms of heating/cooling loads to be calculated or modelled, in kWh/m2/yr.
This are four reasons for this:
a) R values are region specific, i.e. what is required for Auckland is less onerous than required from Bluff.
b) This allows all Healthy Homes designed in accordance with guide to be modelled and will provide better quality results that consider the full wall build-up rather than just assessing the insulation that may fill the space.
c) This also allows the Healthy Home to be monitored to check load assumptions.
2
Kilowatt hours per square metre per year is a standard approach used by both International Best Practice and some NZ based rating tools. A kWh/m2/yr value provides the amount of heating/cooling required to keep a home within a comfortable temperature, year round.
Information on thermal modelling software can be found here http://www.level.org.nz/passive-design/thermal-simulation/
Recommended Healthy Home guidelines for Insulation design are set out in the table below:
