Guidance for complying with new energy efficiency requirements for houses in Northland
This document is issued as Guidance under Section 175 of the Building Act 2004
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What has changed?
New insulation requirements for the upper North Island came into effect on 30 September 2008. They apply to new houses and additions to existing houses.
These changes will mean that homes will be warmer, healthier and less expensive to heat. The cost savings are significant and will pay for any additional construction cost over time.
The Building Code specifies the performance that must be achieved, but not how it must be achieved. However, for convenience, the Department’s Compliance Documents provide a range of ways in which compliance can be demonstrated.
In colder climates, double-glazing will often be needed to meet the new requirements. The warmer climate in Northland makes it easier to meet the requirements without using double-glazing.
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How can compliance be demonstrated?
There are three main ways1 to check for compliance with the Building Code energy efficiency requirements. They are the:
- Schedule Method
- Calculation Method
- Building Performance Index (BPI).
The schedule method
The Schedule Method uses a series of tables that include the performance level of insulation (R-values) for walls, floors, roofs and windows. There are tables for timber-framed houses, as well as solid timber and high mass materials, such as concrete. Limitations on the use of these tables are provided in the notes. In particular, the glazed area is limited to 30% of the total wall area and the R-value for glazing must be at least 0.26. An R-value of 0.26 can be achieved using double-glazing in an aluminium frame. Single glazing with low-e glass in either a wooden or uPVC frame provides another option. This option gives an R-value of 0.272
The R-value tables are included in the energy efficiency Acceptable Solution H1/AS1 and can be downloaded free at www.dbh.govt.nz. Also needed is a copy of the New Zealand Standard NZS 4218:2004, which is available for purchase at Standards New Zealand .
The calculation method
The Calculation Method allows building components with lower R-values to be used, provided the additional heat loss from these components is offset by reduced heat loss in other building components. For example, windows with lower R-values can be used if higher values are achieved in the walls, floor or roof.
The Calculation Method is described in New Zealand Standard NZS 4218 and is one way to achieve the requirements of the Acceptable Solution H1/AS1. H1/AS1 can be downloaded free at www.dbh.govt.nz, and NZS 4218:2004 is available for purchase at Standard New Zealand .
The building performance index
The BRANZ ALF (Annual Loss Factor) Method can be used to calculate the Building Performance Index (BPI) - a measurement of a building's thermal energy efficiency. The ALF Method takes into account the climate, together with the building's dimensions, design, orientation, insulation and construction. It calculates the theoretical heating energy for the house.
This heating energy figure is then used with the following BPI formula:
heating degrees total x (floor area + total wall area)
The Building Code requires the BPI of houses to be no more than 1.55. If the BPI exceeds 1.55, then the design will need to be modified.
ALF is available free from www.branz.co.nz.
Total wall area:
| 174 m2
||62.2 m2 (including 2.7 m2 of skylights)
|Heating energy calculated by ALF:
|Heating degrees total for Whangarei:
12 x (170 + 174)
| = 0.64 < 1.55 (therefore complies with H1)
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Is double glazing required in Northland?
There is a positive cost-benefit to installing double glazing in Northland. The reduced on-going energy bills outweigh the initial capital cost associated with installation.4
Other advantages of using double glazing include:
- improved comfort
- a wider range of solar control options (by the use of selective coatings)
- reduced condensation
- reduced cold spots and draughts near windows
- reduced noise
- increased re-sale value.
Double glazing is required if the designer chooses to demonstrate compliance with the Building Code using the Schedule Method included in Acceptable Solution H1/AS1.
However, if designers choose to calculate the Building Performance Index, in most cases, double glazing will not be required for housing in Northland. Because of the warmer climate in Northland, most designs can demonstrate Code compliance (using the Building Performance Index) with single glazing.
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Guidance on using single glazing in Northland
The Department of Building and Housing has analysed a wide range of typical designs. This analysis shows that most houses in Northland will comply using single glazing (i.e., achieve a BPI of less than 1.55), provided:
- the glazing area is 50% or less than the total wall area, and
- the R-values for walls, floors and ceilings in the table below are used, and
- all the notes in the table below are observed.
Table of minimum R-values for Northland5
|Building thermal envelope component
||Minimum R-values (m2 oC/W)
||High thermal mass construction6
- Carpets or floor coverings are not included in the floor R-value.
- The R-values for glazing refer to whole window R-values (glass and frame). The values in this table are for standard WERS windows (see Appendix G, of NZS 4218).
- There are no R-value requirements for the opaque parts of a door or a door set.
- Total area of skylights must be no more than 3m2.
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What if the design falls outside of the parameters of this guidance?
If the design does not comply with all the above limits, then designers will need to undertake a BPI calculation to check that the BPI value does not exceed 1.55. This can most easily be done by using the ALF software found on the BRANZ website.
Other methods can also be used to calculate the BPI if they can be correlated to the ALF method. AccuRate NZ is one such example7.
The Department recommends that homeowners who want to exceed the above limits seek expert advice on thermal performance. Large glazing areas may cause over-heating in summer and excessive heat loss in winter.
ffective shading and other passive thermal design features would be beneficial. The ideal area of windows (for good thermal design) is not easy to determine – design factors that should be taken into account include:
- insulation levels
- amount of thermal mass
- orientation of the glazing
- size and geometry of the house.
Information on the principles of passive solar design is available in a booklet titled “Designing comfortable homes: Guidelines on the use of glass, mass and insulation for energy efficiency”, which was published by the Cement and Concrete Association of New Zealand and the Energy Efficiency and Conservation Authority.
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What if the design does not meet the BPI requirement?
If the BPI value exceeds 1.55, there are a range of options to change a non-compliant design to a compliant one, such as:
- using higher performance windows
- moving windows (to increase solar gain)
- reducing the window area (particularly on the south side of the house)
- improving the floor, wall or roof insulation
- using additional thermal mass.
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- There are other ways to comply with the Building Code Energy Efficiency requirements, including using the modelling method in NZS 4218 or by proposing alternative solutions to be approved by building consent authorities.
- Single glazing with clear glass in an aluminium frame achieves an R-value of 0.15.
- the measured heating degrees total for Whangarei is actually 8.5 but the BPI calculation requires a minimum value of 12. The minimum 12 applies in all locations throughout Northland.
- BRANZ report QC 5048 NZBC Clause H1 Review house insulation cost benefit analysis.
- While the table above may be of assistance, it does not form part of an acceptable solution. Accordingly, building consent applications must be assessed on a case by case basis and it is up to applicants to show compliance with the Building Code.
- Solid wall construction (concrete or rammed earth) where the heat capacity of the walls reduces the energy used for heating and improves comfort.
- AccuRate NZ is building thermal simulation tool used by the Energy Efficiency and Conservation Authority (EECA) in their Home Energy Rating Scheme. The correlation of ALF and AccuRate is outlined in an article in the October 2008 edition of Codewords.
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