Complying with insulation requirements for houses in Northland

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1 Complying with insulation requirements for houses in Northland Many houses in Northland will comply with the Building Code clause H1 Energy Efficiency without needing double glazing, due to the warmer climate. However, the Building Performance Index (BPI) will need to be used to show compliance with clause H1. Published on 1 October st edition Licensed building practitioners, Territorial Authority, Building consent authorities, Carpenters, Designers, Electricians, Gasfitters, Plumbers, Roofers How can compliance be demonstrated? There are three ways to show compliance with the insulation requirements in clause H1 of the Building Code. They are the: Schedule Method Calculation Method Building Performance Index (BPI). The schedule method The Schedule Method specifies R-values (thermal resistance) for walls, floors, roofs and windows. There are sets of R-values for timber-framed houses, as well as solid timber and high mass materials, such as concrete. Limitations on the use of the R-values are provided. In particular, the glazed area is limited to 30% of the total wall area. Page 1 of 5

2 The R-value for glazing must be at least 0.26, which can be achieved using double-glazing in an aluminium frame. 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 R-values in the walls, floor or roof offset the increased heat loss through the windows. The Calculation Method is described in New Zealand Standard NZS 4218 and is one way to achieve the requirements of the Acceptable Solution for clause H1, H1/AS1. The building performance index The BRANZ ALF (Annual Loss Factor) Method is 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 of a house. ALF is available free from BRANZ ( Using AccuRate NZ gives you information on how to calculate the theoretical heating energy This heating energy figure is then used to calculate the BPI as follows: BPI = heating energy / heating degrees total x (floor area + total wall area) The Building Code requires the BPI to be no more than If the BPI exceeds 1.55, then the design will need to be modified. Example: House location: Whangarei 2 2 Floor Area: 170 m Total wall area: 174 m 2 2 Glazed area: 62.2 m (including 2.7 m of skylights) Heating energy calculated by ALF: 2,632 kwh/year Heating degrees total for Whangarei: 12 BPI = 2632 / 12 x ( ) = 0.64 < 1.55 (therefore complies with H1) Page 2 of 5

3 Double glazing in Northland Double glazing will be required if designers choose to show compliance with H1 using the Schedule Method, included in Acceptable Solution H1/AS1. However, if designers choose to use the Building Performance Index to show compliance with H1, in most cases, double glazing will not be required for housing in Northland. Because of the warmer climate in Northland, most designs can demonstrate compliance with H1 (using the Building Performance Index) with single glazing. Using single glazing in Northland Calculation of the BPI for a wide range of typical house designs in Northland have shown that most houses in Northland will comply with H1 using single glazing provided: the glazing area is 50% or less than the total wall area the R-values for walls, floors and ceilings in the table below are used all the notes in the table below are observed. Using double glazing 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 3 m2. While the above table 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 clause H1 of the Building Code. Page 3 of 5

4 Designs outside of the parameters Designs that do not comply with the above limits may still comply with clause H1, but compliance will need to be shown by ensuring that the BPI calculation for the design does not exceed If the BPI exceeds 1.55, there are a range of modifications that can 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. Good design for energy efficiency Designers and homeowners who want to exceed the above limits should seek expert advice on thermal performance. Large areas of glazing may cause over-heating in summer and excessive heat loss in winter. Effective shading and other passive thermal design features are beneficial. The ideal area of glazing, for good thermal performance, is not easy to determine. Design factors that should be taken into account include: climate 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, published by the Cement and Concrete Association of New Zealand and the Energy Efficiency and Conservation Authority. Advantages of using double glazing include: reduced on-going energy bills improved comfort a wider range of solar control options (by the use of selective coatings) reduced condensation reduced cold spots and draughts near windows Page 4 of 5

5 reduced noise increased re-sale value. This information is published by the Ministry of Business, Innovation and Employment s Chief Executive. It is a general guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case. Expert advice may be required in specific circumstances. Where this information relates to assisting people: with compliance with the Building Act, it is published under section 175 of the Building Act with a Weathertight Services claim, it is published under section 12 of the Weathertight Homes Resolution Services Act Page 5 of 5