New H1 requirements for houses - Q and A
In October 2007, Clause H1 of the New Zealand Building Code was changed to require improved thermal performance in all new houses in the South Island and the North Island Central Plateau. These tougher requirements will be phased in throughout the rest of New Zealand, and will be effective for the whole country on 30 September 2008.
Late last year, the Department of Building and Housing and BRANZ ran a seminar series to discuss the changes with designers and building officials. These seminars prompted many questions about H1. Some of the questions were about the recent changes, while others highlighted the need for better understanding of the Building Code requirements for energy efficiency generally. This article is intended to answer some of the most common questions.
How do I prove compliance with the new H1 rules?
The thermal performance measure in Building Code Clause H1 (Energy Efficiency) is the building performance index (BPI). The BPI is calculated using the computer programme ALF3 (Annual Loss Factor method). If the ALF3 calculation for your house is less than the limits given in the Code, then you will have demonstrated compliance.
A simpler way to demonstrate compliance is by using the Acceptable Solution H1/AS1. This entails using the insulation values for walls, ceilings and floors prescribed in NZS 4218 (the 'schedule method' or the 'calculation method'), as modified by the Acceptable Solution.
Another way to demonstrate compliance is to use the 'modelling method' prescribed in NZS 4218, which is cited as the Verification Method H1/VM1.
Should you wish to put forward an alternative solution proposal, you will need to satisfy the building consent authority that your design will meet the Building Code performance requirements.
What are the changes to the Building Code?
The Building Code Clauses A2 and H1 3.2 have been changed to refine the definition of the building performance index (BPI), and to improve the thermal performance of houses. This effectively requires houses to use about 30% less heating energy than before and, in practice, means that most new houses will need better insulation.
The changes come into effect in stages as follows.
- 31 October 2007 - Zone 3: South Island and North Island Central Plateau
- 30 June 2008 - Zone 2: North Island districts south of Franklin and Thames-Coromandel Districts (excluding Central Plateau)
- 30 September 2008 - Zone 1: Districts north of Franklin and Thames-Coromandel Districts inclusive
What are the main changes to the Acceptable Solution H1/AS1?
Because of the recent changes to Building Code Clause H1, the Department has also changed Acceptable Solution H1/AS1. The changes to H1/AS1 include referencing the 2004 version of NZS 4218 (previously the 1996 version was referenced). The insulation R-values in the Standard have also been increased. In H1/AS1, the higher R-values come into effect in a staged way throughout New Zealand. However, the new Standard (NZS 4218: 2004) became effective for the whole country on 31 October 2007.
30% glazing limit
Another key change designers need to be aware of with the new 2004 Standard is that the schedule method can only be used when the glazing ratio is no greater than 30%, and the glazing ratio of the east, south and west faces is no greater than 30%. The 2004 Standard now requires the use of the calculation or modelling method for glazing ratios over 30% (this was only recommended in the 1996 version).
Skylights
Another significant change in H1/AS1 is that the schedule method can only be used if the total area of skylights is less than 1.2 m2. If the area is larger than this, the calculation or modelling methods must be used.
Is double-glazing mandatory?
Double-glazing is not mandatory.
While double-glazing is not specifically mentioned in either the Building Code or the Acceptable Solution, we expect that it will be used extensively to meet the new H1 requirements. For some designs in some locations, the building performance index will not exceed 1.55 for a house with single glazing, making double glazing an optional choice for the owner.
How do the new H1 rules apply to garages and conservatories?
The requirements of H1 only apply to conditioned spaces.
New attached garages or conservatories that sit within the building thermal envelope, and so are part of the conditioned space, must comply with the new H1 rules. For example, this includes conservatories that are openly connected to the interior of the house and are actively heated or cooled.
Attached garages or conservatories that are unconditioned and are outside the building thermal envelope do not need to comply with H1. In these circumstances, any walls, windows or doors that sit between the garage or conservatory and the interior of the house will need to be appropriately insulated, as these will form part of the building thermal envelope.
See Part 2.3 of the NZS 4218: 2004 for more information.
Why are the solid construction R-values different in the Acceptable Solution H1/AS1?
For houses that use solid construction, it is important to realise that the lower wall R-values for solid wall construction account for:
- the performance benefits of thermal mass; however, thermal mass must be used in conjunction with good passive solar design to increase comfort and to reduce energy use (refer to the notes in the tables for solid construction in the Compliance Document)
- higher roof R-values; this is a trade-off to reduce the wall insulation by increasing the roof insulation
- higher floor R-values for some options; this is a trade-off to reduce the wall insulation by increasing the floor insulation.
How do I analyse a mixture of solid and non-solid construction for H1?
The most robust way to analyse a combination of different construction types in the same building is to use the computer programme ALF3 to calculate the building performance index (BPI), and to ensure that it does not exceed the limit in Clause H1.
However, most people would argue the best, and certainly the easiest, way to analyse mixed construction is to use the calculation method in the Acceptable Solution (refer NZS 4218: 2004, Part 3.2). The Acceptable Solution for H1 has three different R-value tables that correspond to three distinct types of external wall construction: non-solid (typically timber-framed), solid timber and other solid wall construction (typically masonry and rammed earth).
In the Acceptable Solution, it is acceptable to combine the different construction types using the Calculation Method provided you follow these rules.
- Do not mix and match the R-values (ie, for walls, roofs, floors, windows and skylights) from the different tables. For example, the non-solid construction roof R-value must not be used in the place of the solid construction roof R-value.
- The R-values for each component (ie, wall, roof, floor, window and skylight) should be used in the same proportions and should correspond to the different construction types used in the design. For example, if the design has half timber-framed walls and half masonry walls, then the R-values for Table 1 can be used for half the area and the R-values from Table 2(a) can be used for the other half of the area.
- Alternatively, the highest R-value can be selected from the different construction types and used for each component (ie, the highest wall R-value, the highest roof R-value, etc). This approach is inherently conservative and will result in better thermal performance than the Building Code requires.
Are there any insulation requirements for doors in the Acceptable Solution H1/AS1?
There are no insulation requirements for the opaque parts of a door or door set if the schedule method contained in the Acceptable Solution H1/AS1 is used (refer to NZS 4218: 2004). If the calculation method is used, the total area of doors that exceed 3 m2 must be treated as a wall.
Glazing in doors is part of the total area of glazing. Hence, glazing in doors must be considered when calculating the glazing ratio.
The exemption of opaque doors from insulation requirements in the schedule method has been included to ensure that the schedule method is easy to apply and not too restrictive. However, the door exemption is not intended to allow large areas of a house to be un-insulated; nor does it indicate that doors are typically well insulated.
What are the insulation requirements for opaque joinery, such as wooden or aluminium louvres?
If the Acceptable Solution is used to show compliance with Clause H1, then opaque joinery, other than doors, should be treated as either a window or a wall.
The reason for this is that all parts of the house's thermal envelope must limit heat loss consistently with the criteria specified in the Building Code or in the Acceptable Solution (see the R-value tables in H1/AS1 and NZS 4218: 2004). Any reduction in the R-values specified for the walls, floors, roofs and windows will result in additional heat loss, and the house will not comply with the Acceptable Solution.
Note that insulation (ie, R-values) can be traded off between different parts of the building using the calculation method, the modelling method or the BPI (building performance index). These methods allow louvres to be used in houses when a louvre does not meet the R-values specified for walls or windows in the schedule method.
Where can I get more information on the new H1 rules?
These changes have been publicised through media releases and the Department's BC Update 69, which is available from the Department's website.
More information can be found in:
Disclaimer
This article is not a substitute for legal advice. This article is published as general guidance only. If you have questions regarding application of the law to a particular set of circumstances, the Department recommends that you seek independent legal advice.