Energy efficiency Code compliance for repairs, extensions and relocations

H1 compliance

This article outlines building work that is required to comply with Building Code Clause H1 Energy Efficiency. It is guidance offered by the Department to help designers, builders and territorial authorities reach a common understanding of which building work is required to comply with Clause H1. This article is guidance only and is not a substitute for legal advice.

What is the law? - Relevant background

The Building Act 2004 ('the Act') requires all 'building work' to comply with the Building Code,¹ to the extent required by the Act. 'Building work' also has a wide-reaching definition,² which at face value means that almost any work on a building will need to comply with the relevant clauses of the Building Code.

There is no limit on the amount or size of the building work that must comply with the Code. For example, replacing a window in an existing house with an identical window comes within the definition of building work and consequently needs to comply with the relevant provisions of the Building Code. Even replacing a pane of glass in a window falls within the definition of building work in the Act.

Schedule 1 of the Act exempts some types of building work, for example so-called 'like-for-like' repairs, from needing a building consent. However, even this unconsented work must still comply with the Building Code.

In relation to Building Code Clause H1, H1 states that certain buildings must be constructed to have adequate thermal resistance. For houses, the minimum thermal resistance is specified and has recently been increased. However, the Code does not describe the thermal resistance of individual windows, walls, floors or roofs; only their combined performance. The level of performance specified for individual elements in H1/AS1 could be used as a benchmark for the repair or replacement of individual elements. However, this is not a requirement.

Repairs and replacements

Repairs or replacements in an existing building do not need to be upgraded to meet the new Clause H1 requirements. However, a building cannot perform worse after an alteration,³ which in relation to H1 means that after the repair or replacement the building must be no less energy-efficient.

For example, if an old wood-framed window is replaced, any of the following replacements are ok.

1. A new wood-framed window of the same size (ie, 'like-for-like' replacement - the material is the same, therefore the thermal resistance is the same), or
2. A new PVC-framed window of the same size⁴ (ie, PVC windows have the same thermal resistance as wooden windows), or
3. A new aluminium framed window of the same size, plus additional insulation added elsewhere (eg, roof, wall or floor) to offset the lower thermal resistance of the new window,⁵ or
4. A double-glazed aluminium framed window of the same size (note, this will exceed the thermal resistance of the original window).

Common sense is required in assessing the required performance (ie, thermal resistance) of a repaired or replaced building element because Clause H1 of the Building Code does not specify what the performance for each element is. It is therefore reasonable to accept repaired or replaced building elements that do not strictly meet the energy efficiency performance of the old building element, provided it has a minimal effect. Situations where a slightly lesser performance would be acceptable might include when the availability of an 'identical' replacement is limited (eg, standard sizes/dimensions may have changed slightly since the original element was constructed), or other considerations such as the use of second-hand parts which have slightly different sizes/properties. In considering the performance of the thermal envelope in Clause H1 (as compared to the lighting or hot water performances in H1), the requirement to 'limit uncontrollable airflow'⁶ should not be forgotten in the case of a repair or replacement. That is, the overall energy efficiency of the building may be the same after the repair/replacement if a decrease in thermal resistance is offset by an increase in air-tightness.

A reasonable rule-of-thumb is to allow alterations and repairs that:

1. are less than 2 percent of the total area of the thermal envelope, and
2. perform no less than 20 percent below that of the original building element.

For example, an old single-glazed wooden window may be replaced with a single-glazed aluminium window if the area of the window is less than 2 percent of the area of the thermal envelope of the building. The thermal resistance of the single- glazed aluminium window is R0.15, which is 20 percent less than the thermal resistance of the single-glazed wooden window, R0.19. In a typical house, this would equate to reducing the total thermal resistance by less than 1 percent. It is highly unlikely that the cost of installing insulation elsewhere in the building would be less than the small increase in the cumulative energy costs (note, any increase in air-tightness would also help to counter the loss in the thermal resistance).

Additions and extensions

Any new construction, such as additions or extensions to a house, must meet the requirements of Clause H1, but the rest of the building does not have to be upgraded to comply with H1. The new construction could be as small as cutting a window into an existing wall, or could be as large as adding a whole new storey to an existing building.

Additions or extensions involve both new construction and the alteration of an existing building. An altered building must comply with Clause H1 to at least the same extent as it did before the alteration,⁷ or put another way, the overall energy efficiency of the building cannot be made worse by the alteration. Note that this does not over-ride the requirement for the new construction to fully comply with H1.

Typically this means that an addition or extension (ie, the new construction) must comply with Clause H1, while the existing parts of the building that are unaffected do not need upgrading. The only time existing parts of a building would need upgrading is if the existing building performs less energy efficiently because of the addition or extension. However, any upgrading required is not to the level set in Clause H1, but to bring the building back to the level of thermal performance it enjoyed before the addition or extension.

Example - no upgrading

If a new room is added to the side of an existing house, then the extension (ie, new floor, roof, walls and windows) will need to comply with Clause H1. The existing parts of the house that are untouched have the same performance (ie, thermal resistance) in this example after the alteration as they did before. The thermal resistance of the altered house is at least as good as it was before the alteration (in fact the overall thermal resistance has probably improved given that the new extension will comply with H1), and therefore no upgrading is required.

Note that parts of the existing thermal envelope that are enclosed by the alteration (eg, the side of the house onto which the extension is built) will cease to be part of the thermal envelope in the altered building.

Note, if the Schedule Method ⁸ is used to show compliance with Clause H1, then the glazing ratio should be calculated using the wall and glazing areas of the altered building, not just the extension.

Example - upgrading is required

If a double-glazed aluminium window (R0.26) is inserted into an existing wall (R0.5-R2.0), then the window itself will comply with H1/AS1, but the thermal resistance of the building envelope will be reduced. In this case, some upgrading of the existing building would be required to ensure the building performed at least as well as it did before the alteration. In this example, sufficient insulation would need to be added elsewhere in the thermal envelope to offset the loss in thermal resistance at the new window.

Disclaimer

This article is not a substitute for legal advice. This article is published as general guidance only. If you have questions about the interpretation of the law or application of the law to a particular set of circumstances, the Department recommends that you seek independent legal advice.

---

1. See section 17 of the Building Act 2004, All building work must comply with the Building Code to the extent required by this Act, whether or not a building consent is required in respect of that building work.
2. See section 7 of the Building Act 2004, Interpretation. The definition of 'building work' includes construction, alteration, demolition and removal. 'Alter' and 'construct' are also defined and include respectively: to rebuild, re-erect, repair, enlarge and extend a building; and to design, build, erect, prefabricate, and relocate a building.
3. Repairs and replacement are included in the definition of 'alter' - refer to section 7 of the Building Act 2004, Interpretation. Section 112 of the Building Act 2004, Alterations to existing buildings, describes compliance requirements of an altered building.
4. The material is different, but the thermal resistance is the same (ie, the performance is no worse than before).
5. The thermal resistance of a single-glazed aluminium window is R0.15, as compared to a single glazed wooden window, R0.19.
6. See NZBC H1.3.1 - the thermal envelope of a building must be constructed to, '(a) provide adequate thermal resistance; and (b) limit uncontrollable airflow.'
7. The definition of 'alter' includes to enlarge or extend a building - refer to section 7 of the Building Act 2004, Interpretation. Section 112 of the Building Act 2004, Alterations to existing buildings, describes compliance requirements of an altered building.
8. The Schedule Method is describedin NZS 4218: 2004 and forms part of the Acceptable Solution for H1.