Code compliance can be a grey area issue for partial renovations.
One area of difficulty is where only a portion of a space is to be upgraded – say a room is enlarged by moving out one wall and the remaining parts of the existing walls and ceiling remain unchanged.
In BRANZ’s view, a strict interpretation of Building Code requirements is that only the new work needs to comply with the Building Code. However, building consent authorities may disagree.
Also, it is often beneficial to upgrade existing areas at the same time as renovation work is carried out. For example, if a room is being enlarged, it is prudent to upgrade to modern standards the thermal envelope of the entire enlarged space, not just the extension – if this is not done, the benefits of the new construction are partially negated.
In other circumstances, the best approach may be to use an Alternative Solution to show that the materials and methods used in the existing structure meet Code requirements. As one example, an Alternative Method could be used to show that the existing cladding meets Code requirements and therefore a room extension can be clad using the same materials and methods.
However, by law a partial renovation must not reduce the performance of the existing structure.
In some areas such as provision of insulation, there will be a significant difference in performance between the old and the new construction, which potentially reduces the performance of the space. This is not permitted – when a building is altered, the Building Act requires that it comply with the Building Code ‘to at least to the same extent as before the alteration’. For insulation of walls, which is generally the main area of concern, strategies include, in increasing order of preference:
- increasing the level of insulation in the new construction and the ceiling of both old and new to offset the lack of wall insulation in the existing walls – this will not avoid the heat loss through the existing walls, but will have some impact on reducing overall heat loss; the benefit will be greater where the area of the addition is large in relation to the original area of the space
- providing double glazing (or even triple glazing) to new windows
- where adjacent spaces do not have wall insulation, by regarding the perimeter of the new extension (particularly when it is a living and/or sleeping space) as the thermal envelope and insulating both external and internal walls of that space.
Other areas where consequences of partial upgrading may need to be considered include:
- installing larger windows into an existing wall where the thermal performance of the wall must be no worse than that before the alteration work was done
- bathrooms and other wet areas where current requirements for impervious finishes may be difficult to match with original materials that are required to be retained
- acoustic and fire separation requirements in buildings that have been converted into flats
- stair design
- barriers and handrails
- fencing of and access to pools and spas.