Structural problems in art deco houses include undersized framing, deterioration due to moisture, and problems with foundations and subfloor.
Renovation work should begin with a detailed survey of the structure of the house. Use a structural engineer to assess and advise on:
- the condition of the structure, in particular foundations, lintels and roof members and wall bracing capacity
- loadings, particularly if walls have been moved or removed
- strengthening requirements.
The engineer should check any previous modifications to the house, particularly if walls have been removed or the site has been excavated. An engineer’s advice should also be sought if excavation or removal of walls is proposed, or if an upper floor or part upper floor is to be added.
The existing framing in art deco houses is generally undersized compared to the current requirements of NZS 3604 Timber framed buildings.
However, the use of native timbers, which generally had greater strength than timber used today, means that in many situations undersized framing may not be a problem. Evidence of undersized framing includes movement (springiness) in floors and sagging roofs or ceilings.
Where there is evidence of undersized framing, options to remedy the framing include:
- flitch a new member alongside the existing
- use engineered steel beams or LVL (laminated veneer lumber) beams where walls are being removed – these may be able to be concealed in the ceiling space
- install additional piles and bearers to the subfloor.
Problems with foundations and floors
Moisture and weathertightness
Potentially dangerous structures
As part of the renovation project, the condition of any chimney should be assessed by an engineer to ensure that it is structurally sound.
Even apparently sound-looking unreinforced chimneys can collapse in an earthquake. Removal of a chimney does not require a building consent under Schedule 1 of the Building Act. This exemption is limited to any building up to 3 storeys high as long as the removal does not affect the primary structure, any specified system or any fire separation (which includes firewalls protecting other property). Any repair work that is necessary – for example, making good the gaps left in a roof after chimney removal – can also be done without a consent. In all cases, work must still comply with the Building Code to the extent required by the Building Act.
If the chimney is still used or the owner wishes to retain it, it could be strengthened. The most practical approach adds steel angles on the external vertical chimney corners and then 25 x 3 mm steel bands around the outside of the chimney, fastened with coach screws to the wall framing. The other option if the chimney is still in use is for the most hazardous part (above the roofline) to be replaced with a lighter weight metal flue.