Structural problems in villas include undersized framing and potentially dangerous structures such as brick chimneys with failing mortar.
Existing framing of villas is likely to be undersized for the span when compared to the current version of NZS 3604 Timber framed buildings. While old dry native timbers may be capable of longer spans, the sagging of floor joists, ceiling joists and rafters can be a problem in villas. (In one instance, the ceiling and rafters of a villa with a clay tile roof had sagged 60 mm at mid span over the life of the building.)
Options to remedy undersized framing include:
- the use of strongbacks supported off load-bearing walls to provide support to ceilings and rafters (Figure 1) – jacks may be needed to lift the existing structure back into line before the new framing is installed
- flitching a new member alongside the existing
- where walls are being removed, use engineered steel beams or LVL (laminated veneer lumber) beams – it is often possible to conceal a steel beam within a roof space
- adding new bearers and piles to the subfloor.
For most villas, the original brick chimneys are likely to be the most dangerous element simply because the original lime mortar has lost strength and the risk of damage is greatest if the chimney were to collapse.
As part of the renovation project, the structural condition of any chimney needs to be assessed by an engineer to ensure it is structurally sound. Chimneys also need to be assessed for fire safety if the fireplaces they serve are to be used for heating.
Removal of a building element such as an unsound chimney does not require a building consent. 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.
Chimneys that are considered structurally sound can have the joints raked and repointed to restore their condition.
Other structures associated with villas that may need assessment by an engineer are:
- retaining walls and any modifications to the building itself such as excavations under the floor
- where walls may have been removed in a previous renovation
- lack of foundation lateral support
Another consideration is holding down roof structures against uplift – veranda posts may be enough to hold up the roof against gravity but insufficient to hold down the roof in very strong wind.