Structural problems in 1940s-60s houses may include undersized framing, inadequate bracing, and unsafe chimneys.
Any renovation work should begin with a detailed survey of the building structure. If there is any evidence of structural defects a structural engineer may need to be engaged to:
- assess the existing condition of the building such as undersized framing, chimney instability, wall removal, excavations, suspect ground conditions
- identify the causes (and remedies) for structural damage to the building
- assess loadings on the building, particularly where an upstairs addition is proposed
- advise on the condition of the foundations and roof
- advise on strengthening and bracing measures required
- determine the spacing of framing members used.
Also see foundations and subfloors and moisture and weathertightness.
If there is evidence of undersized framing or inadequate bracing, particularly due to the removal or modification of loadbearing walls, options include:
- install beams where walls have been or are to be removed – these may be concealed in the roof space
- provide additional support to rafters by installing strongbacks supported on load-bearing walls
- install a flitch plate to the existing beam or support
- install additional foundation support
- add new wall, floor or roof framing between existing framing.
Where the structure has been modified by the removal of an internal wall or by installing a larger window this may have affected the amount of bracing provided. Bracing requirements for houses of this period were also less than that required now.
Retrofitting bracing to resist earthquakes is a good thing to do. BRANZ has a bulletin outlining how to upgrade piled foundations. BRANZ research has also confirmed the effectiveness of simple retrofit solutions to strengthen foundations of existing houses on sloping hillsides.
As part of a renovation project, the condition of chimneys should be assessed to ensure that they are structurally sound (brick and mortar condition, absence of cracks and so on) (Figure 1).
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.
Clearances between any timber framing and the chimney or flue need to be checked. Modification will be required where there is insufficient clearance.