1970s houses may need strengthening as part of any renovation.
All renovation work must begin with a detailed survey of the building structure. It may be necessary to engage a structural engineer to:
- assess the structural condition of the building and identify potential structural weaknesses
- assess existing and proposed loadings on the building, particularly where an additional floor is proposed
- advise on the structural performance of the existing foundations, floor structure and roof framing
- advise on the strengthening and bracing required particularly where the building is being altered or extended.
Previous modifications such as excavations, the removal of a wall, or the addition of a partial or full upper or lower level, as well as proposed new work, may require engineering input for additional strengthening or bracing.
The building survey should identify loadbearing walls that have been removed (if any) and assess the remaining supporting structure to be sure that it is adequate. If modifications are to be carried out, the survey should determine how they can be accommodated.
If the structure requires strengthening this may include:
- installing beams where walls have been or are to be removed - beams may be able to be concealed in the roof space
- providing additional support to rafters by installing strongbacks or steel beams supported on load-bearing walls
- installing a flitch plate to an existing beam or support
- installing additional foundation support such as extra piles and bearers or underpinning.
If loadbearing walls have been removed, there may also be evidence of inadequate bracing. Generally the bracing requirements for houses built during the 1970s were less than current Code requirements, and wall removal would exacerbate this problem, so any new work should address and upgrade bracing if necessary.
Although chimneys were generally constructed from clay brick or pre-cast reinforced concrete, as part of a renovation project their condition should be assessed to ensure that they are structurally sound and safe for use if the fireplaces are to be used. Total or partial removal should be considered if they are considered unlikely to survive a moderate earthquake.
Other structural problems may be present in foundations and subfloors - for example, inadequate foundation bracing, joist and bearer spans that are too long, piles that have been removed, and poor ground bearing.