The state houses built during the 1940s and 1950s commonly used rimu for the framing, although miro may also have been used. Although related to matai, miro is similar in performance to rimu. It can be identified by its golden colour and dark markings in the grain like matai.

During the late 1950s and through the 1960s, Building A grade rimu use reduced, and No. 1 framing grade radiata pine became the most common framing timber used. From 1952, it was often boric treated.

Non-loadbearing walls could be constructed from lower grade (Building B grade) rimu or No. 2 framing grade radiata pine timber.

Typical construction

Studs and plates

Wall framing typically consisted of rough sawn 4 x 2” (100 x 50 mm) timber studs fixed to top and bottom plates – gauged framing did not come into common usage until the mid 1960s.

The studs may have been checked into the top and bottom plates, particularly where rough sawn timber was used to accommodate the variation in plate thickness and allow the studs to be cut to a common length.

Until 1943, the typical stud height was 9’ (2.7 m) but this gradually reduced (probably as a cost saving measure) so that by 1960s the standard stud height was 8’ (2.4 m).

External and internal loadbearing wall framing was built on site and erected first, with the bottom plates of external walls fixed directly over the floor joists. (Prenailed wall frames became available during the late 1960s.)

Loadbearing internal walls were likely to be on either side of the central hallway, but this was dependent on the roof configuration. Internal, non-loadbearing wall framing was usually erected after the floor had been laid. Studs were typically spaced at 16” (400 mm) centres to suit the 4’ (1200 mm) wide plasterboard which was fixed vertically.

Dwangs or nogs (horizontal timber blocking between studs), were installed in horizontal rows at a maximum of 32” (800 mm) centres or as required to provide edge fixing for sheet lining materials – two rows for plasterboard and three rows for hardboard.

Bracing

Bracing was provided by 6 x 1” (150 x 25 mm) timbers fixed at approximately 45° between the top and bottom plates and housed into each stud where they intersected. 4 x 2” (100 x 50 mm) or 3 x 2” (75 x 50 mm) dog leg or solid bracing (framing at 45 degrees fitted between the studs and dwangs) was likely to have been used later in the period.

The bracing strength of existing construction is often not known. What should be used in the bracing calculations required by building consent authorities when repairs or renovations are planned?

BRANZ tested a range of older bracing systems to provide wall bracing ratings. The results can be found in BRANZ Study Report SR305 Bracing ratings for non-proprietary bracing walls.

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Two-storey construction

Platform construction was typically used for two storey houses. This is where there are effectively two walls of framing (one for each level) separated by the floor joists of the first floor, so studs are not continuous from top to bottom. Bracing runs between the bottom and top plate separately for each storey.

Figure 1: Diagram of elements of platform construction.

Lintels

The early houses of this period were built before the first New Zealand standard, which set out minimum timber sizes, was published, so lintels over door and window openings are likely to be undersized by today’s standards.

Building paper and insulation

Building paper was generally installed on the exterior face of the wall framing, but it was not always used in some parts of the country (particularly in the north).

Insulation was not installed in the wall framing of state houses of this period.

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Post and beam and spine wall construction

In some houses, post and beam construction was used. Alternatively, a central spine wall was built up to the roof ridge to support the rafters. Both methods of construction eliminated the need for ceiling joists and allowed for raked ceilings that followed the roof slope.

This construction was particularly used with low-pitched roofs, and even if the stud height was low, the raked ceiling provided additional internal height and sense of spaciousness.