Typical construction

Timber

During the 1970s, the timber used for framing was generally visually graded No. 1 Framing grade pinus radiata, although Building A rimu and Douglas fir were available.

Non-loadbearing walls could be constructed from lower grade No. 2 Framing grade radiata pine.

Early in the decade, wall framing was typically wet or green and allowed to dry after the walls were erected. With the introduction of LOSP treatment the use of dried timber framing, particularly for pre-nailed wall frames, increased.

Wet timber lintels and beams and long span floor and ceiling joists, unless propped until dry, were often subject to sagging as roof loads were applied.

Construction

Frames were typically constructed on site (with the builder doing the timber grading as he sorted through the delivered packets of timber), although pre-nailed frames became available as the decade progressed.

Sizes and spacing

The introduction of NZS 3604 in 1978 gave specific requirements for wall framing sizes and spacing.

Wall framing typically consisted of gauged 100 x 50 mm timber studs fixed to 100 x 50 mm top and bottom plates. The standard stud height was 2.4 m.

Studs were generally spaced at 450 mm centres with dwangs, or nogs (horizontal timber blocking between studs) installed in horizontal rows at 800 mm maximum centres, or as required, to provide edge fixing for sheet lining materials, or to support internal joinery.

Early in the period, bracing (Figure 1) was solid angle bracing consisting of lengths of 75 x 50 mm or 100 x 50 mm timber cut and fitted on an angle between the studs and the dwangs (Figure 2).

As the decade progressed, the timber bracing was replaced with a cut-in 25 x 25 mm galvanised metal angle punched for nailing (Figure 3), as it was much easier and quicker to install.

Figure 1: Application of bracing (dwangs omitted).

Figure 2: Solid timber bracing.

Figure 3: Metal angle brace.

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Bracing calculations for renovation or repair

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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Flooring and bottom plates

Where a particleboard floor was installed, all wall framing was erected on the particleboard floor. If a timber strip floor was to be installed, external and internal loadbearing wall frames were erected before the flooring was laid, so bottom plates were fixed directly over the floor joists.

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Building paper and insulation

Kraft (black) bitumen impregnated building paper was installed on the exterior face of the wall framing. Synthetic building wraps became available during the early 1980s. Insulation within exterior walls was not a mandatory requirement until 1978, so it was not generally installed (see Insulation).

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Developments

Developments during the period related to framing also included:

• prefabricated panelised internal wall systems
• the widespread adoption of metal joist hangers, multigrips and timber anchors
• use of site-fixed nail plates to wall plate junctions, instead of the halved joints traditionally used
• the use of masonry anchors
• hot dip galvanised metal brackets.

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Two-storey wall framing

Framing for two-storey construction was typically platform framing, where lower walls were erected, floor joists installed, and the particleboard laid to provide the platform on which the upper floor walls were constructed and erected.

Platform construction effectively utilises two walls of framing (one for each level) separated by the floor joists of the first floor. Studs are therefore not continuous through both levels and bracing is also separately run between the bottom and top plate of each storey.