Wall framing: original details
Wall framing, consisting of studs and top and bottom plates, was rough sawn 4 x 2” (100 x 50 mm) timber.
Timber used
Rimu became the most commonly used timber for bungalow construction due to its relative abundance and the shortage of kauri.
Miro was also sometimes used. It is a very similar timber to rimu in performance (although related to matai) but is a harder, more durable timber. It can be identified by its golden colour and the darker markings in the grain. Other native timbers that were used where they were available included matai, tawa, and beech species.
Bottom plate
The bottom plate was fixed directly over the joists before the flooring was laid.
Studs
The typical stud height, which had come down from 12’ (3.6 m) in the villa to 10’ (3.0 m) in the transitional villa, had reduced again in the bungalow, typically to 9’ (2.7 m).
Studs were typically spaced at 18” (450 mm) centres and sometimes housed into the bottom plate. This allowed them to be cut to a common length as the housing accommodated the variation in the sawn timber dimensions of the plates.
It was also considered to reduce the risk of the stud framing from twisting – always a risk with rimu. (Jeremy Ashford reports seeing studs bowed so far that they were completely outside the wall-line, and purlins turned 90º).
Dwangs
Horizontal timber blocking between studs, called dwangs or nogs, was not used in the earlier bungalow construction, but was sometimes used to provide fixing for the sheet lining materials such as plasterboard and asbestos-cement board, that became available during the 1920s.
Loadbearing walls
The loadbearing walls were the external walls and generally one or both of the internal walls on either side of the central hallway, depending on the roof configuration.
Internal walls other than those parallel to the corridor were generally non-loadbearing. As these were often constructed after the flooring had been laid, it is also likely that where they joined the external walls, they were constructed after the sarking had been fixed to the inside of the external framing. If this is the case, the internal wall framing is not likely to be connected to a stud in the external wall framing.
Bracing
Bracing for lateral stability was provided by 6” x 1” (150 x 25 mm) timbers fixed at 45° to the studs and housed into each stud and into the top and bottom plates where they intersected with them (Figures 1 and 2).
Figure 1: Bracing housed into studs and plates.
Figure 2: Timber diagonal bracing housed into studs.
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.
Lintels
Lintels over door and window openings, unless spanning a very large opening, tended to be a 4 x 2” (100 x 50 mm) plate laid on the flat even in loadbearing walls. This is undersized by modern framing requirements. Some brick bungalows had concrete lintels.