The maximum permitted crooks in NZS 3631:1998 for 90 x 45 mm studs are:
• up to 3.0 metres long – 10 mm
• up to 3.6 metres long – 15 mm
• up to 3.9 metres long – 20 mm
• up to 4.5 metres long – 25 mm
• up to 4.8 metres long – 30 mm.
Studs with the above crooks may be straightened with a saw cut in one edge, no deeper than the centre line of the stud, with no more than two cuts per stud. Studs are usually pulled from the uncut side towards the cut side with a wedge being driven into the cut(s) in the stud to straighten it. When straight, nail 19 mm (minimum) thick timber fishplates (the width of the stud) to each side of the stud. Both fishplates must extend 225 mm minimum above and below the cut(s) (Figure 8.6 in NZS 3604:2011).
No more than a quarter of the studs in any run of wall are permitted to be partially cut to allow them to be straightened. No two adjacent studs are permitted to be partially cut and straightened. Cutting and straightening of trimming studs (single or double) is not permitted.
Reproduced from BRANZ Guideline January 2015