There may not be a gap larger than 2mm in general and 5mm on longer “skarf cuts” of 300mm or more in length. Although this is difficult to attain with the poor quality of SA Pine, this is a design and SANS 10243 & SANS 1900 / ITC-SA requirement.
As fabricator and quality approved plant, LCP Roofing uses various simple methods to achieve this on the framing table, including jigs, stapling and clamping so that nail plating can be done according to, and exceeding minimum requirements.
All structural timber used in roofing construction in South Africa has to conform to SANS 1783-1 and SANS 1783-2.
This timber is graded at the sawmill as either grade 5 [S5] or grade 7 [S7]. If a truss plant is accredited, it may re-grade S5 to S7 at the plant. Once graded, timber may not be “ripped”, that is a 152mm wide plank may not be ripped into 2 x 76mm planks. Furthermore “black cross” timber may not be regraded.
The supplying mill must supply its graded timber clearly marked with the grading mark. It is VERY IMPORTANT to note that a truss plant purchasing GRADED timber is NOT exonerated from checking that the timber dimensions are indeed correct.
A truss fabricator that does not check timber dimensions will not be able to blame the supplying mill should a failure be proved due to a dimensional issue. LCP Roofing, through its SATAS accreditation is obliged to check ALL incoming product for dimensional accuracy.
It is our experience that some timber purchased from various mills and agents, NOTWITHSTANDING GRADING MARKS, does NOT comply with SANS 1783-1 & SANS 1783-2.
As client, you must then ask yourself the question – does my fabricator as a SATAS or SABS accredited and quality mark holder check & verify all incoming material for dimensional accuracy and CAN THEY PROVE IT?
LCP Roofing has extensive experience in the roofing business and our teams have seen their fair share of common errors that are made during the rood erection phase. This article is written in the hope that we can help you prevent such mishaps from happening on your building site. We’ll use images and diagrams to explain and discuss each of these problems in detail.