Hennie Viljoen, marketing manager at MiTek Industries South Africa, on the required protocol when erecting a roof structure
The roof of a building is considered an engineered product. As a building is designed to suit the owner, and the National Building Regulations (NBR) categorically state that the owner shall – where a rational design is required – appoint a competent, professional person (such as an engineer or architect) to carry out that design. Even if there is no rational design, there must still be a design in terms of the NBR.
This leads to the definition of a rational design, namely one that is carried out by a competent person who applies their (rational) mind to provide the solution to the questions posed by that design or, as the NBR state, ‘any design involving a process of reasoning and calculation and may include any such design based on the use of a code of practice or other relevant technical documents’.
Every individual job must be subject to engineering approval of sorts. In the case of domestic housing, any structural engineer (not geotechnical, electrical, chemical and so on) can take responsibility for the roof design and act as the competent engineer, provided they are competent by way of training and expertise; that they receive a copy of the design and check it; that they go on site and inspect the completed structure (or send a competent employee); and that they are a registered professional engineer with adequate, current professional indemnity insurance.
Several rules related to engineering are relevant to the roofing industry, and while some are obvious, others are not. The former are usually governed by SANS 10400 and the NBR. MiTek, of course, has several experts on staff and offers the service at extremely competitive rates.
Any building to which the public (including employees) has access is considered a public building. These cover all buildings categorised under the NBR Table 1, excluding classification H3 & H4 (domestic dwellings). Any dwelling used as a B&B or boarding house (H5) is also considered a public building.
In terms of the required licence agreement between parties, MiTek must be the signing engineer. The company will always appoint a professional team of experts when dealing with public buildings.This team is typically headed by an architect and includes a quantity surveyor, as well as several engineers (such as geotechnical, civil, structural, fire, electrical and so on).
In some cases the structural engineer will take responsibility for the roof, but mostly only if they first obtain a MiTek certificate. When issuing or being required to issue a manufacturing certificate, it’s important to note that it differs from an engineering certificate.
MiTek South Africa’s engineering department offers roof-inspection services for new and existing roof structures.
BY THE BOOK
According to regulation 11 (2) of the construction legislation (2014), it is imperative that building owners ensure that inspections of that structure are carried out periodically by competent persons in order to render the structure safe for continued use; that the inspections are carried out at least once every six months for the first two years and annually thereafter; and that the structure is maintained in such a manner that it remains safe for continued use.
The NBR deem the owner responsible for the roof structure, regardless of the type of building (house, office, hospital, and so on). In fact, the rule is that, where a rational design is used, a professional, competent person must be appointed by the owner to carry out that design.
The roof inspection is an important part of the design process, and therefore the engineer (or a qualified appointee) must inspect and sign off the complete design. All rationally designed roofs need an inspection by the design engineer or their competent appointee. Roofs built in accordance with the ‘deemed-to-satisfy’ rules of the NBR should be checked for compliance by the architect/owner/building inspector. No engineer is required. Simply put, all roofs need to be inspected. The owner is responsible for payment, either as part of their roof supply invoice or their fees payable to the professional team.
The inspection can be conducted by the designer or their qualified appointee, provided the designer is registered with the Engineering Council of South Africa and competent in terms of education and experience. (A registered lift inspector, for example, cannot inspect or sign off a roof, and neither can a registered chemical or electrical engineer.)
The inspection is signed off by the engineer (not the appointed inspector) who takes full responsibility for the design and who must, in terms of the ECSA, have professional indemnity insurance. The roof should also be inspected by the fabricator thereof – this saves time and money, and it helps train the erector. They should check that the roof is erected in accordance with the design assumptions. This is an ideal situation but does not happen often. Once the fabricator is satisfied the roof is right, they can notify the engineer to arrange the formal inspection and sign-off. Ultimately, it is the engineer who will sign the completion certificate and be responsible for the completed roof.
Often in the case of public buildings, the system engineer is not the appointed engineer, but by signing off the roof and supplying the fabricator with a certificate, they accept that the appointed engineer will look to them as being responsible should anything go wrong with the roof. For this reason, MiTek certificates always note the inspection date, in addition to the presence of any other on-site traders who may have interfered with the trusses and caused the certificate to be voided. Managing this is the responsibility of the appointed, overall engineer or of the owner, who retains complete responsibility.