Nov 172011
 

All buildings must have a strong, serviceable,

stable and durable design-Part B

Why do you suppose we need structural design professionals to be involved in every aspect of building processes? I’ve thought about this often, since we’ve done a load of DIY projects that involve building, and we have seldom had professionals help us. But the point is that any building or structural element, however simple it may be, must be built in accordance with accepted principles of structural design. For instance we don’t just pile bricks on top of one another without sandwiching suitably mixed mortar between them – although I have visited an amazing home in Johannesburg where an architect totally defied this principle and built an incredible home on Linksfield ridge out of bricks sans mortar! But this is not the norm. Similarly, we don’t balance poles together like pick-up-sticks in the hope that they will stay in place.
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The Role of the Regulations in Structural Design

As the national building regulations state:

“Any building and any structural element or component” must be designed to “provide strength, stability, serviceability and durability”.

It is also vital that buildings are designed so that if the structural system is in any way overloaded they won’t collapse with disastrous consequences.

The regulations also state that these design requirements shall be “deemed to be satisfied” when buildings are designed in accordance with this section of SANS 10400-Part B, namely Structural Design.

When I last accessed the SABS online to see if these section of the regs was available, it wasn’t. However, there is no doubt that it will ultimately list all the other standards that designers should refer to when undertaking structural design. UPDATE: This is now available from the SABS at a cost of R369.36

Structural Design must be in Accordance with National Standards

It is essential that all structural systems are designed and built by professionals. It is also essential that all materials used are suitable and SABS approved.

Some of the SANS that are used by structural designers are:

  • SANS 10100-1: The structural use of concrete (specifically Part 1: Design)
  • SANS 10162: The structural use of steel
  • SANS 10163: The structural use of timber
  • SANS 10164: The structural use of masonry

There are also various SANS that focus on the basis of structural design and actions for buildings and industrial structures. These relate to a variety of actions that are caused by self-weight and imposed loads, wind, seismic action, thermal elements, geotechnical elements, and even cranes and machinery.

Lastly, there are international standards that should also be followed, some of which are available from the SABS.

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Dimensions

  91 Responses to “Structural Design”

Comments (86) Pingbacks (5)
  1. Hi there,

    I was wondering, is there a differens between building a house on the
    sea edge and building somewhere in land? if so.. were can I find these
    regulations regarding to this matter? I am looking for what the
    differences are.

    Thank you,

    Kind regards,

    Henk

    • Henk, the National Building Regulations relate to all building in South Africa, but there are some specifications in terms of coastal structures versus those inland. Roofs are one area where there are differences. But there isn’t somewhere that you can refer to that details coastal versus inland. You will need to plough through the full Monty … or ask a “competent person” for advice.

  2. WHERE CAN I FIND INFORMATION ON THE REGULATIONS ON THATCH ROOFS ?

    • Johan there isn’t a section, as such, in the National Building Regulations that deals with thatch, but thatch is covered in Part L: Roofs. Specific sections that refer to thatch roofs include:
      The table for maximum truss spans for various rafter and tie-beam sizes (which you will see if you click on the link, above). Thatch is in the category Class B.
      The table for the number of connecting devices – also Class B. In addition, the regs state that the centre-to-centre spacing of trusses relevant to Class B covering should not exceed 760 mm.
      The table for maximum spans for rafters – again Class B.
      The table that gives minimum roof slopes and sheet end laps – which we haven’t included. Thatch with a thickness of 150 mm should have a MINIMUM slope of 45 degrees; and a thickness of 300 mm should have a slope of at least 35 degrees.
      Fire resistance and combustibility issues also apply. You will find these in Part T: Fire Protection of the NBR – a VERY lengthy document that was updated considerably in the recent amendments. e.g. If the thatched roof is bigger than 20 sq m the building must be located at least 4.5 m from the boundary (not the usual 2 m). Size also affects other elements including sprinkler systems. Municipalities also have regulations on thatched roofs – contact yours for their requirements.

    • Johan I have updated the section on Roofs (http://sans10400.co.za/roofs/) – including the tables. I have also added a section on thatch roofs.

  3. Greetings Penny,

    Is it possible to build three houses on one foundation slab and declare them free hold? Give individual title deeds for each “structure” ?

    • This is out of the realm of building regulations, apart from which anything like this – if possible – would have to go through a number of legal processes. A lawyer will have to answer your question.

  4. I have been doing work in Lenasia, and was asked to erect a structure that was supplied to me. No soil tests were done but we were told to carry on. The client then brought an Engineer to site, as he didn’t know if the foundations we dug were right. The Engineer told us that he was satisfied with the dept and the width, but we have to put steel into the foundations. He then had another person there whom I don’t know, who said that in Lens they never put steel into the foundation. Then the steel were delivered. There are no drawings for the steel structure, although the supplier says that he can get an Engineer to give drawings. No drawings were submitted to the Local Government, and no approvals were obtained. We now have a problem with some of the structure and I need to speak to someone who can advise me what to do.

  5. Is it mandatory to use an Architect? If not, how would I obtain the building plans?

    • The National Building Regulations state that all building applications must be accompanied by a declaration by a person registered in terms of a “built environment professions council” (the main one being the South African Council for the Architectural Profession (SACAP) in terms of how the applicable functional regulations will be satisfied (e.g. the complexity of the project, and site sensitivity in terms of the environment). This person will need to be sure that the plans have been correctly drawn up. Architects, draughtspersons, designers and architectural technologists are all qualified to draw plans.
      If you are referring to existing plans, these should be lodged at the offices of your local council, and you can usually get a copy of the plans from them. I am pretty sure that an architect doesn’t have to make the application for you.

  6. If I have a good computer program that enables me to draw plans, is that good enough?

    • It might be, but you will have to have the endorsement of a registered professional since the NBR states that a “competent person” must oversee the project. So if you drew the plans, you’d have to pay a registered professional (e.g. an architect or draughtsman) to sign the plans and submit them on your behalf. It’s rather like a builder pulling in all the wiring for an electrical system; a qualified electrician will have to check that it is done correctly and sign of the job before the council will allow the wiring to be connected to the grid.

  7. What is a structural design professional?

    • Peter-John, a structural design professional is someone who is qualified to design buildings and draw up plans in terms of the requirements of the National Building Regulations and SANS 10400.The South African Council for the Architectural Profession (SACAP) is the controlling body, so all structural design professionals must be members of SACAP to be able to practice.

  8. Hi Penny,
    Im an owner builder. From step one, which is drawing up my own plan, and which is my question.
    Why must i be a member of sacap to draw up a plan? My main concern is, they (sacap) are violating my constitutional rights, then also. If they are not involve in the approval of the plans at the local municipality, then why must i pay their fees and for what?
    The local municipality, do have their own quilified building inspectors (architects & engineers), whom you pay for their service. So why must you pay people (sacap) for service they did not rendered?
    Trust to hear from you soon,
    Best regards,
    Aubrey

    • Aubrey, You have to be a “competent person” in terms of the National Building Regulations (2008). This means that you have to be a qualified professional. If you are not a qualified professional, be it an architect, draughtsperson, architectural technologist etc, then you are not allowed – by law – to draw up your own plans. Further, the law states that such a person must be “registered in terms of a built environment professions council”. SACAP is the regulatory authority for the architectural profession and as such is responsible for providing for registration of persons within the architectural profession. It has absolutely nothing to do with your constitutional rights! If you are a qualified professional, you are bound by law to register with SACAP. “Only persons who are registered with SACAP may practice or render architectural services directly to the public. According to Section 18(2) of the Act, a person may not practise in any category unless registered with SACAP.” Payment to SACAP would be for registration and membership, not for services rendered.
      Prior to the new regs, owner builders could do their own plans, as could many unscrupulous builders who were ripping off the public. The new law is their primarily to protect the public and help to improve our construction industry as a whole.

      • Very interesting, as a professional myself I totally understand the Law, but I recently had the case where I had to get a SACAB member to submit a plan for a carport, while I am a professional civil engineer, also registered with a professional body. I just thought that was taking it a bit far.

        • Steph, as I understand the regs, you, as an engineer, are a “competent person” and so could have done the plans, provided you have the relevant training. The law does not specifically state members of SACAP are only allowed to draw plans. But I suppose not all engineers are “competent” to draw plans. By the same token, there are certain plans that MUST be drawn by engineers. I think there are times that people like you need to challenge the authorities. As you say “interesting”.

  9. Dear all,

    I have a community facility zoned stand and need to build a 500m² building for the community. Do I need an architect to draw up my plans or can I use a draughtsman? Will a 20×30 building need steel structure.

    • The National Building Regulations state that all structural plans must be drawn up by a “competent person”. A qualified draughtsman is considered to be a competent person, provided of course this person has the skills to draw up plans for the structure concerned. Sometimes you might need an engineer.

  10. Please advise me, i have a single storey residentila house, but it does have a double stoery ready slab on the top. can i build a divider wall on the top of a certain room that does not have a matching wall on the bottom floor, will there be pressure on strain on the slab.
    Eg: the lounge on ground floor, i want to build two equal rooms in the equivelant space on the top floor
    please advise
    Thanks
    Rajan

    • Rajan, you need plans to do anything. You CANNOT simply build unless plans have already been approved for additional construction work. This is primarily for safety reasons. So your next step should be to either contact someone who is “competent”, who can draw plans for you; or to contact your local authority.
      I can though say that you would be able to build walls on the slab that don’t “match” provided the slab can support these walls. But even if the wall continues above, if the slab cannot support the second-storey structure, you’ll have problems.

  11. Penny,
    I want to terrace about 11 metres of the bank in front of my Unit using Corobriks Geolok 300 retaining blocks. The slope of the bank is about 45 degrees. I want to use two rows of blocks – approx 400mm high, which will prevent soil erosion. The trustees have agreed to the installation of the blocks, but have requested that a certificate of stability from an engineer be produced before the work can commence. The contractor advises that this is not required as it is less than one metre high.
    Please provide me with guidance.
    Hope to hear from you soon.
    regards
    Ravin.

    • Ravin if you required permission from the trustees (or body corporate) of your complex to build a retaining block wall, you will need to abide by their requirements. The National Building Regulations detail minimum requirements, but local authorities and individual complex owners/trustees etc have the right to demand additional steps be taken (including assurances from engineers on whatever it is they are concerned about). Corobrik may be able to supply you with some kind of certificate that would meet their needs, or advise who could supply this without you having to incur unnecessary expense.

  12. Good day Penny,

    I am not in the building industry, but I do have a question regarding the structural integrity of dividing walls. We moved into a flat and this flat has a dividing wall between the laundry room and one of the bedrooms. It is clear that this wall was built in later and does not form part of the original structure. From what I can see, the wall is built on top of the cement floor and only to just below the ceiling. No “puzzle-like integration” (excuse my lack of better description) seems to exist between this dividing wall and the original walls on both its ends.

    My question is: Is this acceptable building practice? Is there any building regulation that states that this may or may not be done (in a residential building)? I am concerned about the structural integrity of this wall. Could you comment on this and point me to some document that addresses this issue?

    Thanks

    • Jan-Hendrik, all walls in buildings should be on the plans submitted to council (or the municipality) and should show how they are meant to be built. You say this wall is built on a “cement floor” (it would be concrete – i.e. made with cement, sand and stone)… but is it built with bricks or blocks, or is it a dry wall? If built with bricks at a later stage, the question is whether the concrete base is sufficient to act as a foundation. The other question is whether the wall ties in with the other walls – this would be what you describe as “puzzle-like integration”. If it is in fact a freestanding wall, apart from the legality issue, it may not be a problem. But I can understand your concern.
      Do bear in mind that not all walls are load bearing.
      The National Building Regulations (see Part K: Walls of SANS 10400) cover all the specs for walls including both masonry (brick or block) and timber-framed (i.e. dry) walls. These include height, support, thickness etc. There is also a section on free-standing walls.
      Another issue is that the wall divides what you describe as a laundry room and bedroom. The NBRs are very strict when it comes to plumbing. It could be that a portion of what is now a bedroom was converted into a laundry … If so, I’d be worried about this.
      Perhaps you should have a look at some of the other flats in your block and see if they are configured in a similar way. If you are renting and are seriously concerned about the integrity of the wall, contact your local authority and ask if they can send a building inspector to look at the structure.

  13. Penny,
    What would be the minimum requirements for a dwelling in the Limpopo province concerning the geo-technical assessment of the soil where the construction is planned?
    Would the structure design be influenced by the geo-technical information?
    Trust to hear from you soon,
    Best regards,

    Christo

    • It isn’t where the dwelling is to be built (e.g. Limpopo), but rather the soil and environmental conditions that are important. And essentially the requirements relate to safety. The structural design would definitely be affected by geo-technical information if the soil or subsoil is unstable – this could be due to the presence of dolomite, heaving clay, collapsing sand etc.
      The National Building Regulations state that it is the responsibility of the local authority to notify owners/builders (or the “competent person” who submits plans to build on a plot.). But of course anyone buying land should do some investigations prior to purchase, because unstable soil can add hugely to the cost of building.
      If there is unstable soil (or subsoil, or slopes) in the area, then a geotechnical site investigation will be required to ascertain whether the site may be built on at all – and if so, what steps must be taken to ensure the building will be safe and stable.

      • Penny,
        In the case of a picnic spot being developed by a private entrepreneur, what will be the governing body that make decision on such cases. In the Limpopo province who would the best to sought advice in case of complication with structural design aspects for private dwellings.
        Thank you very much for your timely reply.
        Trust to hear from you soon,
        Best regarrds,

        Christo

        • Picnic spots are not covered in the building regulations!
          In terms of structural design aspects for private dwellings in Limpopo, you should start by contacting the local authority (or relevant municipality) in that particular area.

  14. Structural design outlines the essential issues of how a building should be constructed in a manner that the building shall sustain any actions which can reasonably be expected to occur and in such a manner that any local damage cannot compromise the effective purpose of a building. Skilled professionals are required and they need to comply with the principles of structural design so that the function of the building can be utilised to the optimum.

  15. The structural design talks about the way the building should be design to withstand all the overload,it must be built according to the excepted principle of structural design,also the building must be built by professionals and it must be stable

    • Thank you for taking the time to comment on this blog post. Indeed it is essential that accepted principles of structural design are followed and that professionals are employed. It worries me that sometimes people sidestep these vital issues!

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