Nov 152011
 

Regulations for Foundations-Part H
A Focus on Safety

Foundations, Part H, of any structure, large or small, must be built to safely transmit all loads of the building to the ground. If foundations are not correctly built, walls may crack and at worst, could even collapse.

While the National Building Regulations specify general requirements for foundations, it is the deemed-to-satisfy rules contained in SANS 10400 that give you more detailed information about how to ensure that your foundations comply.

Furthermore, the building regulations require you to have a competent person involved in the build of your home. You must also have plans drawn up according to the regulations AND the requirements of your local authority. This will ensure that the necessary controls are in place, and should guarantee that your structure will be safe and legal.

In addition to 10400, there are other South African National Standards (SANS) that deal with foundations. For example:

  • SANS 2001-CM2 covers construction works for a variety of foundation types (strip footings, pad footings and slab-on-the-ground foundations) for masonry walling.
  • SANS 10161 covers the design of foundations for buildings in general.
  • SANS 10746-2 relates to information technology, specifically open distributed processing. The reference model for this standard is foundations.
  • SANS 12575-2 which covers thermal insulation products, specifically exterior insulating systems for foundations. This is highly technical and really only for the professional use of commercial/industrial installers of foundations.

All these standards are available for a nominal fee from an SABS office or from the SABS online store.

The SABS also holds certain international standards, many of which were formulated by the International Standards Organisation (ISO). ISO standards relating to foundations refer to thermal insulation (ISO 12575-2:2007), thermal performance of building in cold weather, when there is frost (ISO 13793:2001), and information technology (ISO/IEC 10746-2:2009).

There is another IEC (International Electrotechnical Commission) standard available: IEC 61773: Overhead lines – Testing of foundations for structures.

How the Building Regulations Have Changed

The National Building Regulations and Building Standards Act, 1977 was amended substantially in 2008. In terms of  Part H of the regulations  the amendments amounted to an expansion rather than an alteration as such.

Previously H1 GENERAL REQUIREMENT (1) read:

“The foundation of any building shall be designed to safely transmit all the loads from such building to the ground.”

It now reads:

“The foundation of any building shall be designed and constructed to safely transmit all the actions which can reasonably be expected to occur from such building to the ground and in such a manner that any local damage (including cracking), deformation or vibration do not compromise the efficient use of a building or the functioning of any element of a building or equipment within a building.”

How to Ensure Your Foundations Comply
With the Regulations

Part H and Part B (which covers structural design) of the building regulations go hand in hand. So basically, if your foundation is designed and the concrete placed in accordance with the requirements of Part B, you’ll be safe.

Part B “establishes the representative actions and impacts applied to building elements and structural elements, and their structural response to these representative actions and impacts”. It “also establishes requirements for rational designs and rational assessments, Agrement certification and buildings on dolomite land”. This Part of SANS 10400 was only approved on August 31, 2012, four years after the legislation changed. It is available from the SABS for R369.36 incl. VAT.

Part H, (available from the SABS for R427.50) approved at the same time as Part B, “establishes the representative actions and impacts applied to foundations, and the response of structural elements to ground movements. Buildings that comply with the requirements of this part of SANS 10400 will also comply with the structural design performance parameters established in SANS 10400-B. It contains simple design and construction requirements for foundations for certain masonry buildings to accommodate a relatively small range of ground movements”.

In addition, there are a variety of other SANS available that relate to structural design, although most are intended for industrial and larger commercial structures, with a couple relating to the structural use of timber (SANS 10162-1 and 10163-2).

Empirical rules for foundations as specified in SANS 10400-1990 were relatively basic, following good building practice. For example:

  • The basic rules for foundations relate only to walls that are placed centrally on foundations – which ensures that they will safely transmit loads; AND are built on good quality ground soil – NOT heaving soil or shrinkable clay. So if there are ground issues on your site, or special foundations have to be designed by an engineer for some other reason, you cannot rely on the dimensions specified below.
  • Basic, uncomplicated foundations should be constructed with concrete that has a compressive strength of at least 10 MPa at 28 days, OR concrete that is mixed proportionately by volume in the ratio 1:4:5 cement:sand:stone. Mixing by volume involves carefully measuring out of the materials in a same sized container. A wheelbarrow may be used, but it is not a suitable method for large building projects.
  • Continuous strip foundations should be at least 200 mm thick, unless laid on solid rock.
  • The width of continuous strip foundations should be at least 600 mm if the foundation is for a load-bearing or free standing masonry wall, or a timber-framed wall that supports a tiled or thatched roof (which should, of course be constructed according to the building regulations), OR 400 mm if the wall is a non-load bearing internal wall or a timber framed wall that supports a metal sheet, fibre-cement sheet or light metal-tiled roof.
  • If a strip foundation is laid at more than one level, it is important for the higher portion of the foundation to extend over the lower portion for a distance that is equal at least to the thickness of the foundation. If there is a void between the top section and lower section, you will need to fill the void with concrete that is the same strength as the concrete used for the foundations.
  • Sometimes people thicken an existing concrete slab to form a foundation. In this instance, the TOTAL thickness (ie the concrete INCLUDING the original slab) must be at least the thickness that is usually required for continuous strip foundation (200 mm). The width of the thickened portion under the floor slab must be at least the thickness of a continuous strip foundation (see above).
  • The only time you won’t have to add additional thickening is when the walls are timber-framed and NOT load-bearing.
  • If a pier is built into the wall, or forms a part of the wall, the thickness of the foundation to the pier must be the same as the foundation required for the wall itself. The length and width of the foundation to a pier should project by 200 mm at any point on the perimeter of the pier (see drawing).
  • The thickness of the foundation to a supporting sleeper pier or sleeper wall must be at least 150 mm; the length of width of the foundation to the sleeper pier must be at least 450 mm; and the width of the foundation to the sleeper wall must be at least 300 mm.

If you are building a simple structure (a granny flat, a garage or perhaps a freestanding workshop) on flat ground or on a site that is easily levelled, you can rely on these dimensions and specifications. But don’t forget that the building regulations require you to draw up plans which a “competent person” must submit to your local authority for approval BEFORE you start construction of the foundations.

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Floors

  110 Responses to “Foundations”

Comments (107) Pingbacks (3)
  1. We are looking at building a rock (natural stone) cottage on an incline (hill side) (rocky soil).
    At the bottom of the slope the site will have retaining walls (rock) of about 1m high, ontop of which the house walls (single storey) will be built.
    Natural stone is quite heavy. How deep and wide do the foundations have to be and will 10MPA strength be strong enough or do we need to consider re-bar? The resultant wall will then be 1m (footing) + 2.4m wall = 3.4m. We’re planning light roof (corrigated iron).

    • Hi Aletta,
      I would love to help you but any advice would be thumb-suck. The law requires that you have a “competent person” draw up plans and by the sounds of what you are wanting to do you will probably need an engineers report before starting construction. I know it might seem a bit “over the top” but that is what the regulations require.

  2. Goeiedag
    Ons huis is nou vier jaar vandat dit opgerig is deur ‘n bouer wat
    geregistreer was by NHBRC, ons het ‘n verbandlening aangegaan. Die
    vloerteels aan die binnekant van die skuifdeur lig nou op a.g.v.
    klammigheid. Het ons nou enige eis vir die herstel daarvan. Watter
    inligting benodig u nog om ons hierin behulpsaam te wees?

    JJJ van Rensburg
    Wistariastraat 13
    Blue Horizon Bay
    Port Elizabeth

    Sel 0842998977

  3. HI,We built a house on a newly established estate. Part of the
    problems we have encountered was that the 1st 3 months of moving in
    our patio tiles have collapsed, our doors in the house do not close
    properly – even though the builder has “shaved” them a few times. and
    finally, after being in the house for just over a year, we noticed
    that our courtyard gate was rotting. The builder “fixed” this by
    painting over the rot. There are a few gates on the estate with the
    same problem. We have now been told by the developer that according to
    the NHBRC court yard gates are not covered and they are not liable to
    replace them. Please advise.

    • Hi Kim,
      I think that as far as the gate is concerned, he is right. But that sounds like the least of your problems.
      You need to establish why the tiles have “collapsed” and why the doors in the house do not close. You say that the doors are inside the house so I assume that they have not got wet and swollen. If so, then you have to look if there are any cracks starting to appear above your doors or anywhere along your walls. If there are, then these could be settling cracks. BUT not being able to close the doors suggests that the problem could be more serious. Ask the builder for a meeting to explain why there is so much movement in the building so that the doors cannot close, if he tells you that it is because of the clay content, then he should have put extra reinforcing in the foundations if he knew this. You do have recourse to the NHBRC who cover these things. Have a look on our NHBRC Q&A page. There is also a link at the bottom of that page for their contact numbers.

      • Kim I don’t believe you should be relying only on recourse to the NHBRC. Their warranty is limited (usually 5 years for structural defects) and very specific, and since this is happening within such a short period of time, the developer must surely be held liable. Check your agreement with the developer very carefully – if need be get a lawyer involved. You probably also have recourse in terms of the Consumer Protection Act. I’d be interested to know which developer this is. There are several major players in the building industry that continue to deliver shoddy workmanship and get away with it.

  4. i bought a plot and plan house in a area, i stay about months in the
    house and in and out side it start to crack, my nr are 083xxxxxxx for
    more information

    • Hi Mark,
      I am sorry but we do not make phone calls. You will need to supply us with more information if you want us to give you some advice. It sounds as if you have a claim if the cracks are serious and not just normal “settling” cracks. Contact the agent who sold you the house and point out the problem to them. If you got a bond from a bank on the house they will need to send an inspector to check the house because the house is the security the bank holds and must be solid and not cracking up.

  5. hi Penny
    i intend to build a lounge and garage /patio as an extension to the existing house, however i would like the foundation of the new lounge and garage to be strong so that in future it must allow me to add rooms on top of the garage and lounge (double storey) how deep must the foundation be?thickness of the walls and any other information that i will require.

    thanks in advance
    Desmond

    • Desmond, if you are building an extension then you will need a competent person to draw the plans. This person will be able to advise you in terms of exactly what it is you plan to do in terms of foundations. My book on Owner Building has some very useful info, and you can also read what the NBR say. I have already given a fair bit of detail on this subject on the web site. There are too many variables for me to be able to give you a simple answer here.

  6. Hi there Penny I am planning to build a house from vibracrete panels what type of foundation would be required as I know the posts go 600mm down but not sure of floor.

    • Lionel, minimum foundations should be no less than 200 mm deep and no less than 600 mm wide – but of course that is for bricks and mortar. If posts are to buried 600 mm deep, the footings should be at least 200 mm below these. BUT – if your are using these posts and panels for a “house” you DO need plans. And the plans will state what foundations you need. AND THEN, the local authority will still have to approve these. A “jimmy” house could have a dirt floor. A slab though should be at least 200 mm deep. My book on Owner Building might help you.

  7. hi Penny
    im about the to build a dinning and covered patio area to my house(waiting for plans from council) both of which will have ibr sheeting for my roof The ground in the area is very rocky, can you please give me the depth and width for the foundations and do i require re-inforcing (re-bar)
    thanks

    • Marcus, that information should be on your plans. Depth, width and reinforcing will depend, not only on the condition of the ground, but also on the structure itself.

  8. For a project I need to discuss foundations on the Vaal river. Where can I find info on the type of foundation required near a river? Surely we need to know what kind of soil is present.

    • I discuss problem soils in my book, Owner Building in South Africa. But you are correct in saying that you need to know what type of soil is present on site. So it is the Vaal River area rather than just generally a river, that you need to worry about. Areas in and around Jhb, Pta, Welkom and Bloem commonly have sand that moves a lot and collapsing sand is common. Much of the Free State has heaving clay. You should be able to find this information on the Internet.

  9. Hi Penny,
    I just wanted to know,what is the procedure if I want to make my existing house into a double storey?

    • Sudhir, It depends on the existing foundations.So your first step should be to access the original plans. If you don’t have them, your local authority should have them on file. If the foundations are not adequate to support a second storey built with bricks/blocks and mortar, your best bet will be to look at timber frame using relatively lightweight materials. Either way you are going to need a qualified person to draw up plans for you to submit to council.
      Another option might be to go into the roof – if it is pitched.

  10. hi i just want 2 know the size of foundation of a 3 story. And the types of foundation and why there differ

  11. I was wondering if i need to put reinforcement into my foundations for a double garage/ store room/ accomodation?

  12. Hi Penny

    Is strip foundation specifications for a double storey with concrete first floor and chromadek roof the same as for a single storey?

    Thanks very much.

    • The specification given in the Building Regulations and SANS 10400 are MINIMUM specification for building. The greater the load, the more substantial the foundations will need to be. It is the local authority’s responsibility to check that the dimensions and other specs – e.g. reinforcement – are sufficient for the plans that are submitted. So in a word: “No”.

  13. Hi Penny,
    Thanks for the reply. Could you also send me info on the manufacturing of roof trusses, please. I would also appreciate drawings of trusses and specifically how to join into an existing roof.

    Thanks

    Danie

    • Hello Danie, I have added a section on roofs and roof trusses relating to the National Building Regulations. http://sans10400.co.za/roofs/
      I have also included a drawing of different roof trusses from our book, The Complete Book of Owner Building in South Africa.
      I cannot advise specifically how to join your two roofs, as I have no idea of the design of the existing roof. The simplest option – which will work if the extension continues in a straight line from the existing house – will be to continue the line of the rafters, and to construct them in the same way as those that were originally used. For example, if they roof was designed using six bay Howe trusses, then you continue the extension with these. Obviously the pitch will then need to be identical as well.
      I will add some more information relating to the manufacture of roof trusses at the beginning of the week. In the meantime, I hope this is helpful.
      Kind regards
      Penny
      PS We totally revised Owner Building last year, and an all-new edition will be published soon.

  14. I need the specifications for foundations for a granny flat – Cape Town area

    • Hello Daniel, we have added information about foundations which should help you. Go to National Building Regulations, Building Regs Part 1 – Foundations; or follow this link
      http://sans10400.co.za/foundations/
      You might also find an article on casting a slab, that is on one of our sister sites, useful. This particular slab was in fact constructed for a factory-manufactured timber “granny flat”.
      The site is http://www.howtoinfo.co.za
      Cast a Concrete Slab … which you will find under Building & DIY
      or follow this link
      http://www.howtoinfo.co.za/cast-concrete-slab/
      If you require more info let us know.
      Kind regards
      Penny
      Follow this link

      • Hi Penny,

        Can you please tell me when do you need plans for an open carport? Its got a corrorated iron roof with 4 tube steel pillars supporting it and open on the sides. But its built on a concrete slab thats about 1 meter high and is raised. I don’t know what’s inside it. The land is sloping so the house is built at the bottom about 6 meters down. There were no plans submitted to town planning and it’s not on the sectional title plan. Thanks. I can email a photo if it would help.

        • Any structure that has a solid roof should have a plan. Generally a carport with steel posts would be constructed with the posts embedded in a concrete footing. If you can get hold of a copy of our book Build Your Own Carport & Pergola (Struik Publishers 1994), you will see that these should be approx. 600 mm x 600 mm x 600 mm. I am presuming that the concrete slab is simply a surface for parking, rather than a foundation. If it is raised, it might have been filled with soil or rubble. Do email a pic, it will give us a clearer picture.

          • Hi Penny, thanks. How do I attach a picture? I don’t see a button for it?

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