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. Whats the depth of a three storey building with a proposed lift

  2. I want to build a Three Storey building with a Lift, Pls adive whats the minimum depth of the foundation is to be.

  3. Hi there
    I am wanting to build a double storey house in a rural site, please advise as to how thick and wide the foundation and the top floor slab. I intend to put the grass roof.
    I assume your book can be assisting also for me to know more about building, how can I get a copy ?

    • Please read our post on foundations where you will get all the info you need: foundations There is a picture of our book on every page of the site you just have to click on that and you can buy it online.

      • Hi Janek
        I am in the process of doing extensions on my house and I need a book that will explain to me what process the builders should go threw from digging to completing the foundation at floor level. Can u assist?

        • Morne, we have done the most comprehensive and best selling book in SA detailing all the steps on building a house, extensions go through all the same processes. This can be ordered through Kalahari. Look at our website and click on the link on the left “Get this best-selling book today”

          • Hi there!i live in carletonville west of jhb and I would like know if I am allowed to build about 8 small cottages in a 1000sqm stand to rent it out?

  4. We are busy building our first house via a contractor.

    We are now at foundation level for a while now with work not really continuing, due to a number of reasons the contractor mentioned. Someone mentioned to me, that as far as they are aware the foundation had to be done on one day. Our contractor did it over two days though. Is it true that there is a problem if it was done over more than one day?

    Kind regards.

    • Ideally foundations and slabs should be placed in one go. These “emergency joints” are fairly common. It should not be a problem so long as the “construction joint” is done correctly. There should be a sloped edge (not smooth but rough)so that the fresh concrete can overlap the older concrete and make a good bond. It is recommended to brush the older edge with a wire brush before placing the new batch.

  5. Hi i wuld like to know,what happens if i just casted a slab then it started to rain imediatly afta casting?does this mean i mst demolish the slab and redo it again or can i just do screting on top?please reply,i thank u in advance!

    • You should be OK so long as it was not a flood that washed away a lot of the cement. The longer the slab is kept damp while it cures the better it is for the slab. So lond as it is not too wet you can screed on top but just try to let it dry slowly as fast drying can cause cracking.

  6. Hi,How deep must the foundation be for a boundary wall? Build with standard 190 x 190 building blocks.

    • Hi Wynand, The size of the foundation does not only depend on what bricks or blocks are used but how high the wall is going to be so that the foundations can bear the weight safely. Here is the standard formula for walls:
      Footings
      You can read up more on our other site:
      http://www.ownerbuilding.co.za/concrete-foundations/

      • How deep below ground level should the foundation be?

      • I have a question.my company is mandated to build a 1800m x2.1 m boundary self standing wall and I don’t know how deep the foundation must be

      • Hi Wynand/ Janek

        This formula is a basic guide only and should not be used to construct any load bearing walls. The footing size is dependant on a few more factors other than those mentioned. The first step in foundation design is to know the existing soil conditions and to determine the load bearing capacity. This can be done by taking a standard DYNAMIC CONE
        PENETROMETER (DCP) TEST.
        The second step is to determine the load (self load + imposed load) which should preferably be determined by an structural engineer.
        The third step is to take the ultimate load and calculate the foundation width and depth accordingly.
        If the calculated foundation size is smaller than what is shown on the above image, then it is recommended to use the image as a nominal foundation size.

        Hope it helps.

        • Hi Arno, Thanks for the added info, you are right there are always other factors that have to be considered that is why Architects and Engineers study for so many years to be able to work out all these calculations.

  7. what is the minimum time recommended for any foundation to cure before building can be started?

    • Hi Maret, Soil, atmospheric and weather conditions as well as altitude all affect the drying and curing time of concrete foundations, but usually a day or so of drying should be OK. Just take care in very hot and dry conditions to keep the concrete damp (not wet) and let it cure properly.

  8. HI.
    I have a huge school project that i have to do and i was wondering if you could help me.

    i have to design and a school pavilion which can be at and maximum 30m by 100m but im planning on making it smaller. and i want it 3 stories high. I’m try to figure out the thickness off the concrete foundation that i should use and the type of concrete i should use to keep my building standing with all the correct laws and regulations in place.
    please help.
    thanks.

  9. Who can certify foundation and floor with a certificate?

    • At what stage Liezl? I’m not sure about certificates, but both the NHBRC and the local authority check foundations and floor.

      • The NHBRC are more worried about what they can get out of the deal. They are also very incompetent and do not assist at any stage if a problem occurs.

      • Hi
        Our builder has recently poured the slab for our new house and then discovered the dimensions where incorrect (to small) He has subsequently added on the extra +- 300mm onto the existing slab which was poured over a week ago –
        Should the additional slab be “tied” in some how to the existing slab to avoid cracking etc? or is it ok to simply add on?
        thanks so much
        R Robertson

        • I am not sure if you are talking about the foundation slab or the floor slab. If it is the floor slab, this should be resting on the foundations, and if made bigger it won’t. if it is the foundation slab, this should have been approved by the local authority before the concrete was placed. I think it is more important to be sure that the groundwork (i.e. the trenches) were prepared correctly. You shouldn’t have a problem placing concrete in batches – it happens all the time when there is a big area.

  10. Hi I bought your book but can’t find any details on a double foundation We don’t intend to build double storey but we want to do a hight pitched light steel frame roof with chromodek & have the option to go up & use the loft space should we later want to. Can we do single foundation reinforced or must it be double foundation or must it be double and must every double foundation also be reinforced. What are the specification (formular) for double foundation? Thank you

    • Charlie, if you are building you need plans drawn up by a competent person. That person is qualified and will know what to specify for the foundation, depending not only on your roof structure, but also on the design of your house, including the walls.
      Also, I think you are confusing terms here. You don’t have a “double foundation” because you are building a double storey building. The size of the foundation is determined by the weight it has to carry. Most foundations should be reinforced, but that reinforcing also needs to be specified by a competent person. The rule of thumb to use is explained on page 99 of my book (on page 101 of the old edition). Essentially the width should be the width of the wall plus twice the thickness of the concrete. But you would increase the dimensions to improve the load bearing capacity of a double storey. If you decide to use the loft space at a later stage you will need to submit a rider plan that indicates the class of occupancy according those given in Part A, General Principles and Requirements of SNAS 10400.

  11. I am looking at building a 3 line double brick wall with square pillars every 3000mm (4 brick pillar, 18 lines up). Total length will be 20 meters. These openings will have palisade panels in. My question is this, will a 200mm deep foundation be sufficient for this, 400mm wide?

    • Werner, rule of thumb when building foundations is to ensure that the width of the foundation is equal to (or greater than) the thickness of the wall plus twice the thickness of the concrete. This in turn ensures that the concrete forms a 45 degree angle between the base of the wall and the bottom edge of the foundation. Since you are building pillars, you need to use the dimensions of the pillar – not the wall. And BTW we call them courses, not lines 🙂 Another good rule of thumb is that strip foundations should never be less than 200 mm deep or 600 mm wide. Standard bricks measure 222 mm x 106 mm and your mortar joint will be about 10 mm = 338 mm + 400 mm = 738 mm (if the foundation is 200 mm deep). So you should make the width about 750 mm.

  12. I am looking to build a home but want to use one of these standard roof structure they use mostly for stores and so on 20 x 9x 3.6 (h). They will supply me with full engineering drawing. Now my question is I still have to do the walls and foundation separate from the roof do I need a separate plan or do I still need a plan at all not sure of the complete process to follow. Do I need land surveyors. If f someone can help me with a general Idea of my steps to follow for my plans and before building starts I would highly appreciate it I am in the Pretoria area

    Regards

    • Dirk I suggest you buy a copy of our book Owner Building in South Africa. It takes you through the whole process from buying land, getting plans drawn (including the role of land surveyors), building, finishing and landscaping. Alternatively take the time to read through this entire site – and our sister site. You will glean quite a bit from what we have written and posted.
      To briefly answer your questions: You need a full set of plans as described in Part A of SANS 10400 (see General Principles & Requirements on this site). The engineering drawing for the roof will then be submitted with your other plans – you need a competent person to do this. The link I have given you is to our other site where the concept of a competent person is described. This is required BY LAW!
      If your boundaries are not accurately demarcated you will need a land surveyor to check these.
      Contact your local authority (Tshwane) for further information – e.g. any bylaws you need to be aware of. You can also download the Tshwane Town Planning Scheme from this site. I have given you the link.

  13. Hi We have a lot of water draining in the area where the foundation was dug. An engineer is coming out as we’ve been pumping the water out for four days, but it keeps filling up. What to do?

    • Hi Janine,
      I am not sure what area you are in or what your soil conditions are as some areas have a high water table during the wet season. This happened to me on one of the houses that I was having built on a sloping site and we discovered that it was an underground stream. The solution was to install a drainage system to divert and channel the water away from the foundations which was quite a mission. The engineer that you have called will certainly be able to advise you on the best solution.

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