Concrete Foundations
A Concrete Foundations Placing Guide
Cast Your foundations
This guide will help owner-builders to cast the concrete foundations. These foundations are for external brick walls around a new house, or for extensions of an existing house.
THE NHBRC (National Homebuilders Association Council) requirements for house foundations:
For single-story buildings with tiled or sheeted roofs in stable soil conditions, the minimum width of strip concrete foundations should be 500mm for external walls and 400mm for internal walls. If a reinforced concrete roof is required on the house then the minimum width is 750mm for external walls and 600mm for internal walls.
Trenches
Trenches on sloping ground can be stepped with a minimum of 400mm overlap. Sloped trenches must not exceed the 1:10 gradient.
The minimum depth of the strip concrete foundations trenches must be at least 400mm below the original ground level.
The average minimum thickness of the concrete foundations must be at least 200mm. The strength of the concrete used for unreinforced strip footing must be at least 15MPa or better. For a double-story building reinforced foundations would require 25–30MPa.
Trench sides
Trench sides and walls must be as near to vertical as possible. Trim the sides of the excavation to avoid holes being filled with concrete on the side faces. This will require more concrete than estimated and will be a waste.
When you have finished the excavation measure the actual depth, width, and length of the trench, and calculate the actual volume of concrete that you will need. Always add an additional 10% to allow for wastage and unforeseen circumstances. See our tables here: Concrete mixes by weight & volume
Placing
When placing your concrete foundations there are a few things to consider.
Clear the soil that was excavated well away from the edges of the trench to stop it from falling back into the trench and contaminating the concrete. If you are using wheelbarrows to ferry the cement then place planks along the edges where there is soft bedding such as fill material to prevent loose soil from falling into trenches due to the weight of the wheelbarrows.
Gently wet the excavation trenches before placing the concrete to avoid moisture being drained out of the concrete mix into the surrounding soil as this could weaken the foundation.
Compact the concrete to remove any air bubbles. This will increase the density and strength.
Curing
Fresh concrete needs to be protected from drying out too quickly. Gently spray water over the concrete foundations as soon as the concrete has set. In hot dry areas, the concrete can be covered with plastic sheeting to stop the concrete from drying too quickly. Remove the plastic and spray water onto the concrete every so often to prevent it from drying too quickly. When concrete loses moisture too quickly either by evaporation or absorption by the surrounding soil, it shrinks and if the concrete is not malleable, it will crack. See our article on drying in cold weather.
Here is an extract about water and concrete from a Wiki article:
The most destructive agent of concrete structures and components is probably water. Indeed, water often directly participates in chemical reactions as a reagent and is always necessary as a solvent, or a reacting medium, making the transport of solutes and reactions possible. Without water, many harmful reactions cannot progress or are so slow that their harmful consequences become negligible during the planned service life of the construction. Dry concrete has a much longer lifetime than water-saturated concrete in contact with circulating water. So, when possible concrete must first be protected from water infiltrations.
How soon can bricklaying start on the foundation?
Forty-eight hours after placing the concrete. You can build the first 500mm of brickwork above the surrounding ground level. Then you must carefully wet the concrete thoroughly and backfill your trenches with soil. Seven days after placing the concrete foundations strips, they should be strong enough and your walls can be built up to roof level. At this stage, the concrete should have reached 60% of the final strength.
Read more about concrete:
https://cemcon-sa.org.za/information-hub/information-centre/
Is one layer of 9mm mesh enough in one storey house strip foundation or must be double layered, with spacers/stools between the two?
Hi, Please help me pass the NHBRC exam, I read the NHBRC Guide and SANS 10400 could not give me most of the answers to pass the exam
I just want to say your answers are very informative and direct… Thank you
You don’t say how far off ground level the existing floors are. But since the previous owner has successfully filled beneath the floor of three rooms, do what they did. I assume they would need to be filled with concrete to create a slab. You should use a registered builder to do the job, and possibly consult with an engineer.
Hello Please advise I have an old house with suspended floors not many people can give me advise. I’m at my wits end with these suspended floors. 3 rooms of the original structure have already been filled by the previous owner
Currently 3 rooms and the passage still have suspended floors I want to fill these floors and I need advise and competent person that could do it for me please assist
Hello Please advise I have an old house with suspended floors not many people can give me advise. I’m at my wits end with these suspended floors. 3 rooms of the original structure have already been filled by the previous owner
Currently 3 rooms and the passage still have suspended floors I want to fill these floors and I need advise and competent person that could do it for me please assist
Hi Penny
Am currently in the process of extending, plan has been submitted and approved. We are waiting for inspection now as the digging has been done. My question is exactly how long must we leave the foundation to set before going up with brick laying? I seem to be disagreeing with my builder.
Good Morning All
If you extend by adding a 5m x 5m with an approved plan, does an engineer only inspect the soil and foundation? or do they need to inspect walls and roof, as the building is being done?
thanks
Al
Hi a municipality want you to include a builders deposit and a builders fee when you submit your building plans. Please explain what these items are.
Does maxibrick one line allows i as a builder to do a slap roofing? So does the block brick( those of 2 holes in it) do a double storey?
I am building a double garage. I would like to know how thick the slab should be.
Hi. Can u advise how long it takes to get a house plan approved in Tshwane
Hello… im building single storey home on a steep rocky slope in rural area. 1. Do we need reinforcements 2. What is maximum length of wall of levelled ground…. from ground to level with steep
Reinforcement is very imortant bcz it is the one that holds stucture not the contrete. If contrete fails. Reinforcement will hold it together for as long as those steels are very rusty at some point but that on it own can take for like around 80 years
Iam a qualified builder, if you need any help. 0629766282 whatsapp or call
hi Penny, my neighbour wants to build a double garage but we have a boundary wall. he now wants to break the wall down and rebuild so he will have more space on his side. is this legal to do? it was never discussed and is not on the plans in detail.
Hi specialists
I’m. Building a double storey in rural on a g5 soil and only reinforced where only the house would be double storey,And my builder is someone who has done this job U numerous occasions and he worked with contract before any advice please???
Hi I’m specialists
I’m. Building a double storey in rural on a g5 soil and only reinforced where only the house would be double storey,And my builder is someone who has done this job U numerous occasions and he worked with contract before any advice please???
Hi
I just start a construction company. I’m still doing compliance I’m left with NHBRC I will write on leve1
I just ordered a book on line tittle Owner Building In Southern Africa. Just before paying i noticed it was published June 2012.
Did you publish any book after this , I would like to buy the latest version.
Regards
Bongiwe
Hi i just wanna know How I could mix one bag of cement with How many wheelbarrow of redymix
Hi,
For evaluation the size of foundation, In SABS is there any provision of Increase in Soil bearing capacity under the effect of Wind and Seismic. If yes can you provide some reference.
Thank you,
Hi
I am building a porch with the highest part of the wall being 1.8m high. A trench foundation has deen dug with measurements of about 400-500mm depth and 600mm width. The soil is hard/ rocky clay soil.
I would like to find out if I should include steel in the foundation.
I have dug trenches for an extention of garages and the trenches are constantly in water on one end as if there is some source underneath. What can I use to syop and dry up this water prior to pouring concrete?
I am looking for the minimum depth (thickness) of a reinforced concrete first floor. What is the standard thickness for a normal house?
Thank you
Hi, I am building a 2 storey house in the village in Zeerust north west. My challenge is that it is a clay soil area. What would you advise to be the depth and width of the foundation and the level of concrete filling from the ground. I tried to find an engineer to assist but most of them are far.
Hi Penny
I bought your book to do a research before embarking on my project later this year around May.I must say it’s very informative book for anyone who intends building a house soon.
My only concern is I could not get all the info I need with regards to brick works,the kind of bricks I need with regards to building a double storey house on a clay rich soil and the seizes or reinforcement steel to use.It seems like I get different info and advise from people who claim to know.
Any links or advice with regards to this subject matter will be appreciated
Good day I will like to find out about using ready mix or normal concrete for foundation. Can I go for concrete
Hi,
I’m drawing up some plans for a new house…
What I want to know (and the NHBRC) handbook is not very clear about it).
I’m using a strip foundation and need to know if the compacting rules (Controlled or Engineered) apply for under the concrete on the strip?
Does the same rule apply when doing a Foundation wall that will extend 1m above natural ground and need to be filled under the foundation floor?
Thank you
Hi. I am planning to build a double storey on clay inland coastal soil which needs piled foundations. Where can I find more details on this method? Does anyone want to sell me their sans 10400 handbook?
Hi, please can you let me know where do I find out if my house is build on clay soil. I recent had an insurance claim which was rejected because of that.The assessor made the assessment by just looking at the soil.
Thank you
Elnola
We are interested in purchasing a land so we can build our house, the challenge is the house has doundstion of 7 room, how much does it cost roughly to remove foundstion?
Hi.
What are the specifications for a double storey house foundation? I see it says 750 mm for the outside walls and 600 mm for the inside walls but it doesn’t mention the dept. The house will be constructed with bricks. Can anyone kindly assist. Thank you in advance.
Hi I am having a 8m2 veranda lifted due to the heavy rains we suffered in KZN recently. The ground is very sandy and slopes away from the garden flat. Is there any specific procedures I must follow besides the building regs.
I understand. Just one question. Is it law to build a house on foundation? What if the house is 50+ years old an built without fiundation. And yiu want to make some changes?
How deep must a vibrecrete pole be concreted in the ground
hi what size of blocks that must be used to build a double storey house?
I have a park home and want to build on a room using concrete floor and building a wooden frame work with newtec side panels with sink roof. Do I need plans draw up to extreme onto a park home.
I also want to put up a 2 bedroom Wendy house do I need plans to be drawn up before I can erect them
Io Reader.
I’m planning on having a shed/workshop build (single-standing,4 x 4m.).
My enquiries: am i allowed to use concrete blocks(395x190x145 mm.) for the walls;is it permissible to build left of the centre line,closer to the outer edges of the foundation;can the foundation width be 400 mm.(as i’m building single walls,145 mm. wide).
Thank you.
Hi what is the Foundation standard size for a 140mm block foundation wall
Hi
Don’t know how active this is as I see the last replies was in 2014. I want to know is I remove my concrete slab wall and rebuild with concrete block wall, do I need approvals and plans. wall will be 1.8m.
Thanks
Morning.
I’m looking to build a DBL story (7m high) what should the depth and width of my foundation be?.
I will be reinforcing the foundation.
Thanks
Annelie, There is a misconception in SA that if you live on a farm or small holding you can build without plan approval. The law states that all buildings in SA have to have plans approved by the nearest local planning department. If it is a new house you will have to register with the NHBRC or get an exemption from them as an owner builder. The house has to conform to the SANS10400 building standards. The SANS10400 has no standard for a plastic bottle house building method. Any non-standard construction method needs to have approval from the SABS. The best advice is to contact an architect who knows what the process is and get his help for your approval. Another bit of advice here is that if you do build illegally and later you want to sell the new buyer will need plans especially if they apply for a bond from a bank. You will be in for penalties and you will have to do plans anyway.
Hi. I am planning to build a plastic bottle house like this one: https://diyprojects.ideas2live4.com/2015/10/02/how-to-build-a-house-using-plastic-bottles/. I want to know what the specs are for the foundation I will need to build. The walls of these structures are extremely strong on its own but I know I still need a foundation. Any help here would be appreciated because I would like it all to be legal and get my certificate even if it will be built on a plot or farm.
Please advise
Lucas I am not available to answer calls telephonically. If you have questions please ask them here.
Hi Penny. Can you please give me your nr. I have a coyple questions i want to ask you.
No structure should be built without concrete foundations! Chances are if weather conditions are bad (e.g. heavy rain or strong wind) the house might collapse and kill you! You also need plans that should be approved by the local authority!
Have a look at my book Owner Building in South Africa
You certainly need approved plans and may need a structural engineer’s certificate. Whoever draws your plans will be able to advise.
I presume you have plans? If the structural engineer is the competent person in charge of your build he/she should be checking on the build regularly. For the structure to be passed by council, it’s imperative that the building inspector is called in to check the foundation trenches – BEFORE you throw the concrete. He must also check at roof height (plus the roof trusses). All plumbing must also be checked by the building inspector. If you don’t follow this procedure you won’t get an occupation certificate.
I m doing extension for my house(bondhouses) ,should I call structural engineering or building inspector for foundation?
A property owner has a plan for a single storey office building. He decides to change it into a double storey. What are the requirements especially with slabs (foundation and upper storey one) Also load bearing walls. Is is imperative to have a Structural Engineer’s certificate for the upper slab?
hi, is it regulations to have rebar in the foundations. if not, is it recommended? also is it necessary to put waterproof sheeting in prior to cement pouring?
thanks a mil
Hi.
I wanna build a small house of 30sq m and not willing to use stone(concrete) in foundation in rural land of Mokoane, it will be build out of home made cement block bricks. Will it resist for fewer years of my life, I will be 52 yrs old this December.
Thank you
Hi Erik, If your plans were approved by council and they did not call for an engineers certificate then no you do not need one. The responsibility for your build rests with your “competent person”.
The architect is correct.
Are you required to have a structural engineers certificate if you a single storey dwelling with corrugated roof built. Councils plans were approved and foundations adhered to SANS 10400.
Hi Elbie, You were not forced to enrol with us as we are not the NHBRC and do not do registrations, please go to the correct website: http://www.nhbrc.org.za/ NOTE: the last time I checked their website was down so you can try and call these numbers: (011) 317 0000 / 0800 200 824
We are building a house in Pongola Villa. I would like to know if all the houses in this complex are enrolled as well as in town. We were forced to enrol with you. When can we expect inspection. I expect from you to come very often as we are paying for this. I would like to hear from you soon.
Thank you for your time.
Kind regards
Elbie Rouw (082 898 5738)
You should have reinforcing!
It has nothing to do with the number of bedrooms in your house, it depends on the wall size. If there are going to be one-brick walls (230 mm thick) then your foundation must be 200 mm thick and 630 mm wide.
What is the standard size of width and depth of the building trenches in a normal 3 bedroomed house?
Building a double storey without reinforced but used ready mix and rocks where hard we didn’tremove
My guess. The engineer wants to get a foot in the door. So that if the soil tests say there is not need for a reinforced foundation designed by an engineer, he will have done something for which you will owe him.
If the wall is to be under 1,8 m it will be classified as minor building work, in which case you may not require plans or need a building inspector to inspect anything. But you do need to notify them that you are planning to build the wall, and you need to be sure that you don’t build on council property. Ask them what their requirements are.
Patrick, your architect is correct. The NBR states that “a competent person” must draw plans and design various elements of buildings (including foundations). The work involved will determine what qualification this person must have – a draughtsman, architect, engineer are all classified as competent persons, but, as an example, only an engineer would be able to design foundations for a high-rise building. In Part H: Foundations of SANS 10400, foundation design is discussed and basically it states that the design will usually be based on accepted design procedures and good building practice, or on “rational design methods in accordance with recognized engineering principles and practices”. In practice it is true that engineers usually draw structural details for plans (when required), including the position and cover required for reinforcement in foundation concrete. However, I don’t believe that an engineer’s design is always required when reinforcement is used – though it would be if the soil is problematic (e.g. dolomite or heaving clay, or if the soil is contaminated in any other way). Also, many architects include straightforward reinforcement in foundations as a matter of course – even where soil tests are not required by council. Ultimately it will be up to the local authority to decide. As a matter of interest, Geotechnical site and environmental conditions are covered in Part F: Site Operations of SANS 10400. This places the responsibility for calling for geotechnical reports fairly and squarely on the shoulders of the local authority. Usually this is based on known unstable soil conditions in the area. i.e. It is not something that is mandatory on all properties.
Trevor, Part K: Walls of SANS 10400 has a lengthy table that specifies minimum depths of bed joint reinforced lintels required over openings of various spans up to 3,5 m – but this is in relation to the wall size (thickness) and roof span. The number of courses is specified here – but the other factor is the height of the course (depending what you are building with). Your plans should have been drawn up with reference to this.
Hi There.
Would like to find out how many rows of bricks must there be from above the lintels of an arch or window to the roof trusses. The length of the opening is 3.6 meters.
Thanks,
Trevor
My plans for extensions to my house have been submitted and I have received approval regarding extension of building lines. My request to start building before approval was declined due to extensions been less that 500m2. The foundation trenches have been dug and the engineer has done DCP soil tests and I am waiting the results. The engineer is maintaining that whatever the results of the soil tests are (need re-enforcing or not) he needs to design the foundation and then inspect them once done, whereas the architect is saying that the engineer only needs to design the foundation if the soil tests determine that re-enforcing is required. Note: approval of plans not yet granted. Kindly advise on who is correct.
I have corner property and we are starting with building a wall. What is the minimum requirement that has to be in place (in terms of trenches/pegs) for the inspector to give the go ahead?
There are two articles on the site that tell you exactly how to measure this out 1) concrete-mixes and 2) concrete-mixes-by-weight
Hi.
I’m using 10 litre buckets to measure the quantity of stone and sand for concrete of 20mpa with 13mm stone.
Please advise on the number of buckets of each per 50kg of cement.
Thank you