Site cleaning and stripping
Before any foundation excavations can be undertaken, a site must be properly prepared and cleared by removing all rubble and plant material such as grass and shrubs. If the site is saturated with groundwater, or if a natural flow of rainwater occurs across the site, a proper drainage system must be incorporated to drain the water to the municipal storm-water system. Care must also be taken not to generate unnecessary dust and noise pollution.
Anybody building a house is allowed to erect a temporary builder’s shed on the stand, and is obliged to provide the necessary sanitary facilities for the workers on the site.
Bulk earthworks and excavations
The owner must ensure that all earthworks and excavations are safe and stable. Excavations deeper than 3 m must be designed by a competent person, and must be approved by the local authority. All excavations for strip foundations must be level (horizontal). Where an excavation runs across a slope in the land, it must be stepped into horizontal sections. All excavations for strip foundations must be at least 300 mm deep.
It is recommended that a land surveyor be appointed to ensure that the house is set out correctly within boundaries and statutory building lines.
On completion of all foundation excavations, and before any concrete is placed, a building inspector from the local authority must be called out for a compulsory foundation inspection. During this inspection the dimensions and level of the excavations will be scrutinised. It will also be ascertained whether the builder has kept to the approved building plan, and whether the layout is positioned as indicated on the plan.
The foundation of a building must be designed in such a way that it can easily transfer the weight of a wall and roof to the ground. In order to achieve this functional regulation, the deemed-to-satisfy rules include the following specifications.
Concrete mix to be poured into the excavation must produce strength of at least 10 MPa after 28 days. This is obtained by mixing one part cement, four parts sand and five parts aggregate (usually 20 mm stone). The thickness of the foundation must be at least 200 mm, and when a step is formed, the top layer must overlap the bottom layer by 200 mm (the thickness of the layer). The width of the foundation strip must be at least 600 mm for load-bearing (usually all outer) walls, and 400 mm for non-load-bearing (usually all inner) walls. In the case of non-load-bearing inner walls, it is also permissible to provide a thickening in the floor slab instead of a foundation strip. If this option is preferred, the thickening in the floor slab should be 200 mm.
Building of foundation walls
A foundation wall is the wall built on top of the concrete foundation strip to the height of the floor slab. All foundation walls must be 230 mm (two bricks) wide. If a foundation wall is going to be higher than 1.5 m, the house should be stepped to accommodate the slope of the land. If such a foundation wall is also used as a retaining wall, it is advisable to build it 345 mm (three bricks) wide.
Backfill of foundation walls and damp-proofing
Once the foundation walls have been built to floor level (also called the plinth), the inside of the house must be filled up (backfilled) to floor level. It is usually possible to use the same material that was excavated for the foundation strips, so always try to leave this material close by.
In order to prevent sagging beneath the floors, it is important to compact this backfilled material to closely resemble the natural density before excavation.
This is easily accomplished by replacing the filling in layers of 150 mm and compacting each layer properly with a mechanical or hand compactor. This process will be improved if the layers are sprayed with water to dampen them. Always take care, however, not to soak the material completely as this will wash out all the fine material that is supposed to fill the smaller openings.
Continue backfilling until the final level is one brick below the final floor level, which will also be the thickness of the concrete floor slab. Try to make this top layer as level as possible.
Pouring of floor slabs
The concrete floor slab must be 75 mm thick (one-brick course thick) and should consist of 10 MPa concrete, mixed from one part cement, four parts sand and five parts 20 mm aggregate.
In areas where groundwater is a problem, it is advisable to place a suitable plastic waterproofing membrane of 0.25 mm on the filling prior to pouring the concrete. This membrane must be folded upwards to the thickness of the slab around the perimeter. An overlap in the membrane must be at least 150 mm.
It is advisable at this point to consult with your plumber and electrician to ascertain whether any services such as electricity conduit or drainage pipes should be placed in position before concrete is cast. This will save time and cost by eliminating chiselling and breaking out parts of the concrete slab at a later stage.
On completion of the floor slabs, the walls of the house must be bricked up to roof height, securing all door- and window frames in place in the process.
Always place door- and window frames on an exact vertical plane, and make sure you provide horizontal support for doorframes to prevent them from bending inwards from the pressure of the surrounding walls. Once again, this will be the last opportunity to make minor alterations. For instance, you cannot request a new load-bearing wall if a proper foundation has not been provided for it.
Before laying the first brick, a damp-proof course (DPC) should be provided in the form of a continuous waterproof layer the width of the brick wall. DPC is placed beneath ALL walls to prevent damp from the earth from rising into the walls.
It is good building practice to brick up the walls of the entire building simultaneously.
All window frames and openings for wider types of doors like sliding doors must be provided with a reinforced layer along the top of the opening to carry the weight of the wall above the opening. This can be done either by using a prefabricated concrete beam called a lintel, or by physically building a lintel using bricks and a kind of wire reinforcement called brickforce. It is also advisable to build a layer of brickforce into a wall on approximately every sixth layer of brickwork.
All outer (load-bearing) walls are built 230 mm wide (two bricks placed alongside one another), while most non-load-bearing (inner) walls are built 115 mm wide. If an inner wall is higher than 3.3 m, it must also be 230 mm wide.
It is standard building practice to build roof ties into the top six layers of outer walls. Wire or hoop ties can be used, and the purpose is to tie the roof structure to the walls.
Remember the following deemed-to-satisfy rules when considering the layout of the various rooms of the house:
Backfill and waterproofing
If the house is built on a slope that has been excavated and backfill is needed on the outside of the house against the wall, such a wall must be 345 mm (three bricks placed alongside one another) wide. A thick plastic sheeting of 0.25 mm should be built into the wall vertically, to prevent moisture from penetrating the building. This sheet is added in-between the outer and central layer of bricks. Backfilling is done in 150 mm layers and compacted thoroughly.
It is advisable that a structural engineer be appointed to design a retaining wall.
On completion of all the walls, a carpenter can erect the roof structure, comprising either beams for a flat roof or roof trusses for a pitched roof. Since the roof is an extremely important structural element of a house, it is vital that a competent person do the design. Remember, a roof is subjected to its own weight, which can be considerable in the case of a heavy concrete tile roof, and to wind forces, which can be considerable in the case of a lighter, sheet-metal roof. It is therefore always advisable to have the roof structure properly designed and constructed.
These days it is much easier and safer to make use of the services of one of many prefabricated roof companies that take the exact measurements, create a computer-aided, engineered design, assemble the trusses in the factory, and erect them on site according to specification. Local authorities require an engineer’s certificate for the design and erection of a roof structure.
The minimum slope of a flat, sheet-metal roof is 5°, but this may be decreased to 3° if long, single-span plates are used. The minimum slope of a pitched concrete tile roof is 26° without waterproofing, and 17° with an under-tile waterproofing membrane.
During roof construction, it is the plumber’s job to fit drainage valleys and flashings on walls, chimneys and ventilation pipes that run through the roof. Please note that some local authorities require a roof-structure inspection as well.
Once the roof cover has been completed, the fitting of rainwater gutters and down-pipes as well as fascia boards is optional.
The owner-builder should take note of the fact that, on average, once the roof is completed, about 50% of the building costs should have been spent.
Plumbing and electrical work
Once the walls have been bricked up, it is the plumber’s responsibility to install water and drainage pipes in the walls and floors. Underground waste-water drainage pipes should also have been installed by now and inspected by the local authority. This is called the open-drainage inspection, and is conducted by the building inspector once the pipes have been installed, but before they are covered with soil. This must be done by a qualified plumber.
The entire water reticulation system is connected to the municipal water connection point on the stand boundary. At this stage the owner will be requested to indicate the position of all garden taps. Since it will be difficult to change these positions later on, due consideration should be given at this point.
Simultaneously, an electrician will install conduit pipes in the walls and roof structure to accommodate all the electrical cables for the house’s electrical system. All electrical wiring starts off from a central point, called a distribution box, which again is connected via an underground cable to the municipal electrical connection point on the stand boundary.
Both the water pipes and electrical conduit pipes are installed in the walls by chasing grooves into the brick walls and mounting the pipes inside these grooves. Please note that unplastered inner face-brick walls require much more ingenuity from the bricklayer because all the pipe work must then be built into the brickwork.
Once the electrician and plumber have fitted the pipes into the walls, plasterwork may commence. This is a specialised trade to be performed by an accomplished tradesman. Always make sure you use proper plaster sand.
It should be pointed out here that there are, in fact, three types of sand used in the building trade, which vary in their degree of fineness: concrete sand is the coarsest, followed by dagha or mortar sand, and plaster sand which is the finest.
Ceilings and cornices
On completion of the plasterwork, a ceiling contractor can move in to fit the ceilings, which are usually suspended from the roof structure, and may be made of gypsum board, fibre-cement board or even timber planking such as pine or meranti. The edges of the ceiling are usually rounded off against the walls with some kind of cleat or a prefabricated quarter-round of gypsum board, called a cornice.
Please note: it will be easier for the plumber to fit the geysers before the ceilings are installed.
Once the ceilings have been fitted, the plasterer may move in again to do the finishing layer on the concrete floor slabs, called the screed. This is a thin layer of sand and cement mix, and is used to make the floor absolutely level. The floor tiles or carpets will be fitted on top of the screed later.
Finishing trades and outside work
At this stage the building site becomes very busy as many different tradesmen hurry around to finish their jobs. The tiler will be laying wall and floor tiles where specified, the glazers installing windowpanes, and the carpenter hanging all the doors and fitting the locks, as well as installing the built-in cupboards and curtain rails. Once the house can be closed and locked up at night, it is time to install the kitchen cupboards and appliances such as the stove and oven. The electrician will now complete his job by fitting the wall plugs, light switches and light fittings, while the plumber will be installing the bathroom fittings, baths, basins, toilets and showers.
At some point during this stage, the electrician will request a final electrical-installation inspection from the local authority, while the builder and plumber will request final building and drainage inspections. Once all the disciplines have moved out of the house, it is time to install the carpets and skirting boards to finish everything off.
Before the final inspection, all building rubble must be cleared and removed. Landscaping and gardening may then commence, including paving where needed, as well as garden and screen walls. Although gardening and paving may commence earlier, care should be taken not to jeopardise building work on the house.
Sources: The South African Institute of Architects Practice Manual, June 1999;
National Building Regulations and Building Standards Act, Act 103 of 1977, as amended;
the National Home Builders Registration Council (NHBRC) website.