BuildingBlog.net is a blog full of building blocks on planning, designing and building your own home in South Africa, where most houses are built brick-by-brick. Brick walls may be left uncovered if face-brick is used, or plastered and painted if stock bricks are used. Fact of the matter is, during the construction of a house, various materials are used, which must all be sourced and bought in the correct quantities before or during construction of the house.

Once you have decided to go the owner-builder way, you will have to rely on subcontractors to execute the physical building work. You will have to source, select, appoint and supervise different subcontractors, one for each building trade. You can either trust a subcontractor to measure the relevant quantities and buy the required materials from various suppliers, or you can do it yourself. Here is how to do it yourself:

Strip foundations

You can calculate roughly how much concrete will be required to pour the strip foundations by measuring the length of all the outer and inner walls on the building plan. The scale of a building plan is usually 1:100, meaning that 1mm on the plan represents 100mm on the ground, or then 10mm (1cm) on the plan is 1 000mm or 1m on the ground. To calculate the total volume of the strip foundations, you need to multiply the total length of the outer walls (on the ground) by 0.6 (600mm) and by the thickness of 0.2 (200mm) and the total length of all the inner walls by 0.4 (400mm) and by 0.2 for the thickness. This should give you a rough indication in m³ of how much concrete you will need for the strip foundations. In the case of a smaller house, one may prefer to mix this quantity of concrete on site by mixing 1 part cement, 4 parts sand and 5 parts aggregate (usually 19mm stone) in a concrete mixer, or much better, this quantity of premixed 10MPa concrete can simply be ordered from one of various ready-mix suppliers.

Bricks for the walls

You will require enough bricks to build all the outer and inner walls, as well as the foundation walls (the walls above the strip foundations but below the floor level of the house). As explained the post Building a house, foundation walls are built with two rows of brick next to each other (also called a one brick wall which is 220mm wide) and can be built with stock bricks which are much cheaper than face bricks. All outer walls are also one brick wide, while interior walls are half brick (110mm) wide.

To measure how many bricks are required to build the entire house, you need the total surface area of all the brickwork to be built. Start off by using the total length of all the walls (already measured above) x the height of the walls as indicated on the building plans. Remember to double the length for each foundation wall and each outer wall (two rows of bricks in them, remember?). Once you have added up the surface areas of all the walls, divide it by 55 to get a rough estimation of all the number of bricks you will need. Why 55? This is how many standard South African bricks are built into one square meter of brick wall. This task is best done on a room-by-room basis, but be careful not to double-count bricks in shared walls between two rooms.

Strictly speaking, the surface areas of all the windows and doors must be subtracted from your total brick surface area, because they are holes in the walls with no bricks in them! However, since it is alway a good idea to order about 10% more bricks than calculated to make up for wastage and miscalculations, rather use the original calculated figure as is.

The floor slab

As explained in Building a house, once the foundations walls have been bricked up and backfilled to floor slab level, it is time to pour the concrete for the floor slab. As in the case of the concrete for the strip foundations, this concrete can be mixed on site (in the same ratio as for the foundations) or (preferably) order it as a ready-mix from a suitable supplier (same strength specification). How much concrete? Measure the total surface area of the entire ground floor of the house over the outer walls and multiply it by 0.075, the thickness of the slab, which is also the height of one brick. This will give you the quantity of concrete required in m³. Up to now you were compelled to take measurements from your building plan and apply the scaling factor to calculate real quantities. However, once the foundation walls have been built, you have the real McCoy on the ground and you should only take actual measurements from the portion(s) of the house already built. This will result in much more accurate quantities.

Other wet trades

You will also need the surface areas of the walls to calculate the quantities required for the mortar (building-sand/cement mix - also referred to as dagha in the trade) to hold the bricks together, as well as for the plaster mix (plaster-sand/cement mix) for all the walls to be plastered. Quantities for the mortar must be measured from the plan, as the walls have not been built yet, but quantities for the plasterwork should be measured from the completed walls. In reality, your bricklaying and plaster subcontractors should be able to tell you from experience how much sand and cement will be required for the mortar and the plasterwork.

However, if you want calculate the quantities yourself, or at least check your tradesman's figures, use the following empirical formulae: To lay 1 000 bricks, you will need 3 bags of cement and 0.6 m³ of building sand, or in more practical terms, 1 bag of cement with 3 wheelbarrows of building sand. For exterior and interior plasterwork, for 100m² of 15mm thick plaster you will need 10 bags of cement and 2m³ of plaster sand. This translates to 1 bag of cement with 3 wheelbarrows of plaster sand.

Specialised trades

The measurement of quantities for specialised trades like plumbing, electrical and roofing are best left to the subcontractor that you employ for the particular trade. The plumber will best know how many meters of water pipes, waste pipes and soil water pipes will be required for your house, and in many cases, the true quantities are only verified on completion of the job. The same goes for the meters of electrical wiring required to wire a complete house.

As stated previously, the total roof is best left to a roofing specialist. It is always much easier and safer to make use of one of many pre-fabricated roof companies' services. These companies take the exact measurements, conduct a computer-aided design, assemble the trusses in the factory, and erect them on site according to specification. They also issue an engineering certificate, as required by the local authority. To calculate the number of roof tiles needed to cover your roof may not be quite so easy, but it boils down to calculating the total square meterage of the roof to be covered with tiles, and divide that figure by the square meterage of one tile. Once the roof trusses are up, the surface area of the roof can be measured on site, and the size of one tile can be measured physically as well.

Screed and ceilings

The quantities for both of these items can easily be measured from the already built structure. Screed to the floors is placed in the same ratio as plaster to the walls, while the surface area of the ceilings should pretty much coincide with that of the floor screed.

The rest

When building a house, there are many other materials to measure which must all be bought in time to be built into the house. Materials like waterproofing membranes, damp proof course (DPC), brickforce, lintels, roof ties, gutters, downpipes and fascia boards, window and door frames, doors, glazing, floor covering and skirtings as well as ceiling boards and cornice can all be measured from either the plan or the built structure itself.

Remember that when you are an owner builder, your subcontractors probably are better known to the main suppliers of building materials, and probably have 30 days accounts with them. Your subcontractors are therefore more likely to negotiate better discounts on building materials with the suppliers than you as a once-off individual owner-builder will be able to do.

Or, alternatively...

In the post on I need a building plan!, I referred to the drafting of a building plan as a specialised subject that should best be left to a trained, skilled and experienced person, in other words, a competent person. If the task of measuring and calculating the quantities of materials to be ordered for constructing your house seems far too daunting for you to do yourself, you can always refer the task to a quantity surveyor. Quantity surveyors are registered professional people who are trained to do just that - measure quantities! Like in the case of architects, you can always refer to the list of trusted consultants to find a quantity surveyor I personally know and trust to recommend to you.