It’s also a relatively economical and well understood building material. 

Key features of concrete construction

Concrete is made from Portland cement mixed with sand and gravel (aggregates) and water. Cement is made by heating limestone and clay, then grinding it with gypsum. The powder, when mixed with water and cured over several weeks, turns into a hard solid.

Cost

Concrete is relatively cheap to use. However, transport can be costly.

Concrete masonry walls are usually used for exterior and load-bearing walls only.

Concrete slabs on the ground are cheaper than timber floors, and are now standard practice in many homes.  A damp-proofing barrier is necessary.

Strength

In general, concrete is strong in compression but needs reinforcing steel to make it strong in tension.

Ease of construction

Concrete is familiar to the majority of building professionals.

Durability and weathertightness

Concrete can be very durable. There are many buildings overseas made from concrete that survive from Roman times.

Though concrete will allow moisture to penetrate, it can be made water resistant with the right additives and sealers.

Earthquake-resistance

Concrete homes can be made earthquake resistant if they are correctly designed, and have sufficient reinforcing steel in the right places. 

Fire resistance

Concrete is fire resistant.

Pest resistance

Concrete is vermin proof.

Is it compatible with passive design?

Concrete is not a good insulator. You’ll need additional insulation to keep temperatures at a comfortable level.

Concrete is good at absorbing and retaining heat during the day, and radiating it out at night when temperatures fall. On summer days, it can absorb heat from the surrounding air and keeps your home cooler.

With concrete construction, doors and windows can be placed where needed to make maximum use of the sun’s warmth and breezes for cooling.

Concrete is a good sound insulator. However, without carpet, sounds inside your home may echo.

Is it right for my site?

Topography and site impact

Concrete floor slabs are generally used on level sites. However, a suspended concrete floor (see concrete slabs below) can be used to minimise the excavation required on a sloping site.

Climate

Concrete homes are used in all climate conditions.

Types of concrete construction

Concrete slabs

Concrete slab construction is now the most common way to lay a ground floor on flat ground.

Thermal mass

In winter, a slab floor can absorb solar heat and then radiate it out during the evening to keep your home warm. If you’re using concrete as a source of warmth, don’t cover it with carpet where the sun shines on it - this acts as an insulator preventing the slab from warming up. However, not having a floor covering can also make the concrete floor less forgiving if you trip or fall.

Reinforcing

Slabs generally include steel reinforcing to minmise cracking.  There is also an option to use fibre mixed into the mix as reinforcing. Large slabs are designed to have some movement joints.

Heating systems

Slabs can have water pipes or electrical cables embedded in them for heating and cooling. If anything goes wrong with these embedded systems they are very hard to fix.

Insulation

In most climate conditions a concrete slab will need to be insulated around the edge, and possibly underneath.

Suspended floors

Commercial buildings usually have reinforced concrete slab floors on all levels. These slabs can be pre-cast to speed on-site construction. This can also be done in domestic construction but will need to be insulated on the underside.

Concrete blocks

Walls can be made from hollow concrete blocks which are laid like bricks. These blocks are also called concrete masonry units (CMUs).

Reinforcing

Block walls are reinforced with steel during construction. After the reinforcing is put in place, concrete is poured into the hollows.

Insulation

Standard concrete blocks don’t have enough insulation to meet the Building Code’s minimum requirements. Insulation can be added to the outside or inside of the wall.

Design and installation

To avoid cutting blocks to size it is preferable to design buildings to fit standard block sizes.

Palette-loads of blocks are heavy, and are likely to need trucks with cranes to move them. This may not be possible in some locations.

Block laying should be done by a skilled block layer.

Curing concrete

All fresh concrete should be cured for the first week or so. This can be achieved using a fine water spray, laying a polythene sheet or wet hessian over the top, or using a chemical curing compound. If water is used, sand can be piled up around the edges of the slab to retain a wet surface layer.