Footings and foundations: what you need to know

Footings are the part of your build that carries the load into the ground. Get them right and everything above stays level and solid for decades. Get them wrong and you see cracked walls, uneven floors and doors that stick. The right footing depends on your soil, your loads and your design.

Foundations and footings: what the words mean

People use these two words interchangeably, so let me clear it up. The foundation is the ground itself – the soil or rock your home sits on. The footing is the concrete element that spreads the building’s weight onto that ground. When a client asks me to “do the foundations”, they usually mean the footings and slab. Both matter, because a footing is only ever as good as the ground under it.

The main types of footing

There is no single right footing. The type is chosen to suit the loads above and the ground below. These are the ones I build most often.

Strip footings. A continuous strip of reinforced concrete that runs under a load-bearing wall. The strip spreads the wall’s weight along its length. Strip footings suit brick and blockwork on reasonably stable ground, and are common under fences, garden walls and single-storey homes.

Pad footings. Isolated square or rectangular pads that carry a single concentrated point load, such as a post, a pier or a steel column. You will find pad footings under decks, carports, sheds and the posts of a patio. Each pad is sized for the load it carries.

Raft slabs. A raft, or slab-on-ground, combines the floor slab and the footings into one stiffened concrete raft. Thickened edge beams around the perimeter and across the middle give it stiffness. The raft floats on the ground and moves as one piece, which is why it works well on reactive clay. Most modern homes and concrete shed slabs use this approach.

Waffle pod slabs. A waffle is a raft slab poured over a grid of polystyrene pods sitting on the ground. The pods form a deep grid of beams under the slab without deep excavation. Waffle slabs are quick, use less digging, and perform well on reactive sites. That is why they are popular right across South East Queensland.

What determines the footing design

Several things decide which footing you need and how big it has to be.

• The soil. This is the big one. A site classification under AS 2870 tells us how reactive and how strong the ground is. Reactive clay, common across Logan and the wider region, calls for stiffer footings than stable sand or rock.
• The loads. A single-storey home, a double-storey home, a heavy tiled roof or a steel-framed shed all push different weight into the ground. More load needs more footing.
• The structure. Brick, block, timber frame and steel each behave differently and are supported differently.
• The slope and the fill. A sloping block, or ground that has been filled, may need deeper footings, piers or retaining walls and footings to reach stable ground.

Change any one of these and the footing changes. That is why a footing that was perfect for your neighbour may be wrong for you.

Engineering and certification

For anything structural, footings are not a guess. Here is how the process runs in Queensland.

A soil test classifies the site. A structural engineer then designs the footing and slab to suit that classification and the loads above, and issues drawings. For work that needs it, a building certifier checks the design and the finished job against the approval. On the paperwork side, the engineer’s Form 15 and the builder’s Form 16 confirm the design and the construction meet the standard.

My job as your concreter is to build exactly to that engineered design – the right beam depths, the right steel, in the right places, at the right concrete strength. With more than 18 years on the tools and an Advanced Diploma in Building Construction, I read the drawings properly and build to them. I am QBCC licensed (licence #15372237) and fully insured, so the work is covered and compliant.

Why footings are worth getting right

You never see your footings once the job is done, which is exactly why some people are tempted to save money on them. It is a false saving. Every crack in a wall, every sloping floor and every jammed door traces back to the footing and the ground beneath it. Fixing a failed footing under a finished building is one of the most expensive repairs there is. Getting it right the first time costs a fraction of that.

Good footings are quiet. They do their job for the life of the building and you forget they are there. That is the outcome I build for on every concrete foundation job, and it is a big part of why clients across Logan and South East Queensland rate our work 4.9 stars from 37 Google reviews.

Talk through your footings before you build

If you have a build, shed, deck or extension coming up, get the footings right from the start. I work across Logan, Ipswich, the Brisbane southside and the Northern Gold Coast, from concreting in Springwood to Daisy Hill and beyond. Call David Bunce on 0450 404 518, or book a quote and site assessment, and I will walk you through the right foundation for your project.