Footings & Floor Construction

The type of footings used for a new home will be suggested by the home designer with possible consultation with a geo-tech consultant. The factors that influence the type of footings are:

• Weight of building
• Wall construction type and height
• Soil type
• Slope of the block
• Budget
• Drainage requirements on the block

There are five main types of footings:

Strip Footings

A Strip Footing is a relatively small strip of concrete placed into a trench and reinforced with steel. The footing supports the load of the exterior walls and any interior wall that is load bearing or supports a slab such as for a bathroom. Strip footings can be used for both traditional timber and concrete floors. They are one of the most common footing used in Australia.

Concrete pad footings.

A concrete pad footing is the simplest and cost effective footing used for the vertical support and the transfer of building loads to the ground. These footings are "isolated" ie there is no connection between them. They are also reinforced.
Holes are dug (say 400mm wide x 400mm deep) into the ground and fitted with a reinforcement cage then filed in with a concrete mix to ground level.
Concrete pad footings are used to support light weight timber-framed houses.

Pole Construction (Post and Concrete)

For this type of footing a hole is dug into the ground about 800mm wide x 1600mm deep. A pole is then placed into the hole and ready mixed concrete is back filled around the pole. Pole construction footings do not require steel reinforcement (or an engineer) and are therefore also one of the least expensive footings types.
Pole Construction is the most economical way of constructing a pier/footing on sloping land but engineer's details will be required for the builder and certifying authorities. A few essential considerations are:

1. How long the poles will need to be and the spacing?
2. What will be the correct height of all poles?
3. How far down will the pole will need to penetrate?
4. How will the concrete around the pole need to be finished to reduce wood rot?
5. What will the diameter of the poles need to be?
6. What are the poles are made of (steel or timber)?

Grout Injected Piles

Where it is impossible for a footing to be constructed, a pile which is both pier and footing is used.
This method is only used in unstable or potentially unstable soils such as mud flat estuary areas and beach front etc. Grout injected piles are "isolated" footings and/or piers, which are cement grouted (not concrete) and steel reinforced, with an overall diameter of around 600mm.
The piers are installed by inserting a cork like screw (Metal Auger) attached to a Backhoe in to the ground. The Auger screws all the dirt out of the pier hole that will be around 6 meters in depth. Once all the dirt is removed the grout is injected through the end of the rotating Auger into the hole. As the hole fills with grout the rotating Auger is slowly removed ensuring no dirt collapses back into the hole. The Auger machine drills out the pier holes with minimal disturbance to adjoining soil and structures. Mini piles use the same process and materials as grout injected piles but are around 200mm in diameter

Timber Piles

Timbers piles are a more cost affective method of constructing structural piles. Timber piles are long timber poles around 6000mm in length and 400mm in diameter that are hammered deep into the ground by a pile driving rig (big hammer). The piles are driven into the ground their full length or until the pile hits bedrock. If the pile hits a floating bolder it will skew in the ground but the pile will be amply stable to support a floor structure. Pile driving vibration can disturb adjacent buildings, resulting in cracking, failure and even collapse.