Ensure you build on a firm foundation

17 March 2016

Before building, your soil will need to be tested to ensure that the structure of the home foundation is appropriate for the type of ground it will rest on.

Paal will help you through this testing and analysis procedure. The right time to do it is before your plans are drawn up or during the drafting process.

“When customers first come to us, they are naturally enough unfamiliar with the topic,” Paal housing consultant Michael Christie said. “We’re happy to discuss it and provide the advice they may need.”

Classifying your soil

A geotechnical engineer/surveyor will go to your site with a drilling rig and bore holes in the ground to check the degree of compaction and obtain samples to send to the soil lab for analysis.

Your site will then be classified according to the amount of ground movement that might be experienced. This can range from Class A through to Class P, with the most common category being Class M equating to moderately reactive clay or silt sites.

Paal is often able to introduce its customers to suitable testing engineers in their region.

Once you have the soil results, you can engage a structural engineer to design the slab and footings – an inexpensive exercise. Again Paal can put you in touch with an appropriately qualified person.

Designing the base

The engineer may recommend a raft concrete slab with edge beams, or for less stable soils a waffle pod concrete slab that has additional ribs. The slab may rest on sand fill or on a styrofoam box, which is a good insulator.

Rarely, if you will be building in a flood zone or where there is land slippage, you may need to choose a foundation of stumps or piles, bearers and joists.

If your site is sloping and you choose not to excavate a flat foundation, then stumps or piles will be necessary. For a brick veneer home, they will typically cost an additional $35 per square metre over the price of a concrete slab.

“It’s our job at Paal to make all this as straightforward as possible, so don’t hesitate to talk to us and draw on our many years of experience,” Michael said.