Why do I need a soil test? Modular home footings and reactive soil sites explained.

The footings of your home are incredibly vital, and a soil test is the most critical part of getting this right. In this article, we go over the process that must be followed to ensure that your house is built right – from the ground up!

So, read on to find out about soil tests, soil classifications and the different types of footings used in the modular home industry!

First up – why do I need a soil test?

soil test rig onsite by soiltech

The main reason we need a soil test before the building is to find out the underlying soil conditions and characteristics of the site.

A geotechnical engineer conducts a soil test by boring down, in two or three separate locations within the building footprint, to test the soil. The soil tester will take a sample of the ground at different depths for testing. Back in the laboratory, the earth will be tested using several different parameters, and a soil classification assigned to the site. This is called the Soil Test Report.

What are the different soil classifications and what do they mean?

soil classification explained by Soiltech

How does soil classification affect my home?

The structural engineer will interpret the results of soil classification. This data will influence the design and type of footings the engineer designs for your new home.

Types of foundations for modular homes & what kind is best for my house

So, what types of foundations are available to you? Well we can generally divide the types of foundations up into three main categories:

block footings for modular homes

Block Piers are the traditional “cheap” relocatable home piers. You may have seen these in caravan parks or on older relocatable home. The home is just placed on stacked concrete blocks and chained to the ground.

The advantages of these foundations are that they are incredibly cheap and easy to install.

One of the main disadvantages for this sort of system is that they are only suitable for A or S sites due to the fact there is no resistance to soil movement.

westbuilt bored piers foundation system
Example of a typical Westbuilt modular home footing system

Bored Piers are the most common type of footing. These involve drilling 300mm to 450mm diameter piers to a depth specified by an engineer, installing reinforcing and pouring concrete. Many builders, including Westbuilt will install adjustable steel stumps with concrete footings.

The advantages of this system are that the concrete foundations are durable and very resistant to soil movement – meaning less chance of cracking in your finished home.

The disadvantage of this system is that it is very labour intensive and costly.

surefoot foundation system

Screw Piles / Surefoot Foundations are an engineered footing system. Screw piles involve screwing a large metal screw into the earth while the Surefoot system involved hammering metal piles into the ground around the bearing plate.

The advantages of these types of systems are that they are straightforward to install, and labour and materials use are minimised.

There are a few minor disadvantages especially in sites that have much rock.

Building on black soil

reactive soil

One of the frequent questions asked by our clients, especially clients looking to built modular homes on sites in western QLD and North Western NSW is what is involved in constructing a house on black soil.

Westbuilt believes in designing a footing system to suit your exact site and home. Depending on the results of your soil test we will recommend either a bored pier or Surefoot foundation system for your black soil site.

Each system is designed to minimise the effect of extreme soil movement seen on black soil sites.

Conclusion

team of professionals designing a modular home

So, as you can see from the above points, a soil test is a critical, and initial, part of building your new home. At Westbuilt, we believe in following a design process that enables us to provide our client with the certainty and trust that comes from a well-designed modular home.

Find out more about custom designing your new home here.

LOOKING TO BUILD FROM A CUSTOM DESIGN?

If you have your own vision for your house, we are happy to work with you to design the perfect layout that is tailored just for you.
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