So you've finally decided to take the plunge into home ownership - congratulations! Now comes the fun part of designing your dream home. Before you dive into choosing fixtures and flooring, there's an essential first step many homeowners overlook that could cost you big time down the road.

When your builder suggests doing a few soil tests to determine the foundation for your new home, don't assume two boreholes will be enough. Given how much is riding on getting your foundation right, you'll want to push for at least three or four boreholes, both inside where the house will be as well as farther outside. It's a little extra upfront, sure, but it will give you the most accurate picture of what's under there - and for the lifetime of your home, that peace of mind will be priceless.

The Importance of Thorough Soil Testing Before Building

So you've purchased your dream block of land and are ready to start building. But before the diggers move in, it's critical to understand the soil and rock below. Unfortunately, 75% of homeowners make the mistake of relying on only two boreholes for site testing. For accurate results, we highly recommend three to four bores - both within and outside the building envelope.

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Why More Boreholes are Better

Additional boreholes provide a more comprehensive analysis of the varying soil conditions across your site. Simply put, the more you test, the more you know about what's below the surface before building.

  • Two boreholes alone may miss underlying issues like soft spots, fill, clay, wet areas/underground water or rock ledges that could compromise your home's structure or require additional concrete piers.
  • Identifying soil inconsistencies upfront allows your builder to strengthen the design and prevent potential problems down the track, like uneven floor levels, cracking walls, and drainage issues.
  • The small added cost of extra boreholes is minor compared to the expense of fixing issues caused by inadequate site testing. As the old adage goes, an ounce of prevention is worth a pound of cure!

We understand the desire to keep costs down, especially when building a home. However, skimping on-site investigations is a false economy, and the resulting structural problems can be a nightmare to rectify. Do yourself a favour - invest in comprehensive soil testing. Your home's foundation and peace of mind will thank you!

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Why Most Builders Only Require 2 Boreholes

Most home builders only require/or request two boreholes on your property to determine the soil conditions before designing your new home's foundations. Typically, they locate bores within the building footprint diagonally opposite house corners. The problem is that two boreholes aren't enough to accurately understand the ground below.

Why you need more boreholes

For a typical-sized residential block, two boreholes will only provide information about a tiny percentage of the total land area. There could be pockets of reactive or unstable soil, tree roots, underground streams or hard rock just meters away that go undetected.

Additional boreholes, preferably three or four, are well worth the minimal upfront investment. They provide a more comprehensive overview of soil types and conditions across your block, allowing your builder to design foundations and footings suited to your site's specific needs. The extra boreholes are invaluable for structural integrity, preventing potential issues down the track, and peace of mind.

  • They detect variable soil types to determine the appropriate foundation design for your home.
  • Before construction, they locate potential hazards like tree roots, clay beds, or underground streams.
  • They provide greater accuracy and confidence in the soil test results, especially for larger blocks.
  • They help avoid the risk of structural damage by identifying adverse soil conditions not found in the initial two boreholes.

While two boreholes will suffice for preliminary planning approvals, we strongly advise paying a little extra to fully understand your soil and site conditions before finalizing your new home's design and foundations. It's worth doing right the first time for such a significant investment.

The Risks of Inadequate Soil Testing on Structural Design

Having only two boreholes to test the soil on your property before building is risky business. While it may seem like an easy way to save a few bucks upfront, it could end up costing you big time down the road.

Structural issues

The structural integrity of your home depends entirely on the foundation it's built upon. Inadequate soil testing means your builder is designing and constructing your foundation without a complete picture of the ground beneath. They may miss soft spots, erosion risks, or soils that expand and contract drastically with moisture changes. Any of these issues can lead to cracking foundations, tilting structures, and other damage within a few years of building.

For peace of mind and the safety of your investment, spend the extra money to get a full assessment of your soil from multiple testing points. You'll rest easier knowing your home is supported fully and built to last.

Drainage problems

Two boreholes also won't uncover potential drainage issues across your whole property. Maybe that back corner stays soggy for days after it rains or the ground slopes in ways you can't see from the surface. Without identifying these trouble spots beforehand, you could end up with a flooded basement, mold issues, and costly repairs to redirect water flow.

Proper drainage is essential for any home. Don't gamble with only two boreholes - get the full picture of how water moves through and is absorbed by the soil on your property. Your builder can then design solutions to keep your foundation dry and avoid damp, unhealthy conditions inside the home.

Expansive soils

Some soils contain high amounts of clay that expand when wet and shrink when dry. These expansive soils can damage foundations, roads and any other structures built upon them. Two boreholes likely won't detect if you have these soils and how much they may expand.

For the safety and stability of your home, invest in additional soil testing before building. The small upfront cost will give you peace of mind that your foundation is built to withstand the unique conditions of the ground below. Why risk it? Get the right assessment done from the start.

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How Additional Boreholes Can Prevent Foundation Issues

While two boreholes may seem sufficient to determine the structural design of your new home’s foundation, many homeowners end up with foundation issues that could have been avoided by investing in additional site testing.

How Additional Boreholes Can Prevent Foundation Issues

Having only two boreholes means your builder is making assumptions about the soil composition across your entire block of land. However, soil types can vary greatly, even on small sites. Additional boreholes, especially around the perimeter of where you plan to build, give a more accurate assessment of the soils that will actually support your home’s footings and slabs.

With more data from extra boreholes, your structural engineer can spot potential issues, like reactive soils, that require specific foundation solutions to prevent future damage. They may recommend concrete piers that extend down to more stable soil or a reinforced slab. These precautions add to upfront costs but save you from expensive foundation repairs down the road.

Some signs you may have reactive or unstable soils include:

  • Cracks appearing in walls, floors or foundations
  • Doors or windows that stick or won’t close properly
  • Uneven or sloping floors
  • Plaster that crumbles or falls off

If any of these issues appear within the first few years of construction, poor soil conditions are often the culprit. Additional boreholes, along with a thorough geotechnical report, should be non-negotiable before building on sites where soil problems are common. An investment of a few thousand dollars upfront for extra testing could save you tens of thousands in the future.

Don’t make the critical mistake of assuming two boreholes will give your builder an accurate picture of your soil and foundation needs. Insist on additional site testing to ensure your home’s stability and prevent issues from arising once construction is complete. Your new home is a huge investment, so take the time to do thorough soil testing - your peace of mind and bank account will thank you later!

Asking for 3-4 Boreholes in Your Preliminary Service Agreement

Asking your builder to conduct 3-4 boreholes during the preliminary site survey and soil testing phase will provide a more accurate assessment of your land’s substrate and ensure structural stability.

Far too often, builders will opt for the minimum - just 2 boreholes - to get a rough idea of soil conditions before designing your home’s foundations. However, soil can vary dramatically across a block of land, and 2 boreholes may not detect unstable pockets or rocky outcrops.

Additional boreholes within the proposed building site and further away will paint a more detailed picture of your soil’s composition across the entire block. Your builder can then design footings and structural supports to suit the soil precisely. For the relatively small additional cost, extra boreholes provide invaluable information and peace of mind that your home's structure is suitable for the land.

Some key things extra boreholes will detect include:

  • Soft, unstable soil pockets that require concrete piling for support.
  • Hard rock layers that need to be dug out or require altered footing designs.
  • Soil acidity or alkalinity levels that may corrode certain building materials if not addressed.
  • Groundwater levels to ensure adequate drainage and waterproofing.
  • Soil bearing capacity to determine if extra-deep or widened footings are required for structural stability.

While the initial site survey and accompanying soil report will determine if the land is generally suitable for building upon, additional boreholes provide a level of detail and precision that can make or break a building project. For most homeowners, a house is the single biggest investment you will make. Ensuring structural integrity through comprehensive soil testing and analysis should not be overlooked.

Insist on 3-4 boreholes in your preliminary site survey agreement. The small upfront cost will provide vital information to design and build a structurally sound home suited perfectly to your block of land. Your builder will thank you for it, and you'll rest easy knowing your home is tailored precisely for the soil it's built upon.


So there you have it, the critical mistake that 75% of homeowners make before building their new home. Don’t be tempted to cut corners and assume two boreholes will give you an accurate picture of your soil. For a relatively small additional cost upfront, the peace of mind and certainty you’ll gain from a few extra soil tests is invaluable. Remember, your home’s foundation is the most important part—get it right and you’ll enjoy your dream home for years to come. But get it wrong, and you could face some very expensive problems down the road. Spend a little now, save a lot later. Get the extra boreholes done and start building your home with confidence, knowing it’s supported by a foundation as solid as a rock.