Whether constructing single-family homes, skyscrapers, or superstructures, choosing the proper foundation is essential. The foundation of any building serves two main purposes — distribute the weight from load-bearing walls to the soil or bedrock beneath and keep groundwater or soil moisture out.
The topography, geology, and pedology (the study of soil) on your construction site in addition to the size of your building and other factors, like the type of construction, will determine the type of foundation that is appropriate for your building.
Foundations are perhaps the most vital element of any building, so you need to get them right.
The foundation is so important because it supports the weight of the building that is placed on top of it. The foundation transmits the loads to the ground below and supports the building so that it does not “settle” or sink into the soil. If the foundations of the building are inadequate, it can often mean catastrophic failure of the building, with the building severely cracking or even collapsing.
Foundations can be either shallow (up to a metre into the soil) or deep (where the foundation has to be sunk quite a ways into the ground in order to provide sufficient weight-bearing support. They can be made from timber, steel, or concrete, but concrete foundations are the most commonly used these days.
Types of House Foundation
Basement foundations are most commonly used for homes in colder climates. Unlike crawl spaces, a basement can provide additional living spaces in homes. They can be completely enclosed, or they can be partially enclosed with windows and doors framed into the structure.
A full basement foundation begins with a hole of at least eight feet deep to accommodate an underground living space whose floor space matches most or all of the home’s ground level. You’ll place structural foundation walls on concrete footings that run the perimeter of the basement. Those footings need to be placed at least 12 inches below previously undisturbed soil and at least 12 inches below the frost line. You’ll then pour beams, erect foundation walls, and pour a cement slab inside the walls.
The obvious advantage of a basement foundation is the extra living space it can provide; in fact, it can double the home’s square footage if homeowners decide to finish it. Basement foundations are durable and resistant to fire and extreme weather.
You’ll often find them in cold climates, such as in the Midwest, Mid-Atlantic and Northeast regions, because the home’s foundation must be placed below the frost line regardless, to prevent the home from shifting during freeze and thaw cycles. They can be heated or air-conditioned with the rest of the house.
A basement is the most expensive foundation type, and unless you’re building a daylight basement—a basement built on a hillside that opens to the daylight on at least one side—this the space created by this type of foundation can feel cave-like, as it lacks natural light. It’s not advisable to build a basement if you live in an area with flooding risks. And even in an area that’s not prone to flooding, experts recommend installing special equipment, like a sump pump.
Although not a popular option in Australia, if the house has the right climate and water table for it, a home in Australia can benefit from having basement foundations and use underground space for a variety of purposes, such as basement parking.
For homes built on a slope, the daylight basement, which has at least one side embedded in the ground from floor to ceiling, can be a nice alternative to a full basement foundation, even allowing a separate entrance to the home.
Crawl spaces are the most common type of foundations, as they are suitable for all climates. Sometimes called raised foundations, they are built above the ground with just enough space underneath. This space provides access to fixtures such as pipes, and mechanical installations, and it creates room for mechanical maintenance in the house. While they are not used as living spaces, a crawl space can also be used as storage for small items.
Crawl space foundations come with great benefits, but there are important factors to consider when building them. Dampness is one such factor. It is important to note that items placed in crawl spaces are susceptible to mould and mildew growth due to water vapour seeping from the ground. It is best to build crawl spaces with barriers that will protect the interiors from dampness and prevent odour, spores, and pests from entering the home.
Short foundation walls on concrete footings, or stem walls, form the foundations of houses with crawl spaces. They form a space that’s exactly as it sounds: a slightly elevated space below a house through which you can crawl, and often provides enough room for storage, a furnace, and other equipment.
A major advantage of crawl space foundations is the protection of the home. By lifting the base of the house, its walls are protected from flooding and other environmental hazards. The space allows easy access to plumbing, wiring and other mechanical systems. And raising the base of a house elevates the entire home, which can result in a more aesthetically pleasing house. It’s also a less expensive option than digging a full basement.
These types of foundations are especially common in warmer climates. They’re also a popular choice among architects designing homes where earthquakes occur frequently.
While crawl space foundations are more resistant to termites because of their elevation from the ground, they are prone to mould and mildew because of the moisture that can accumulate below them. While they’re a less expensive option than a basement, crawl space foundations require maintenance: homeowners will need to make sure below-ground walls are free from cracks, check for leaks around plumbing components, and instal vapour barriers to keep it dry.
Pier and Beam
In coastal areas, the best way to anchor a home above the soil that’s constantly shifting, flooding, or eroding is to build a pier and beam foundation (also known as “piers and pile” or “pier and post” foundations). You’ll often find them in areas prone to hurricane conditions or major flooding. They need to support the home and protect it from moisture, so they require serious planning.
They work in the same way an ocean pier does by fixing long pillars—often over 15 yards long to reach the solid ground—into the deepest layers of stone and soil. Builders use them with heavier homes because the pillars displace the weight of the house over a large area, preventing the home from sinking.
You’ll need to bring a structural engineer on board to oversee a project since they’ll need to do a soil analysis to make sure you’re building the structure in the right conditions. Driving concrete piers requires heavy equipment, so you’ll need to prepare for the added time and expense.
Pier foundations are a popular choice when a limited budget is a significant factor in construction. With the house built on a foundation elevated from the ground, space underneath allows access for electrical and plumbing maintenance.
When not ventilated properly, they are susceptible to mould growth, and wooden floors on houses with pier foundations are more prone to rot. But many still opt for pier foundations because of their advantages. Aside from being affordable and durable, unlike other foundation types, pier foundations can easily be used on sloped sites. They are also regarded as an environmentally friendly building option for homeowners.
A slab foundation, sometimes called a monolithic or mono slab foundation, is a flat concrete slab that rests on the ground and is poured in one single piece. The main advantage of a monolithic foundation is that they’re less expensive and quicker to construct.
Slab foundations are more common in warmer locations. After digging perimeter footings then removing and grading some soil, builders pour concrete directly into the soil to create cement slabs.
The installation is a simple process. A concrete-embedded beam runs about two feet deep around the perimeter of the slab, and wire mesh and steel reinforcing bars are embedded in the concrete. Since buildings that sit on a slab don’t have crawl spaces, homeowners won’t have to worry about the maintenance issues a crawlspace can present.
A property poured concrete slab won’t have weak points that could crumble over time and cause costly foundation repair issues. But you won’t usually find them in cold climates: As the ground freezes and thaws, cracks can form in the concrete and it can shift.
One notable downside of the slab construction is that sewer and drainage pipes are put in place before the concrete is poured. In case of a sewage or plumbing problem, you’ll have to cut into the slab to access the pipes.
Despite a few disadvantages to using slab foundations, many still favour slabs, especially for development projects, because materials for slabs are affordable, and the foundations are easy to build. They also function as good insulators, and they prevent all forms of wildlife from nesting under homes.
Wood might seem like an unusual choice for a foundation, but it became a popular choice in the 1960s. Builders will use preservative-treated wood that is resistant to decay and easy to install. Because they don’t require concrete pouring or labour-intensive masonry work, wood foundations are faster and less expensive to install.
Builders can also insulate these foundations and create a warmer crawlspace—and a less drafty house. Fun fact for those who doubt the durability of wood construction in the right climate: Archaeologists have found beams made of Cyprus wood in Egyptian pyramids that are over 6000 years old.
Certain woods, such as cypress, redwood, and cedar are impervious to insects and mould, but since they’re costly, the lumber industry has created ways of treating other lumber to give it similar characteristics. Still, they may not last as long as concrete foundations and can only be used in completely dry soil.
Who Designs Foundations for Homes and What is Involved?
House foundations are designed by an engineer and take into account the soil that the home is to be built on, the slope of the land and the weight of the building. At HP Constructions, we have the best home constructions selection to make your house a dream come true.
Before an engineer can design a footing system for your home, they will require a soil report. The purpose of the soil report is to test the bearing capacity of the soil and what level of reactivity the soil will have to moisture conditions. The soil test is done by taking samples of the soil at several locations across the site (referred to as bores). These samples are then tested in a laboratory and classified into the categories set out in Australian standard 2870.
The soil classification considerations for construction are set as follows:
- A – Stable Non-Reactive, Applies Most sand and rock sites with little or no ground movement from moisture changes.
- S – Slightly reactive clay sites, which may experience only slight ground movement from moisture changes
- M – Moderately reactive clay or silt sites, which may experience moderate ground movement from moisture changes
- H1- Highly reactive clay sites, which may experience high ground movement from moisture changes
- H2 – Highly reactive clay sites, which may experience very high ground movement from moisture changes
- E – Extremely reactive sites, which may experience extreme ground movement from moisture changes
- P – Problem soil – Sites with inadequate bearing strength or where ground movement may be significantly affected by factors other than reactive soil movements due to normal moisture conditions. P sites include soft or unstable foundations such as soft clay or silt or lose sands, landslip, mine subsidence, collapsing soils and soils subject to erosion, reactive sites subject to abnormal moisture conditions and sites that cannot be classified in accordance with the above classifications.
The soil classification will help the engineer determine the depth of foundation, the grade of steel to use and strength of concrete to be used.
All foundations need to be founded in natural ground. The natural ground is referred to as undisturbed ground on the site. If the natural ground is particularly deep or the site has uncontrolled fill on it, the foundation will need to be bored through the poor soil and into natural ground. These are called bored piers and are common throughout Melbourne.
Concrete strength is referred to in MPA. Standard slabs will require a 20 or 25 MPA concrete. Stronger slabs may require 32MPA concrete. The steel is added to give the concrete more strength and stiffness. Steel mesh reinforcement is added for additional strength.
The engineer will call up the mesh by the required size to achieve the needed stiffness for the slab. Square mesh is designated by the following sizes SL62, SL72, SL82, SL92 or SL102. The first digit refers to the diameter of the bars. The last digit refers to the spacing of the bars. For example, SL72 has diameter 7 mm bars, which are on a grid of 200 mm apart. The higher the rating, the stronger the mesh.
The more steel, the stronger the slab. Stronger slabs may have two layers of mesh as opposed to the one normally used.
In addition, the soil report will determine the depth that the concrete rib of the slab is to be founded in the ground. Generally, the deeper the founding depth, the stronger the slab.
In residential construction, the main types of foundation systems:
- Strip Footing
- Concrete Slabs
- Suspended concrete slabs.
With today’s modern architecture and difficult sites, it is not unusual for all four types of foundations to be used in one house.
How Much are House Foundations?
Foundations are sometimes charged at a cost per square meter. However, laying foundations is more than just the type of foundation; there are other considerations that you will need to account for in the planning of this, which we can talk to you about. These include drainage, heating and sealing. Making sure you include everything you need for your house foundations upfront can save you in the longer term. Looking for the best home constructions? Look no further! Hitch Property Constructions has the ultimate list of home designs for you to choose from.
Can You Soil Test Prior to Purchasing Land?
You can purchase a block subject to a soil test. However, that’s more of a legal matter under the contract. If you did purchase subject to a soil test, there would need to be a condition met, allowing you not to proceed. So it wouldn’t be subject to soil test, but rather subject to a soil test that meets specified criteria in your purchase contract. i.e. contamination, rocks, poor soil conditions. All soils will have a foundation plan and design that will work albeit an expensive alternative to normal soil conditions if that happens to be the case. If that’s an issue for you, speak to your legal team for further information.
Depending on the size, location, and geotechnical challenges facing your project, the decision to build shallow or deep foundations may be clear. Still, the exact type of foundation may be more nuanced. Given the importance of a building’s foundation to its overall structural integrity, getting this decision right is essential.