Buildings are, unsurprisingly, pretty heavy and soil is pretty easily moved. This means that buildings need carefully considered elements in their foundations to ensure that the soil doesn’t shift under them. These are called footings, but what are footings in construction and how do they work?
Understanding Footings
Footings are specialist structural components which serve to distribute the weight of a building more evenly. They’re typically made from concrete and sit below foundation walls or columns which support the building above.
They’re effectively giant concrete pads and spread the weight of the elements above them more evenly across the ground below. This helps to avoid issues like sinking, settling and shifting which can cause anything from cracks to total collapse.
Types of Footings
When you ask ‘what is a footing in construction’ the answer is always going to be ‘if you want a detailed answer, it depends’. There’s a lot of nuance.
As there are so many different types of buildings and so many different places that we build them, it should come as no surprise that footings come in various shapes, sizes and configurations.
The most commonly used footing types include things like:
- Spread Footings: Common in residential and smaller commercial buildings, spread footings are designed with a base wider than the structure above it. This tapered design distributes the weight of the building over a larger area, reducing pressure on the soil beneath. Spread footings are a popular choice for new residential construction due to their efficiency and reliability.
- Strip Footings: Strip footings are buried lengths of concrete, set into the soil. They’re used to distribute the pressure from load-bearing walls. How deep and wide they are depends on how heavy the wall they’re supporting is and the local soil conditions.
- Pile Footings: Pile footings consist of a long concrete pillar driven deep into the ground. They’re particularly useful in areas with unstable, sandy soils or other weaker patches of ground. They can be dug down until they hit the solidity of the bedrock if necessary.
- Mat Footings: Mat footings are a large concrete pad, spreading the weight of the building above over as wide an area as possible. These distribute the weight over a larger area, reducing the pressure on any one piece of ground. They allow a shallower excavation without compromising on structural strength.
The Role of Footings in Structural Stability
We’ve answered the question ‘what are footings in construction’ but what are they actually for and how do they work?
Load Distribution
As we mentioned above, buildings are heavy. They also don’t tend to be perfectly balanced- one corner will almost always weigh more than its neighbour. When you place something heavy on a soft surface, it tends to sink in to it.
Combine these two facts and you’ll see the problem. Without consideration of how the heavy load will push against its foundations, you can end up with one corner sinking further than the rest, wrecking the building.
Foundation footings aim to reduce this problem by spreading the weight more evenly. The part of the building in contact with the ground is designed to spread the weight, distributing the pressure over a wider area. This avoids issues like subsidence and shifting, boosting structural stability.
Adaption to Soil Conditions
Dirt is never just dirt. There are almost infinite combinations of loam, clay, sand and other features that mean that what works in one location might not in another. Some soils are easy to compact, others will crumble away with the lightest pressure.
The various different designs of footing allow architects and builders to adapt their work to local conditions. Pile or spread footings allow tall, heavy structure to be built on weaker, less stable soils but aren’t needed on more clay-based ground where other types would be better.
Before making any decisions about appropriate footing types, it’s vital to test the soil.
Reinforcement and Design
Concrete footings allow architects a much freer hand when it comes to design. The introduction of rebar to strengthen the concrete further enhances this freedom- allowing hugely heavy buildings to be constructed on soil that would have struggled to support them in previous generations. Pisa probably wouldn’t be so famous had the builders of the leaning tower had access to this simple technology.
More fundamental than the use of rebar, the depth and width of the footings plays a massive role in their effectiveness. The wider and deeper they are, the more strength they offer and the more effectively they can distribute weight. The exact specifications will vary from project to project, but they’ll be tightly controlled by local building codes and regulations.
Challenges for Footings in Moisture-Prone Areas
We’ve spoken a little about some of the challenges for concrete footings in areas with weaker soils and how to circumvent these issues. Another set of challenges comes from the damper conditions found in places with heavy rain and higher water-tables.
Impact of Groundwater on Footings
Concrete is sturdy stuff- we’ve got examples of it which have survived literally thousands of years. That being said, it’s not magical and it’s not impervious to damage. Given enough time, water will wreak havoc on even the best constructions causing issues like erosion and cracking, weakening the footings.
Water pooling around the footings or the forces exerted by hydrostatic pressure will eventually cause damage. Keep an eye out for signs like:
- Cracking: Not just in the footings themselves, but in the building they support
- Uneven settlement: Also known as subsidence. This is where one side of a building starts to sink relative to the others.
- Weakening of the footings: Moisture exposure will weaken concrete over time. This is made worse in colder climates with regular freeze/thaw cycles.
To avoid these problems, careful consideration needs to be given to drainage and water management.
Footings and Basement Waterproofing
A crucial aspect of understanding “what are footings in construction?” is their role in basement waterproofing. As mentioned earlier, concrete is vulnerable to water damage, making a well-designed water management system an essential component of construction.
Footings not only require protection from moisture to maintain their integrity but can also contribute significantly to keeping the structure above them dry.
French drains are a key component in preventing moisture damage to footings. These drainage systems consist of a perforated pipe surrounded by gravel and filter fabric, which collect and channel groundwater or surface runoff away from the foundation. By lowering the water table and preventing water from pooling near the footings, French drains reduce hydrostatic pressure and protect the concrete from cracking, erosion, and long-term water damage. This not only safeguards the footings themselves but also helps maintain a dry and stable basement environment.
Key Waterproofing Solutions
Certain waterproofing methods will protect both your footings and your basement space. These can be added later but for the most effective results, they’re well worth incorporating into the initial construction:
- French drains: Divert water away from footings and basement walls
- Sump pumps: Avoid water rising up through your basement slab
- Waterproof membranes and coatings: Wrap your footings and basement walls in waterproof layers.
Repairing and Retrofitting Footings
If the worst should happen and your footings do get damaged, all is not lost. It’s often a fairly disruptive job but structural repairs are usually possible. Techniques like underpinning can boost stability while cracks, settling and water damage can all be rectified.
It goes without saying that any work on the footings will require excavation and that comes with mess, noise and costs. That being said, all of these pale in significance when compared to the consequences of not carrying out the work when needed.
It’s well worth using this opportunity to take preventative measures too. Install and improve the waterproofing around your footings while repairs and modifications are underway to avoid future issues.
Best Practices for Footing Installation
As such a vital component of any construction, getting the footings right is key to a construction project going to plan.
Before the first drop of concrete is poured the local soil conditions should be thoroughly examined. This allows the architects and builders to gauge exactly how wide, deep and reinforced the footings should be. Elements like the strength of the soil, how high the water-table is, the bedrock and the frost line should all be considered. It also allows them to make an educated decision on any extra features that might be needed.
It’s vital that all of these choices align with local building codes and regulations. These rules are put in place by local authorities to ensure that buildings are safe and provide a minimum standard for construction. Failure to adhere to these codes can lead to problems down the line: buildings which can’t be insured, hefty fines and, of course, collapse.
Waterproofing Integration
It’s well worth getting a running start on your basement waterproofing while installing footings. Not only will starting now make your basement a comfier, dryer space, it’ll protect the footings themselves too.
Systems like French drains and sump pumps are most effective when installed alongside the footings. Starting at the very beginning of construction means that problems with waterproofing need never arise in the first place. Dryness is built in from the very start.
So, what are footings in construction? Absolutely vital.