What are Helical Piers?
Helical piers – also known as screw piles, helical piles, or helical anchors – are a kind of foundation or anchoring system that involves literally screwing a pile into the ground. Helical piers are remarkably strong and work by transferring the load of the structure to which they are attached into the pier. In the same way, a screw in a wall can hold up a heavy painting, so a helical pier can provide a robust foundation for a home or other building type.
Helical piers were initially invented to keep ships and lighthouses in place, despite being built on surfaces like mud or sand; they’re now used as an environmentally-friendly way to keep homes in place. You may not have thought about using helical piers for your home, but after reading this guide, you may have changed your mind.
What is the history of helical piers?
As with any invention that has major ramifications yet is surprisingly simple, helical piers have a few different potential sources. The first person to document the idea of helical piers was Alexander Mitchell, a blind civil engineer. Mitchell experimented with a variety of different foundation types, all with the goal of providing additional stability to buildings based on mud or sand. He documented his design for a helical pier in the 1840s, although there are examples of structures using helical piers for around a decade earlier.
The first recorded use was for ships’ moorings in the 1830s. Ships would moor next to mud or other soft ground and could use a helical pier to create a solid connection that wouldn’t loosen over time. This principle soon came to be applied to other structures – most notably in the building of lighthouses, which, by definition, tend to be built on sand, mud, or other soft ground.
Since then, helical piers have been refined and are now made of different types of metal (rather than the earlier wood) and have become ever more complex. Regardless of the usage type, there is a helical pier design that will work. It’s all a far cry from Alexander Mitchell screwing in a wooden helical pile to the shores of Lough Belfast in the nineteenth century.
WHAT ARE HELICAL PIERS MADE OF?
One of the best things about a helical pier is that it is a relatively simple system. Indeed, it is broadly based on the idea of a screw – one of the original six ‘simple machines’ used to change the direction of a force. Although there is a wide range of different helical pier styles, they all have the same two key components in common:
This will usually take the form of a round piece of pipe surrounded by plates (or helixes). These give the piers the stability to hold great forces. The larger the plates, the less depth is required to create the load capacity of the pier. Smaller plates are used if the required depth is greater. The size of the plates is usually defined by local building codes, which in turn is defined by the soil type. In South California, for example, the lead configuration is usually 8/10, meaning that the first flight is 8 inches in diameter, and the second is 10 inches.
The extensions attach to the leads and allow the leads to reach the required depth within the soil. There are a number of different lengths available, from 3 feet to 20 feet. The typical installation depth is around 21 feet but can be as much as 200 feet, depending on the soil type, the size of the structure that is being anchored, and the number of helical piles. All of these shape the forces involved. The deeper the pier, the greater the stability.
HELICAL PIERS VS. PUSH PIERS
Because helical piers have a number of different names, depending on where in the world (or where in the United States) you are, the terminology can get confusing. However, it’s important to understand that there are some terms that are related that are not synonyms. ‘Push piers’ is one of these.
Screw vs. push
As the names may suggest, they have fundamentally different ways of entering the earth below a home. A helical pier has plates that have to be screwed into the earth. By contrast, a push pier needs to be ‘pushed’ into the earth.
Affect on foundation
A push pier is a way of jacking up the foundations of a house. Once the push pier is inserted, a jack pump on each one will raise the house before securing everything in place with brackets. By contrast, a helical pier does not use the foundation as a counterweight, meaning it is far gentler on the structure of your home. If you’re using it to secure the foundation of your home (as will be discussed before), then the bracket is installed to the helical pier, which holds the foundation up.
In general, push piers are better for commercial, large, or particularly heavy buildings. In addition, they tend to perform better when the foundation is a concrete footing or foundation wall. Helical piers are better for smaller buildings (i.e., homes) because they don’t require the weight of the building to provide stability.
WHY USE HELICAL PIERS IN HOME CONSTRUCTION?
The most common reason why helical piers are used in residential homes is to provide additional structural integrity. They are less commonly used as the foundation in the first place and more often used to supplement an existing foundation system – particularly in older homes. In many parts of the United States, older homes were built on unsuitable soil and have therefore shifted or sunk over time.
This leads to sagging or cracking in the foundation stone, which can lead to major problems in the overall solidity of the home (culminating, if left unchecked, in the collapse of the building).
A survey of the subsidence of the house will determine the number and location of the helical piers. Unlike push piers, you can insert helical piers at any angle. This means that they are relatively unobtrusive. Moreover, since they don’t require a great deal of soil to be displaced, the whole process requires less work than may be expected. All in all, installing helical piers is usually a day’s work for a professional team.
Once the helical piers are inserted under the foundation of the home, they are bracketed onto the foundation, providing stability in both directions – meaning that the shifting soil won’t cause the foundation to fall or heave upwards. For a relatively small amount of work, therefore, your home will be far more stable, and it will be almost impossible for any further subsistence to take place. The results are instant, unlike concrete slabs or the like, which require time to cure.
HOW MUCH DO HELICAL PIERS COST?
The first response to the question of cost is how much it would cost to not install the helical piers. If the foundation of your home is cracking, which can cause major damage to the structure of the home, the costs can run to the tens – if not hundreds – of thousands of dollars.
By contrast, helical piers are extremely cost-effective. The usual cost of a helical pier is between $15 and $30 per foot. For a typical 20-foot helical pier (of the type that would be used in Southern California), therefore, you can expect to pay somewhere between $300 and $600 each.
As mentioned above, one of the key benefits of helical piers is that they are relatively easy to install. A construction team operating at your home can install up to 40 helical piers in one day (although you’d be unlikely to need that many). Assuming you require 10-20 helical piers, the total cost of the project will likely be somewhere between $3,000 and $12,000.
Again, you need to compare that to the cost of not doing the work, as well as the cost of other types of foundation repair. In addition, you should factor in the cost of disruption; installing helical piers will not cause any major problems outside of the day’s work. All in all, it’s an extremely cost-effective solution to a potentially very expensive problem.
One of the most endearing (and enduring) elements of helical piers is their simplicity. Using one of the simplest engineering concepts – a screw – a helical pier can provide a great deal of strength. If your home is sinking into the soil, you can be thankful for a technology designed to keep large structures from shifting in the sand. Helical piers, if appropriate, can provide a cost-effective, robust, and instantaneous solution to your problem.