Why Are Helical Piles Better Than Concrete Sonotube Footings?
So you are considering building a new deck in your backyard or replacing an old deck. If you are replacing an old deck, then it was likely built using concrete sonotube footings as the foundation. In phoning around to get estimates, you are now learning about helical pile footings and prospective companies are trying to sell you on their advantages. But what's wrong with concrete footings? Why do I need to spend that extra money? I mean, my old deck had concrete footings and they seem fine after all these years. So what's the problem?
Well, there really isn't a problem. Concrete sonotube footings have been the traditional way of setting the foundations for backyard decks for many years and that's simply because that has been the only technology available for all of these years. But because they are "traditional", does that mean they are the best method to use?
Let's dive in!
What are Concrete Sonotubes?
Concrete sonotubes are basically foundational piers that contain concrete bound and held in place by a cardboard tube referred to as a "sonotube". For deck building, the width of these sonotubes are generally 8", 10" or 12" wide but unfortunately, the width of every tube varies slightly.
In Ontario, and many parts of Canada, concrete sonotube footings must be at least 4 feet deep so that the bottom of the footing is below the typical frostline. Also, the bottom section of the footing must have a "bell" shape so that the bottom of the footings is wider than the main art of the pier. This is to help lock the footing in place and prevent yearly frost from pushing the footing upwards during the winter.
Disadvantages of Concrete Sonotubes
The biggest and most important issue with concrete footings is yearly frost heave which causes the footings, and therefore your deck to move up in the winter and back down again in the spring. This movement can be minor or it can be quite severe.
So, can't these footings be installed in a certain way to prevent frost heave? Yes ...... and no. In order to prevent or limit frost heave, concrete sonotubes should be installed so that they are at least 4 feet below ground (or according to the frost line in your local jurisdiction) AND the bottom of the footing should be flared or bell-shaped so that it is wider than the main pier. But even when built this way, this is still no way to guarantee that the footings will not be subject to frost heave. The additional problem is that the vast majority of concrete sonotubes are not installed with a proper flared bottom even though this is required by the building code. Given the fact that many homeowners choose to have their decks built without a building permit and are looking to save a few dollars, many builders and post hole contractors simply dig a straight hole and pour the concrete into the tubes without making any effort to create a flared bottom as doing so adds time, effort, materials, and therefore cost to the installation.
Also, while many old decks look fine on the surface as a result of only minor movement of the footings during the winter months, from our experience at Deco Decks, no matter how well the footings are installed and even when passing inspection, there is no way to know for sure that they will not be subjected to significant frost heave. We have experienced many instances where even when things were done the right way, there was still significant movement of the footings.
As a result, concrete footings cannot be guaranteed. At Deco Decks, for example, we offer a 3-Year Workmanship Warranty but that warranty does not cover concrete sonotube footings due to their unpredictable nature.
What are some of the other disadvantages of concrete sonotubes?
They require extensive excavation of earth which can make for a messy building site which is not a problem if you are building a low deck and the underside will be covered, but when building a deck which will have an exposed underside, this additional earth now under the deck, can pose a visual and practical problem.
If concrete footings are being installed in soft soil, unlike helical piles, there is no way to correct for the soil and despite all appearances, concrete footings will sink in soft soil over time.
They require a inspection PRIOR to pouring concrete which can lead to delays.
They cannot be installed in the rain as any additional water in the holes will affect the strength of the concrete mix and will further delay their installation.
The mixture of concrete is not always consistent from builder to builder and from post hole contractor to post hole contractor thereby compromising the strength and longevity of your deck's foundation.
Many builders and post hole contractors do not install these footings in a way that creates proper water runoff at the top of the footings where the concrete meets the wooden post thus causing the pooling of water on the top of the footings which causes premature rotting of the bottom of the posts.
They increase the build time because they require the concrete to cure before building on them.
While concrete sonotube footings are the traditional method for installing footings for your new backyard deck, they are not ideal. But mainly due to cost considerations, many homeowners still opt for these types of footings. Nevertheless, it's important that as a homeowner, you are able to make a fully informed decision and are aware of the potential issues down the road.
What are Helical Piles
While helical piles have been around for a very long time, there availability and practical use in small residential construction is relatively new but they provide significant advantages over traditional concrete footings. Basically, helical piles (or screw piles) are 7 foot metal rods of varying thickness with a screw-like device on the bottom of them.
To install these piles, a small drilling rig is used to literally screw them into the ground. No digging or excavation is required. During the drilling process, a gauge is used to monitor the pressure and the torque of each pile to ensure that they will be set to an engineer's specification and thus once set, they will not move.
As mentioned, these piles are 7 feet long and if the proper pressure is not reached on the first pile, 3-5 foot extensions can be added, one at a time, until the desired pressure is reached, which typically happens in soft soil.
Advantages of Helical Piles
The major advantage of helical piles is the fact that they are completely resistant to frost heave. Once installed to the engineered pressure, they are guaranteed not to move. Some companies, like Techno Metal Post, even have plastic sleeves on each post which allows any frost to grab the sleeve without grabbing the post itself, thus providing an extra layer of protection against movement.
The additional benefit of helical piles for your new deck are that they are "engineered", meaning they come with a conformity report which stipulates that they have been graded by an engineer for the purpose they are being installed. This effectively eliminates a building inspection for your footings and all that is required is to submit your conformity report to the project building inspector.
Because they are engineered, helical piles are guaranteed for up to 30 years, while concrete sonotubes cannot be guaranteed at all. So while helical piles are generally more expensive, because of their guarantee, over the long term, they actually turn out to be less expensive than concrete sonotubes on a yearly basis plus you have the added peace of mind.
Other Benefits of Helical Piles
They are more environmentally friendly and their installation eliminates any excavation of earth so they end up being a much cleaner installation with minimal site disturbance.
They can be used in a variety of soil conditions from "soft" soil to frozen soil (meaning they can be installed in the winter).
The construction of your new deck can begin immediately after installation thereby eliminating any delays.
Hopefully this information helps you to make an informed decision on whether to go with traditional concrete sonotube footings or helical piles. If you have any additional questions please do not hesitate to reach out to us by email or through our "Let's Chat" feature at the bottom of the page.