How the two differ in kind
These are not two versions of the same thing. A poured pier is a hole filled with concrete: it works by pressing down on whatever happens to be at the bottom of that hole, and the strength of the whole arrangement is a bearing value copied off a drawing. A helical pile is a steel shaft with one or more helix plates on it, screwed into the ground by a hydraulic drive head until the torque needed to keep it advancing reaches the figure the designer asked for. Both finish as a column below the frost line holding up a beam. What differs is what anybody actually knows when the work is done.
That is the argument in one line. Installation torque correlates with capacity — it is the basis of the pull-out calculator on this site — so every helical pile is a small, cheap test of the soil at its own location, and the installer hands over a log of what each one reached. It is an empirical correlation rather than a load test, and on critical work it does not replace one, but it is measured in the ground the pile is standing in. The pier's equivalent is somebody looking into an open hole and agreeing it looks like the material the drawing assumed. On uniform ground that is fine and has been fine for a century. On a site with old fill, a buried garden, a filled ditch nobody remembers, or a soft lens under one corner, the assumed bearing value is the weakest link in the entire structure and nothing about a finished pier will ever tell you which one landed on the soft spot.
Wet, soft ground sharpens all of it. A hole in saturated soil does not stay a hole — the sides slough in, water stands in the bottom, and what gets filled is an uninspectable shape wider than the cylinder arithmetic predicted, unless it is cased or the concrete is placed through the water properly. A screwed shaft displaces soil instead of removing it, so there is nothing to collapse and nothing to pump. Against that, the pier's advantages are the ordinary ones and they are not small: it is the foundation your inspector most likely has a table for, its diameter makes it stiff where it stands proud of the ground, and it is the only one of the two that a competent owner can genuinely build alone over a weekend.
The factors that actually differ
| Helical screw piles | Poured concrete piers | |
|---|---|---|
| What proves it will hold | Measured on the way in. Torque at the end of installation correlates to capacity, so each pile is verified where it stands and the torque log is a record of what that one achieved. | Assumed from the drawing's bearing value and confirmed, at best, by an eye at the bottom of the hole before the concrete goes in. Nothing afterwards reports back. |
| How deep it ends up | Discovered rather than drawn. The shaft advances until the torque criterion is met and extensions are added until it is, so final depth is an outcome — and part of the price. | Set by the drawing: below frost and onto competent material. Meet worse ground than expected and the hole goes deeper — or wider, if what you are short of is bearing area rather than frost cover, and width is the punishing direction because volume climbs with the square of the diameter. |
| Soft, wet or filled ground | Its home ground. Displacing soil rather than lifting it out means no excavation to cave and no water to dewater; the helix keeps turning until it finds something worth bearing on. | Where it fights. Saturated sides slough inward, water collects in the bottom, and the result is over-break — more concrete than calculated, in a form nobody can inspect. |
| Spoil and disturbance | Close to none. The ground is pushed aside, not removed, so there is no heap of arisings, little damage to a finished garden, and less carnage among mature tree roots. | A barrow of spoil per hole to spread or cart away, and an open excavation that stays a genuine site hazard until it is filled. |
| Uplift and frost jacking | The helix is an anchor plate, so tension capacity is designed for and testable — which is exactly what a roofed deck in wind and a heaving clay both ask of a foundation. | Resists uplift with its own weight and side friction unless it is belled, reinforced and tied to the frame; a rough, fat shaft also gives freezing ground more to grip on the way up. |
| Stiffness above the ground | A slender column. Where it stands proud, lateral load and unbraced height become a design item — bracing, a heavier shaft, or raked piles rather than an afterthought. | Diameter is stiffness. A fat concrete column shrugs off side load and free height that a pipe of the same capacity would need bracing designed around. |
| Weather window | Goes in through frost, rain and mid-winter. The rig does not care what the temperature is doing, which can rescue a build season that has already closed for concrete. | Cold and hot weather placement are procedures, not preferences, and concrete that freezes before it gains strength never fully recovers what it lost. |
| Who installs it, and what you are buying | A contractor with a machine, always. The price is installed and carries a mobilisation component whether you need a handful or a hillside — but the marginal pile is cheap once the rig is on site. | The foundation a determined owner can actually build. Your own labour substitutes directly for a contractor's, so the bill can be little more than concrete, tube and disposal. |
| Changing it later | Unbolted, unscrewed, relocated, sometimes reused — and a bracketed cap can be re-levelled with a spanner when the structure or the ground moves. | A permanent object. Re-levelling means jacking the structure off it, and removal means breaking out concrete and carting the pieces away. |
Which one, and when
Choose helical screw piles when…
- The ground is soft, wet, peaty or fill of unknown depth — the case where a hole will not stay a hole and the drawing's bearing value is really a guess.
- You need to build on it immediately, or the season for concrete has already shut and the frame is booked.
- There is real tension in the load path: a roofed deck, a pergola, a tall screen, or clay that lifts things every spring.
- The structure might move, be removed, or need re-levelling — leased land, a relocatable cabin, a consent with an end date on it.
- Disturbance must stay minimal: mature roots, a finished garden, nowhere to stack spoil and nowhere for a truck to stand.
Choose poured concrete piers when…
- Firm, well-drained ground that stands open on its own, where the assumed bearing value is credible rather than hopeful.
- You are supplying the labour. On a small deck, a weekend of your own digging is precisely the cost a specialist quote is made of.
- The design is ordinary enough to sit inside the prescriptive footing tables the inspector already works from.
- Piers stand well proud of the ground and carry side load, where diameter is doing structural work rather than just filling a hole.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- Do helical piles still have to reach below the frost line?
- Yes. The helix has to bear in ground that does not freeze, for exactly the reason the bottom of a pier does — anything bearing inside the frost-affected layer gets lifted with it. Depth for frost and depth for competent material are independent requirements and either can govern, and the torque criterion is what tells you the second one has been satisfied. What a pile genuinely has on frost is a smaller, smoother shaft for freezing ground to grip and a plate below resisting the lift, where a straight-shaft pier opposes jacking with little more than its own weight.
- Which one costs more?
- No figure here, because the two costs are not even the same shape. A helical pile comes as an installed price with mobilisation inside it, so a small job carries the whole cost of getting a rig to your street while the last pile of a long day is comparatively cheap; its open variable is depth, because a pile that will not reach torque takes extensions. A pier is concrete, tube, disposal and labour — and that labour can be yours, which is the single biggest reason small owner-built decks land where they do; its open variable is the ground, because over-break in soft soil quietly takes more concrete than the cylinder arithmetic predicts. Neither calculator on this page quotes money — one turns a final installation torque into a capacity, the other turns diameter, depth and count into a volume of concrete — but between them they pin down the two quantities the quotes will actually turn on, which beats a rule of thumb that has never seen your site.
- Can I install helical piles myself?
- Realistically no, and not because the screwing is difficult. What you are buying is the torque record: capacity is inferred from the torque at the end of installation using a factor published for that specific shaft, read off a calibrated head on a machine capable of delivering it. Hand-driven anchors exist for guying and light tie-downs, but a capacity claim under a deck rests on equipment and documentation a homeowner does not have. If supplying your own labour is the point of the exercise, that is an argument for piers, not for improvising piles.
- Will the steel corrode away underground?
- It is a design question with a published answer rather than a yes or a no. Galvanising plus an allowance for sacrificial thickness is how service life gets assessed, and the soil's resistivity, chlorides and disturbance all feed into it — aggressive soils, cinder fill and coastal sites are the ones that deserve looking at instead of assuming. Concrete is not exempt from the same conversation: sulfates in soil attack the wrong mix, and reinforcement with too little cover rusts and splits a shaft from the inside. Both are durable when specified for the ground they are going into, and both have a failure story when they are not.
- Can either one go in under an existing structure?
- This is where they stop being interchangeable. Helical piles are routinely driven alongside an existing footing and bracketed to it to underpin something that has settled, using limited-access equipment that fits in crawl spaces and against walls — a whole retrofit industry exists because a shaft can be advanced without excavating beneath the thing it is holding up. Getting a poured pier under an existing structure means digging under load, which is a slower, more carefully sequenced and considerably more nervous job. If your question is a sagging deck or a settling addition rather than a new build, the comparison is largely over before it starts.
- Will the inspector accept helical piles?
- Usually, on paper. The route is the manufacturer's evaluation report, a design from whoever is stamping your drawings, and the installation torque log handed over at the end as evidence that each pile met its criterion. Poured piers often need less than that: for an ordinary deck they may sit inside a prescriptive table the inspector already has in front of them, which is a real and underrated advantage of the boring option. Ask before you design either one, because an engineer's letter is a genuine line item on one side and frequently not on the other.