Ground screws and concrete piers both create load-bearing points below the frost line to resist frost heave. Screws install fast with no curing and suit sloped or awkward sites, but depend on suitable soil. Concrete piers are proven, adaptable and often cheaper in materials, but need digging, forming and curing. The right pick depends on your soil, site access and timeline.
Once you’ve decided your outdoor sauna needs load-bearing points below the frost line — the usual answer on frost-susceptible soil — the next question is how to make them. The two mainstream options are ground screws and concrete piers. Both do the same job; they just get there differently. Here’s how to choose.
What they have in common
Both create fixed points that carry the sauna’s weight down to below the local frost line, so seasonal freezing can’t lift and tilt the structure. Both need to be level, correctly spaced and deep enough for your frost depth, and both work best with good site drainage. Get either right and frost heave stops being your problem. For the wider picture, see best foundation for an outdoor sauna.
Ground screws
A ground screw is a galvanized steel shaft with a helical thread, driven into the ground to a depth chosen for your frost line. The sauna’s frame or platform bolts to the screw heads.
Strengths: very fast to install — often a single day, with no concrete to cure — minimal excavation and spoil, easy levelling, and a natural fit for sloped or awkward sites where digging footings is a chore. Nothing to wait for means you can build immediately.
Limits: they depend on suitable soil. Very rocky ground can stop a screw, and some soils don’t give the right hold. Per-point cost is usually higher than a bag of concrete, and proper installation often wants the right driving equipment.
Concrete piers
A concrete pier is a footing poured below the frost line — in a form tube or a footing-and-post arrangement — with a bracket or post to carry the structure.
Strengths: proven and adaptable. Piers can be formed to suit almost any soil and load, materials are inexpensive, and the method is well understood by any builder. On straightforward, accessible ground they’re hard to beat for value.
Limits: more labour and time — digging to frost depth, forming, pouring and waiting for the concrete to cure before you build. Getting multiple piers level and true takes care, and excavation produces spoil to deal with.
Side by side
| Factor | Ground screws | Concrete piers |
|---|---|---|
| Installation speed | Fast; build the same day | Slower; dig, form, pour, cure |
| Excavation / mess | Minimal | More digging and spoil |
| Soil suitability | Needs suitable soil; poor in rock | Adaptable to most conditions |
| Sloped / awkward sites | Excellent | Workable but more effort |
| Materials cost | Higher per point | Lower (concrete is cheap) |
| Labour / time cost | Low | Higher |
| Frost performance | Good below frost line | Good below frost line |
How to choose
- Rocky, unknown or difficult soil? Piers are more adaptable; screws may not drive.
- Sloped, tight-access or want to build now? Screws shine — fast, clean, level.
- Straightforward, accessible ground on a budget? Piers are excellent value.
- No power or equipment on site? Piers rely on hand tools and concrete; screws often want driving gear.
Because soil is the swing factor, it’s worth confirming your ground conditions and local frost depth before committing — and, on a marginal site, getting a professional opinion.
Common mistakes
- Not reaching the frost line. Whichever you pick, depth is everything.
- Assuming screws suit every soil. Check the ground first; rock defeats them.
- Rushing pier curing. Let concrete reach strength before loading it.
- Neglecting drainage. Both perform better on a well-drained site.
- Levelling carelessly. An out-of-level base carries through the whole build.
Next steps
With the foundation sorted, move to the cold-climate envelope and insulation. Still weighing the overall approach? Start with best foundation for an outdoor sauna, and bring in a qualified builder or structural engineer where soil and load raise real questions.
Frequently asked questions
Are ground screws as good as concrete piers?
For many saunas, yes. Both carry the load to below the frost line and resist heave when installed correctly. Screws are faster and cleaner; piers are proven and adaptable. Soil is the deciding factor — screws need suitable ground, while piers can be formed to suit most conditions.
Do ground screws work in cold climates?
Yes, provided they reach below your local frost line and the soil suits them. Their length is chosen for frost depth, and they carry the sauna's load beneath the freezing zone so frost heave can't lift it. They can struggle in very rocky ground.
Which is cheaper, screws or piers?
It varies. Concrete piers are often cheaper in raw materials but cost more in labour and time; ground screws cost more per point but install in hours with no curing and less excavation. On a hard-to-access or sloped site, screws can work out competitive.
How deep do they need to go?
Both must reach below your local frost line so they aren't heaved by freezing soil. Frost depth varies widely across Canada, so confirm the requirement for your area before choosing screw length or pier depth.
Can I install ground screws myself?
Small screws can be hand- or tool-driven, but getting them to the right depth, level and load capacity often calls for the right equipment and know-how. For a sauna you want them accurate and reliable, so professional installation is common. Piers likewise reward careful, level work.
Which lasts longer?
Both are durable when done right. Quality galvanized steel screws resist corrosion for decades; properly poured concrete piers are long-lived too. Longevity depends more on correct installation, drainage and soil than on the choice itself.
