A concrete pier foundation supports an outdoor sauna on individual footings poured below the frost line, carrying the load beneath the freezing zone so frost heave cannot lift it. Piers are proven, adaptable to almost any soil, and inexpensive in materials, and they leave a well-drained, ventilated space under a raised floor. The trade-off is more labour and time — digging to frost depth, forming, pouring and curing — and the care needed to get multiple piers level and true.
Concrete piers are the workhorse foundation for framed outdoor saunas in Canada: proven, adaptable, and inexpensive in materials, they carry the sauna’s load down to below the frost line where winter cannot lift it. They ask for more labour than a gravel pad and more patience than ground screws, but on the right site they are hard to beat for value and reliability. This guide covers how pier foundations work, how they are built, and where they fit.
What a concrete pier foundation is
A concrete pier foundation supports the sauna on a set of individual footings — poured concrete piers — rather than a continuous slab. Each pier reaches down below the frost line, and the sauna’s frame or floor platform sits on top, raised above the ground. This creates a drained, ventilated space beneath the floor, which helps keep the structure dry.
Piers suit almost any soil because they can be formed and sized to the conditions, which is a big part of their appeal on variable Canadian ground.
How piers beat frost heave
The whole principle is depth. Frost heave happens when moisture in the upper soil freezes and expands, lifting whatever sits on it. By pouring footings that reach beneath the depth that freezes, the load-bearing points sit below the heaving layer, so the frozen soil cannot lift them. Paired with good drainage, this keeps the sauna level season after season.
The number that makes this work is your local frost depth, which varies enormously — from under a metre in milder areas to well over 1.5 m in the coldest regions. Confirm the frost depth (and any permit requirements) for your area before you dig; it is the single figure a pier foundation depends on.
Building a pier foundation: the sequence
The method is well understood by any builder:
- Lay out the pier positions to match the framing plan and load.
- Dig each footing hole down below the frost line.
- Form the piers — commonly form tubes or footing-and-post arrangements.
- Add drainage at the base as the soil requires.
- Place reinforcement as designed.
- Pour the concrete and set any brackets or posts.
- Cure the concrete fully before loading it.
- Frame the sauna’s floor platform level and true across the piers.
The two make-or-break points are reaching frost depth and getting all the piers level, so the floor starts flat.
Spacing, number and load
A pier foundation needs enough piers, correctly spaced, for the sauna’s load. A large cabin or sauna house needs more and larger piers than a small two-person sauna. The spacing follows the framing plan; getting it right, and every pier level, is what carries a stable floor. This is where design care pays off, and where a professional opinion helps on anything substantial or on difficult soil.
Pros and cons
Advantages
- Proven and adaptable to most soils
- Reach below the frost line, resisting heave
- Inexpensive in materials
- Leave a drained, ventilated space under the floor
- Well understood by any builder
Limitations
- More labour and time than screws or gravel
- Digging, forming, pouring and curing
- Getting multiple piers level takes care
- Excavation produces spoil
- Slower to build on than a same-day screw install
Cost
In materials, piers are cheap — concrete for a few footings costs far less than a full slab. They can cost more in labour and time than a simple gravel pad, but usually come in below a frost-protected slab. On a straightforward, accessible site they are excellent value; on a tight or sloped site, weigh them against ground screws, which install faster. Treat any figure as an approximate range — see our cost guidance.
When piers are the right choice
Concrete piers suit:
- Framed saunas on frost-susceptible or variable soil.
- Sites where you want a drained, ventilated space under the floor.
- Builders who value a proven, low-material-cost method and don’t mind the labour.
If you want a same-day, low-excavation install or you’re on a slope, compare with ground screws; if you want a solid, permanent, washable floor, consider a slab.
Common mistakes
- Not reaching the frost line — the piers heave.
- Uneven piers, carrying an out-of-level floor through the build.
- Rushing the cure before loading the concrete.
- Too few or under-sized piers for the load.
- Neglecting drainage, which supports the frost defence.
Next steps
If piers suit your soil and sauna, confirm your frost depth, design the spacing for the load, and get every pier level. Then move to the cold-climate build and insulation. Start with best foundation for an outdoor sauna, and compare piers directly with ground screws.
Frequently asked questions
How do concrete piers stop frost heave?
By carrying the sauna's load down to below the frost line. Piers are poured as footings that reach beneath the depth that freezes in winter, so the frozen, heaving layer of soil cannot lift them. Paired with good drainage, this keeps the sauna level through the freeze-thaw seasons, which is why piers suit frost-susceptible ground.
How deep should sauna piers be?
Below your local frost line, which varies widely across Canada — from under a metre to well over 1.5 m in colder regions. The footings must reach beneath the depth that freezes so they aren't heaved. Confirm the frost depth for your area, and any permit requirements, before you dig, since this is the number that makes piers work.
How many piers does a sauna need?
Enough to support the sauna's frame at the right spacing for the load — more and larger piers for a bigger, heavier sauna, fewer for a small one. The spacing and number follow the framing plan and the load. Getting them correctly spaced and all level is what carries a stable, true floor through the build.
Are concrete piers cheaper than a slab?
Often, in materials — concrete for a few footings is far less than a full slab. Piers can cost more in labour and time than a simple gravel pad, but they usually come in below a frost-protected slab. They also leave a drained, ventilated space under the floor. Compare against ground screws for a faster, cleaner install.
Can I build a sauna on concrete piers myself?
A capable DIY builder can, but it is exacting work: digging to frost depth, forming, pouring, and getting multiple piers level and true, then framing accurately on top. Mistakes in depth or level carry through the whole build. On difficult soil or slopes, professional help or advice is worth it.
Piers or ground screws for a sauna?
Both carry the load below the frost line. Piers are proven, adaptable to most soils and cheap in materials, but need digging, forming and curing. Ground screws install in hours with no curing and suit sloped or awkward sites, but depend on suitable soil. Match the choice to your soil, timeline and site — see our comparison.
Do piers need drainage?
Yes — like any foundation, piers perform best with good site drainage that carries water away, so there is less moisture in the soil to freeze and heave. Reaching below the frost line is the primary defence, but drainage supports it. The raised, open space piers create under the floor also helps keep the sauna dry.
