How to Build a Sauna Platform: Elevated Base Construction Guide

How to Build a Sauna Platform: Elevated Base Construction Guide

An elevated platform lifts your sauna off the ground, improves drainage, protects the bottom from moisture, and can solve uneven terrain without major excavation. It's one of the best foundations for an outdoor sauna, especially on sites where a concrete pad isn't practical or the ground slopes.

Building a sauna platform is a weekend project for someone with basic carpentry skills. Here's the complete process, from planning to the last deck screw.

Why Build an Elevated Platform?

• Moisture protection. Raising the sauna 6-12 inches off the ground prevents ground moisture from wicking into the wood base. This is the number one enemy of outdoor sauna longevity.
• Airflow underneath. Air circulation under the sauna keeps the bottom dry and prevents rot.
• Drainage. Water drains through and away instead of pooling under the sauna.
• Level surface on uneven ground. A platform can be leveled with posts of different heights, adapting to slopes without regrading.
• Clean entry. A slightly elevated sauna creates a natural step up, keeping dirt and debris outside.

Planning Your Platform

Size

The platform should extend at least 6-12 inches beyond the sauna footprint on all sides. This provides a margin for placement, allows water runoff from the sauna to clear the edge, and gives you a small step area around the door.

Example: If your sauna footprint is 6' x 8', build your platform at least 7' x 9'. Bigger is fine - many people extend the platform in front of the door to create a small deck or landing area.

Height

6-12 inches off the ground is the typical range. Higher than 12 inches and you'll want stairs or a step. On sloped ground, the uphill side may be just off the ground while the downhill side is 12-18 inches up.

Weight Capacity

Your platform needs to support:

• The sauna itself: 500-2,000 lbs depending on size and construction
• Users: 200-400 lbs for 2 people
• Heater and stones: 100-200 lbs
• Snow load (cold climates): varies by region

Total: plan for 1,000-3,000 lbs distributed across the platform. This isn't extreme - a properly built deck frame handles this easily.

Materials

Note: The platform itself uses pressure-treated lumber because it's in ground contact and exposed to weather. This is fine because the platform sits under the sauna - not inside where heat would cause off-gassing. The sauna itself sits on top of the platform with its own untreated wood floor.

Step-by-Step Construction

Step 1: Site Preparation

1. Clear the area of vegetation, rocks, and debris.
2. Remove the top layer of sod/topsoil where the platform will sit (4-6 inches).
3. Lay landscape fabric to prevent weed growth underneath.
4. Spread 2-4 inches of crushed gravel over the fabric for drainage and stability.
5. Compact the gravel with a hand tamper or plate compactor.

Step 2: Set the Foundation Supports

1. Lay out your pier/block locations. Place them at corners and every 4-6 feet along the perimeter and interior.
2. For concrete deck blocks: set them level on the compacted gravel. Use a long level or string line to ensure all blocks are at the same height. Adjust by adding or removing gravel underneath.
3. For sonotube footings: dig below the frost line, place the tube, fill with concrete, and set a post bracket in the wet concrete. This is more work but more permanent and stable.
4. Double-check level across all supports in both directions.

Step 3: Install Beams

1. Set your beams across the support piers, running the length of the platform.
2. Secure beams to the piers/blocks with post brackets or structural hardware.
3. Check that beams are level and square (measure diagonals - they should be equal).

Step 4: Install Joists

1. Install a rim joist (perimeter frame) around the outside of the beams using joist hangers.
2. Install interior joists perpendicular to the beams, 16 inches on center. Use joist hangers at each connection.
3. Crown all joists up (the natural bow in the lumber should face upward).
4. Check for level across the top of all joists.

Step 5: Install Decking

1. Start the first deck board flush with the outside of the rim joist.
2. Leave a 1/8" gap between each board for drainage and expansion.
3. Screw each board with two screws per joist (pre-drill to prevent splitting).
4. Use galvanized or stainless steel deck screws.
5. Let the boards run long over the edges, then snap a chalk line and cut them all at once for a clean, straight edge.

Step 6: Finishing

• Install a fascia board around the platform edges for a clean look and to cover the end grain of the joists.
• Add a step or stairs at the sauna door location if the platform is more than 8 inches above grade.
• Apply a wood preservative or stain to the deck surface for extra protection.
• Confirm the platform is level one final time before placing the sauna.

Common Mistakes to Avoid

• Skipping the gravel base. Without gravel underneath, water pools under the platform and accelerates rot, even on treated lumber.
• Not going below frost line. In cold climates, shallow supports will heave when the ground freezes, shifting your platform and sauna. Use sonotube footings that go below the frost line.
• Making it too small. The platform should be bigger than the sauna footprint. Extra overhang protects the edges and gives you a landing area.
• Using untreated lumber for the frame. The platform frame is in ground contact or near ground contact. It must be pressure-treated or rot-resistant material.
• Forgetting drainage slope. A very slight slope (1/8" per foot) away from the sauna door ensures water runs off rather than pooling on the platform surface.

Cost Estimate

For a 7' x 9' platform:

• Concrete deck blocks: $80-120
• Pressure-treated lumber (beams, joists, decking): $300-600
• Hardware (joist hangers, screws, brackets): $50-100
• Gravel and landscape fabric: $50-100
• Total materials: $500-900

If you hire a contractor, add $500-1,500 for labor.

Looking for a sauna to put on your new platform? Browse our outdoor sauna collection. For other foundation options, see our sauna foundation guide and site preparation guide.