How to Build a Sauna Floor

Use a tape measure and lawn flags to mark out the dimensions of your sauna foundation onto the piece of land where you intend to lay the foundation. Make sure the foundation is large enough to hold the structure, plus a few inches for a small 2- to 3-inch ledge around the perimeter in case of soil movement. Measure out the necessary dimensions with the tape measure then place lawn flags around the area to mark the location.

Measure the height of the pavers with the tape measure. Add 3 inches to the height for the stone and sand base then dig to that depth with a spade. Slope the floor 1/4-inch away from any nearby structures for every foot of floor length. Compact the foundation hole by running a vibratory plate compactor over its surface.

Place a layer of foil vapor barrier into the foundation hole that extends 6 inches from the sides of the foundation with the shiny side face-up. This vapor barrier will prevent moisture from the soil working its way upward into the building.

Pour a layer of crush run in into the floor base that is 2 inches thick. Crush run is a crushed stone mix made of a variety of different-sized stones and stone dust that compacts to a strong base for paver foundations. Run a vibratory compactor over the stone to compact it flat. Add additional crush run and compact it again to bring the layer up to a 2-inch compacted depth.

Cover the crush run with a 1-inch-thick layer of masonry sand to serve as the base for the pavers. Compact the sand then add a second layer to bring it to the 1-inch compacted depth.

Install paver edging around the edges of the foundation to hold the pavers in place. Cut the edging to fit the perimeter with a hacksaw as needed. Secure the pavers in place by driving steel spikes through the mounting holes of the pavers every 2 feet and into the ground with a mallet.

Place the concrete pavers around the perimeter of the foundation hole and set them tightly against the paver edging. Only one row of pavers is necessary as you’ll be filling the rest of the surface with decorative gravel. Place a carpenter’s level over the pavers and adjust them so that they’re level with one another. Press higher pavers further into the sand layer and add more sand beneath low pavers to give them additional height.

Pour masonry sand over the pavers and use a broom to sweep the sand into the gaps between the pavers. Cover the pavers with a rubber mat then run the compactor over them to shake the sand to the base of the joints. Repeat the process until the joints are filled completely. Sweep the excess sand into the center of the floor.

Measure the length and width of the unpaved center of the foundation structure. Cut wooden strips of 1-by-4 planks to match the length of the unpaved floor less 1 inch to serve as floor joists with a circular saw. Cut a plank for every 12 inches of floor space. Lay the joists onto the compacted sand on the 4-inch sides spaced every 12 inches, beginning an inch from the edge of the floor. Make certain you have two joists on either edge of the floor spaced 1 inch from the edge. This may result in a small gap between the last two joists.

Cut deck pieces from the 1-by 4 planks that measure the width of the unpaved floor minus 1/2-inch. Drive two nails through the deck pieces at each floor joist location. Leave a 1/4-inch gap between the ends of the deck pieces and the edges of the pavers to allow for soil movement. Leave a 1/8-inch gap between the boards.

Place the point of a nail set onto the center of each finish nail and give the head of the set a tap with the mallet to drive the nail head beneath the wood.

Use the edge pavers to construct the wall foundation area and build the rest of the structure. After completion, seal the gap between the pavers and the walls with a silicone sealant to prevent moisture from seeping into the wall base.