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How to Build a Freestanding Sauna | Setting up the DIY Prefab Modular Sauna Kit

The freestanding prefab sauna kit may be assembled indoors or outdoors, and may be relocated thus it's sometimes called a "modular" DIY (Do It Yourself) sauna kit

This 10 step article and the 8 part video series applies to the indoor AND outdoor prefab sauna kits

If building your sauna indoors, ignore the portions regarding the sauna base and roof. Click to view our outdoor prefab modular sauna kit sizes, and indoor prefab sauna kit sizes in the store.


How to Build the Prefab Sauna — Hover over each image with a still mouse to read the caption, or watch the videos at right

Video screenshot: Wooden Base for Outdoor Sauna KitVideo screenshot: Vapor barrier for outdoor saunaVideo screenshot: Plywood over a wooden base makes for a stable baseVideo screenshot: Cedar frame acts a track fitting the slot in the bottom of the sauna wall panelsVideo screenshot: Bottom of sauna panel fitted to trackVideo screenshot: Making the corner of the outdoor saunaVideo screenshot: Slide the prefab panels into placeVideo screenshot: Panels form the walls of the freestanding sauna roomVideo screenshot: Sauna panel includes the doorVideo screenshot: Corner trim is added to complete the lookVideo screenshot: Installing the sauna benchesVideo screenshot: Installing the sauna ceilingVideo screenshot: Adding the sauna roofVideo screenshot: Tongue and Groove siding encloses the roofVideo screenshot: Ridgecap for the saunaVideo screenshot: Installing the sauna flooring or duckboardVideo screenshot: Sauna trim around the door

10 Steps to Building the DIY Prefab Sauna Kit

If for some reason any of the videos below do not play, you may view our play list on YouTube: How to Build a Sauna. If we can be of more help, please email us or call us at 1.800.426.3929 or read on. Thanks!

IMPORTANT: First note that the exterior size of our prefab modular saunas is 8" wider and longer than the size in the title of the prefab sauna. For example, a 5'x7' prefab sauna is 5'x7' on the INSIDE, the OUTSIDE or exterior measurement is 5'8' x 7'8" — 8" more. In a 5'x7' sauna, this means 8 more square feet to relax and stretch your legs out!

We set a temporary wooden base and seal with plastic

1. For this video, we set a pressure treated wooden base. Other options for your sauna base are cement slab, pavers, or a deck

The wooden frame was just to make it easy to set up the sauna's base from start to finish. Most outdoor saunas are set on a cement slab, pavers, tile, or a deck, or other. However, a wood base does make relocating your sauna to another location much easier. Wood can rot over decades, especially when in contact with dirt. So, always use pressure treated wood as a base, or use something more permanent.

2. Cover your pressure-treated wooden base with a vapor barrier and plywood

Again if are setting your sauna on a cement slab or pavers or a deck, then this step is not necessary. If you want a wooden base, then after your base is square, staple some 6mm plastic. This acts as a vapor barrier and protects your sauna's sub flooring from moisture.

IF you live in an area where ants are prevalent, you might consider putting diatomaceous earth under the plywood as pest control. This is one of the few natural remedies which make ants turn around fast. Diatomaceous earth will cut into an ant's exoskeleton, so they avoid it entirely. Caution: Do NOT breath diatomaceous earth. It is an extremely fine dust and can agitate your lungs. Always follow the manufacturer's label during application.

The plastic is then covered by two sheets of plywood. If desired, you could cover the plywood with hardy board and tile.

3. A cedar frame acts as a slot and a base plate for the panel bottoms to slide into place

We add a base plate on top of the plywood which acts as a slot to align our prefab sauna walls

On top of the plywood, we lay down four cedar 2x3s to act as a track or a base plate for our prefab panels to simply slide on to easily. Once square, you and your buddy can grab a sauna wall panel.

Panels are 6'4" tall x 4" deep, but their width varies as needed for your project. At a minimum a panel is 2 ft wide. We understand you may need your sauna walls easy to maneuver. So, we endeavor to make your sauna walls exactly how you'd prefer them. IF you'd like one piece walls, we are quite happy to oblige you.

Start in the corner where two wall panels are screwed together to start the shape of the sauna. The bottom of the panel is slotted to fit exactly on the track. Slide the first panels into the corner. Squeeze them snugly to eliminate any gaps.

Once together, open the top plate package. The top plate (or board) secures the top of the wall, so they do not tip over during assembly. Two screws are enough to assist, later you can return to tighten and add more screws.

4. Continue adding your sauna wall panels. Notice the labels on the vertical side of each panel marking its position in the room

Sauna wall panels form a sturdy room and the top plate boards add extra strength

After completing one wall and the start of another, you can add another top plate. The top plate will assist you in assembling the sauna walls and prevent them from tipping.

The top plate also slides into place securing the corners and side walls.

5. Add your door panel to complete the sauna

The door is prehung in the panel, so there is no framing, squaring or hanging. The door is simply another panel helping expedite a fairly easy assembly. Just square the door panel with the adjacent panel. Test the door opening and closing and secure in place. We provide a handle and self-closing bomber hinges. A 13"x13" window is standard in all our doors. ALL PANELS COME PRE-INSULATED INCLUDING THE SAUNA DOOR.

6. Add exterior and interior trim and sauna benching

Exterior trim is attached and sauna benches installed

After setting your trim pieces in place, you'll notice they don't quite reach the top. This is intentional. Later, a facia board will cover the top rim transitioning into the roof.

When attaching your exterior trim, use finish nails. The deck screws are unneccessary and somewhat unsightly. The 1x2 covers the seams. Go around the sauna attaching the corner trim pieces and covering the seams.

In many case, the sauna kits we build do not have a seam. We call our customers to see if they prefer a one piece wall and if you can handle it at your site. These saunas kits can built indoors or outdoors, so while no seams are great. It's not if you can't manuever the wall panels down stairs into a basement, etc.

The sauna benches come precut and pre-built. In this video, we fasten the low bench to the wall. A couple of deck screws per bench leg is enough. The legs will sit flush with edge of the bench face. The high bench facing which borders the wall can also be attached with screws. So benches do not slide off their supports.

Typically, we put the ceiling panels before installing our sauna benches, but the lighting was much better to film bench installation with the ceiling off. After your benches are in, you can cover the sauna interior wall panel seams. We provide a duckboard flooring kit which comes a panel they will simply lay in the door.

7. Add the ceiling panels

Sauna ceiling panels are placed and face boards attached

The ceiling panels are all the same, just notice the labels "front" and "top". The ceiling panels should be flush and sqaure to the edges of the sauna walls. Once in place, toe nail in place (we are not using nails though), rather screw in at about 45º into the top plate.

Now, we put on a 1x6 piece of trim to cover the edges of the ceiling panels. It comes flush with top of our corner trim pieces we put on earlier. Use finish nails to minimize to hide the nails.

If you were putting this package indoors, then you can move to the steps after installing the sauna roof.

Ceiling panels come preinsulated with R-11 fiberglass insulation and sauna foil. If desired you can certainly add more insulation batting above the ceiling and under the roof.

8. Set and secure the sauna roof in place

Sauna roof is set and secured. Side paneling is nailed under the gabled sauna roof

Here we are using in our outdoor sauna roof kit. These are heavy, so shipping can be a cost concern. You do have a few roof choices: gabled, slant, or you may need a custom roof. Or of course, you can build this kit in an outdoor shelter and solve the roof problem altogether.

After setting them in place, use 3" deck screws to secure the roof assembly to the sauna ceiling. The gabled ends of the roof assembly ends are covered by precut tongue and groove pieces.

Start the first row above the facia board around the ceiling panels. It will be the longest piece. Nail your finish nails in the tongue. The next piece's groove will slide over the tongue and cover the nail.

The roof comes pre-shingled but the ridge cap needs to be covered. We start with a piece of tar paper over the ridge cap. And then place the first ridge cap at the end. We like to hang first cap slightly beyond the edge, and inch or so. Then, nail down with shake nails. We overlap the caps about eight inches for best coverage.

9. Sauna Flooring

Sauna duckboard (flooring) is assembled and put in the walkway

The flooring that touches your feet is a style and comfort option. Duckboard is a precut cedar kit which cover an 18"x48" area, and is sold separately. Of course, we can custom size anything built out of cedar.

Typically, sauna bathers don't need the entire floor covered in cedar, just the walkway. Aesthetically, it's pleasing and more uniform to cover the entire floor with duckboard, but it's up to you. More than looks, duckboard is soft on the feet and since the floor will run much colder than the rest of the sauna, duckboard is warmer to the bare foot sauna bather.

Assemblying the duckboard is just a matter of laying down the longer pieces and overlapping the rows squarely. Then screwing together. In our How to Convert an Existing Room to a Sauna article and video series, we provide a video demonstrating duckboard assembly.

10. Last Step: Door Trim and Handle

Sauna door trim and handle are attached

Finishing your sauna is a great feeling. Just knowing that you are supporting your health, and that soon you'll be actually using your sauna.

Of course, the ambiance of a sauna is fantastic. And there are many ways to create an inviting sauna, especially with lighting, steam, cool water, comfortable benching, accessories like head rests and leg rests, back support, salt lamps, and birch venik.

Here we've saved the easy items for last. Just adding our remaing 1"x3" door trim and door handle. Again you the finish nails for the trim. Fasten your sauna door handle with deck screws in the pre-drilled hande holes. The sauna door includes a bomber hinges which ensure it self-closing.

Next you may wondering ... What about my sauna heater?

We do provide panels with conduit for your sauna heater wiring and light, to make wiring your sauna heater, lights and control box super easy. 

In this video, we did not show you how to install your sauna heater as you may be using gas, electric or even wood. Watch how to install your electrical sauna heater in this portion of our Convert an Existing Room to a Sauna article and video to see how to mount your heater. And some good information about adding rocks to your heater.

We hope you have enjoyed this presentation on building the prefab sauna kit, and we thank you for you business. Click to view our outdoor prefab modular sauna kit sizes, and indoor prefab sauna kit sizes.



Cedarbrook Sauna + Steam

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