Designing a Mobile Sauna Under 2,000 Pounds

In recent years mobile saunas have picked up steam. Recently this post on Reddit really sucked me in. Living south of Boston with so many great beaches, kettle ponds, and lakes I can’t help but scrap all my ideas for a sauna building and go deep on mobile.

Our first month of the year “January” dip into the lake and another adventure with my wood burning mobile sauna!

A few weeks ago I was scoping out the true cost of an 8×12 sauna building (on land, not a trailer) using the Sauna Times plans. At the time I quickly looked at what it would cost to make it mobile and with large enough trailers being $3,000 or more, I let it go. But by downsizing from 8×12 to say 5×8 or 6×10 the cost of the trailer drops to about a third.

After some digging around it looks like Tractor Supply is the best place for trailers near me. They deliver them free to your local store and there’s one half an hour from me. They’ve got a 5×8 trailer for $899 and 6×10 for $999.

At first I was wishfully thinking I could build a sauna-and-changing-room-combo building but weight is a huge constraint unless you have a legit truck. My wife and I have a Jeep Wranger and RAV4 Hybrid. Both vehicles max out at about 2,000 pounds tow capacity. The Rav’s official tow capacity is 1,750 but this Youtuber had good luck going through mountains with a 2,000 pound load. For a few moments I entertained getting a(n also tiny) pick up truck but it’d be a little too crazy to get a truck specifically for sauna.

This 4×4 Ford Ranger from ’99 towing a dark green sauna would look mint. If it’s got the tow package it can handle a load just under 6k pounds. $3,400.

As they say, constraints breed creativity.

With loads of optimism I fired up Google Sheets, thinking for sure I can build a 6×12 sauna with a changing room on one of these tiny trailers. Using this handy wood species calculator and weight details from product pages, I came up with some early estimates. It looked like a 6×12 build would be about 2,500 pounds. With my poor estimation skills it’s probably more like 3,000. I tweaked the sheet to allow for experimenting with various dimensions.

I realized I can’t go any bigger than 6×9 which means no changing room. It’ll have to be the ar or a pop-up shower tent!

Assumptions and iffy bits:

  • I’ll use clear tongue & groove white pine on the inside. It’s local, it’s cheap ($1.20 per SF), and I’m looking to do this build on a low budget.
  • I’m guessing removing the trailer gate saves me 200 pounds.
  • I haven’t quite finalized the floors but given the trailer itself has a deck I doubt I’ll put in a full platform with 2×6 rafters and all. This is missing from the cost and weight estimates. I wonder if I can get away an uninsulated floor and basically bolt 1/2″ plywood on top of the trailer deck, covered in cement board.
  • LP SmartSide panel is the lightest siding after vinyl, looks decent, and lasts a while. I’d love to use local rough-cut pine but makes my siding almost 600 pounds vs 400. Plus the rough cut pine is likely to be green and even heavier.
  • I’ve no idea about the cost and weight of the roofing.
  • I’m using seagrass for insulation and the weight at 100 pounds is a wild guess.
  • I haven’t built in the weight of the door, windows, hardware, bolts for securing the building to the trailer, nails and probably a few other things.

I’ll probably end up shooting for 6×8. Even that’s a stretch at an estimated 2,133 pounds.

I’m tempted to follow my buddy Sauna Matt’s advice from a phone call this morning: Buy the trailer and get started. Maybe I’ll end up in that red pickup after all.

The estimates are easiest to to see in Google Docs. You’re welcome to grab a copy and play with it by going to File > Make a Copy.

I’m Insulating My Sauna with Seagrass

My cousin Spencer is a Native American and one of my favorite people on earth. Thanks to Spencer, I learned about eelgrass a couple years ago and lately I’ve been thinking about insulating my sauna with it. Sure, it’ll only save me about $300 and I’ll have to work for it but it’ll be a good conversation starter.

Spencer lives on tribal lands along the coast of Massachusetts. He has many outdoor passions like foraging and gardening. One day a tribe elder approached him to pass along knowledge of a seaweed called eelgrass. He told Spencer to go to the beach, collect eelgrass washed up on the shore, and apply a 6-10″ layer to his garden bed like mulch. Spencer was skeptical at first yet after some experimenting he became an eelgrass convert. Eelgrass releases nutrients into the soil to help plants grow better. More importantly to Spencer it acts like a sponge, slowly releasing water into the soil and allows gardeners to water less.

Recently, I started learning more about eelgrass. Sure, it’s great for gardening, but it turns out it also cleans ocean water, reduces erosion, and provides habitat for creatures. (A great study on eelgrass in Massachusetts.) One of the most fascinating facts about eelgrass is it was used as insulation for hundreds of years in America before fiberglass was invented.

Live eelgrass on the ocean floor
Photo credit @theclf

In the early 1900s, entrepreneur Samuel Cobalt noticed huge mounds of seaweed washed up on beaches in the Boston area. After exploring potential uses, he learned houses going back to the 1600s and earlier used this seagrass known as eelgrass for insulation. It turns out eelgrass has a high concentration of silicon which makes it great for retaining heat and deadening sound while also being fire and rot resistent.

Eelgrass is also sustainable as only dead material is used. It naturally separates from the roots in the ocean floor and floats to the surface. Cabot launched Cabot’s Quilt, gathering large quantities of eelgrass to process it into insulation, complete with a paper lining and everything.

Build Warm Houses — That is the only way to cheat the devouring demon in your cellar who burns your money and poisons you with gas!

Shortly after Cabot’s Quilt launched, eelgrass suffered a blight in the 1920s which forced the company to turn turn to importing eelgrass from overseas. Still, the company did well for decades. Amazingly Radio City Music Hall is insulated with eelgrass and renowned for its acoustics. When fiberglass took off in the 50s it was the begininning of the end. Cabot lives on, offering wood stains.

Modern studies are being done on eelgrass in the Boston area where stocks have dropped 58% since the 1950s. It’s unlikely Cabot’s Quilt would’ve survived even if fiberglass wasn’t invented. Scientists don’t really know the cause of the continued drop since the 50s. Luckily there’s still enough eelgrass washing up on the shores to keep my little sauna toasty.

From the Massachusetts MarhineFisheries study on eelgrass, studying Plymouth Estuary located south of Boston MA USA. In 1950 there were an estimated 3,500 acres of eelgrass. By 2012, less than 1,000 acres remained representing a 58% population loss. A 2014 survey shows further widespread loss. Studies are due to resume after the pandemic.