Insulation Is Overrated: Why Some Saunas Break the Rules — and Still Bring the Heat

Do all saunas really need to be insulated?

When most people think of building a sauna they think of essentially building a small house. Siding, insulation, studs, and walls. Insulation is essential when building a house, but do we really need it for a sauna?

What insulation is great at -- keeping a building the same temperature with very few fluctuations for a long period of time. This is amazing for an application like a home where you want it exactly 70°F for 24 hours a day. But a sauna? We generally only need a sauna hot for no more than a few hours, sometimes less if only for a quick session. 

What insulation isn't great at -- getting a building really hot, really fast. Come get nerdy with us for a second.

How thermal mass changes the sauna heat equation.

• In a traditional sauna, there's a lot of thermal mass — materials like cedar walls, insulation, benches, tile, rocks, and the stove itself all absorb and retain heat. Often, the first 30 minutes of heating is spent warming up these cold surfaces before the air temperature can truly rise.
• In a NorthUp sauna, there’s significantly less material and insulation to absorb heat. With less thermal mass, the stove can begin heating the air almost immediately. As a result, we’ve seen temperatures climb past 200°F in as little as 30 minutes — even in the middle of a Minnesota winter. Traditional saunas often take up to 90 minutes to heat.
• Additionally, due to the greenhouse-like nature of a NorthUp sauna, direct sunlight can cause up to a 75°F solar lift compared to the outside ambient temperature before even lighting the stove!

The potential downsides of less insulation

What heats up fast will also cool down fast — and that’s the natural tradeoff when you have less insulation and heavy materials. While traditional saunas can stay hot for hours after the fire dies down, a NorthUp sauna’s lower thermal mass means you’ll need to keep feeding the stove to maintain higher temps for those occasional long all-day sessions.

That said, we believe we've struck the perfect balance. We didn't skip insulation altogether — NorthUp's walls are built with a high-performance thermo material boasting an R-value of 1.6 — remarkably close to the 2 R-value you'd get from a classic barrel sauna with 1.5" cedar walls despite being significantly lighter and thinner. Sure, it’s not the R-12 of a fully insulated 3" rock wool build, but it allows us to do something those saunas can’t: hit 200°F in just 30 minutes and enjoy 360° of panoramic views through transparent walls.