That unused shed in your backyard is sitting on top of one of the most practical DIY sauna projects you can take on. A shed to sauna conversion lets you skip the expense and complexity of building a new structure from scratch while still ending up with a high-performance sauna that rivals purpose-built models. You already have a roof, four walls, and a foundation — the heavy lifting is done. What remains is insulating, sealing, heating, and finishing the interior to handle the extreme temperatures and humidity that a sauna demands.
This guide covers the entire process from start to finish: evaluating whether your shed is a good candidate, planning your layout, choosing the right insulation and vapor barrier, selecting a heater that matches your space, wiring and ventilation requirements, interior finishing, and the common mistakes that derail shed conversions. Whether you're a seasoned DIYer or picking up a hammer for the first time, you'll have everything you need to turn that neglected outbuilding into a backyard wellness retreat you'll actually use.
Why Convert a Shed Instead of Building from Scratch?
Building a sauna from the ground up means pouring a foundation, framing walls, raising a roof, and weatherproofing the entire structure before you even start on the sauna-specific work. A shed conversion eliminates all of that. The shell already exists, which typically saves 40–60% compared to a ground-up build. Most homeowners complete a shed to sauna conversion for somewhere between $2,000 and $8,000 in materials, depending on the heater they choose and the condition of the existing shed. A comparable new-build sauna structure often runs $10,000 to $20,000 or more once you factor in foundation work, framing lumber, roofing, and contractor labor.
Beyond cost, a conversion is faster. A reasonably handy homeowner can complete the project over two to four weekends. The permitting process is also simpler in most jurisdictions since you're modifying an existing outbuilding rather than erecting a new one — though you should still check with your local building department before starting any work, especially for electrical modifications.
There's also a sustainability angle. Repurposing an existing structure keeps materials out of the landfill and reduces the lumber, concrete, and energy that a new build would require. And if you ever decide to sell your home, a well-built backyard sauna is a genuine value-add that attracts buyers.
Is Your Shed a Good Candidate?
Not every shed is worth converting. Before you invest a dollar in materials, spend an hour doing an honest assessment of what you're working with. The three things that matter most are structural integrity, size, and material.
Structural Integrity
Walk the interior and inspect every surface. Look for soft spots in the floor that indicate rot, check the roof for leaks or sagging, and examine the wall framing for signs of water damage or pest activity. Push on the walls — they should feel solid, not flexible. A sauna's heat and humidity cycling puts stress on the structure, so any existing weaknesses will get worse over time. If the framing is compromised, you'll need to sister new lumber alongside damaged studs or replace sections before proceeding.
Pay special attention to the foundation. Sheds sitting directly on soil or on deteriorating cinder blocks will settle unevenly and create gaps that leak heat. A concrete slab, concrete piers, or pressure-treated skids on a gravel pad are all acceptable foundations. If your shed is sitting on bare dirt, consider adding a gravel pad and new skids before starting the interior work.
Minimum Size Requirements
The hot room itself needs to be at least 4 feet by 6 feet for a tight two-person sauna, though 6 feet by 8 feet is the sweet spot for comfort and proper heat circulation. Ceiling height matters too — aim for at least 7 feet, and ideally 7.5 feet or taller if you want to follow Finnish sauna building principles where the top bench sits at or near the level of the heater stones. Use our sauna heater size calculator to determine the cubic footage of your space and the heater output you'll need.
If your shed is 8 by 10 feet or larger, you have the option to frame an interior partition wall and create a small changing room or cool-down area. This is a worthwhile addition — it gives you a place to sit after your session, keeps cold air from rushing directly into the hot room when the exterior door opens, and provides a spot for hooks, a bench, and towel storage.
Shed Material: Wood, Metal, or Plastic?
Wood-framed sheds are by far the best candidates for conversion. They accept insulation between studs, they're easy to modify with standard carpentry tools, and they provide a stable structure for attaching interior paneling. Whether your shed is stick-built with plywood sheathing or a prefab panel design from a big-box store, it will work as long as the framing is sound.
Metal sheds are a poor choice. They conduct heat rapidly, they're nearly impossible to insulate effectively, and condensation forms on the interior metal surfaces in ways that create ongoing moisture problems. If a metal shed is all you have, you'd get a better result buying or building a small wood-framed shed specifically for the conversion.
Plastic or resin sheds fall somewhere in between. They won't rot, but they aren't designed to handle sauna temperatures and may warp or off-gas at sustained heat above 150°F. They're also difficult to fasten interior framing and paneling to. In most cases, they're not worth the trouble.
Planning Your Layout
Before you pick up a saw, sketch your layout on paper or use a free room-planning tool. You need to account for bench placement, heater location, door swing, ventilation openings, and electrical routing.
The heater should be placed on the wall closest to the door, typically in a corner. This keeps the hottest zone near the stones and allows natural convection to circulate heat toward the far wall. Benches should be arranged in an L-shape or tiered configuration with an upper bench and a lower bench. The upper bench is the hottest seat, and the lower bench offers a cooler option for those who prefer less intensity or are just warming up.
Leave adequate clearance around the heater — every model has specific minimum distances to combustible surfaces, typically 4 to 12 inches on each side for electric heaters and 18 inches or more for wood-burning stoves. Check the manufacturer's installation manual for exact specifications. If you need help visualizing different configurations, our guide to sauna bench height and the Finnish Rule of 230 explains how ceiling height, bench height, and heater placement work together for optimal heat distribution.
Plan your ventilation at this stage too. You'll need a fresh air inlet low on the wall near the heater and an exhaust vent higher on the opposite wall. More on this in the ventilation section below.
Step 1: Prep the Shed
Empty the shed completely and strip the interior down to bare framing. Remove any existing shelving, drywall, oriented strand board (OSB), or other interior sheathing that isn't part of the structural wall. You want to see studs, and you want to inspect every inch of the framing for damage before you begin insulating.
Repair or replace any rotted framing members. If the exterior sheathing has gaps or damage, seal them with exterior-grade plywood and caulk. The exterior shell needs to be weathertight before you add insulation — any water intrusion from outside will destroy your insulation and create mold problems behind your vapor barrier.
Address the floor. Many shed floors have gaps between boards that allow cold air to seep in. You can install rigid foam insulation between the floor joists from below if the shed is elevated, or lay rigid foam board directly on top of the existing floor and then cover it with a durable, easy-to-clean surface. Concrete slab floors should be sealed with a concrete sealer to prevent moisture from wicking up. Whatever flooring material you choose, it needs to handle heat, moisture, and bare feet — smooth wood planks, duckboard-style removable floor grates, or tile all work well.
Step 2: Insulate the Walls and Ceiling
Insulation is what separates a sauna that heats up in 20 minutes and holds temperature effortlessly from one that takes an hour to warm up and runs your electric bill through the roof. A shed conversion lives or dies on the quality of its insulation.
For walls, the target is R-13 to R-19 depending on your climate. Standard 2x4 stud cavities accept R-13 or R-15 batts. If your shed has 2x6 framing (less common but ideal), you can fit R-19 or higher. For the ceiling, aim for R-26 to R-30 — heat rises, and the ceiling is where you lose the most energy. Double-layering batts with the second layer running perpendicular to the first is an effective way to hit higher R-values in the ceiling.
The best insulation materials for saunas are mineral wool (rock wool) and fiberglass batts. Mineral wool is the preferred choice because it's naturally moisture-resistant, doesn't absorb water, and maintains its R-value even in humid conditions. It also has a higher temperature tolerance than fiberglass. Fiberglass batts work but can lose effectiveness if they absorb moisture, which makes a properly installed vapor barrier absolutely critical. Avoid spray foam in sauna walls — closed-cell foam can trap moisture against the framing, and some formulations off-gas at sustained high temperatures.
For a deeper dive into insulation materials, R-value targets by climate zone, and the correct wall assembly order, read our complete sauna insulation guide.
Step 3: Install the Vapor Barrier
The vapor barrier is the single most critical moisture-control layer in your sauna, and it's also the step that DIY builders mess up most often. In a sauna, the vapor barrier goes on the warm side of the insulation — directly over the face of the studs, between the insulation and the interior wood paneling. This is the opposite of how vapor barriers are sometimes installed in standard home construction in certain climates, so don't let general construction advice lead you astray.
Use an aluminum foil vapor barrier specifically designed for sauna use. Standard polyethylene sheeting (Visqueen) is not rated for sauna temperatures and can degrade, shrink, or off-gas when exposed to sustained heat above 170°F. Aluminum foil barriers withstand temperatures well above 200°F, and they serve double duty by reflecting radiant heat back into the sauna room, which improves heat-up time and energy efficiency. Our sauna vapor barriers are designed specifically for this application.
Installation is straightforward but demands attention to detail. Staple the foil to the face of the studs with the shiny side facing the interior of the sauna. Overlap all seams by at least 2 to 3 inches and seal every seam with high-temperature aluminum foil tape — not standard duct tape, which fails at sauna temperatures. Seal around all penetrations including electrical boxes, vent openings, and any pipes or wires that pass through the wall. The goal is a continuous, unbroken envelope. Any gap or unsealed seam allows moisture to migrate into the insulation and framing, where it causes mold and rot that you won't see until the damage is extensive.
For detailed installation steps and common sealing mistakes to avoid, see our sauna vapor barrier best practices guide.
Step 4: Install Furring Strips and Interior Paneling
After the vapor barrier is in place, install horizontal furring strips (typically 1x2 or 1x3 lumber) over the foil, perpendicular to the studs. These strips create a small air gap between the vapor barrier and the interior paneling, which allows any condensation to drain rather than pooling behind the wood. This air gap also improves the foil's radiant heat reflection since reflective barriers work best with an air space in front of them.
For the interior wood paneling, use tongue-and-groove boards in a species that handles heat and humidity well. The most popular options for sauna interiors are:
Western Red Cedar — The classic sauna wood. Naturally resistant to moisture and decay, dimensionally stable at high temperatures, and produces a pleasant aroma when heated. Available in clear and knotty grades.
Thermo-Aspen — Heat-treated for enhanced durability and moisture resistance. Light in color with a clean, modern appearance. Splinter-free and low in resin, making it comfortable against bare skin. A top choice for contemporary sauna builds.
Alder — A softer hardwood with a warm, honey-toned color. Handles sauna temperatures well and stays cool to the touch relative to denser woods.
Hemlock — Uniform in color with a subtle grain. A good budget-friendly option that performs well in sauna environments.
Avoid pressure-treated lumber, pine with heavy resin content, and any engineered wood products (plywood, MDF, OSB) inside the hot room. Pressure-treated wood contains chemicals that can off-gas at high temperatures, and resinous woods will bleed sticky sap that's difficult to remove and uncomfortable to sit on. Browse our full selection of sauna-grade wood for walls, ceilings, and benches, and use our sauna wood calculator to estimate exactly how much material you'll need for your dimensions.
Install the tongue-and-groove paneling horizontally on the walls and ceiling, nailing through the tongue into the furring strips. Work from the bottom up on walls so the groove faces down, which prevents water from collecting in the joint. On the ceiling, start from one wall and work across.
Step 5: Choose and Install Your Heater
The heater is the heart of your sauna, and getting this choice right will make or break the entire experience. You have three main options: electric, wood-burning, or infrared. Each has distinct advantages depending on your shed's setup, your budget, and the sauna experience you're after.
Electric Sauna Heaters
Electric heaters are the most popular choice for shed conversions because they're the easiest to install, offer precise temperature control, and require virtually no maintenance beyond occasionally replacing stones. They heat a bed of sauna rocks using electric elements, and you pour water over the stones to create steam (löyly). Sizes range from 2 kW for very compact saunas up to 18 kW or more for large rooms.
The standard sizing rule is approximately 1 kW per 50 cubic feet of sauna space. A typical 6-by-8-foot shed conversion with a 7-foot ceiling (336 cubic feet) needs roughly a 6 to 8 kW heater. Uninsulated surfaces like glass doors or windows effectively add cubic footage to your calculation because the heater must compensate for the additional heat loss. Use our electric sauna heater size calculator for a precise recommendation based on your room's dimensions and materials.
Most residential electric sauna heaters operate on 240V and require a dedicated circuit installed by a licensed electrician. Smaller models in the 2 to 3.5 kW range are available in 120V configurations that plug into a standard household outlet, but these are only suitable for very small saunas under about 150 cubic feet. Browse our complete selection of electric sauna heaters from brands including Harvia, HUUM, Saunum, and Amerec.
For smaller shed conversions where floor space is tight, wall-mounted heaters save valuable real estate by attaching directly to the wall behind the bench. Larger sheds with room to spare benefit from floor-standing heaters that hold significantly more rock mass for bigger, softer steam.
Wood-Burning Sauna Stoves
If your shed doesn't have easy access to electrical service — or if you simply prefer the traditional experience of a crackling fire and the softer heat that wood produces — a wood-burning stove is an excellent option. Wood stoves don't require any electrical connection for the heating element itself (though you'll still want electricity for lighting), making them ideal for off-grid or remote locations.
Wood stoves require proper chimney installation, which adds complexity to a shed conversion. The chimney must extend well above the roofline for proper draft, and the stove needs non-combustible floor protection (a concrete pad or metal sheet) and generous clearance to combustible walls — typically 18 inches or more, which can be reduced with heat shields. A double-walled insulated chimney pipe must be used wherever the pipe passes through the wall or roof to prevent heat transfer to combustible materials.
Stove sizing follows similar principles to electric heaters — match the stove's rated capacity to your room's cubic footage. Our wood-burning stove sizing tool recommends specific models based on your sauna's dimensions. You can also explore our full range of wood-burning sauna stoves from Harvia, HUUM, Narvi, and Cozy Heat.
Infrared Panels
Infrared heaters work differently from traditional sauna heaters. Instead of heating the air and stones, they emit radiant infrared energy that heats your body directly. They operate at lower temperatures (typically 120–140°F versus 160–195°F for traditional saunas), use less electricity, and don't produce steam. If you prefer a gentler heat or want the simplest possible electrical setup, infrared panels are worth considering. They can also be combined with a traditional heater for a hybrid setup. Explore our infrared sauna heaters and use our infrared panel calculator to determine how many panels your space needs.
For a detailed comparison of all three heater types, read our guide to choosing the right sauna heater.
Step 6: Electrical Work
Unless you're going with a wood-burning stove and battery-powered lighting, your shed conversion will need electrical work. This is the one part of the project where hiring a licensed electrician is not optional — it's essential for safety and code compliance.
Most 240V electric sauna heaters require a dedicated circuit with a breaker sized to the heater's amperage draw. A typical 6 kW heater draws 25 amps and needs a 30-amp breaker with 10-gauge wire. Larger heaters require proportionally larger breakers and heavier wire. The electrician will need to run the circuit from your home's main panel to the shed, which may involve trenching for underground conduit or running overhead wire depending on the distance and your local code requirements.
Inside the sauna, all wiring must be rated for high-temperature environments. Standard Romex (NM-B cable) is rated to 90°C (194°F), which is at the upper edge of sauna operating temperatures. Many electricians prefer to use high-temperature leads or conduit within the hot room itself. Light fixtures must be rated for wet/damp locations and high temperatures — standard household fixtures will fail. Switches and controls should be mounted outside the hot room or in the changing area where they're not exposed to extreme heat.
Check whether your jurisdiction requires GFCI protection for sauna circuits. Many areas do, and some heater manufacturers require it as a condition of their warranty.
Step 7: Ventilation
Proper ventilation is essential for air quality, even heat distribution, and the longevity of your sauna's interior materials. A sauna is not meant to be an airtight box — it needs a steady supply of fresh air to replace the oxygen consumed by the occupants and to prevent the air from becoming stale and uncomfortable.
The standard ventilation configuration uses two openings: a fresh air inlet and an exhaust vent. The inlet should be located low on the wall near the heater, typically 6 to 12 inches above the floor. Incoming air passes over or near the hot stones, which warms it immediately so it doesn't create a cold draft. The exhaust vent goes on the opposite wall, positioned higher — either near the ceiling or at bench height depending on the ventilation style you're using. A simple adjustable vent cover on each opening lets you control airflow during your session.
For a wood-burning stove, the combustion air supply and chimney draft provide some natural ventilation, but you'll still want a dedicated fresh air inlet to ensure adequate oxygen in the room. Never seal a sauna room completely when a wood stove is in use — carbon monoxide buildup is a serious and potentially fatal hazard.
The total vent area should be sized to allow a complete air exchange roughly 6 to 8 times per hour. For a small to medium shed sauna, two vents of approximately 4 by 8 inches each are typically sufficient. You can find sauna-specific vents and vent covers designed for high-temperature environments in our parts collection.
Step 8: Build the Benches
Sauna benches should be built from the same heat-tolerant wood species used for your wall paneling — cedar, thermo-aspen, alder, or hemlock. The bench frame can be built from standard construction lumber (SPF — spruce, pine, or fir) since the frame is hidden beneath the seating surface and doesn't contact skin. The seating surface itself must be smooth, splinter-free, and made from a wood that stays relatively cool to the touch at sauna temperatures.
A two-tier bench arrangement is standard. The upper bench should be wide enough to lie down on comfortably (at least 24 inches deep) and positioned so the bather's head is at or near the level of the top of the heater stones — this is where the heat and steam are most intense. The lower bench serves as a step and a cooler seating option, typically 18 to 20 inches deep. Leave enough space between the upper bench and the ceiling for the bather to sit upright without hitting their head — a minimum of 42 inches is comfortable for most people.
Shop our selection of sauna bench wood and use our wood calculator to estimate bench materials alongside your wall and ceiling cladding.
Step 9: Hang the Door
The sauna door needs to seal well enough to retain heat but must always open outward (away from the hot room) for safety — you need to be able to push your way out if you feel faint or if the door sticks. Sauna doors are typically shorter and narrower than standard interior doors to reduce the opening size and minimize heat loss when the door is opened.
You have two main options: a solid wood door for maximum insulation and a traditional look, or a tempered glass door for a modern aesthetic that lets light into the hot room. Glass doors don't insulate as well as wood and effectively increase the cubic volume your heater must warm, so factor this into your heater sizing calculation. Our sauna door collection includes both wood and glass options, and our comprehensive sauna door guide covers sizing, swing direction, glass types, and installation details.
Step 10: Finishing Touches and Accessories
With the structure, insulation, paneling, heater, and benches in place, the finishing touches transform your converted shed from a functional sauna into one you'll actually enjoy spending time in.
A bucket and ladle for pouring water over the stones is essential for any traditional sauna — this is how you create steam (löyly) and control the humidity. A thermometer and hygrometer mounted on the wall let you monitor conditions. Heat-safe lighting sets the mood, and a backrest on the upper bench adds comfort for longer sessions. Browse our full range of sauna accessories to outfit your new space.
On the exterior, consider adding a small deck or landing outside the door as a cool-down area. If you plan to use the sauna year-round, a path of stepping stones or gravel from your house to the shed keeps your feet out of the mud. And if your region gets harsh weather, a waterproof sauna cover or proper exterior stain will protect the shed's outer shell and extend its life.
How Much Does a Shed to Sauna Conversion Cost?
The total cost depends on the condition of your existing shed, the heater you choose, and how much labor you do yourself versus hiring out. Here's a realistic breakdown of what to expect for a typical 6-by-8-foot shed conversion:
Insulation and vapor barrier: $200–$500. Mineral wool batts for walls and ceiling plus aluminum foil vapor barrier and tape.
Interior wood paneling: $3,000–$6,500. Tongue-and-groove cedar or thermo-aspen for walls, ceiling, and bench surfaces. Cost varies significantly by species and grade.
Sauna heater: $2,000–$5,000+. A basic wall-mounted electric heater starts around $500, while premium models from brands like HUUM and Harvia with WiFi controls run $1,500 to $3,000. Wood-burning stoves with chimney kits fall in a similar range. Check our heaters under $1,500 for budget-friendly options, or explore complete heater packages that bundle the heater, controller, and stones together.
Sauna door: $1,000–$1,500. Wood doors are on the lower end; tempered glass doors are higher.
Electrical work: $500–$2,000. Running a dedicated 240V circuit from your panel to the shed, including trenching, conduit, and the electrician's labor. Distance from the panel is the biggest cost variable.
Benches, vents, lighting, and accessories: $1,000–$3,000.
Total estimated range: $10,000-25,000 for a complete DIY conversion with professional electrical work. If you hire a contractor for the full build-out, add $2,000 to $5,000 in labor.
Common Mistakes to Avoid
Shed to sauna conversions fail for predictable reasons. Knowing these pitfalls ahead of time will save you from costly rework.
Skipping the vapor barrier or using the wrong material. This is the most common and most damaging mistake. Standard polyethylene plastic sheeting is not rated for sauna temperatures. It will degrade, shrink, and allow moisture to penetrate your insulation and framing. Always use an aluminum foil vapor barrier designed for sauna environments, and seal every seam and penetration with foil tape.
Undersizing the heater. A heater that's too small for the room will struggle to reach temperature, run constantly, wear out faster, and deliver a disappointing experience. Always calculate based on total cubic footage plus adjustments for cold surfaces. When in doubt, size up — a slightly oversized heater that doesn't have to run at full capacity will outlast one that's constantly maxed out.
Neglecting ventilation. A sealed sauna with no fresh air supply becomes stuffy, uncomfortable, and potentially dangerous with a wood-burning stove. Install proper inlet and exhaust vents.
Using the wrong wood inside the hot room. Pressure-treated lumber, pine with visible resin pockets, and any engineered wood products (plywood, OSB, MDF) have no place in a sauna hot room. They off-gas, bleed sap, or delaminate at high temperatures.
DIY electrical work. Sauna heaters draw significant amperage and operate in a high-temperature, high-humidity environment. Improperly sized wiring, missing GFCI protection, or amateur connections are fire and shock hazards. Hire a licensed electrician.
Ignoring the floor. Shed floors with gaps between boards let cold air in and make the sauna nearly impossible to heat efficiently. Seal, insulate, and finish the floor properly.
Converting a metal or plastic shed. Metal sheds conduct heat out of the sauna as fast as the heater puts it in, and condensation problems are constant. Plastic sheds can't handle the temperatures. Stick with wood-framed structures.
Shed Conversion vs. Buying a Pre-Built Sauna
If the DIY route isn't for you, pre-built outdoor saunas are an alternative worth considering. They ship with insulation, vapor barrier, interior paneling, benches, and often a heater already integrated — you place them on a prepared pad and connect power. The trade-off is higher upfront cost and less customization. A quality pre-built outdoor sauna typically starts around $4,000 for smaller models and can run $8,000 to $15,000+ for larger cabins with premium features.
A shed conversion makes the most sense when you already have a suitable shed, you enjoy DIY work, and you want full control over the layout, materials, and heater selection. A pre-built sauna makes sense when you want a turnkey solution with minimal construction work and don't mind paying a premium for convenience. Explore our complete sauna packages if you'd like a middle ground — these kits include the heater, interior materials, and accessories, and are designed to be installed into an existing framed and insulated space like a converted shed.
Maintenance After the Conversion
A well-built shed sauna requires minimal ongoing maintenance, but a few regular habits will keep it performing well for decades.
After each session, leave the door open for 15 to 30 minutes to allow the interior to air out and dry. This prevents moisture from lingering on wood surfaces and inhibits mold growth. If you're in a humid climate, a small battery-powered fan in the doorway speeds up the drying process.
Inspect the exterior of the shed seasonally — check the roof for leaks, re-caulk any gaps in the exterior sheathing, and make sure the foundation hasn't shifted. Inside, look for any discoloration or soft spots in the wood that might indicate moisture intrusion behind the vapor barrier. Sauna wood can be treated with a sauna-safe interior wood finish to protect and preserve the surface.
Replace sauna stones every one to two years or when they begin to crumble and lose their ability to hold heat and produce steam. Check your heater elements annually for signs of corrosion or buildup.
Start Your Shed to Sauna Conversion
A shed to sauna conversion is one of the most rewarding home projects you can take on — it's achievable for most DIYers, delivers genuine health and relaxation benefits you'll use for years, and adds real value to your property. The key is doing each step correctly: assess your shed honestly, insulate and seal the interior properly, choose a heater matched to your space, and hire a professional for the electrical work.
If you're ready to get started, our heater sizing calculator and wood calculator will help you spec the right equipment and materials for your specific shed dimensions. Need hands-on guidance? Our free custom sauna design service provides personalized layout recommendations, heater sizing, and a complete materials list tailored to your project. Reach out to us at info@havenofheat.com — we've helped hundreds of homeowners through this exact process and we're happy to help you too.
*Haven Of Heat and its affiliates do not provide medical, legal, electrical, building, financial, or professional advice. All content published on this website is for general informational and educational purposes only and should not be relied upon as a substitute for advice from qualified professionals. Always consult a licensed medical provider regarding health-related questions, and consult licensed contractors, electricians, inspectors, or local authorities for installation, electrical, building code, zoning, HOA, or safety requirements. Local codes and regulations vary by jurisdiction.
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