You walk into your steel building on a cool morning and the inside of the arch is beaded with water. Sometimes it drips. Owners often call this "sweating," and it's one of the most common questions we get once the weather turns. The good news is that condensation has a clear cause, and it's very manageable once you know what's driving it.
Why Condensation Forms
Air holds moisture. Warm air holds more than cold air. When warm, moist air inside your building touches a surface that's colder than its dew point, the air can't hold all of that moisture anymore, and it turns into water on the surface. It's the same thing that happens on a cold drink on a summer day.
Steel changes temperature quickly. On a clear night, the panels cool off fast, while the air inside stays warmer and holds the moisture from the day. By morning, the underside of the arch is the coldest surface in the building, and that's where the water collects.
Condensation isn't unique to steel buildings. Any building without proper ventilation will have it. Steel just shows it faster because it doesn't hide the moisture inside a wall cavity the way wood framing does.
Where the Moisture Comes From
Before you can fix condensation, it helps to know what's putting water into the air inside your building. The usual sources:
• A new concrete slab. Fresh concrete releases a lot of moisture as it cures, and it can keep doing so for weeks or months.
• Ground moisture. A slab without a vapor barrier underneath can keep wicking moisture up from the soil.
• Livestock. Animals breathe out a surprising amount of water vapor.
• Vehicles and equipment. Trucks and tractors carry in rain, snow and mud that evaporates inside.
• Unvented heaters. Propane and kerosene heaters without a flue put water vapor straight into the air as they burn.
• Stored material. Damp hay, grain or firewood gives off moisture as it dries.
Fix #1: Ventilation
Ventilation is the first and most important fix. Moving moist air out and drier air in keeps the humidity inside from building up. Duro Span offers two types of ventilators for our buildings, gravity and turbine, or you can install a custom ventilation system. If you're already seeing condensation in an existing building, the most common answer is simply to add more ventilators.
Ventilators work best with a path for air to come in, too. That can be as simple as a vent lower on the end wall. You can see the available options on our
accessories page.
Fix #2: Insulation With a Vapor Barrier
Insulation keeps the inside surface warmer, so it stays above the dew point. Our clear-span, trussless design accepts any conventional insulation: spray foam, fiberglass rolls or rigid foam. Duro also offers insulation and 4" and 6" insulation pins as accessories.
The detail that matters most is the vapor barrier. With fiberglass, you need a continuous, sealed vapor barrier on the warm side of the insulation. If moist air gets behind the insulation through gaps, it will condense on the steel anyway, and now the water is trapped in the insulation where you can't see it. Closed-cell spray foam bonds directly to the panels and acts as its own air and vapor barrier, which is why many owners choose it. Our
insulation options article compares each type.
Fix #3: Control the Source
• Put a vapor barrier under your slab. It's a standard step, and your concrete contractor will know it. It's much harder to add later.
• Ventilate well while a new slab cures.
• Use vented heaters when you can, so combustion moisture goes outside.
• Let wet vehicles and equipment drain and dry near a door or vent.
How Climate Plays In
Where you build affects how much attention condensation needs. In the humid Southeast, in states like Georgia, North Carolina and Tennessee, air carries a lot of moisture for much of the year. In the high desert of New Mexico, Utah and Nevada, the air is drier, but the big temperature swing between day and night chills the steel quickly after dark. In colder areas, heated buildings in winter are the classic case: warm, moist air inside and freezing steel outside. All three can be managed. They just call for a slightly different balance of ventilation and insulation.
Plan for It Before You Order
Condensation is far easier to prevent than to fix. When you request a quote, tell us how you'll use the building, whether you'll heat it and whether animals will be inside. We'll help you plan the right ventilators and insulation accessories up front, so they arrive with your building instead of becoming a project later.
Ready to price a Duro Span building?
Request a free quote or call 888-848-2011 to talk with a Duro Span steel building specialist.