Condensation Causes and Control: What Your Building Is Trying to Tell You

A fogged window on a cold morning may not seem like a cause for concern. Most people wipe it away and move on. But condensation is often more than a temporary nuisance. In our experience, it can be one of the earliest signs that moisture, temperature, and air movement within a building are no longer working together as intended.

Condensation occurs when moist air contacts a surface cool enough to lower the air temperature to its dew point. When that happens, water vapor turns into liquid water. While the process sounds simple, the impacts on a building can be more complex.

The challenge is that modern buildings are designed differently than they were decades ago. Today’s construction emphasizes energy efficiency, tighter building envelopes, and improved insulation. These advancements provide significant benefits, but they also reduce uncontrolled air exchange with the outdoors. As a result, moisture generated within the building is more likely to remain indoor unless managed through ventilation and humidity control. Due to this, moisture management through air barrier design, vapor control, insulation, and HVAC operation must be a deliberate part of building design and operation.

Everyday activities generate moisture. As warm, moist air moves through a building, it can come into contact with cooler surfaces. If it reaches a surface at or below its dew point temperature, condensation can occur.

Our clients typically consider condensation as an isolated issue. At Lerch Bates, however, we see this as a symptom of a root problem. It can indicate elevated indoor humidity, uncontrolled air movement, inadequate ventilation, thermal bridging, or building enclosure components that are not performing as intended. The key to resolving condensation is identifying the underlying conditions that create it, rather than addressing the resulting moisture.

LB has identified three primary strategies for controlling condensation:

The first is reducing indoor moisture levels. Limiting unnecessary moisture sources and properly exhausting activities that produce humidity can significantly reduce condensation risk.

The second is preventing moisture from reaching cold surfaces as well as allowing materials to dry out. Water vapor moves from areas of higher vapor pressure to lower vapor pressure and can travel through gaps, penetrations, and some building materials. Properly designed vapor retarders and well-sealed building assemblies help minimize this movement while vapor permeable components allow for drying to occur.

The third is maintaining warmer interior surface temperatures through improved enclosure design. Key strategies include optimizing insulation type and placement, minimzing thermal bridging, detailing transitions to maintain continuity, and selecting products with appropriate thermal performance and condensation resistance.

These strategies may sound straightforward but implementing them successfully requires understanding how a building functions as a system. A solution that works in one property may not be appropriate for another. Climate, occupancy, enclosure design, and building operation all influence moisture behavior. LB takes this a step further by performing heat and moisture analyses (hygrothermal) for wall and roof assemblies as well as thermal modeling to assess specific details. These computer-based models simulate existing conditions and evaluate the likelihood of reaching dew point temperatures at interior surfaces or within wall cavities.

This is where building science becomes valuable. Rather than focusing solely on the visible effects of condensation, building science looks at the relationship between heat, air, and moisture. By understanding how these elements interact, property owners or building designers can make informed decisions that improve durability, performance, and occupant comfort.

For building owners and facility managers, condensation should not be ignored, nor should it automatically be viewed as a major failure. Instead, it should be seen as a signal to

investigate how the building is managing moisture. In many cases, early evaluation and corrective action can help prevent larger issues down the road.

At Lerch Bates, our experts help clients understand these relationships and identify practical solutions to enclosure and moisture-related challenges. By addressing the causes of condensation rather than just the symptoms, buildings can perform more effectively for years to come.

Contact us today to get started.