## Why Does Condensation Occur on New High-Efficiency Windows?
Interior window condensation occurs on high-efficiency windows because they are designed to be more airtight and energy-efficient. These windows are typically made with multiple panes of glass with insulating gas in between, a low-emissivity (Low-E) coating on the glass, and airtight seals around the frame.
When the indoor temperature is higher than the outdoor temperature, warm, moist air comes into contact with the cold surface of the window. The moisture condenses into water droplets on the glass, creating visible condensation. This process is known as the **dew point** — the temperature at which air becomes saturated with water vapor and starts to condense.
High-efficiency windows are more airtight, which reduces the amount of warm, moist air that escapes from the home. That trapped moisture can lead to interior condensation if there isn't enough ventilation or if indoor humidity is too high.
## How to Prevent Window Condensation
The fix is almost always about **ventilation and humidity control**, not the windows themselves.
### 1. Relative Humidity
The amount of moisture in the air relative to its temperature is **relative humidity (RH)**. Generally, when indoor RH exceeds 50%, you'll start seeing window condensation. Aim for **30-50% RH** to prevent it.
### 2. Indoor Sources of Moisture
Many activities generate moisture: cooking, showering, doing laundry, even breathing. These activities raise indoor humidity and can lead to interior window condensation. Proper ventilation in kitchens and bathrooms is essential to minimize moisture build-up.
### 3. Insufficient Ventilation
A lack of ventilation lets moisture accumulate in the air. Make sure your home has adequate ventilation — including bathroom exhaust fans and range hoods in the kitchen.
### 4. Temperature Differences
Interior condensation also occurs when there's a significant temperature difference between indoor and outdoor environments — most commonly in winter when it's cold outside and warm inside. Maintaining a consistent indoor temperature throughout the home helps reduce condensation.
### 5. Window Coverings
Window coverings like blinds and drapes can contribute to interior condensation. They block airflow around the window, creating a barrier that traps moisture against the glass. Make sure your coverings allow for proper ventilation and air circulation around the window itself.
## Summary
Interior window condensation on high-efficiency windows is **normal** and is caused by a combination of relative humidity, indoor moisture sources, insufficient ventilation, temperature differences, and window coverings. Proper ventilation, indoor humidity control between 30-50%, and a consistent indoor temperature are the key to preventing it.
If you've handled all of those and still see persistent condensation in a specific area of your home, [contact our team](/contact) — that pattern can sometimes indicate a specific airflow or insulation issue worth investigating in person.