The dew point in your attic changes based on 2 factors.
- Temperature and humidity
Why it matters: Knowing the dew point will help you understand when water will become a problem in the attic.
🧮 By the numbers: Right now, the temperature in my attic is 81 degrees and the relative humidity (RH) is 59%.
- I can plug those two numbers into a dew point calculator.
- The dew point is 65 degrees.
🤔 What does it mean?
- The dew point tells you the SURFACE TEMPERATURE where water will condense out of the air.
- Any part of my ductwork that’s metal and not well insulated can easily get to 65 degrees —> the cold air flowing through it is 55 degrees.
- The copper line carrying cold refrigerant through the attic to the air handler is cooler than 65 degrees as well.
🥊 The bottom line: Any surface in your attic that reaches the dew point will condense water.
- That water will drip from the surface onto insulation, your ceiling, etc.
✅ For your Smart Homeowner list
- This is one example of how water can be a problem in hidden spaces in your home — which includes the attic, crawl space and even inside walls.
- And it’s why air sealing and insulating are the best ways to keep water out.