Humidity Gone Rogue

Frozen attic condensation can cause a frost like appearance on the inside of your attic

Rogue : a deceitful and unreliable scoundrel.

Seems funny to apply the word “rogue” to humidity. But during midwest winters it fits. Here’s why:

Every winter is bound to have a couple days to a couple weeks of below zero weather. When temperatures start to rise, homeowners start to notice brown spots on their ceiling that resemble roof leaks. This could be a sign of a roof leak; it could also be a sign that the home’s humidity was too high during the cold temperatures- causing attic condensation to freeze.

Furnace humidifiers are often forgotten to be adjusted during winters and create too much humidity. This moisture freezes when it hits your attic
Furnace humidifiers are often forgotten to be adjusted during winters and create too much humidity. This moisture freezes when it hits your attic

Many homes have humidifiers on their furnaces. Almost all new homes have this or homes with real wood floors. It’s a great thing to have, but homeowners need to be mindful of appropriate humidity levels. If the humidity is set higher than it should be during negative temperatures, the moisture rises up to the attic and before it can escape, it hits the bottom of the snow covered roof and freezes. Sometimes icicles even form off the nails! Once the weather warms up and one of the first things to thaw is attic condensation. Depending on high the humidity has been set on your house, this can be a decent amount of moisture coming down – thus causing brown spots on ceilings. It looks identical to spots from roof leaks.

What is the appropriate level of humidity for your home?

If the outside weather is…

  • 20 to 40 degrees, humidity should be less than 40%
  • 10 to 20 degrees, humidity should be less than 35%
  • 0 to 10 degrees, humidity should be less than 30%
  • -10 to 0 degrees, humidity should be less than 25%
  • -20 to -10 degrees, humidity should be less than 20%
  • below -20 degrees, humidity should be less than 15%

This will prevent attic condensation, mold, or any other issues caused by overly humid and warm air.

What about you?

These guidelines are the optimal levels to make your home comfortable, but what about the people living in it? Dryer air is not always the best for us to live in but there are ways to keep both you happy and your home comfortable. Instead of using whole house humidifiers use individual ones when you are using the room. Use programmable timers to turn on and off humidifiers. Buy indoor humidity sensors – these range from $5-$50. Click here to see the “indoor hygrometers” on


It’s so easy to forget to monitor or change your humidity. Many people don’t even realize this is what’s going on until it’s too late – brown spots appear! If this happens to you, don’t  panic but it’s still good practice to have a trusted roofer inspect to confirm no roof leaks.


Proper Roof Ventilation

Most people know that their roofs need to be ventilated, but you might find yourself asking these questions: What is the purpose of ventilation? What does proper ventilation look like? How do I know if my roof ventilation is functioning? What are signs that my roof isn’t properly ventilated? And finally what are my options and how do I pick? Hopefully this article will answer those questions for you.

Heat and moisture attack and destroy the home; besides the weather, we create humidity with our day to day activities such as showering and cooking. If not removed, heat and moisture can cause your paint to peel, your insulation to become wet and flat, mildew and mold, rotting wood, crumbling shingles, and higher utility bills. Ventilation adds longevity to your roof system, which is why all shingle manufacturers include it within their warranty; you don’t want to void that!

Appropriate ventilation keeps the air flow going throughout your attic. The air flow pulls the heat and moisture out of your attic. In the summer, ventilation keeps your attic cooler- this is desirable for 2 reasons. First and most obviously, your AC bill will be lower because your home won’t retain heat. The second reason requires a quick explanation about shingles. The granules on the outside of your shingle aren’t there just to make your house look pretty but it protects the fiber layers underneath (the heart of every shingle). These granules have been formulated to withstand elemental damage such as hail and heat. During the summer months, the shingles cannot protect the underneath side from heat. They just weren’t made for that. Keeping your attic cooler in summer through ventilation guarantees that the shingles won’t cook from the inside out.

Mold in the Attic
Mold in the Attic
Ice layer in the attic
Ice layer in the attic

There are many signs that your roof’s ventilation is not adequate. Without climbing into your attic, you can tell that it isn’t functioning correctly if your house won’t cool in the summer.  once you are in your attic, look up; if you see mold you know that moisture is not escaping. In winter this moisture freezes and in extreme cases becomes a sheet of ice; as this ice melts you essentially have rain in your attic. This will ruin your insulation and your ceiling drywall. If your ventilation was installed incorrectly, the exhaust vents turn into intake vents which will suck snow into your attic.

Exhaust vents must be at least 3 feet higher than the intake for the air to be pulled continuously.
Exhaust vents must be at least 3 feet higher than the intake for the air to be pulled continuously.

Knowing your ventilation options go hand in hand with knowing what is needed. Proper ventilation is 50% intake and 50% exhaust, many installers go into a job that needs better ventilation will just add more exhaust vents but if it can’t be exactly 50-50 it’s better to have more intake than exhaust. Vented soffit is where you get your intake.

The exhaust vents need to be on the same side of the ridge so they don't turn into intake vents.
The exhaust vents need to be on the same side of the ridge so they don’t turn into intake vents.

In the same attic body, keep all exhaust vents installed at the same level, same side of the ridge, and same style of vent to ensure that the exhaust vents don’t turn into intake vents. Venting options include but are not limited to box vents, ridge vents, and turbine vents (also known as whirlybirds). Ridge vents are better than box vents because they are placed at the peak of your roof where heat rises to. The tricky part about ridge vents is having the proper ratio which I’m not going to go into the crazy equations, but just know that your contractor should be aware of this to get proper air flow with ridge vents. Whirlybird vents are great because they actively pull out the heat while all other ventilations just rely on the heat to create the flow.

Different styles of exhaust vents.
Different styles of exhaust vents.

Happy Venting!