Condensation Problems in a Nutshell

In early Winter and early Spring it is especially important to be on the lookout for condensation issues in the attic areas of homes. If attic condensation is noticed, it is important to address it immediately. Ventilation is key to prevent excess condensation. When warm, moist air from your house gets into your attic and is quickly cooled (like when it comes into contact with your roof deck), it can cause condensation and frost, which melts when the temperature warms back up and drips right back down into your insulation and attic floor.

When warm, moist air is stuck in the attic, the roof deck (and the nails sticking through it) freeze the moisture from the air, which builds up to little icicles on each nail head. These melt during the day and can also cause small leaks all over the attic space. Less moisture to build up means less water in your insulation (to cause dangerous mold) or in your ceiling, and, of course, less ice damming on your roof.

Is It a Leak or Internal Humidity?

Finally, what you might think is a roof leak might actually have nothing to do with your roof — it’s just built-up humidity inside your house! Moist air can actually condense on the drywall that you might see from your room, but not from the attic moisture at all. The watermark is only on the inside of the house, normally near a corner. This occurs if the attic insulation is not covering that corner, and cold air is able to get into the attic at the soffit vent near this corner. The fix for this is more insulation over that spot, and controlling the indoor humidity.

How to Actively Prevent Condensation

If you haven’t had a problem yet, you can be actively preventing them from popping up in the first place! Here are some ideas:

• Check your humidistat: If your home has one, make sure it is not set above 30. The colder the weather gets, the lower your humidistat should be set. Generally older houses do not have a humidistat, but lose enough moisture through their windows and siding that condensation may not be a concern.
• Keep your vents open: Air circulating everywhere will keep a better balance of humidity, reducing the chances of excess moisture building up in any one area.
• Reduce humidifier use: Introducing a lot of extra moisture to the air can lead to more frost buildup in your attic, even with an otherwise sufficient amount of venting.
• Run exhaust fans: Run the exhaust fans in your bathroom and kitchen when you’re working in those rooms, and for 15-30 minutes after a particularly long, hot shower, to help bring your indoor humidity levels back down to normal. Just make sure these fans actually vent to the outside and not just into the attic!
• Clear the eaves: Peek into the attic and make sure your insulation is not tight against the deck of the roof at the eaves. Air needs to come in from there and the insulation can cut off that air flow.
• Check soffit vents: Check your soffit vents around the house to make sure dust or paint has not suffocated air intake to the attic.
• Cover pans when cooking: Cover pans when cooking, if possible — we totally understand the need for getting a good browned crust on a roast, so this isn’t always feasible, but if your food won’t be affected, throw the lid on.
• Cross-ventilate: Open a window on opposite ends of the house, just an inch or so, for a little while. The cold air introduced into your home won’t freeze you out, but will lower the overall humidity of your home.

Remediation and Insulation

If there is consistent condensation forming on the underside of your roof deck, proper ventilation needs to be added to the home. Either by clearing clogged vent areas or by potentially adding a powered vent fan into the gables ends of the structure.

Adequacy of insulation should also be considered. If there is condensation forming on the roof deck, sealing the air off from the living area of the home from the attic space with proper insulation can significantly reduce the cycling of water vapor.