Attic Condensation - Where is This Water Coming From?

I thought I'd take a minute to answer a question that past remodeling customers, our architect's clients, and friends have asked - this year has been especially troublesome with varying temperature swings. Please share with your friends!

It's not often you head over to your friends house and get into an in-depth conversation about their attic! Who would want to talk attics? It's usually kitchens and other areas of the home. So, lets talk attics.

Attics are uninviting places to be – scorching hot in the summer with that ‘attic’ smell and freezing cold in the winter. Rarely do homeowners spend much time in their attic to inspect the health and condition of the space, so if there is a problem in the attic, the owner typically doesn't see the issue until buckets are set up catching water. We have had a number of calls this winter from past remodeling customers telling us ‘our roof is leaking’ or ‘we have moisture coming in.' Our first question is: did it leak in the summer? So far, all responses have been NO!

So, what is causing this phenomenon?

The main cause for moisture in an attic is when there is warm air moving from the heated space (living area) into unheated areas when the weather outside is cold. Warm air holds water vapor and will form liquid on cool surfaces (think house windows on a cold day – there is sometimes moisture). This transfer, when cold, will form frost in the attic. When the warmer days occur, the frost then melts! See Figure 1 below from Cornell University study for a better understanding of this. Heat escapes through unsealed penetrations such as recessed can lights, vent pipes etc. Another thing to keep in mind is moisture within the house: are you not controlling a humidifier properly, is the dryer vent connected properly and venting outside, are you using exhaust fans or air exchangers when showering (and 10-15 minutes after showering)? This creates more humidity than normal and can cause issues. Does your roof have adequate ventilation? Are your soffit vents clear?


I was at a home last week with my FLIR thermal imaging gun, which allowed me to identify a few cool spots. Warm meets cold = frost / condensation. This is where the owner recognized the visual damage on the wall. We plan to repair the insulation of the entire roof since there are so many problems.

How do we fix this? - Seal any air leaks into the attic. Typically done on the attic side.

In our new homes and remodels (when attics are a part of the scope of work), we utilize spray foam insulation, which creates an air seal over the entire attic including any and all penetrations. Due to our spray foam usage, attic condensation has not been present in any of our new homes or remodels where the attic is involved. Our clients love the spray foam insulation and our homes are healthy because of it.


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Michels Homes

5959 Centerville Road,

Suite 250B,

North Oaks, MN 55127

Phone. 651-653-1210