Winter condensation on windows in a house that is very well insulated.

This is my first post and I hope I have the formate correct, I live and build in central Pennsylvania. I built a house in 2004 using what I thought were the best practices at the time to insure it was tight and very well insulated. Took great pains to properly vent all bathrooms, dryer and range. I used Tyvek house wrap and a 6 mill vapor barrier on walls and ceiling. Used a pre-fab basement wall system that creates a very dry basement. Customer works for a propane gas co. and had a high efficiency gas hot air system installed.  They are having a very hard time with condensation on their windows in the winter. They are very unhappy with me because they feel the house is to tight and I should remove the plastic vapor barrier.  The only thing I changed was using Crestline windows instead of Anderson.                              As a side note I built 6 new homes using all of the same building techniques in my area and had none of these problems. We have discussed the use of exhaust fans allot and they assure me they use them. It is just Mom, Dad and a teenage girl so not an excessive amount water usage.     What should the RH be in the winter and should I just buy them a de-humidifier.  Oh, Yea they do have a heat recovery system they use when the temp reaches 50 degrees. Any help would be welcome.

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If reducing indoor RH has "ameliorated the moisture problem", then the problem is far more likely to have been excess indoor humidity than the window units. Poor installation, without air-sealing the perimeter, is more likely to cause condensation and icing problems than the actual window unit, since it's next to impossible to reach freezing indoor conditions unless there is outside air leakage.

Robert.  I suspect you are correct.  Is there anything I can do to remedy "air sealing the perimeter," in a completed home?

Assuming that the windows were installed square so that the sash close tightly and the weatherstripping is intact, you can remove inside window trim (casing and sill apron) on all four sides and inject low-expansion window/door foam.

If you're sealing a lot of windows, it's worth buying a foam gun and canisters, which offer far more control and don't have to be completely emptied after each use.


we have reduced utilization of our gas logs.

Ventless logs?  There's the moisture source.  

Eric, if you spend $1000 sealing windows and nothing changes, how will you feel?  

Would you go on a diet without first stepping on a scale?  

The first step is a comprehensive assessment of your home.  This needs to include at the very least a blower door leakage measurement, which should be done BEFORE ANY work is done.   You need to know where you started to understand how well your diet went.  And the blower door will help you understand if it's your windows, baseboards, rim joist, or attic penetrations that should have first, second... priority.  

Understand what illnesses you have before running off half cocked fixing things that may not be broken and missing things that are.   Good luck!

You're responding to Robert Hamilton's recent query, not the OP Eric Fletcher.

Robert knows what his problem is - too much indoor humidity and condensation and icing on his windows. He has already substantially corrected the humidity problem and wants a solution to the window problem.

For that, he doesn't need a full energy audit and blower door test and since it's a focused problem with a focused solution.


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