Small amount of condensation OK or harmful?
I’m just moving into my new construction house and am noticing that there’s a small amount of condensation on the bottom of the windows during cold nights. I do have a hygrometer and my relative humidity is normally around 43% – 47% in both my basement and first floor. So the basic question, is this ok or should I be concerned? I’m also a little confused on two common, yet conflicting assumptions. First, many consider the optimal relative humidity to be between 40% – 50% for comfort. However, colder climate homes need to be sub 40% or 30% to truly eliminate condensation issues? So which is the better rule to follow? Here’s some additional details:
– Zone 5 Climate (but on the milder side of this zone)
– 2” R8 Roxul Comfortboard exterior insulation with siding over a rainscreen
– R23 mineral wool between the studs
– I do have an HRV, but that doesn’t seem to do much about the relative humidity
– my wall assembly is pretty vapor open by most standards. Given the exterior insulation, I used a class III vapor retarder on the inside. If there ever was condensation around the sheathing, it should easily dry out given my vapor open WRB, roxul comfortboard and rainscreen.
– given the house is new construction (built over a period of about 18 months), it still could be drying. I have a finished basement with a slab, concrete kitchen counters, a very large tiled shower with mortar base, and did veneer plaster walls throughout.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
My money is on the new construction moisture. Might be worth running a small dehumidifier for the next few months. I like to see nothing over 40% RH in winter on average, though you may need 30% max to avoid condensation during particularly cold weather. But if it's only appearing as fog or stationary droplets on the windows - and not running down and pooling - and dries up after a day or two, it's probably not a big deal.
When one lived up north, one would monitor the ten day forecast and look for nights when temps would get into ~mid/low 20s or teens etc. and then turn down the humidifier on those evenings, just enough to keep house humidity in the 20s-30s... and this would help things.
What also helped was ensuring blinds were not all the way down or closed.
It was a matter of condensation on windows or lower humidity levels, on those nights, and deciding what was worse/better for the house.
It would be interesting to see if your condensation is only on cold nights; are there blinds closed and what the humidifier is set at.
However, this is nothing more than from existing up north and not from advice received.
Keep Winter humidity low. If necessary, do this by increasing ventilation.
Did I miss seeing the U value of your windows?
The U factor of your windows will and the outdoor temp will set the upper limit for your indoor humidity. If you try to get 55% indoor humidity with single pane windows when it is -20° outside, it is not going to happen.
I would recommend running a dehumidifier for the first year after construction. There is a lot of moisture all the building materials that needs to dry out.
Walta
My new house has this problem the first year. Definitely run a dehumidifier or increase ventilation.