GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Choose between window condensation or gaps in hardwood planks?

lazukars | Posted in Mechanicals on

I built a new home in 2017. This is our first winter living in the home, and I’m running into a humidity problem.


In the fall I noticed that my 5″ wide solid oak hardwood floor had some millimeter gaps between the planks. As any concerned homeowner would do, especially for a brand new home, I researched why these gaps were happening. After doing a little research I learned that hardwood flooring can shrink when its relative humidity is below 33%. This was a sign of relief as something could actually be done to remedy the problem. So I purchased a humidifier and cranked it up to 43% RH. Once the entire home’s RH got up to around 43%, that solved the problem. A lot of the gaps shrank and the home was more comfortable to live in in general. However increasing the humidity caused an entirely new problem. That is, window condensation started forming on my double pane windows. I live in Cleveland, Oh and the temperature of this particular week was anywhere from 10 – 30 deg F. So again, I researched why this window condensation was occurring. And again, and come to find out, condensation on the windows is a sign of too much humidity in the home. Honeywell actually recommends that Relative Humidity in the home be no higher than 35% when its 20 deg outside, no higher than 30% when it’s 10 degs outside, and no higher than 25% when it’s 25 degs outside.

So you can see the problem here. Too much humidity can cause windows and interior wall cavities to condense. But on the other hand, too little humidity will cause hardwood floor gapping problems.

Does that mean I have to live with one of these problems. Are there any solutions to addressing both of these problems simultaneously?

More notes about the home

– Its got 1″ closed cell foam along with blown in cellulose in 6″ wall cavities. Also, a 1″ thick layer of Roxul covers the exterior of the house.

– The heating is in-floor radiant heat

– The home has an ERV unit installed.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    Wood moves. Gapping between your floorboards during the winter is normal, especially if the flooring contractor installed the boards in humid weather.

    Learn to love the wintertime gaps between your floor boards. If you want a floor without gaps, you can always install laminate.

    (And by the way, pay attention to the indoor relative humidity advice from Honeywell. Operating a humidifier can damage your house -- so disconnect your humidifier now.)

  2. user-2310254 | | #2


    It is possible you need to dial back the ventilation rate. How big is your house, how many occupants, and what type of ERV?

  3. Expert Member


    Unfortunately, to avoid cracks, flooring needs to be at a specific moisture content when it is laid. The level depends on the anticipated summer and winter humidity levels and indoor temperatures. Your flooring was acclimatized to a high level and when it dries below that the problem occurs.

    At this point there are really only two viable solutions. As Martin put it: Learn to love the cracks, or keep the indoor humidity low and refinish the floor with filler between the boards.

    Some years ago FHB published this useful chart (at the bottom of the article):

  4. mark_be | | #4


    In-floor radiant heat is a poor match for wood flooring. As wood heats, it will lose moisture and as it loses moisture it will shrink. In the spring, when you stop applying heat to your floors, they will want to expand. Putting something in the gaps to fill them will probably prevent the boards from expanding and cause more significant problems than the small gaps you see now.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |