I need some solutions for fixing a crack in my oak floors.

My home was built in 2007 and sat empty until my wife and I purchased in 2009. We purchased the home in the summer. In the winter, the hardwood floors split apart in the middle of our home. Each year, the split disappears in the summer and reappears in the winter. The problem is that the crack is pretty severe during the winter. The crack runs the width of my house, a little over 30', and is almost a 1/4" wide. And the crack runs through the middle of my house.

Any ideas? I really appreciate you taking time to comment/suggest.

I am not a professional but had a similar issue in my 1950's ranch with red oak flooring. In the winter, when the humidity would drop because all of the moisture is frozen, the floors would contract leaving spaces (not as severe as what you have) and in the summer the floors would expand do to the increased humidity. The expanding and contracting is natural and putting wood filler between the crack and attempting to match the color likely will not work as it will just be pushed out of the crack when it expands in the summer.

I ended up installing a whole house humidifier which I use in the winter. I installed this because I was tired of waking up with a dry throat not to fix the floors, however I have noticed that the floors do not contract as much as they used to and the gaps are no where near as noticeable. Wait for the professionals to chime in on other possible fixes. However since every board expands and contracts with the humidity I do not think replacing just a few boards will solve your problem.

As the first responder said...higher humidity in summer will cause floor's moisture content to increase and swell the floor to close the crack...lower humidity in winter will cause floor's moisture content to decrease and shrink the floor to open the crack. If you were to keep the house humidity between the summer and winter humidity extremes the flooring would not have this 'extreme' amount of movement. For the hardwood flooring to be happy the house humidity should be kept year round between 40% - 50% or 45% - 55% depending on what source you reference.....in this range the floor will neither shrink nor swell very much, if at all.

Thank you, both, for the replies.

Is there an easy way to measure humidity so I can begin to make sure I keep it between 45% and 55%?

Would you advise against trying wood filler and stain?

Thank you!

My initial impression is that this split probably falls right upon the center joint of the house which coincides with a seam for your subfloor. Moisture control above and below the floor is the best solution.

You can buy a humidistat for under $10. Walmart, HD, Lowes, etc. will have them. Based on readings you may have to set up a humidifier in winter and dehumidifier/AC in summer. Get the floor to humidity midrange and then assess the split.

I will go the hygrometer/humidifier route and see where the split is after I get the reading in the 45% - 55% range.

Thank you for the help.

I bought a hygrometer and let it sit in my living room (w/ flloor crack) for about a day. It is reading 52% humidity.

I was still planning to run a humidifier to try to raise the humidity. Is this still the best plan? What humidity reading should I be aiming for?

Thank you in advance for your help!

That seems to be on the high side of normal humidity. Where are you located, what's the temperature inside the house, outside temp and humidity? Any idea what the summertime humidity is in your area?
Do you have access to a moisture meter to check the moisture content of your floor and subfloor? What are the temperature conditions in the basement (?) below the floor with the split?

I live just south of Chattanooga, TN in northwest GA. I keep it 68 degrees during the winter and 74 in the summer. Winter temp highs usually in 40s. Summer temp highs usually in 90s. Humidity? Don't know.

There is crawl space under the house. I can check the temp there, but it is freezing outside (about 30F) and snowing.

I don't have a moisture meter, but I've never seen any moisture under the house.

Any ideas? Could the crack have more to do with the temp than the humidity differences?

Temp and humidity are related....warmer air can hold more moisture.
What's the crawl space like? Dirt floor, concrete floor? Ventilated?
Also, if your house is currently at 52% humidity I would not push it higher....could cause other problems.
It might be a good idea to be patient and keep track of temp and humidity conditions until the summer when the split closes. With all that info you'll be able to determine what course of action to take.

If you have one large crack running down the center of the house it is very likely that it's a plywood subfloor seam moving over a peir/beam taking the wood with it. The floor would normally have cracks throughout the floor if it was just low interior humidity. If you fill it now come summer the filler will crack and break up making a real mess. The NWFA says gaps that open and close seasonally are normal in plank floors, unsightly yes, bad install not necessarily so.

There is crawl space underneath the floor.

Currently we are 68 degrees inside and about 50% humidity, 40 degrees outside.
During the summer I am expecting 74 degrees inside and 90 degrees outside, and a much higher humidity.

Kevin,
If the subfloor install is the problem, how much of the floor am I going to have to pull up to fix it?

Thank you!

I've made several trips under the house trying to identify the problem.

Here's a pic of what I've found. What do you think?

Yea you floor joist is suppose to be touching that rim joist and I see the plywood seam right above it I say it looks fishy to me. I dont know what has casued it has moved that much.