Dealing with Gaps in Hardwood Floors

January 25, 2011 | by Fred (email) |

hardwood_flooring_gapsGaps in hardwood floors can be a huge visual annoyance. Not only are they an eyesore, they can also collect dirt and dust. Hardwood gaps are generally caused by one of a few installation errors:

  1. improperly acclimating the hardwoods prior to installation;
  2. failing to install the first board perfectly straight in a hardwood flooring installation;
  3. failing to keep boards straight when working around an outside corner; or,
  4. installing boards that are not uniform.

Generally speaking, for #2, #3, and #4, you know the gaps are there immediately after installing the board and you can pull the offensive board out and correct the problem. If you don’t correct the problem during installation, it’s going to be there forever. In best case scenarios, these types of gaps are isolated to a single area, and hopefully are out of sight. Unfortunately, some types of misalignment errors can propagate across a floor, creating gaps that alternate from side-to-side going from one board to the next. If you’ve done a number of hardwood flooring installations, you know what I’m talking about — it can be very annoying to try to correct this type of alternating error during installation, and you may have to decide of a judicious location to leave a countering gap.

For #1 — the most common reason people get gaps in their floors — the problem is much more insidious. It has to do with moisture content of the hardwoods during installation and the change in relative humidity throughout the year.  Most people first notice gaps in their hardwood boards the first winter after installation.

What Causes Hardwood Gaps in Winter?

Gaps first occur in winter because this is the first time humidity is very low, which draws all excess moisture out of the wood. During installation, the moisture content on the surface hardwood wood is usually higher than the subfloor, which has been through many seasonal cycles.

If you properly acclimated your hardwoods during installation (by letting them sit in a conditioned space for at least 10 days), the likelihood of large gaps is greatly reduced. You may still see small gaps open up between boards, but these will likely close during the next spring and summer when humidity levels rise.

If you did not properly acclimate the woods, the winter may have pulled a very large amount of moisture out of the boards – an amount that will never fully return to the wood in the spring and summer. In this case, gaps may become smaller in spring and summer, but they will persist, and may get even larger in the following year. After two full seasonal cycles, the hardwood will reach an equilibrium with the subfloor and environment and the gaps in the wood will be minimized.

It is useful to note at this point that some web sites will suggest that if you have perfectly matched subfloor and hardwood moisture levels at installation, you will not get any gaps. This is not entirely true. Not all wood types respond the same way to moisture, and it is possible that when moisture levels drop, your subfloor could contract at a slower rate than the surface hardwoods, leaving gaps.

Fix Gaps between Boards in a Hardwood Floor

You generally have three options for fixing gaps in a floor:

  1. To avoid seasonal gaps, you can limit the variation in humidity in the house. In the winter, this can be achieved with a whole house humidifier that connects to the furnace. Note that these systems can have drawbacks if they put too much humidity in the air, including promoting mold growth in vents. You will want to make sure your ductwork is very clean before installing a whole house humidifier, but once installed, they can work wonders. During the summer, make sure to run your air conditioner system to draw humidity out of the air, keeping the hardwoods at a relative constant point all year. A good target humidity level is 40-50%.
  2. For non-seasonal gaps, the only non-rip-out solution is to sand down the floor and fill the gaps with matching wood putty, and then refinish the floor. If you have a lot of gaps, wood putty can become an eyesore if not done well. For a systemic issue (across the whole floor), we recommend calling in a professional for this type of work. Once you’ve reached this point, it’s a tough call whether it would be better just to tear out and replace the floor. Which leads us to option 3:
  3. Tear up and re-install the floor (ugh!). You might consider installing engineered flooring, which is much more dimensionally-stable than solid wood.

How to Avoid Gaps in Hardwood Installation

  • Properly acclimate the floors. See this article for some help on that.
  • Install hardwoods in the fall and spring when humidity is moderate, rather than in the summer or winter, when it is extreme.
  • Make sure to lay the first board straight. When laying boards in the center of a room, make sure to keep a consistent, tight pattern.
  • Consider engineered flooring, which is more dimensionally-stable than solid hardwoods.
9 Responses
  1. That particular photo looks like the board shrunk on both sides of it’s width. That one would probably have occurred regardless of what you did….just the horrible reality of what can happen with solid wood.

    Come summer time that board will probably be back to normal. I have yet to see a successful attempt at using filler, that’s because when the moisture level goes back up the filler will be forced out.

    Another solution is using engineered wood 🙂

  2. paintergal says:

    What about gaps in hardwood floors that are old?
    Our house, built in 1939, has a few gaps in the hardwood floors.
    Tearing them out really isn’t an option.
    We haven’t refinished the floors yet. My husband does plan to do that.
    For years, the floors were covered in carpet, if that makes any difference.

  3. Fred says:

    Todd, yep – that board fell into the category of “should’ve pulled it out when we laid it” – probably one of the worse offenders in our floor. Gaps are still there in the summer but much more subtle.

    Painter Gal, When we did my sister-in-law’s 1925 pine flooring, we used a pine-matching wood filler in the gaps and then sanded them. There were such large gaps that the filler did not all come back out (which as Todd points out can be a problem if you have a lot of variability). If you are refinishing, sand the floors flat, then fill the cracks with wood filler, sand again to remove excess filler, stain and seal… My sister’s house’s floors were also covered with carpet and some of the stains in the wood could not be extracted (although we didn’t try bleach or a whitener which may have done it).

  4. JustME says:

    We acclimated our hardwoods for more than long enough before installation. They were installed in late fall and early winter. We live in eastern Nebraska where winters are very dry. The next two winters we noticed considerable shrinkage and gaps between almost every board in all rooms, but especially the Gentleman’s Parlor which has a wood burning fireplace. That second winter we installed humidifiers on both furnaces and have not seen any gaps since. Not sure if this would help everyone, but it did with our 3/4 inch solid oak. It’s been down almost eight years now and all is still well.

  5. mikeshmeed says:

    Just bought a house the flooring has a couple of gaps in th middle of the hallway, I hope to fix it with a hard wood gap tool that you can place between the base board and the first floor board and push the boards together working as a lever, hopfully it will close the gap in the middle of the floor.

    • Fred says:

      If you can squeeze the gap shut and figure out a way to fasten the boards to prevent them from moving, that might work. The problem is that simply pushing the boards together isn’t likely to hold them there for the long term. I’m not familiar with the “gap” tool you mentioned. Do you have a link you could post? Thanks!

  6. Mick hartley says:

    I bought a gym 1 yr ago . This place stud empty for 2yrs . As I refurbished it the hard wood floor in the TV lounge , gaps started to appear on the floor various gap sizes 1/4″ to 1/16″ all in various areas . The floor size is large 25’x11′ feet this as happened over the past few months . How can I close the gaps so not to open as bad as is now. Could you help . I need to be able to carry out work on my own ? I need your advise ( thanks ( mick .

  7. Pete says:

    Had an install done for some prefinished hardwoods. The installer only let them acclimate for 2 days. That was not enough. Now he has to come back and fix the gaps.

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