Posted by Victor Mulbauer, January 19th 2014

Over the summer you’ve invested a significant amount of money to have either your hardwood floors refinished, or have new wood floors installed. Now, just a few months later, it’s winter and you’re starting to see gaps throughout your floor.

Gaps are visibly present throughout the floor. They can be seen running along the length of the picture.
Gaps are visibly present throughout the floor. They can be seen running along the length of the picture.

What on earth is going on? Is there something wrong?

Thankfully, in most situations the answer is no.

What you’re experiencing is perfectly normal for all things made of wood in your home, including your hardwood floors. There is a simple explanation for why you sometimes see gaps in your floor and other times in the year you don’t.

The reason is that wood is hygroscopic. Hygro what??? Let me explain…

When something is hygroscopic it has the ability to attract and hold water molecules from the environment it’s surrounded by. For example… have you ever been to a restaurant and had a salt shaker that won’t let any salt out because it’s all clumped together? This happens because the high humidity levels int he surrounding air have caused the salt crystals to absorb moisture. Now the salt has expanded and clumped together to the point that it can’t come out of the small shaker holes… so you either eat your fries without salt or search for a dry salt shaker on another table.

Exactly the same type of thing happens with wood.

The moisture content of your hardwood floor is going to change depending on the relative humidity of the surrounding air in your home. As the humidity level increases, the moisture content increases too. This makes wood expand. Likewise, when the humidity levels drop, the wood’s moisture content decreases and it contracts or shrinks.

The technical term for this is Equilibrium Moisture Content (EMC).

You may have noticed that wood doors in older homes get tighter in the summer months and are harder to open, but in the winter they’re back to opening and closing normally. Those solid wood doors are dealing with the same EMC issue.

Like doors, this movement in floors is almost noticeable in the seasonal changes between winter and summer. In the summer your house is open, there is lots of humidity in the air and the wood in your floor is fully expanded as it absorbs moisture. Then winter rolls around, it gets cold, you shut up your home and turn the heat on. In turn the humidity levels drop and the wood in your floor releases that moisture it’s been holding and it begins to shrink.

That’s when you start to see gaps forming.

It gets especially bad when we have freezing cold days like we have experienced the last few weeks here in Detroit and everyone’s furnaces are cranked right up and all the moisture is sucked out of the wood. Thankfully these unsightly gaps will disappear when spring rolls around with its increased humidity levels and the heat gets turned off.

But what if you don’t want to wait for summer?

Is there anything that can be done to close the gaps a bit now and keep the floor tight throughout the year?

What Can Be Done to Control the Gaps?

One of the best things you can do to control the gaps in your hardwood floors is try to keep the humidity levels in your home stable throughout the year. In order to do that you will need to add moisture to the air during the drier months.

The easiest way to add moisture during the months you have your heat on is to invest in a humidifier and set it at a level of 45 – 55 percent. (Gaps start to appear when the humidity level creeps below 40 percent). That way the relative humidity in your home will stay stable and your floors won’t contract or expand as much during the year – which means far fewer gaps.

There are two types of humidifiers to choose between. One is a permanent installation that’s connected to your furnace and works throughout the whole house. It gets integrated with the blower system and draws water directly from the main water supply.

Thoughts for Preventing Gaps in New Installations:

There are a few things that can be done before a hardwood floor is installed that will greatly help with preventing gaps down the road…

  • Make sure the wood flooring gets acclimated properly before installation. Once the flooring is delivered we recommend placing it in the room it will be isntalled in for as long as possible. Stack it well spaced out so all the planks are able to acclimate evenly. Two weeks is ideal. Make sure the room is at the temperature and humidity level you normally have it at, or will have it at, for living in.
  • Make sure your installer uses a moisture meter and knows how to calculate EMC. The flooring must be checked for moisture content when it’s delivered to see if it’s within acceptable levels. this will also allow the installer to anticipate future movement. The subfloor should also be checked.
  • When you choose wood flooring, realize that the wider the board is the more seasonal movement will occur within each plank. A 2 1/4 inch wide board will expand and contract far less than a 6 inch or 12 inch wide plank. If you want wide plank floors you really need to put a humidifier on your shopping list as well.
  • Plain sawn flooring will expand and contract roughly twice as much as quarter sawn (or vertical grain) flooring. Quarter sawn is much more stable but it is also much more expensive.
  • Don’t deliver or install hardwood flooring until all wet trades (drywalling, painting, etc.) are finished and the high humidity levels have settled back to normal. If you must have the flooring there while wet trades are working, keep it wrapped in plastic to keep the humidity out and then give it ample time for the moisture content to stabilize before installing it.


In Conclusion…

So as you can see there is nothing wrong with your hardwood floor if you have some gaps in it. Wood is a natural product that predictably reacts to the environment it’s placed in. How much it expands and contracts all depends on the weather and humidity levels you keep in your home. If you’re installing new hardwood, it will also come down to how well your installer understands EMC and prepares the flooring before it is installed.

With a little foresight, being sure to follow the tips above, and investing in the right humidifier, you can greatly limit the amount and size of gaps you will see in your floors until summer rolls around once again.