Flooring Gaps: Causes, Solutions

Question: My hardwood flooring looked great.. but now I have gaps in my floor?

LL Technical & Installation: Before we get into gaps in flooring let’s take a little time and delve into the wonderful world of wood.

Wood has been used for millennia and is used in so many ways - to build houses, make beautiful furniture, form amazing musical instruments and yes... flooring.

There are many species of wood that can be used in different applications. However all wood has one thing in common; it is hygroscopic, which basically means it can absorb or lose moisture, and for flooring it is often in the form of vapor from or into the surrounding atmosphere, until it reaches equilibrium.

Q: Wood absorbs and loses moisture. But what has this got to do with gapping?

LL: Well another property of wood is that when it absorbs moisture it expands and when it loses moisture it contracts.

So if the atmosphere surrounding wood has a lot of moisture creating an imbalance, the wood will absorb and expand until the imbalance is corrected (equilibrium). If the air is very dry it will lose moisture and contract until the imbalance is corrected.

Q: Why does wood expand and contract?

LL: Cells in the wood swell and contract as they absorb and lose moisture causing the change.

This is natural and part of being wood. The wood has no control over how it behaves. 

Here I want to introduce Relative Humidity (RH). This is a measure of the amount of moisture in the air at a given temperature. The RH of the air has a direct relationship with the moisture in the wood or Moisture Content (MC) and when the wood fully acclimate to the RH it reaches Equilibrium Moisture Content (EMC). It sounds complicated, but it is really the wood just getting in tune with the atmosphere. 

Let’s start to look at gaps, and maybe venture into squeaking..

One of the most common complaints with wood flooring is gapping, or separations between edges of flooring pieces. We reviewed that wood contacts when there is a low level of moisture (low RH) in the air causing an imbalance. 

Generally, the majority of gapping occurs during winter months. Air becomes dry outside and then in simple terms we heat it up drying it even more on the inside. You can often “feel” the dryness cracked lips, sore noses and dry skin.

It should be noted, that some areas in the country do have very dry summers and the situation is reversed, this means that the potential for gapping may exist during the summer months as well. Check your local weather or check here for Relative Humidity trends in your area.

Q: But does this really make that much difference, I mean how much of a change are we talking about?

LL: Well the answer is, it depends on the species, and how it is cut from the log and the change in RH / EMC.

There are a lot of factors... But in short: If the RH in your home swings let’s say from 60% to 20% (at 70F) that is a change of 40%. The wood will lose moisture and EMC will change from 11.00% to 4.5% that’s 6.5% change.

*For Red Oak Flat or Plane-sawn planks, milled at 5” wide can contract as much as 1/8”, this will lead to an approx. 1/8” gap between flooring boards. If the plank is narrower, e.g. 3” this could be around 1/16” gap.

Q: What can we learn from this?

LL: The larger the swing, the larger the gap. So controlling RH is critical to keeping gapping to a minimum. 

*It should be noted that all the wood in your home will expand or contract as moisture in the air changes. Doors and windows may swell and stick during rainy seasons. In dry, cold weather, cracks and fine lines of separation may appear in cabinets and furniture.

We call this change Seasonal Gapping which in most cases will close during seasons of higher humidity.

And here is the SQUEAKING call out: Higher levels of RH can cause the gap to totally close and even develop a little friction causing a squeak. Just like a door sticking in humid summer months.

The ideal humidity level is 30% to 50% and an ideal temperature is 60 to 80 degrees. (Maintaining these indoor conditions can even promote a healthier quality of air inside and can sometimes help sinus sufferers!)

Q: Are there solutions?

LL: Here are Pre-installation solutions:

Acclimation. Your flooring needs time to adjust to the normal conditions in your home before installation. Failure to do due diligence in this area can result in problems. See Acclimation in your products installation guide for more details.

Install wider (5” or more) planks using nail with glue assist which, may help with seasonal gapping (it will not eliminate it)

Sort the planks (rack out) prior to installation making sure that widths are the same in each row. This will enhance the look at time of installation.

Follow nailing schedule for product

And Post-Installation solutions:

        Use humidifiers / dehumidifiers to maintain the environment in your home to recommended levels. 

People have also asked "Why is my wood floor squeaking?" or "Why are there cracks in my wood floor?" or "Why are there spaces between my flooring planks?" for example. We hope that this information helps you to prevent flooring gaps and correct flooring gaps if needed. If you have more questions about problems with hardwood flooring please let us know. Our team is glad to help.

LL Flooring Technical & Installation