Is A Hardwood Floor Expansion Gap Really Necessary?
If you want to keep a hardwood floor flat all year round, what is the most crucial element? Here’s a hint. It’s hidden behind the baseboard along each wall. What is it? It is the expansion gap between the wood floor and wall.
There are many rookie mistakes when installing a hardwood floor, but the biggest one is putting the boards up tight against walls and other vertical surfaces. Why? Because a wood floor expands and contracts with the seasons depending on the humidity in the room. As it absorbs humidity from both the air and the sub-floor, the wood expands and needs to move. What happens next depends on the floor’s installation.
Let’s take off that baseboard and uncover the importance of a wood floor expansion gap, why you need one, and the consequences if you don’t plan for it.
What is A Hardwood Floor Expansion Gap?
Bear in mind that any wood floor, especially a floating floor, moves all the time based on the room’s humidity. A solid wood floor expansion gap allows for this movement. When installing a wood floor, it is critical to leave a gap around the room’s perimeter and anywhere the floor meets a vertical surface. That includes all doorways, fireplaces, columns, and around any pipework.
Why Is an Expansion Gap Necessary for a Solid Wood Floor?
As we mentioned, you need to keep space around every vertical object. The gap is critical for a solid hardwood floor to lie flat throughout the various seasons and humidity changes. If the wood planks have no space to expand, they can start to lift or crack.
For example, for red oak, expect it to move 1/16” for every foot across the grain. That means, in a 16 ft wide by 20 ft long room, you’ll need a 1-inch expansion gap, 1/2inch on each side.
The recommended expansion gap for the engineered wood floor is 8mm (5/16 in). For hardwood or bamboo, leave a gap between 10 to 15 mm (3/8 to 5/8 in).
To see more details, view this video.
5 Common Errors That Hinder a Wood Floor’s Movement
As we’ve mentioned, wood reacts to changing relative humidity (RH) and temperature levels daily. It needs to expand or contract evenly across the entire floor area. Wooden floor expansion problems happen when the floor gets obstructed, it can buckle, crown, lift and cause squeaks. Here are five common mistakes that cause these issues.
- Excess Moisture – The floor may have the correct expansion gap, but there is too much moisture getting into the boards. Excess moisture causes the wood flooring to expand more than the gap can handle. Test the site conditions to see if the air has too much humidity or there is moisture wicking up below.
- Excess Moisture from Below – Although the subfloor may have tested dry, there is a possibility that the space below, such as a wet basement or a crawl space, has excess moisture. Check that all areas around the floor, above and below, meet humidity specifications.
- Forgotten Pinning or Spacers – To create a proper expansion gap, installers place spacers between the first board and the wall or other obstacle. One shortcut to spacers is to drive a few brads, called pinning, into the first board to hold it in place. If the installer forgets to remove the pins or spacers, there is essentially no gap.
- Railings or Other “Pinch Points” – Sometimes, other trades install permanent fixtures through the floor and anchor them into the subfloor, such as stair railings or cabinets. Once anchored to the subfloor, it prevents the floor’s natural movement. Doorways and columns are other pinch points. Without a gap, the boards come under pressure, causing them to rise.
- Excess Adhesive – Occasionally, floor transitions, such as door thresholds, have too much adhesive. The excess accidentally spreads, bonding the transition molding, flooring, and subfloor together, preventing the floor’s movement.
Hindering the floor’s movement for any reason means that it will build pressure in the form of one or more raised joints.
Types of Wood Floors and How They Expand and Contract
Wood floors move naturally as the seasons change. Wood has hygroscopic properties. Like a sponge, as it absorbs moisture, it expands, and as it dries, it contracts.
Wider boards expand and contract more than narrower ones making the gaps more noticeable in floors with wide planks. A floorboard expands and contracts much more across its width than the length.
Image Courtesy of Popular Woodworking
The chart below shows a numeric value for the dimensional change in a board depending on the species. F/S stands for Flat Sawn, and Q/S is Quarter Sawn.
Image Courtesy of Popular Woodworking
The higher the number, the greater the movement. There is no tremendous difference between species, so no matter what type of wood it is, a 1/2 inch expansion gap around the room should suffice for any wood floor.
Does Engineered Wood Flooring Expand?
Hardwood Floors Magazine and Purdue University experimented using a sample of solid oak and engineered wood flooring. You can read the details of the experiment in the article, Expansion of Solid and Engineered Rift White Oak Flooring with Increase in Moisture Content.
The experiment included two separate tests using a sample of 4-inch solid rift-cut white oak flooring and another sample of 4-inch rift-cut engineered wood flooring with a 4-mil sawn wear layer and an 11-ply platform. The samples were left outside but covered to react naturally to the temperature and humidity.
The wood expansion and contraction chart below shows the results.
The results showed that engineered flooring expanded about three times less than solid oak. The oak flooring sample expanded in width 0.064 inches or about 1/16 of an inch (about 1.6%) when the humidity changed from 7.4 percent to 14.8 percent moisture content.
However, the engineered flooring expanded just 0.02 inches or 0.5%. The cross laminates in the base material accounted for the lower wood expansion and contraction. If you plan to use solid hardwood, it is critical to include expansion gaps and proper humidity control in the rooms for best performance.
The board’s width has a lot to do with movement. An 8-inch wide plain sawn plank of white oak shrinks twice as much as a 4-inch board of the same cut and species.
This promotional video for bamboo floors provides good visualization and strategy for using expansion gaps.
For most rooms, add an expansion gap around the perimeter of 10mm to 15mm or 3/8 in. to 1/2 in. Use spacers around the wall cut to the desired width.
How Do You Cover the Expansion Gap?
Homeowners and DIYers ask, “Will the expansion gap make my floor look unattractive?” The gap will preserve the floor’s integrity and its beauty by allowing it to move freely.
No one should ever see an expansion gap after installing the baseboard molding. The baseboard or skirting will cover any gaps between the floor and the wall for a tight finished look. Other gap-covering accessories include beading or shoe molding, T-moldings, vent covers, and pipe covers.
Baseboard moldings hide the expansion gap and protect the wall from getting kicked with feet, scratched with toys, or bumped with the vacuum cleaner.
Keeping a Floating Wood Floor Flat
Solid wood expands more than an engineered wood floor. However, when either floor is a floating floor, they expand across the entire room as one unit. A floating floor must move freely over the subfloor. When installing any molding or skirting, never attach it to the floor. Nail or glue it to the wall so that the floor is free to slide underneath it.
There are other ways a floating floor can get pinned down. Did you know that heavy furniture and cabinets can weigh down the floor, preventing it from moving? If a heavy bookcase or island sits atop one end of the floor, the entire floor will only have one direction to expand and contract. The expansion gap may not be wide enough on one side to handle the additional movement and show a gap or create a crowning situation.
Avoid setting furniture or cabinets over 500 pounds directly on top of the floor. Instead, install those items first and build the floor with a gap around them. To see the issues and how to avoid them, watch “Understanding Hardwood Flooring Gaps.” It’s a good overview of the topics we discussed.
Does Your Current Floor Have an Expansion Gap?
Are you having issues with the floorboards lifting or crowning? Chances are there is not enough expansion gap, or it’s pinned down somewhere. The fastest way to check is to remove the baseboard. You can tell if the floor has enough gap or if it’s pinned down.
When it comes time to install a solid oak floating floor, Check out Easiklip, it’s the easiest floating floor to install for DIYers and pros alike. Follow the advice here and leave an expansion gap around the room to keep your floor flat and beautiful for a lifetime.
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