Why Do Deck Floors Have Gaps?

Decks are a common structure outside of homes as they provide space to enjoy the outdoors and spend time with friends and family. While you are on a deck, you may notice that deck floors have gaps between every single floorboard. These gaps are not just a design choice, but they serve several purposes from durability to safety and functionality. This article will cover why deck floors have gaps.

Deck floor gaps

Water Drainage

The biggest reason for leaving gaps between deck boards is to allow for water drainage. Decks here in the Upper Midwest are exposed to rain, snow, humidity, and temperatures ranging from extreme cold to extreme heat. Without gaps, water would accumulate on the surface, leading to pooling, which could cause moisture to soak into the deck's floor and joists over time. This moisture can cause wood to warp, rot, or develop mold and mildew.. The gaps between the boards allow rainwater to flow freely through the deck.

Proper drainage helps to protect the floorboards, but it also protects the underlying structure of the deck, mostly the joists. When moisture is trapped under the surface of a deck, it will rot the surface of the joists. What we hear from our carpentry team is that most floorboards that are rotten are sitting on top of rotten joists. Our team applied wood hardener compound and joist tape to remedy further damage, as full replacement is often unnecessary at the time and extremely expensive.

Airflow

In addition to helping with water drainage, the gaps between deck boards also create airflow. Proper airflow underneath the deck prevents moisture from becoming trapped. This airflow helps keep the wooden boards dry and reduces the risk of decay, which is especially important for wood decks. Without adequate ventilation, decks are more susceptible to the growth of mold and mildew, which can degrade both the appearance and strength of the deck.

For proper airflow, we advise minimizing any sort of covering that is done around the base of the deck. Lattices are an acceptable option for airflow while still preventing animals from getting into the area beneath the deck.

Improper airflow is exceptionally common on decks built too close to the ground. This is why decks are commonly built off the ground by a few feet. A patio is a better option for homes that are close to the ground, as poor airflow is a common reason for premature stain failure.

Coverings such as this can cause ventilation issues

Expansion and Contraction

Wood is a porous material that expands and contracts to humidity and temperature changes. Deck boards must be installed tightly to allow for shrinkage if the wood is freshly milled or treated. This allows for contraction as the board dries out. When dry deck boards are installed too tightly, they have no room to expand during hot, humid weather. If installed too far apart, they leave large gaps as they shrink when the weather turns cold. This can cause the boards to buckle, crack, or even become misaligned. The gaps between the boards provide space for wood to expand and contract naturally, helping to prevent warping and other damage.

Composite decking materials are less prone to shrinking or swelling. Composite will still benefit from the gaps, although gaps will be more of an aesthetic concern as far as size goes. These gaps ensure that the material remains stable and doesn’t experience pressure from its surroundings.

Looks

To add to the functional reasons, gaps between deck boards can also contribute to the visual appeal of a deck. The uniform spacing creates a clean, organized look that is visually appealing. Some deck designs may incorporate wider gaps for a more rustic or relaxed appearance. Smaller gaps can be appealing, but run the risk of buckling. The gap size can be adjusted based on the type of material used, as hardwoods with a tighter grain structure may expand less rapidly than looser-grained pine or fir, which are the most common woods used in deck construction. Read more about hardwood Ipe decking here. 

If you are looking for a deck-staining professional in Wisconsin, Illinois, Iowa, or Minnesota, please contact EcoWash today.