Can Decking Sit in the Ground?

Ground-Level Decks

• The term "ground-level deck" can be misleading because it implies that your finished deck will sit flush with the ground. This isn't the case. All decks require a frame and support system. The frame and support system adds height to the finished deck. A deck should not sit directly on top of the soil, as this will cause wood rot in short time.

  Each corner of your deck frame must have a support post that is secured in the ground. The support posts are the only part of your finished deck that should come into direct contact with the soil. Consider anchoring your support posts in concrete footings for additional stability and decay protection.

Connected Decks

• If you plan to connect your deck to your home directly beneath an exterior door, you must install the deck at the proper height to ensure that you have enough clearance between the doorsill and the decking material.

  Calculate the height of the finished deck before beginning the project. Take the type of support posts you're using and the height of your frame into consideration when making your calculations. You will likely need to excavate soil from your yard in order to fit the decking, frame and supports beneath the doorsill.

Wood Selection

• Ground-level decks are closer to the soil than elevated decks and, as such, are exposed to a higher degree of moisture. Prevent moisture damage and wood rot by purchasing pressure-treated lumber specifically rated for ground contact.

  While pressure-treated lumber stands up to the elements better than untreated lumber does, it limits your decking options. Redwood and cedar, for example, are not available in pressure-treated lumber.

Protecting Your Deck

• Pressure-treated lumber does not grant a ground-level deck absolute protection. If your deck does not have adequate ventilation, moisture levels beneath the deck will likely increase, resulting in mold growth. Reduce the odds of your deck developing a mold problem by leaving small open spaces in the deck frame for proper airflow. Installing flashing around areas where your deck connects to the house and laying gravel beneath the deck's frame will also help redirect water and prevent moisture buildup.