4. What safety features will you need? Unless your deck is built at grade level, you will need to have a railing. There are a few measurements to keep in mind. Limit the space between balusters or horizontal slats to less than 4 inches. This is required by code. Most building codes will allow a railing height to be anywhere from 36 to 42 inches, but keep in mind that a 36-inch-high railing tends to encourage people to hop up and use it as a seat, which defeats the purpose.