Yes, it is generally safe to have a fire pit on a deck, but you must adhere to building codes and take several safety precautions. For both built-in and freestanding models, you must use a heat-resistant barrier, such as a fire pit pad or heat shield, between the pit and the deck. Additionally, consider the weight of the fire pit and ensure your deck can structurally support it, reinforcing it if necessary. The fire pit must also be positioned a safe distance from your house, particularly from materials like vinyl siding, to prevent heat damage.

The life expectancy of deck boards varies widely based on the material, climate, and maintenance. Untreated wood boards typically last 10 to 30 years with proper care, while pressure-treated boards can last up to 50 years. Hardwoods generally outlast softwoods. Composite boards also tend to last longer than natural wood. Environmental factors like arid or humid climates can shorten a deck's lifespan. To extend the life of wood decking, it's important to consistently clean and seal it to protect against moisture, UV light, and insects.

There are approximately 5.33 board feet in a 2x4. You can use the board foot calculator in this article to easily find the answer. A 2x4 is 2 inches of thickness by 4 inches of width, so you need to find the length, with 8 feet being the most common. You’d use the calculator here to multiply 2 times 4 times 8, and then divide by 12, arriving at a total of 5.33 board feet. 

PVC decking tends to be cooler than composite because the material is less dense and absorbs less heat. However, it depends on the deck’s color. A dark-colored PVC deck may run hotter than a light-colored composite deck. If you’re concerned about your deck getting too hot, it’s best to stick to a light color such as beige or gray.