Q: Why would I buy rails when I could use 2x4s? How do the 2x4s keep from falling out? A: The recommended type of guardrails is our metal rails. They go through the loop on the post furthest from you, and snap directly on the near post. While it may seem cheaper to use 2x4s, our galvanized guardrails have a much longer life span and may be re-used time and time again. 2x4s will more than likely only last for a few uses and could be used up in the construction of the roof. To keep 2x4s from slipping, you may install a nail conjoining them together, but this is not necessary. Also, when using 2x4s for rails you must use Douglas Fir #1 or equivalent only. Failure to use approved materials could result in injury, death, or OSHA fines.