Understanding the Difference in Railing Post Lengths

Hello, everyone! Today, we are diving into a question we recently received through our website regarding Westbury Aluminum railing posts. A homeowner asked, “I am having a contractor build a deck with a Westbury Aluminum railing. The railing includes both post kits straight and post kit stairs. These are both 2×2 posts. Straight kits are 37″ long and stair kits are 47″ long. Why are the stair posts longer? Thank you.”

Understanding the variation in lengths between straight and stair railing posts is essential for ensuring the safety and structural integrity of your deck. Let’s delve into the reasons behind the differences between level (straight) and stair posts.

1. Dealing with Level Sections vs. Stair Sections

When installing railing on level areas of your deck, the height of the post typically needs to be slightly taller than the railing itself. This marginal difference, ranging from 1 to 2 inches, accommodates variations in railing materials, such as aluminum or vinyl.

However, stairs introduce a new challenge. With each step, there is a drop-off from one tread to the next, necessitating longer posts to maintain the required railing height and structural stability.

2. Stair Design Differences

Stairs vary in design with differences in the angle of ascent, rise, and run. A standard stair might feature a seven-inch rise with an eleven-inch run for each step. When positioning a post in the middle of a stair run or at the bottom landing, where there is a significant drop, longer posts become imperative to maintain the level height.

3. Height Measurement and Jurisdiction Requirements

The height of the railing on stairs is typically measured from the front edge, or nose, of the step vertically up to the top of the railing. Regulations often stipulate a minimum railing height, commonly 36 inches (always check with your local building code). However, when factoring in the drop between steps, additional post height is necessary to maintain compliance.

4. Visualizing the Height Differential

To better understand this concept, let’s examine a scenario at the bottom of the stairs. While the railing measures 36 inches when crossing the front edge of the tread, the post mounted on the next step down must extend to 40 inches in height to accommodate the drop-off and maintain the 36-inch railing height.

Similarly, at the top of the stairs, where the railing transitions from level to stair railing, a post might be situated further back from the edge of the deck. Here, the railing height continues to rise until it intersects with the post, resulting in a total height slightly over 37 inches.


The difference in post lengths between straight and stair railing kits is a practical consideration rooted in safety and regulatory compliance. By understanding the stair design and railing height requirements, you can ensure that your deck railing not only looks great but also provides the necessary protection for you and your loved ones.

Thank you for reading and stay tuned for more valuable insights from our Product Manager!