Using Composite Decking for Stairs to Get That Indoor Stair Look

Composite Decking for Stairs

Composite decking for stairs is a good way to keep your outdoor stairs as safe and attractive as those inside.

One of my first construction projects was my uncle’s deck, and I vividly recall him saying “good enough for government work!” upon the completion of the stairs. I also vividly recall an endless series of stubbed toes, pratfalls, and trays of food sent flying across said deck throughout my teenage years. It wasn’t until I got some professional experience working under a master carpenter years later that I realized that the two were related, and how completely my uncle had screwed up.

Stairs are one of the most important parts of any structure, and they’re also one of the easiest to make a mistake on. Every rise (vertical height) and run (horizontal dimension) needs to be consistent in order to prevent falls, and an uneven surface on the tread can cause a stumble. My uncle got lucky. His eagerness to call it a day never caused anyone permanent harm. But it easily could have been a tragedy, and when building a deck, it’s important to design, build, and inspect the stairs with safety in mind, whether you’re using wood or composite decking for stairs.

Building Deck Stairs: The Basics

Odds are that at some point during your day you climbed a set of stairs without thinking too much about climbing them, or about what it took to build them. That’s because those stairs were constructed with care and skill. The truth is that stairs are fundamentally hard for humans to navigate, and there has been an extraordinary amount of research into making stairs safer. Even so, stairs are one of the biggest sources of injury in or outside of a home. It takes planning, foresight, and skill to build a set of stairs that aren’t an injury factory.

The challenge is dividing up the vertical and horizontal space between two heights evenly while accounting for the dimensions of the pieces you’ll be using. The relevant pieces of a set of stairs are:

  • Stringers: These are the diagonal pieces of wood that support the stairs on either side. Usually, they are 2×8 to 2×12 pieces of lumber with right angle notches cut out of them. The spacing between stringers is usually 12 inches from center to center.
  • Treads: This is the horizontal piece of the stairway that you step on. These need to be at least a minimum of ten inches in width to provide secure footing, and at least an inch thick to support the weight of someone standing on them.
  • Risers (also known as kick plates): These are the vertical elements that go in between each tread. They’re not strictly required when building stairs outdoors, but they give stairs a nice finished look and can prevent falls by keeping feet from sliding beneath the treads. If used they need to be at least a half inch in thickness.

Risers are not to be confused with the rise, which is the measure of the vertical distance between the surface of each tread. In the U.S., the rise can be no greater than seven and three-quarters of an inch. The first step in building a stairway is to measure the distance between the horizontal surfaces you need to climb, and then divide by eight to get the number of steps needed. This is because when you add in the tread’s thickness of at least an inch, it will be below the maximum rise height. If it isn’t, you simply add another step to the total and start your calculations from there. The horizontal space is more flexible, and you can expand the horizontal space to get above the ten inches minimum of the tread. All of this is necessary in order to ensure safety and is usually such a pain to do in the field that when possible I buy pre-cut stringers and adjust the total height of the project around the prefabricated stairs.

My uncle performed all of these steps, found out that he made a math error after cutting the stringers, then shrugged and carried on. This is tempting after a long day of construction, but not something that you can afford to do if you want to keep your family safe and building inspectors happy (inspectors generally pay special attention to stairs before signing off on a project). Unfortunately, there is no amount of attention and care that can keep stairs absolutely safe as they age.

Typical Problems with Wooden Steps

As wooden boards age, they are prone to mold and mildew. This can easily become a slipping hazard when the wood gets wet. Also, over time, wooden boards are prone to shrink, warp, and otherwise change their dimensions. This can lead to trip hazards like the edge of a board twisting up to catch an unwary toe as it rises. And as the wood’s dimensions shift, fasteners like nails, screws, and bolts can start to come loose, worsening the problem with uneven boards and resulting in boards that are no longer securely fixed to the deck. On the deck’s surface, a loose board is an annoyance, but on a deck’s stairs, a loose board is a safety hazard. Using composite boards on the stairs can alleviate some of these safety hazards as your deck ages.

What to Look for in Composite Decking for Stairs

Composite decking is a combination of synthetic materials like plastic and organic materials like wood or bamboo flour. Due to its synthetic components, composite decking isn’t as prone to rot as wood is, and due to it not being a totally edible surface, composite decking doesn’t mold or mildew in the way that wood often does. There are also fewer paths for water intrusion in a composite board (especially bamboo-based composite), and if the board is fully capped then the decking is even more moisture resistant. Composite boards aren’t a perfect solution though, and there can be some drawbacks especially if composites of a lesser quality are used.

First generation composites weren’t very rigid, and required a lot of bracing underneath to create a walking surface that didn’t flex underfoot. This is carried over in current lower quality composites, which often only have caps on the upper side of the board, leaving the underside vulnerable to moisture penetration. Often, these lower quality composite boards are of an insufficient width to create a stair tread out of a single board, which requires more math, cutting, and work during the construction of stairs, and involves another edge that can be tripped over.

All of these concerns can be addressed by using a quality composite decking system. A few characteristics will help you pick a high-quality composite board. Look for:

  • Rigid boards that don’t require extra support to avoid sagging. The key thing to look for when building stairs is stringer spacing that maintains the 12-inch centerline separation for installation on stairs.
  • Specialized tread boards that are at least 12 inches deep and at least an inch in thickness so that only one board can be used for each tread, creating a clean look and easier installation. Keep in mind that boards that are wider than 12 inches but are less than an inch in thickness are actually fascia boards, and can’t be used as treads because they won’t support the weight of someone standing on them. They can be used as risers or kickplates, however.
  • Capping that surrounds the board and protects the entire thing from moisture intrusion. Some capping is hard and slippery, so for maximum safety choose composite decking that uses a rubbery, slip-resistant capping material.

Stairs built out of quality composites that have these characteristics will be safer to climb as your deck ages. They’ll also look better, too, with a sleek, integrated appearance you usually only find in indoor stairways.

One composite decking system that meets all these standards is Fortress Deck’s Infinity line of composites. It is fully capped, comes dual-sided–with both rustic and exotic hardwood textures on either side of each board–and it provides boards specially designed for use as treads in a choice of colors, from the homey hue of pine to the silvery tones of reclaimed hardwood. I’ve also used other products made by Fortress Building Products, and can recommend their railings and fences, which, like their decking, can transform an entire home and last for years while staying in great condition.

Leave a Comment

You must be logged in to post a comment.