When you are building or replacing a set of stairs there are many variables involved. Among the many things you may think about is the distance that the tread overhangs. So just how far should a stair tread overhang? We have done the research and have answers for you.
Stair tread overhang, also called a nosing, must be between 3/4 inch and 1 1/4 inches. The majority of the US follows the International Residential Code in their local codes, and the IRC defines this requirement. In some areas, local code allows a 1 1/2 inch overhang. If stair treads are 11 inches or more, they do not require an overhang.
There are requirements on the amount of bevel, the curvature of the nosing, and the allowable difference between steps. We discuss this all in more detail, so please keep reading.
Stair Tread Nosings
A stair tread nosing is the amount of overhang a tread of a step has beyond the face of the riser. Some people refer to this as a lip. All treads less than 11 inches are required to have a nosing.
Most stair treads have a minimum depth of 10 inches, and many builders stay close to this minimum. This means there is a good chance that your stairs require a nosing.
Every state in the US except Wisconsin follows the Internation Residential Code (IRC), as does the District of Columbia. The IRC has a section dedicated to stair treads. It states that a stair tread nosing must project at least 3/4 of an inch and not more than 1 1/4 inches past the face of the riser.
The other requirements for nosings are:
- Curvature on the nosing cannot exceed 9/16 inches.
- A bevel on the front edge cannot exceed 1/2 inch.
- There can be no more than a 3/8 inch difference between any two stair treads within the same stairway.
There appears to be no exact industry standard for nosing overhangs, other than to remain within the required range. We found that many builders say they try to stay near the thickness of the step, meaning a one-inch overhang on a one-inch thick step.
Why Do Stairs Overhang?
There are various thoughts on this. The common reasons given are:
- Protection for the stairs
The visibility argument is that the edge of the step is easier to see for people with poor eyesight if it has an overhang. This can prevent a trip or missed stair while ascending or descending the stairs.
Some people point out that the front edge of a step often receives the most force and stress since many people step directly on the edge. By providing this slight overhang, it can protect the structure of the stairs somewhat.
Space is the most common and best answer we found. Many builders want to minimize the linear space used by a staircase. Because the minimum tread depth is 10 inches, the fact that the nosing overhangs up to 1 1/4 inches may add up to a significant amount of space while still meeting the requirement of 10 inches since two treads essentially overlap in the horizontal plane.
The space answer also often mentions that this bit of extra step allows more room for the foot to sit on the tread. It allows room for the toes when ascending the stairs and the heels when descending the stairs, preventing the toes or heels from too easily contacting the riser. If a heel or toe comes into contact with the riser, the result could be a fall.
Some think the fact that code doesn't require a nosing on stair treads 11 inches or more lends credence to the space argument.
Do Stair Treads Have To Be Rounded?
While the building codes, such as the IRC, specify a maximum bevel, they do not often specify a minimum one. But the bevel can be an important feature in some cases.
A bevel can help protect both the structure of the stair tread, as well as a person walking up or down the stairs. This is because a square edge is more likely to splinter or break off. If the leading edge of the tread breaks off, it could cause a person to fall. At the very least, it would likely require a repair or replacement of stair tread, even if no one falls.
Do You Install Risers Or Treads First?
Most carpenters tend to install the risers before the treads and usually start at the top.
The reason to install a tread after a riser is that you want a good fit at the location where the riser meets the bottom of the tread. By placing the riser first, you can raise it to the same level as the top of the stringer, so that the tread will sit tightly against it.
Then the back of the next tread would sit snugly against that riser, creating a tight fit where those two meet. This allows you to move the riser slightly during installation to make up for variations in the width of the risers or variations in the stringers.
Sometimes people place molding under the tread nosing, which covers any variation in the gap. In those cases, some builders lay the treads first. They then sit the risers directly atop the back edge of the treads. Then they place the molding, which covers any gap that may occur between the top of the riser and the bottom of the tread.
What Is The Best Way To Attach Stair Treads?
There are several ways that are commonly used to attach stairs, but the strongest we found, and the least likely to squeak in the future is a combination of construction adhesive and screws. Using the method below, your stairs should be sturdy and squeak-free for many years.
Pre-drill pilot holes in the treads for at least two screws on each side at the position they sit atop the stringers. Drill a countersink hole at the top of each screw hole.
Use construction adhesive to place glue blocks on the inner side of each stringer where the tread will be placed, making sure the top of the glue blocks aligns with the top of the stringers. Run a bead of construction adhesive atop each stringer, the top of the glue blocks, and along the back edge of the tread.
Place the tread on the stringer, and slide it against the riser.
Give several firm taps with a rubber mallet along the front of the tread to set it into the glue between it and the riser. Now give a few firm taps on the top of each side where it meets the stringer underneath.
Screw through the pilot holes and into the stringers.
If using plugs, add glue into the holes above the screw and tap the plugs into place.
If using wood filler, fill the hole at this time.
Trim the plugs, if used, then sand the plugs or filler until it is smooth with the top of the tread.
If you have access to the backside of the risers, run a screw through the back of the riser, into the back of the tread.
Let the adhesive cure completely before walking on the stairs.
Stair treads need to overhang between 3/4 inch and 1 1/4 inches in most locations. Treads 11 inches or deeper do not require an overhang. You should bevel or round over the front edge of the tread to avoid possible damage to the steps or an injury to someone using them.
Before you go, be sure to check out these other guides that may be of interest to you: