Can Joists be Notched? -2021 Code
DIY repairs and remodeling are more popular than ever. You can find a how to video for just about any task you want to handle in your home. While I strongly encourage everyone to become proficient in home repairs, you obviously don’t want to compromise the structural integrity of your home. That would definitely offset any savings from doing the work yourself.
Still, many people do end up going overboard. A homeowner and a sawzall are not always a good mix. If you are going to be working around floor joists, or ceiling joists, it is important to understand what your limits are. If you exceed the limits, you may reduce the strength of the joist to the point where it can support the floors weight and the live load.
For example, if you’re adding a bathroom, and you have a solid run of pipe through an existing joist, you need to make sure its in a permitted area, or the right diameter. You don’t want to cause wobbly floors, or structural damage.
First, there are two main types of joists – solid-lumber joist and engineered joists.
A solid lumber joist is the most common type of joist. Its your standard 2x wood that find at any Lowe’s or Home Depot.
Engineered joists also known as I-joists are light weight structural members that address many of the issues with traditional joists. They are a top flange and bottom flange with a sheet of plywood in the middle.
What is the difference between a joist and a beam?
If you’re an amateur, beams and joists can look the same, but they have different functions. Beams carry and distribute the buildings main loads down the columns, the foundation walls, and to the footers. Joists are horizontal support members for large flat surfaces such as floors. Joists are supported by beams.
What are the limit for cutting, drilling, and notching joists?
The diagram can be confusing at first.
The maximum depth of a notch in a joist is one-sixth of the joist depth. A notch is a cut on the top, or bottom of the joist. This is represented by “D/6 Max”. When determining the depth of a joist, you use the actual size of the joist, not the nominal size. For example, a 2×8 is actually 1.5″ x 7.25″. The maximum notch depth for a 2×8 then would be 1.2″
The maximum length of notches is different – its one-third of the joist depth. This represented by “D/3 Max”. Using the same 2×8 joist the maximum length of a notch would be 2.41 inches.
There are exceptions though. There are always exceptions.
At the end of a joist, the maximum depth of a notch is one-fourth of the joist depth. This is represented by “D/4 Max”. If you are cutting the corner of a 2×8 joist, the maximum depth of the notch would be 1.81 inches. This is common when the bearing point of the joist is a ledger strip.
And last but not least, no notches are allowed in the middle third of the span. Notches can only be made on the outer third of a joist. For example, on a 12 foot joist you can notch four feet from either end. No notches are allowed in the middle four feet.
Drilling has its on its rules
The maximum allowable diameter of a hole can not exceed one-third the depth of the joist. The maximum hole size then for a 2×12, which has actual depth of 11.25, is 3.75 inches. Drilling of joists can not occur within 2 inches of the top, or bottom edges of the joist. The edge of the hole can not be closer than 2 inches to a notch, or another hole.
Engineered Joists are Different.
Engineered joists are designed by…a structural engineer. Every manufacturer has difference requirements and allowances. You will need to consult the manufacturer’s instructions. I-joists generally can have much larger diameter of holes. However, you can not notch I-joists. You can not alter the top. or bottom member in any way.
These Rules Do not apply to Studs
Remember, joists are the horizontal beams that support your indoor floors. Studs are the vertical members in the walls. Studs have their own drilling and notching requirements that we will cover in another blog.
Don’t try to remember any of this.
Unless you’re in home construction , and even then, this can get really confusing. Is the maximum notch depth one-quarter of the joist depth, or was that just at the very end of the joist? Is it d/6 or d/3? A good practice ie to always refer to the diagram, or code. If you try to memorize it, you will eventually end up with some sister joists , which are additional joists installed next to compromised joists.