Accidentally Cut Floor Joist – What To Do?

If you are working on a floor joist and accidentally cut it, you may be wondering how to get it fixed. Fortunately, we have done the legwork on researching this topic for you, and here is what we found.

The following are what to do if you accidentally cut your floor joist:

  • Replace all common nails.
  • Change the entire floor joists. 
  • Support the joist weight with a metal plate.
  • Support joist weight with angle iron.
  • Cut wood beams and nail them together. 

You can fix a floor joist that has been cut without the help of a professional. Keep reading to get detailed information on how to fix an already-cut floor joist.

House framing floor construction showing massive solid wood joists trusses - Accidentally Cut Floor Joist - What To Do

What Should I Do If I Accidentally Cut My Floor Joists?

Floor Beam ConstructionConstruction Lightbox - Accidentally Cut Floor Joist - What To Do

A floor joist, also called a floor beam, is a horizontal structure mainly used to frame floors during construction. They are important in construction as it helps to support the floor weight.

In a situation where you cut the joists, below are things you can do to get it fixed. However, you can call a professional to help you out if you cannot do it by yourself. 

Replace All Common Nails

If you have the right materials and tools, you will find it easy to fix floor joists that were mistakenly cut off. The first thing to do is to get rid of all the nails around the joists. This is to let you replace the joists with a new one. 

Change The Entire Floor Joists

This is another method for fixing an already cut floor joist. In a situation where no extra floor joist can be used to replace the section that was accidentally cut off, you will have to change the entire joist.

You can do this by nailing a new joist beside the initial one. Also, you can utilize OSB boards or plywood in replacing your floor joists.

Support The Joist Weight With A Metal Plate

If you are the type that likes working with materials and tools, you can use metal plates as a support to the weight of the cut-off joist. 

Support The Joist Weight With An Angle Iron

This is similar to using a steel plate with just a little difference. To make use of this, you will be required to cut two pieces of equal-length angle iron and then use bolts, washers, or nuts to secure them. 

Once this has been done, the angle irons will be around the cut floor joists, so they can serve as alternative support.

Cut Wood Beams And Nail Them Together

If you find yourself in a situation whereby you need to support the floor joists but there is no alternative support, here is what you can do. 

First, cut two pieces of wood beams and ensure they have equal joist depth and length. Then, nail the two beams together to fit the cut floor joists. 

What Are The Things To Do Before Replacing Floor Joist?

close up view of a joist truss bracket

There are some things to do before replacing your floor joist. This is to help reduce potential problems that may occur in the long run. They include the following:


Before doing any renovation, you should first let a professional inspect the joists for potential termite or pest infestation, water leaks, or mold damage. 

This step is very crucial because any replacement done without inspection will lead to further damage and this will bring you back to the current situation. So, before working on your floor joist, do all the necessary inspections to have good flooring. 

Choose The Right Lumber Size

Another thing to do before replacing the floor joist is to choose the correct size. The dimension varies, meaning you must measure the floor joists before changing them. You can also hire a professional to assess the correct size that your floor joist should be. 

Choose The Right Lumber

Choosing the ideal type of lumber for your home can also determine the weight and strength of your joist.

Some lumber is bigger than others, and that may be a result of their growth speed. Normally, when a tree grows slower, it is expected to have a thick trunk and stronger lumber. 

Estimate The Joists' Weight

This is simple but you need to consider a few things. You should consider the room where the joists will be installed.

Generally, the pressure applied on rooms and bedrooms with more traffic is different, so choosing the right joist for your room is essential. 

How Much Does It Cost To Replace Floor Joists?

Floor Construction

If you have a damaged floor joist, you can replace it. The replacement cost of a floor joist is determined per square foot. The cost of labor is usually around $65-$100.

Plywood subfloor will cost you $2-$10 per square foot. Sistering or joining old joints with new joints is around $100-$300 per floor joist. Meanwhile, repairing the floorboard costs $3-$5 per square foot. 

How Can Floor Joist Be Reinforced?

The following are several ways to reinforce floor joists:

  • Sistering: This involves permanently attaching a piece of lumber to both sides of an existing joint.
  • Blocking: This is when a piece of wood is installed between two-floor joists at an angle of 90° to provide alternative support in case one or two members need reinforcement. 
  • Bridging: Relatively similar to blocking, but instead of perpendicular blocks, bridges are a grid-like reinforcement and you can use steel or metal. 

How Much Weight Can A Floor Joists Carry?

The floor joists should be able to render support for a minimum of 40 pounds of load per square foot. However, you will be required to reduce the joist's span to 11 feet by 11 inches.

This is so it can safely support the heavy weight when using the 50 pounds per square foot load by 10 pounds per square foot load. Note that if too much pressure is placed on a joist from the main floor, it can move.

Why Do Floor Joists Crack?

Your floor is expected to be smooth and not meant to have ridges. When you notice any sign of uneven flooring, you may want to know what caused them.

The floor joists crack because they support the floor cover, subfloor, furniture, and other appliances that subject it to great stress. Some floor joists may crack under that stress while others may even be weakened during installation.

Floor joists can get cracked for different reasons. This can happen at the area where the bolts are located. 

Some joist holds more weight than other joists because their installation is slightly higher. A slightly bowed joist may give more support.

How Long Do Floor Joists Last?

Floor joists can last for more than 100 years. You can keep using them until your home is old as long as there are no signs of cracks, termites, or molds. However, floor joists can rot under certain conditions.

You can use your floor joists for a long time. All you have to do is to maintain a dry and stable environment. Condensation, pipe leaks, moisture, and termites can shorten your joist's life. 

You can make floor joists stronger so they can last longer. All you have to do is block the joists. You can do this by nailing lumber in between.

Are Floor Joists Structural?

House framing floor construction showing massive solid wood joists trusses

Yes, they are a structural element that can span into an open space, mostly between beams, before transferring the loads to another structural element. 

If you are worried about your home's structural integrity, don't hesitate to call an engineer to inspect it.

To Wrap Up

If you accidentally cut your floor joist, all you have to do is change all common nails or the entire floor joists. Alternatively, you can support the joist weight with a metal plate or angle iron. You can also
cut wood beams and nail them together.

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