How to Replace Floor Joists – #StepbyStepGuide

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Is your flooring squeaking again? Do you feel uncomfortable walking over it? These might be signs of damaged floor joists. If you feel the floor is not providing a ‘give’ while you walk over it, it is about time you get the joists removed or repaired.

Removing and replacing floor joists is pretty difficult if you have no expertise in this field. It is way better to call up a professional who will do it for you. But that is not what you have come here for, right? In this article, we will show you an easy method on how to replace floor joists. We will also be mentioning the signs and red flags you need to be aware of to save your precious flooring in the future.

What are Floor Joists?

Floor joists are long structures made of timber that is mainly used for supporting the flooring that you walk on. It can also be used as the ceiling for the first story of a two-story building or apartment. They are usually used when the architecture has no plans on placing columns or beams in the center of the room.

Floor joists span the entire length of the house and are placed vertically to absorb more pressure from the floor. They are fairly inexpensive ranging from $2 to $3 for every lineal foot.

how to replace floor joists in an old house

How to Check Whether Your Flooring has Joist Problems

There are many easy and hassle-free methods you can choose from the list down below to check whether your floor joists require replacement or not. You might need a few extra tools but do not worry, we are providing you with the list of tools you need.

Use a stud finder:

how to fix floor joists

This is the fastest way to locate a joist. Turn on the device and start from one corner of the room to the adjacent one. The device will start beeping when it finds the end of the joist. Mark the places where the joists end. Slowly move towards the adjacent corner in one direction. Repeat this process until you cover the entire floor. Wherever you find a random beep, mark that spot.

Use a mallet hammer:

how to fix floor joists sagging

Use a mallet hammer and hit the floor. Start from one edge of the floor and move towards the opposite one. If there is a joist, you will hear a sound similar to ‘thud’. This sound will be hoarse and will have a more ‘solid’ response to your action. When you hit a part of the flooring and receive a shallow rather empty voice, this means there is a weak joist or no joist at all under that area. Repeat the entire process and mark out places you have received a shallow response.

Use ice cubes or any rolling item:

How to replace rotten joists and flooring

Take an ice cube and let it start melting for a few seconds. Then, place the ice cube on the floor and give it a gentle push. The word ‘gentle’ is the keyword. If the ice cube accelerates to the opposite side of the room then it’s probably because of a slant in the floor caused by uneven joists. If the ice cube stops midway, take a stud finder and check for any beeps between the starting and the stopping point of the ice cube. If your floors are too sensitive to the water, opting for this method could damage your flooring. Instead of ice cubes, you can use a small marble ball or a pearl to perform the same activity.

Call a carpenter or a professional:

Doing this might save you time. Carpenters and flooring experts can tell you the exact location of the joist and also suggest effective ways of repairing or replacing them. It might be a little tough on your pockets but it is worth the time and effort you will be spending on your knees, thudding your way, covering the entire floor.

Replacing the Floor Joists

You need to reconsider your decision of replacing the joists on your own. Numerous flooring agencies will do it for you, not to mention, without any mistakes. Expect these professionals to ask a sum of $100 to $150 for a joist replacement. For sloping or sagging floor repairs, an average of $5500 is paid. The rates may vary depending on the floor plan and the complexity of the previous joists.

Before getting all worked up, make sure you have good lighting. Collect all the tools we have mentioned later in this article so that you don’t go searching for them in the middle of the repair. Make sure you have your eye protection glasses and rubber gloves on. It is advisable to wear rubber footwear so that you don’t step over bent nails and wood shavings.

Tools you will need:

  • Saw
  • New pack of joists
  • Crowbar or a pry bar
  • Construction adhesive
  • Screwdriver
  • Coach bolts (200mm)
  • Wood preservatives
  • Cable ties
  • Wood screws (60mm)
  • Rubble bags
  • Timber planks

Steps to follow:

  1. Expose the subfloor and then the joists. You could use a crowbar or a pry bar to do so. After you finally see the joists, trace out the rotten or damaged parts. If they look alright, try pushing each joist with your foot to see whether they are weak.
  2. Take a screwdriver and start poking the damaged area to know exactly how much woof to get rid of. Mark the weak area and use the saw to cut the rotten parts out. Let the stronger parts of the joist remain where they are. These will act as guides to add new joists.
  3. Apply wood preservatives all over the new and old joists that are going to be part of the flooring. Wrap the new joist in rubble bags and align it to the old but strong joists.
  4. To keep the new joist in place, you will need two planks of the same width as that of the joists. Use these two planks and sandwich the joist between them.
  5. To hold the entire setup, the drill coach bolts right through the three layers of wood. Coach bolts are enough to secure all three planks.
  6. Repeat this process for all the weak and damaged joists.
  7. Cut yourself some new subflooring and the actual flooring. Take into consideration the pipes that pass through them and drill holes and gaps accordingly.
  8. Coat the new floorings with a few layers of wood preservative and keep it under the Sun for an hour or two.
  9. To place the subflooring perfectly down, drill two small holes on two opposite sides and connect cable ties through them. This will help you carry the flooring and place it down the gap without hurting your fingers.
  10. Screw down the subflooring and the main flooring to finally cover and secure the, now much stronger, joists. Do so by using 60mm long wood screws and screw them 150mm apart.

Advantages of a Strong Floor Joist

Floor joists can be modified on site. This means that a damaged portion of the joist can be sawed out and a new portion, of the same length, can be bolted into the old one. Even when it comes to increasing the span of the joist, the same method can be used. Hence, it saves you the time, effort, and money to get rid of and reinstall an entire joist.

If compared to floor trusses, floor joists are significantly cheaper. Since repairing a joist is like fixing a puzzle, you or the professionals can get the job done in a day or maximum, take up to three days. The repair doesn’t require any design planning as such either.

When it comes to fire safety, a joist is always preferred as it is made of lumber. Lumber takes time to burn, which helps firemen enter the house and have enough time to rescue family members.

The Old Way of Connecting a Joist to a Ledger

The old way connection was to cut an L-shaped slit at the ends of the joist as shown in the picture below and fix that to the ledger. In this method, the slit part of the joist would hang on to a notch in the ledger.

 how to repair floor joists with water damage

When there is too much pressure in the middle of the joist, the ledger pushes the joist, which causes a crack on the joist.

how to replace floor joists and subfloor

The Modern Way of Connecting a Joist to a Ledger

To avoid such cracks, modern techniques promote using metal joist hangers. This hanger fits right around the joist and holds it right in place. All you have to do now is screw the hanger to the ledger and you are good to go.

how to replace floor joist from the basement


Replacing floor joists is not that hard but it is better if you ask a professional to do it for you. We hope this article helped you gain some knowledge about the physics that lies behind replacing a floor joist.

Make sure you take all the required precautions and then begin your work. All the tools must be safely dealt with. Do not keep sharp objects like the blades of a saw lying on the ground. Remember to measure correctly before you actually cut a piece of a joist.

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