It’s Tricky. But It’s Doable - Changing joist out

It’s been a while since I’ve changed a joist out.

My first ever project when I became a carpenter, was to help switch out joist to a house whose previous had completely rotted.

The entire floor system was removed. The easiest way to accomplish, but the most invasive to the entire structure. With all parts are damaged, it was the only way to go. But on occasion, if the joist are the only issue, the work requires more delicate hands.

A temporary wall was built to support the perpendicular joist, that attached to a double joist. This double joist continued out to cantilever the chimney being repaired.

Before removing the joist, it is best to add bracing.

Since this is a cantilever chimney with additional perpendicular joist, temp walls and diagonal braces to the chimney structure where added. Weight distribution is a big conversation in itself. The best advice for this, is if a blade pinches or a sledgehammer is needed to make a framing member move, then pull back and reevaluate the situation.

Contrary to mainstream media, sledgehammers are a last resort. That when used on structural members, result in huge, potentially dangerous, changes that follow.

Oscillating Multi Tool cutting the nails holding the subfloor to the joist. A very important tool for precision demo work, as well as working in tight spaces.

On to removing the older joists.

Depending on the floor above, you can remove one or two joist at a time. It is best to lean toward one joist, but with the hardwood floors tying the subfloor together, I am given the opportunity to remove two joist.

The removal process, involves a circular saw ripping down the length twice. This does not need to be pretty. The goal is to create a wide gap, to release pressure created between the bottom and top of the joist.

An OMT (Osculating Multi Tool) will be your friend to join or continue any cuts. You can try using a reciprocating saw, but it can be more difficult in the small spaces, and the blade has less control.

A savior block is placed between the sill plate and subfloor. Cut at the exact length as the joist width, this helps support the loose structure below to protect the worker below.

In this situation, I include a ‘Savior Block’.

This can be a stack of 6x6 laid on edge on top of one another, or a scrap post stood up. The point of the Savior Block is to stop anything above from coming down on you. The trick is to cut the block to match the joist length, or stack enough blocks so that there is only a 1/8” to 1/4” of drop with the structure above.

Backside of a chisel used between joist and subfloor. This helps to break the bond created by adhesive and provide a space to run the oscillating multi tool to cuts fasteners.

After removing the lower part of the joist, focus is switched to the remaining. With most subfloors today, you can expect everything to be glued, screwed, and nailed. Luckily in my favor, these floors were just glued and screwed.

Construction adhesive dries extremely hard. This is great for bonding material together to create one solid piece. But that bond can be hard to initially break.

The trick is to hammer in the flat end of a chisel to break the bond, and create a little recess to run the OMT for cutting fasteners.

If using the OMT to cut the glue, the heat created by the blade will cause the materials to re-adhere. While the adhesion is weaker, the work is extended.

Additionally, OMT blades can cut screws. It is significantly slower than a nail. Due to nails being made of a soft steel, where screws are made of a hard steel. If screws are present, a flexible metal cutting blade on a reciprocating saw may be ideal.

Entire process of removing a rotted floor joist.

If prying is required, I would be gentle to not cause the flooring system above to flex to wildly. This may cause buckling, which will loosen the flooring above from the subfloor.

In all, safety should be the highest priority when tackling a project such as this.

If at any point, you feel a rise in concern, then step back and reassess the process. And if it is beyond your capabilities, reach out to an experienced carpenter, who can walk you through the process or do the project for you.