Fixing Bad Floor Joist During a Remodel

Its time to finally remodel that failing bathroom with the 50 year old tub and toilet.

Replacing floor joist in old bathroom. We sistered one next to the old one and added another for support of the tub.

As I frequently see and warn my clients about prior to demolition, we may run into a few bad floor joist as we demo out the bathroom. I thought I would give a few tips to dealing with this situation. Commonly, the floor joist tend to rot out around the tub from years of water seeping through the floor. The toilet can also cause this. I have seen it in rare cases where the foundation has even shifted down from bad leaks.

So once the old floor is up and the joist are exposed you will need to sister in or replace the old joist with a new joist to stabilize and reinforce the new floor. Sistering means installing a new joist next to the old one and nailing them together. You will want to run it from one end of the room to the other, ideally on top of the main beams of the house. You may have to shim the board up or rip it down to fit with the old joist. Play attention to leveling all the joist up to each other using a 4 foot level. Once these are in place and nailed up you are ready to install the sub floor decking. I prefer using treated lumber in wet area because of its resilience. Also consider adding more joists near the tub, I prefer 3 at minimum. You should also block in around the toilet to give it plenty of support and give you something to screw the flange into.

Decking is going down

Toilet Blocking

Sistered joist and new joist on left side

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