This topic is full of land mines. Depending on how bad your floor is, your best bet may be to consult with a structural engineer. This article is intended to provide you with basic information on what to look out for. Because issues can be unique, you should seek out specifically-engineered solutions.

Nobody likes to put money where we can’t see the result. Pulling off decking and exposing floor joists always seems to lead to more expenses; however, remember you are putting a lot of money into your investment. Think of your existing floor joists as a foundation. You need a good base to build on if you don’t want future problems. It will cost a great deal more if you have to fix floor joists after the fact. Focus your attention to the existing floor. Most times you can feel a slanted floor. Is the floor soft in an area? Is there different subflooring in an area? These are all reasons to do more investigating. I am amazed at the attempted solutions our contractors did in the past, and not in a good way. About 75% of the renovations we are involved in need some kind of structural help.

1. The primary issue on the photo below is that the old staircase that was removed and rebuilt without proper structure. I see this one a lot. Look closely and you can see the sag in the floor.
2. Verify that all joists engage the beam pocket properly. Buildings move over time and the joists like to slide out. Your joists will also be angled, which causes bearing issues.
3. Make sure that no joist is substantially cut or broken through. Do-it-yourself plumbers were quick to cut floor joist notches so they can easily run their piping. The only cut made was to accommodate a 1/2” conduit. This isn’t a major issue if the joists are good otherwise.
4. Check all your bridging between joists. They like to twist when stressed. The bridging prevents this from happening. Notice two rows in a 20’ wide building.