Easy Tip to Reinforce Floor Joists that Sag

LESLIE: Wendy in Florida is on the line with a question about how to reinforce floor joists that sag in her home. How can we help you?

WENDY: Yes. I’m restoring an old house. It’s about 100 years old. And we had to take up the kitchen floor. And we’ve taken – there’s layers of plywood and whatnot. And in order to get through it and get the rot out, whatever was gone down to the beams underneath the floor – now, the beams are 4×4 and they’re on 28 inches on center. And so I’m wondering – this needs more support and I’m wondering, can we put – instead of putting beams down in between the two so they’re parallel, can we put perpendicular ties across from those two and create boxes to support the floor?

TOM: Can you get underneath the existing floor joists?

WENDY: Well, it’s called “above grade.” And so there’s not that much space. You can get under there. It’s about to my side – to the ground.

TOM: Yep. So here’s the thing: you can’t change the direction of the beams because they usually go front to back for a reason. Typically, there’s a girder in the middle of the structure – the middle of the building somewhere. But if you want to But if you want to reinforce floor joists and support those beams because they’re sagging a bit, what you could do is you could put beams perpendicular to those underneath them. But those, of course, would have to be supported, as well. So I think your options are to put additional beams in in between this big, wide 28-inch gap or to put beams perpendicular underneath.

But if you put them underneath and you still have this wide gap, the other problem you’re going to have is supporting the plywood now or whatever you’re going to need for that. So, in that case, you would have to put some perpendicular spacers in between the beams but those are not – they don’t have any structural value. All that’s going to do is going to give you some additional surface to support whatever kind of floor you put on top of it. Does that make sense?

WENDY: OK. That answers my question.

TOM: Alright, Wendy. Good luck with that project.