All your sagging floor needs is a little support
Floors don’t typically have dips or slants, so when they do, it can be a bit disconcerting. If left unfixed, you’re looking at a slippery slope, including the potential for further foundation damage. But, with the right tools, steps, and know-how, you can tackle this repair yourself—here’s how.
Before you dive into your pick-me-up project of fixing your sagging floors, it’s a good idea to figure out why your foundation is sagging and if you should consider other foundation-repairing methods. Damaged floor joists are one of the most common causes of sagging floors, and knowing how they’re damaged can help you develop the best game plan for your project.
Is your floor sagging above a basement or crawl space? If it is, check your wooden support posts. Look at where these posts meet the floor. Using a screwdriver, poke the wood or try pushing through it. If it feels mushy or seems rotten, this is likely where the problem starts.
Damaged floor joists (these are the wooden beams that run horizontally underneath your floors) usually mean sagging floors. If they’re damaged, that could mean they’re cracked, rotten, or cut. When adding wiring, pipes, or HVAC ducts, floor joists can sometimes be cut improperly during installation.
Does it seem like condensation is always lurking on your walls or even your floors? Excess moisture is harmful to your home, and a build-up could cause rot to grow on your joists. If moisture is the main culprit of the damage, you’ll have to tackle that problem while also fixing your sagging floors. With moisture in your crawl space, you may also need to consider crawl space encapsulation costs to keep the area clean and dry.
Your uneven floors need to be leveled, and to make the floor level, you’ll need to lift it. At this stage, consider consulting a structural engineer. If you’re worried about the structural stability of your home, they can recommend ideas for keeping your home and floors safe and sturdy.
Leveling a floor isn’t something that happens overnight. Getting the correct alignment can take days (or even weeks) since doing it too quickly can cause a lot of stress to your house. Much like moving to a new place, you must give your house time to settle. Leveling a floor can also cause a bit of cosmetic damage to your home, even when it’s done slowly. Don’t be surprised by cracks in your drywall, and you may even see some damage to paint, flooring, and counters.
Once you have your game plan in place, here’s what you’ll need to do: you’ll need a laser level, screw jack, and beam to lift your floor. The laser level will help you determine how much the floor needs to be raised. Place the laser level on areas of the floor where it does and doesn’t sag and use it to mark these areas on the walls. Install a screw jack and beam under the floor joists you want to raise. The metal support in the jack will lift to push the beam into the sagging joist and level the floor. If you have multiple sags along the same floor, consider consulting a professional contractor to speed up your project time and eliminate your spending on expensive tools, like the cost of a steel I-beam.
Before you start putting in new joists, prepare your work area. To do this, remove the blockages around your floor joists. Remember the wiring, pipes, and HVAC ducts we said can sometimes cause floor joists to be improperly cut? Remove them. This can include detaching pipes from valves and removing wires from the breaker box.
Use the size of your existing joists to size your new ones. Record the length of your damaged joists with a tape measure—they should be at least 2x6. That’s a good place to start so that the new joist spans the entire length of the old one, but this isn’t always possible. If that’s the case, use the 2/3 rule to make a partial joist. This means if your old joist is 8 feet long, use a circular saw to cut a partial joist that’s at least 5.25 feet long.
Sistering means you’re adding extra material—like the full or partial floor joist—to strengthen the damaged one. You might need to call your sister (or get some extra hands on deck) because this part of the project often requires more than one person to hold up the new joist and get it level with the old one. You can use bolts, nuts, and washers to keep the beams together and in place, and you can even add extra stability by applying construction adhesive with a caulk gun before sistering the joints.
To fasten the joists together, you’ll need a hammer and 16d nails. When compared to screws, nails have more shear strength. What does this mean? Nails can handle more force from the sides. A screw is more likely to break, while a nail will bend.
To keep the joists together, hammer three nails a few inches apart at the top, middle, and bottom of either end of the partially sistered joist. Because the 2x6 joists are actually 1 ½-feet thick, the 16d nails (about 3.5 inches long) will stick out of the other side. Hammer the nail ends so they bend back into the board.
Once you install your new joists, check your floors. Are they level? They may not be perfect, but sometimes—especially in home improvement—you have to prioritize stability over perfection. If you’re satisfied with the outcome, you can reconnect or reinstall any wiring, piping, or utilities you removed.
Fixing a sagging floor isn’t the easiest project to accomplish independently. Depending on how many floor joists you need to fix, you’re looking at between 5 to 24 hours to complete the project. If you’re apprehensive about the tools, knowledge, and experience needed to repair your floor, you might consider finding a foundation repair contractor to do the heavy lifting. Repairing floor joists cost $40–$60 per square foot, and you’ll also pay around $65 to $100 per hour for labor—anywhere from $330 to $2,400.
