Floor Joist & Sagging Floor Repair

What the Problem Looks Like

• A floor that feels bouncy or springy underfoot, or makes dishes rattle when someone walks across the room
• A dip in the middle of a room — the floor is lower mid-span and comes back up toward the walls
• A floor that slopes consistently in one direction, so things roll or furniture rocks
• Interior doors that have started to bind or swing on their own
• Gaps opening between baseboards and the floor, or drywall cracks running from the corners of door frames
• Soft spots, or hardwood that is cupping, over a damp crawl space

A dip and a slope are different problems. A dip points at the members doing the spanning — joists that are deflecting, or a girder that has bowed between its supports. A consistent slope points at what the structure is standing on — a column that has settled, or movement on one side of the foundation. Reinforcing joists that were never the problem is the most common way to pay for a floor repair and still have a floor that moves.

Cupping on its own — board edges higher than their centers — is usually a moisture reading rather than a structural one; see cupping floors. But moisture high enough to cup a floor is high enough to reach the framing under it, so the two are worth checking together.

What Is Under the Floor

In a typical Triangle crawl space home, the floor is carried by joists running in parallel from the foundation wall to one or more girders through the middle of the house. The girders are held up at intervals by piers or columns, each on its own footing, and the whole frame sits on a sill plate along the top of the foundation wall, closed in by the band joist around the perimeter. Each of those can fail, and each produces a different symptom upstairs.

Common Causes

Moisture and rot

Wood fails first where it stays wet, and in a crawl space that is usually where it touches something else — joist ends bearing on the foundation, the sill plate and band joist, and the base of a wood column where it meets its footing. A column gone soft at the bottom loses bearing and drops, and the floor above drops with it. This is the most common cause we find.

Termites and wood-boring insects

Insects hollow out a member from the inside, so a joist can look intact and have very little left. They are drawn to the same damp wood rot is, so the two are often found together. Treating the insects and repairing termite damage are separate jobs — extermination stops the colony but puts nothing back.

Undersized framing and long spans

Some floors have deflected slowly since the day they were built, because the joists were undersized for their span or the girders were spaced too far apart. Renovations create the same thing: a removed wall that was quietly carrying load, or added weight like a tile floor or stone countertops. Deep notches cut into the bottom edge of a joist for plumbing or ductwork do it too.

Settling or failing supports

Crawl space columns were often built on little more than a pad on soil, and soil that stays wet does not hold the load it did when dry. The column settles and takes a line of the floor down with it.

How We Repair It

Every job starts with a hands-on inspection in the crawl space: probing suspect wood to find out how much sound material is left, checking bearing points and column bases, measuring the floor from below to map where the movement is, and taking moisture readings so the cause is established rather than assumed. We photograph what we find and lay out the repair plan before any work starts.

Sistering

Sistering fastens a new board of the same depth alongside a damaged joist, running bearing point to bearing point, so the two carry the load together. It restores a joist with localized rot, a split, or a bad notch, and it is the most common fix. A sister only works if it reaches bearing at both ends and is fastened along its length — a short board bolted on where it was easy to reach does very little.

Joist, girder, sill plate and band joist replacement

Where rot or insect damage runs the length of a member, or has reached the bearing ends, there is nothing sound left to sister to and it is replaced. The floor is temporarily supported while the old member comes out and the new one is set. The same applies to girders, sill plates and band joists, which are where perimeter rot usually concentrates.

Supplemental supports and piers

Where the framing is sound but the span is too long, the fix is neither of the above: it is a new bearing point underneath — a support column or a drop girder on new piers — that shortens what the joists have to span. Span is the dominant factor in how much a floor bends, so this is often how a bouncy floor gets fixed for good. Where an existing column has settled, it is put back onto something that will carry it. If the movement turns out to be in the foundation itself rather than the crawl space framing, that is foundation repair and we will tell you so.

Floors are leveled gradually and deliberately. Lifting a settled floor system too fast is what cracks drywall, jams doors and breaks tile upstairs — the structure took years to move and it goes back over days, not hours.

Why Moisture Control Comes With It

Wood under a house does not rot on its own. It rots because the space is damp — bare soil giving off ground moisture, water arriving after rain, or vents letting humid summer air condense on cool framing. Putting new lumber into those conditions starts the same clock running again.

So a structural repair plan from us usually has a moisture half: a vapor barrier, drainage, a dehumidifier or full encapsulation, depending on what is keeping the space wet. The order matters too — stop the water and dry the space, then repair the structure, and leave finished flooring until last.

Floor framing is one part of a broader crawl space repair. If your floors have moved, call us at (919) 924-7600.