Sagging Floor, Joist, and Subfloor Repair

Why floors sag

A floor has two layers that matter. The joists are the horizontal framing members that span from wall to beam, and the subfloor is the sheathing (old plank boards in older homes, plywood or OSB in newer ones) fastened across the top. When termites, rot, or an old plumbing leak weaken either layer, the floor loses stiffness. Joist damage shows up as sagging and bounce across a room. Subfloor damage shows up as soft spots, usually in smaller areas near a toilet, tub, exterior door, or wall. Not every sagging floor is termite damage. Undersized joists, notched framing, or a settling beam can cause the same symptoms, and the fix depends on which one you have.

Sagging floor repair: finding the real cause

• Bounce across the whole room often points to joists with lost section, or joists that were undersized for the span to begin with.
• A dip along a line under the middle of the house usually means the main beam or its posts, covered under beam and sill replacement.
• A slope toward an outside wall often traces to the sill or rim joist.
• A soft spot you can feel under a bathroom or kitchen is usually subfloor rot from a slow leak, sometimes with termite activity alongside.
• Floors that tilt in an older house with no soft spots may be long-settled framing that is stable, which may need no structural work at all.

How joist repair works

Most joist repair is done from the basement or crawl space, without touching your finished floor. The common method is sistering, fastening a new full-length joist alongside the damaged one with structural adhesive and bolts or structural screws so the two act as one member. Before sistering, a sagging joist is jacked back toward level slowly, sometimes over days, so the floor and walls above can adjust without cracking. When a joist is too far gone to carry its share, or the damage is at its bearing end, it gets replaced outright. Joist hangers, blocking, and bridging get added where they help the floor share load.

Subfloor repair

Subfloor damage is repaired by cutting out the deteriorated section back to sound material and installing new sheathing that bears on joists or added blocking at every edge. When the subfloor sits under finished flooring, the repair often means lifting the floor covering in that area. Tile, hardwood, and vinyl each have their own constraints, so we plan the opening to keep it as small as the damage allows and tell you up front what finish work will be needed. Where a leaking toilet flange or shower pan caused the rot, the leak has to be fixed before the new subfloor goes down.

Warning signs worth a look

• Dishes rattling in a cabinet when someone walks across the room
• A floor that gives slightly near a tub, toilet, or dishwasher
• Gaps opening at the base of interior walls or under baseboards
• Cracking grout or tile in a floor that used to be sound
• Joists you can see from below that are cracked, notched deeply, hollow, or sagging
• Mud tubes on joists, posts, or the underside of the subfloor

Joist repair near me: what to ask a contractor

When you're comparing subfloor repair contractors or joist repair quotes, ask how they found the cause, whether the joists will be jacked before sistering, what fasteners will join the sister to the original, and how they will handle a joist that is damaged at its bearing. A quote that only mentions leveling compound or new flooring is treating the surface. If the framing below has lost strength, the floor will move again.

Our process

We start with a free assessment from below and above, tell you plainly whether the cause is termite damage, rot, undersized framing, or something else, and write up the repair with a fixed price. Termite-related joist and subfloor work is done after treatment. Ask for the warranty terms in writing before any work starts. If the moisture source is a crawl space problem, our crawl space restoration page covers that side.

Old houses and undersized joists

Many older Berks County homes were framed with joists that would not meet today's span tables, especially in rear additions and kitchens that were expanded over the years. Termite damage on top of an already undersized joist shows up faster as bounce and sag. When we sister those joists, we size the new member to the actual span and load rather than matching what was there, so the repaired floor is often stiffer than it was before the damage.

Common questions

Can a sagging floor be fixed without tearing up the flooring?

Usually, yes. Joist sistering and beam or post work are done from the basement or crawl space. Subfloor damage is the exception, because the damaged sheathing is directly under the finish floor.

Is a bouncy floor dangerous?

Bounce by itself is often a stiffness problem rather than a safety one. Bounce that has increased over time, combined with soft spots or visible damage below, should be checked because it can mean the joists are losing section.

How long does joist repair take?

Sistering a few joists is often a short job. Jacking a long-sagging floor back toward level is done gradually, which can stretch the timeline so the house above adjusts without cracking.

Will the floor be perfectly level after repair?

It will be solid and much closer to level. In a century-old house, forcing every floor dead flat can crack plaster and bind doors, so we agree on a realistic target before we start.

Related guides

• How to Tell If Termite Damage Is Structural
• 7 Signs of Structural Termite Damage
• Termite Damage Repair Cost in Reading, PA: What to Expect