How to fix second-level hardwood floors that are sagging 3/4 inch

A second-floor hardwood sag of about 3/4 inch usually comes from below, not from the floorboards themselves. The fix is to support the framing under that floor, often with a new beam and posts or a lally column carried down to a solid footing, and most floor support work runs $1,300 to $2,500. You get a free inspection first so we can tell you what is actually moving.

Here is what is going on. Your hardwood is nailed to a subfloor. That subfloor sits on joists. Those joists land on a beam, and that beam stands on posts. When the floor up top dips, one of those parts under it has given way. The boards are the symptom. The frame is the cause.

So the first job is to find the cause. We come out, we look in the basement or crawl space under that room, and we check the beam, the posts, and the joists with a level. Three quarters of an inch is real movement. It is worth checking now.

A few things drive a sag like that.

A post settled. The post under the beam might be sitting on dirt or a thin pad that sank. Common in older NH homes. We carry the load down to a proper footing.

The beam is undersized or sagging. An old beam can deflect over the years, especially if a wall or bath was added above it later. We add support under it, sometimes a new lally column, sometimes a sister beam.

A joist is sagging or cracked. One bad joist can pull a strip of floor down with it. We sister it or add support beneath.

The footing moved. If the whole thing settled because the soil under it gave, that points to helical or push piers. We self-perform that work in-house.

We do not shim the hardwood from the top and call it fixed. That hides the dip. It does not hold. Once the frame under the floor is supported and level, the floor stays put.

Cost depends on what we find. Adding a lally column or floor support post is the common one, and that work runs $1,300 to $2,500. If a beam or sill is failing and needs replacing, sill and beam replacement runs $7,000 to $40,000. If the footing itself sank and we have to stabilize the foundation, helical piers run $2,700 per pier for the first three, then $2,200 per pier after that. We give you the number after we see it, in writing, with a free estimate and a quote inside 24 hours.

You may not need the big fix. A lot of these sags are one settled post or one tired beam. Support that, and you are done. We will tell you if that is your case. We will also tell you if it is more.

A little NH framing here. Our soil and our frost both work against a foundation. Water pools at the foundation because the backfill, the loose dirt put back when the house was built, drains slowly and holds water. Then winter frost heave pushes on walls and footings. Over years, a post on a weak pad gives up, and the floor two stories up shows it. That is why we look at the whole path, footing to floorboard, not just the spot that dips.

You want one crew that owns the whole job. We support the frame, we replace the beam if it needs it, and we set the piers if the footing moved. No handing you off. And the work is covered. Floor support and power posts carry a 10-year warranty, helical piers carry a 25-year engineered warranty, and sill and beam work is covered too. See the 603 guarantee.

Start with the inspection. It costs you nothing and it tells you the one thing that matters: what is actually moving under that floor.

Helpful internal reads: structural and foundation repair, supplemental support, helical piers, sill replacement, and foundation repair.

For background on residential floor framing and structural settlement, the U.S. Department of Energy’s Building America program (basc.pnnl.gov) is a solid neutral reference [verify].

Worried about that dip? Call us at 603-610-1770 or book your free inspection and we will tell you exactly what is going on under that floor!

Related questions

Is a 3/4-inch sag in a second-floor dangerous? It is a sign something structural is moving, so it is worth checking, but it does not always mean an emergency. We measure it, find the cause, and tell you how urgent it really is. The free inspection settles that fast.

Can I just refinish or shim the hardwood to level it? No, that only hides the dip. The sag comes from the framing below, so leveling the boards on top leaves the real cause in place. Support the beam, post, or joist underneath and the floor holds.

How long does a floor support job take? Most floor support jobs, like adding a lally column or post, are quick, often a single visit. A beam replacement or pier job takes longer. We give you the timeline with your free estimate.

Do you replace the hardwood too? We fix the structure that caused the sag. Once the frame is level and supported, your existing floor usually settles back close to flat and you decide on any cosmetic refinishing after.