A failing lally column shows up as a sagging floor above it, a beam that has started to bow, or rust eating the base of the post. It means the steel column holding up your floor is losing the fight. Caught early it is a straightforward replacement. Left alone, it drags your floors and framing down with it, and the bill grows every season.
Lally columns are the round steel posts in your basement that carry the beams your floors sit on. They are hidden, so most homeowners never think about them until a floor starts to sag or a door upstairs stops closing right. Here is how to tell when one is going, what causes it, and what fixing it actually involves.
Signs a lally column is failing
You usually feel it upstairs before you see it downstairs. Watch for:
- Sagging or sloping floors above a basement support beam.
- A beam that is bowing or cracked where it rests on the column.
- Rust or flaking at the base of the post, or a column that leans or tilts.
- Doors and windows on the floor above that stick or no longer close square.
- Creaks or pops when you walk across the room over it.
- A gap opening up between the top of the column and the beam, where the post has settled and no longer carries full load.
One symptom on its own can be nothing. Two or three of these together, over the same spot in the basement, is a column telling you it is done.
What causes a lally column to fail
Almost always, water. The base of a lally column sits on the basement floor, which is the wettest, coldest part of the post. In a damp New Hampshire basement, water at the floor wall joint and humidity in the air rust the steel from the bottom up. Rusted steel swells, weakens, and eventually can no longer hold the load it did when it went in.
The other piece is what is under the floor. Many older homes have columns sitting on a thin slab or an undersized footing, set on disturbed backfill that settles over decades of frost heave. When the footing drops, the column drops with it, and the beam it was holding comes down a little too. Wet basement, rusting steel, settling footing. That combination is why a dry basement and a solid column go together, and why we look at your moisture when we look at your columns.
Lally column repair vs replacement
Here is the honest split. A column with light surface rust that is still straight, plumb, and carrying its load may just need the moisture problem around it fixed so it stops corroding. That is the cheap end, and sometimes it is all you need. But once a column has rusted through at the base, bent, or settled, you do not repair it. You replace it. Steel that has lost its section cannot be patched, and stacking blocks or shims under a sagging beam is not a repair, it is a hazard.
So the real question a good crew answers on site is simple: is this column still structurally sound, or is it compromised? If it is sound, protect it. If it is compromised, replace it. We would rather tell you a column has years left than sell you a replacement you do not need yet.
How a lally column is replaced
Replacing a structural column is careful work, because you are taking out something holding up the house while the house is still on it. The process:
- Load assessment. We check which columns and beams are compromised and how the load is carried, so nothing gets moved without support.
- Temporary support. Hydraulic jacks and shoring take the beam’s weight before the old column comes out.
- Remove and reset. The failed column comes out, and we confirm the footing under it is solid. A too-small or cracked footing gets addressed, because a new column on a bad footing just settles again.
- Set the new column. A new steel column is set plumb and adjusted to bring the beam back to level where it is safe to do so.
- Final check. We confirm the floors and beam are level and the load is carried before we call it done.
603 self-performs this structural work with our own crew, not a subcontractor, so the people who assess the load are the ones who lift it.
Why you can’t DIY a failing lally column
This is one to leave alone. Shimming a sagging beam with blocks, or standing a second post next to a bad one, does not distribute the load right and can let go all at once. Lifting a settled column too fast can crack the beam, the drywall, and the floor above it. A structural lift is done slowly, in the right order, with the right equipment, or it does damage. If a column is failing, get someone who has opened these up before.
What does lally column replacement cost?
Cost comes down to how many columns are involved, whether the footing needs work, and whether a beam has to be sistered or replaced too. Rather than guess here, we lay out the numbers on the cost page: see the cost to replace a lally column. The only exact number is the one you get after a free on-site look.
Frequently asked questions
How do I know if my lally column needs to be replaced?
If the column is rusted through at the base, bent, leaning, or has settled and left a gap under the beam, it needs replacing. If it is straight and solid with only light surface rust, fixing the moisture around it may be enough. A load assessment on site tells you which one you have.
Can a rusted lally column be repaired, or does it have to be replaced?
Steel that has rusted through has lost strength it cannot get back, so a badly corroded column is replaced, not patched. The useful “repair” is stopping the water that rusted it, so a sound column does not become a failed one. Shims and stacked blocks are never a repair.
Why is my basement support column rusting?
The base sits on the basement floor, the wettest, coldest spot, so water at the floor wall joint and humid basement air corrode the steel from the bottom up. A wet basement rusts columns. Drying the basement is part of protecting them.
Is a sagging floor from a lally column dangerous?
It is a structural issue, not a cosmetic one, and it gets worse, not better. A failing column transfers stress to the beams and floors around it. It is not usually a same-day emergency, but it is not something to sit on either.
Do you replace the beam too, or just the column?
Only if the beam needs it. If a beam has bowed or cracked from riding on a failed column, we sister or replace it as part of the fix. If the beam is sound, we set a new column under it and level it back up.
Get a free structural inspection
Noticing a sagging floor, a leaning post, or rust at the base of a basement column? Let us take a look. We will tell you straight whether it is sound or failing, and give you a written estimate with no pressure. Call 603-610-1770 or schedule your free inspection. We cover the New Hampshire Seacoast, southern NH, and into Maine and Massachusetts.
See also: structural & foundation repair · lally column replacement cost · basement waterproofing
