How much would it cost to replace the sills on an old house?

Sill and beam replacement runs $7,000 to $40,000. That figure moves with how much wood is rotted, how long a run we have to swap, how the house has to be lifted to get the old sill out, and how easy the work area is to reach. On an old New England house, the price usually tracks the rot, not the square footage.

The sill is the wood beam that sits on top of your foundation wall. The whole house rests on it. In an old house, that sill is often the first thing to go soft, because water and damp air find it before they find anything else. You walk the basement and see crumbling wood, a sag near an outside wall, or a door upstairs that suddenly sticks. That is the sill telling you it has been wet for a long time.

Why does it rot? Old foundations leak. Water pools at the wall because the soil right against the house is disturbed backfill, the loose fill that got put back when the house was built. That fill drains slowly and holds water. Damp rises. The sill stays wet, and wet wood feeds rot over the years. NH frost heave adds load by pushing on the wall through a hard winter. None of that is your fault. It is just what old houses do here.

What drives the cost. The big one is length. A few feet of bad sill near a bulkhead is one job. A whole side of the house is another. Then there is the lift. To pull a rotted sill we often have to raise that part of the house a little, just enough to take the weight off, set new wood, and lower it back. More lift and more support points mean more labor. Access matters too. A tight crawl, a finished room overhead, or a stone foundation can all add time. We do the lifting and the beam work in-house, so one crew owns the job start to finish.

Not every soft board needs a full sill swap. Sometimes the rot is in one short section and the rest of the beam is solid. Sometimes the real problem is the water, and once the basement is dry the wood stops getting worse. You may not need the whole side replaced. We will tell you that when we see it. If your sill is only damp at one spot and the wood is still firm, the fix might be drainage first, not a tear-out.

That is why we look at the water alongside the wood. Sill rot and a wet basement usually come from the same source. If water is the cause, fixing the sill without fixing the leak just starts the clock again. Our Forever Dry System handles a wet basement with full-perimeter interior drainage, a sump pump, a wall vapor barrier, and a dehumidifier. If your problem is under a crawl space instead, that is crawlspace encapsulation, a sealed and dry space so the framing above it stops soaking up moisture. The U.S. Department of Energy notes that up to about a third of a home’s heat loss can come from an uninsulated foundation or crawl, so a dry sealed space helps your comfort too (DOE Building America).

If the sill failing has let the floor or wall move, the fix may pair with other structural work. Carbon-fiber straps for a bowing wall. A power brace. Helical or push piers when the footing itself has settled. Lally columns for floor support. We size that on site, and we put the engineered numbers in writing. You can see all of this on our structural and foundation repair and sill replacement pages.

Old house, old foundation, you worry it is all one giant repair. Most of the time it is not. We come look, we measure the bad wood, and you get a clear quote within 24 hours. The work carries our 603 guarantee, and sill and beam work is backed in writing like the rest of our structural repairs.

Want to know what your sill needs? Call us at 603-610-1770 or book your free inspection. The inspection and the estimate are free, and we will tell you what has to be replaced and what can stay.

Related questions

Can you replace a sill without lifting the whole house? Often yes. We only lift the section over the bad sill, just enough to take the load off, and we use temporary supports while the new wood goes in. A full-house lift is rare for a sill job.

Is sill rot covered by homeowners insurance? Usually not, since most policies treat rot and long-term water damage as maintenance, not a sudden event. Check your own policy and the Insurance Information Institute for what counts as covered.

Do I need to fix my wet basement before replacing the sill? If water caused the rot, yes. New wood on a wet wall will rot again. We often pair sill work with our Forever Dry System so the fix lasts.

What warranty comes with sill and beam replacement? It is backed in writing as part of our structural repair work. We go over the exact terms with you before any job starts, alongside the 603 guarantee.