Beam replacement - the shoring is the job

What is beam replacement?

A carrying beam - often called a girder - runs beneath the floor and collects the load of the joists bearing on it, passing that load down through posts to footings and into the ground. Replacing one means taking that load off temporarily, removing the failed member, and putting a new one in with proper bearing at both ends and proper support beneath. The temporary support is the part that requires real competence, and it is the part most quotes describe in one line. Posts, columns and the footings under them belong to this same job.

Signs you need beam replacement

• A visible sag along the line of the beam, usually showing upstairs as a floor that dips toward the middle of the house
• Splitting, checking or crushing visible in the beam itself, particularly near a post or at the ends where it bears
• Rot, softness or insect damage at a beam end where it sits in a foundation pocket - the classic location, because that is where moisture collects
• A steel post that has rusted at its base, or a wood post with a soft, dark or crumbling bottom where it meets the floor
• A post that is visibly out of plumb, or sitting on a slab with no evident footing beneath it
• Beam ends that have rotated, twisted or slipped off their bearing so less of the member is actually supported than was intended
• Doors and floors above the beam line that have gradually gone out of true while the rest of the house has not
• A previous owner's improvised support - a stack of blocks, a screw jack left in as permanent, a post landing mid-span on a floor rather than on a footing

Seeing something not on this list? Browse structural repair problems by symptom →

How beam replacement actually works

1. 1

   Determine why the beam failed before specifying a new one

   A rotted beam end and an undersized original beam are different problems with different remedies. Rot means water arriving from somewhere - a foundation pocket without ventilation, a plumbing leak, ground moisture in an unconditioned crawl space. Overload or undersizing means the member was never adequate for what it carries, sometimes because a later renovation added load nobody accounted for. Sizing of the replacement is an engineer's determination, based on what it carries and how far it spans.

   Watch forA like-for-like replacement ordered without asking why the original failed. Put a new beam into the same wet pocket and you have bought yourself the same repair on a delay.

2. 2

   Plan the temporary support - and check it reaches the ground

   Before anything is removed, the load has to go somewhere else. Temporary shoring picks up the floor structure on either side of the beam and carries it down through posts to a base that can actually take it. The critical, frequently missed requirement is that the temporary load path continues all the way to solid ground or an adequate footing - not to a basement slab of unknown thickness, and not to a floor with an unsupported void beneath it.

   Watch forShoring posts set straight onto a basement slab or crawl-space soil with nothing spreading the load. A slab is a wearing surface, not a foundation, and concentrating the weight of a house on a small area of it is how shoring punches through.

3. 3

   Bearing - where the new beam actually lands

   A beam is only as good as what holds its ends. That may be a pocket in the foundation wall, a bearing plate, a column, or a new post and footing. The bearing has to be sized, level, dry, and made of something that will not crush or rot. Where a beam bears into masonry, moisture separation matters as much as the strength of the pocket.

   Watch forBearing detail left unspecified in the quote. "Rest it in the existing pocket" is not a specification when the existing pocket is exactly where the last beam rotted.

4. 4

   Posts, columns and the footings under them

   The posts carrying an interior beam transfer a concentrated load into the ground and need a footing sized for it. Original construction sometimes provided one and sometimes did not; later basement finishing has occasionally removed or bypassed one. Replacing rotted or rusted posts often means opening the slab, forming a footing, and setting the new column on a base that isolates it from moisture. Adjustable steel columns are common - permanent ones are a different product from the temporary screw jacks that look like them.

   Watch forA temporary jack post left in place as the permanent support. It is a recurring finding in older basements, it is not what those are for, and an inspector will call it.

5. 5

   Access and staging - getting the member in

   A long beam has to physically reach the middle of a basement or crawl space. Sometimes it does not: the stair turns, the doorway is too narrow, the crawl-space hatch is small. Options are a member built up in place from multiple pieces, a steel section craned through a window or an opening cut for it, or an engineered member specified in transportable lengths. This is a genuine constraint that changes both method and price, and it should be settled at the site visit.

   Watch forNobody measuring the route in. Discovering on installation day that the beam cannot get to where it is going means an improvised splice made under time pressure, which is the worst way to arrive at a structural connection.

6. 6

   Lifting - slowly, or not at all

   Where the floor above has sagged, the question of whether to lift it back is separate from the question of replacing the beam. Recovery is done gradually over days or weeks, not in an afternoon, because everything above - drywall, tile, plumbing, door frames - has settled into the sagged position and will crack as it moves back. Full recovery is often neither achievable nor desirable, and an honest contractor says so before starting rather than after the ceiling opens up.

   Watch forA promise to bring the floor fully level. Some of the sag is permanent set in the framing, and chasing the last of it does more damage than it repairs.

7. 7

   Permit, inspection and closing out

   Replacing a primary carrying member is structural work and generally requires a permit, with the engineer's specification supporting the application and inspection points before anything is concealed. Connections, bearing and post bases are exactly what an inspector wants to see, and they are exactly what gets covered first.

   Watch forA schedule that puts insulation, drywall or a crawl-space vapour barrier back before the inspection. If it is covered, it comes off again - at your expense, and after an argument about whose fault the sequencing was.

8. 8

   Deal with the water before you finish

   Where the failure was rot, the repair is only half done when the beam is in. Crawl-space ground moisture, an unvented foundation pocket, poor exterior drainage or a leak overhead all need addressing, or the new member starts the same clock as the old one - frequently a separate trade, and frequently the line that gets dropped when the budget tightens.

   Watch forA quote that replaces the beam and is silent on moisture. Ask directly what is being done about the source, and get the answer in the scope.

What does beam replacement cost?

Wide range, driven far more by access, shoring and post footings than by the beam itself. A short accessible span in a walk-out basement and a long member craned into a low crawl space with new footings are not comparable jobs. Get shoring, footings and moisture work priced as named lines.

See the full beam replacement cost guide - by material, size and region →

If the number is the problem, here are the ways people pay for it →