Beam replacement — the shoring is the job

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 for: A 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.

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 for: Shoring 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.

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 for: Bearing 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.

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 for: A 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.

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 for: Nobody 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.

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 for: A 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.

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 for: A 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.

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 for: A 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.