Fixing a Damaged Floor Joist
Repair Sagging, Cracked or Broken Floor Framing.
By Rob Robillard
I recently had to repair a floor joist that had cracked. I suppose somewhere in the world there are floor joists that need to be repaired that have wide open, clear joist bays, with no pipes, wires or obstructions. Unfortunately, that’s not my world.
This joist was installed in 1863 and was located directly below where a heavy refrigerator now lives. From initial inspection it appeared that someone had notched the joist too much and then installed a makeshift patch. The notch was made where the floor joist recessed into a wood beam, supported by chimney corbeling.
Corbeling is an “old school,” overlapping arrangement of bricks with each course extending farther out from the vertical of the wall than the course below. Corbeling was done for decoration or to support structural beams, like in this situation.
My guess is that many years back, an old vent or furnace pipe ran through this location, and the contractor needed to cut this section of joist to accomplish the installation. Today, this type of notch is not allowed by code.
Notches can compromise the strength of floor joists, although some notches are acceptable, depending on their location as dictated by the International Residential Code [IRC]. Here’s a good rule of thumb:
- Notches should be no deeper than 1/6 the depth of the joist.
- Notches at the end of the joist should be no deeper than 1/4 the depth.
- Limit the length of notches to 1/3 of the joist’s depth.
Not only did the aggressive notching doom this joist, it affected the structural integrity of the floor system above. To make matters worse, the refrigerator above our joist was causing the floor to sag.
A severely, cracked or sagging floor joist can get worse over time, causing the floor above it to slope or become unleveled.
Tools & Materials Required
Structural screws and joist hangers if applicable
Framing lumber or laminated lumber if needed for strength
Hydraulic jack or metal jack posts
Misc. hand tools
Impact driver and accessories
Correcting a problem joist is an easy repair and is usually accomplished by fastening a new joist next to a damaged floor joist, doubling the thickness of the framing member. This is referred to as “sistering.”