While installing some new recessed lighting in my attic today, I noticed this split in one of the ceiling joists. The split is about 4 ft 6 in long starting from the end of the joist. The joist is a 2x12 and is about 19 ft long. The joist is only supported at the ends; there are no other walls or supports underneath it.

split joist

How urgent is it to address this? What options do I have for a repair that would be acceptable? The only way I could get another 19 ft joist there to sister the entire joist would be to open up the ceiling.

EDIT: Additional context

The house was built in 1979. It is a single story house in a sort of U-shape:

House Layout

The joist in question runs along the top of the living room, which has a raised 10 ft ceiling (rest of house has 8 ft ceilings). Here is a view of the living room. The split in the joist in question is above the sliding glass door and runs from the left side of the picture to the right side. The width of the living room along the joist is about 18 ft:

Living Room View

Here is a view of the ceiling looking the opposite direction. The joist still runs left to right across the picture:

Living Room Ceiling

This is a view in the attic looking towards where the joist is split. This picture shows how the ceiling is raised. The ceiling joists run from the front of the picture to the back and are perpendicular to the rafters for the roof. The split is on the far side of the attic:

Attic View

This view shows a close up of how the joists are supported in the foreground of the previous picture:

Near Side Support for Ceiling Joists

This shows how the joists are attached to the frame on the far side (where the split is):

Far Side Support for Ceiling Joists

EDIT: Nearly final result

Here's what the nearly final result looks like (I still need to replace the block that was between the joists): Sistered section

I was able to get a 10 ft board in place to sister with the joist with the split. I used pairs of 3/8in bolts spaced about 24 in apart to bolt it together. Near the split, I put the bolts below the split and put one extra one in. I used construction adhesive between the joist and the sistered joist.

In the area that was split, I also drove a few 8in lag screws vertically through the joist. It wasn't able to close the split, but hopefully it helps: enter image description here

  • 3
    Sistering an 8 or ten foot piece should be more than enough. Think it is more of a repair when you get to it, than have it done yesterday, but sooner the better. A crack going top to bottom is the very bad type, the one you is common and usually not a concern, except for your size.
    – crip659
    Commented Feb 20, 2022 at 23:30
  • Is there a perpendicular wall underneath any part of that span? If so, how far from the plate to that wall? Commented Feb 21, 2022 at 1:37
  • @AloysiusDefenestrate No, just at the ends of the joist.
    – Eric
    Commented Feb 21, 2022 at 1:38
  • Agree that a shorter sister would be adequate, though I'd lean toward 12-14' (in spite of how awful that might be). If that's not going in through the attic hatch, think about opening a hole under the roof. Commented Feb 21, 2022 at 2:14
  • 2
    That is some very tidy wiring on the right-hand wall! Whatever you do, be sure you don't drive a nail into your wires or damage them when maneuvering the new/patch lumber into place.
    – FreeMan
    Commented Feb 21, 2022 at 15:38

1 Answer 1


I'll start off by saying that nothing you read on this site or anywhere else is a substitute for an on-site professional. There may be aspects to the situation that we can't see and you weren't aware are critical. You should have someone local take a look. That out of the way, here are my thoughts.

This isn't an urgent situation.

  • These joists appear to only support the ceiling. I see no evidence that they carry even the roof, let alone other portions of the structure.
  • The crack looks old. It doesn't have the bright, fresh signature of a new break.
  • It primarily follows the grain of the board. Since large timbers nearly always show "checking", or shrinkage cracks at some point, it's not at all uncommon to see similar cracks in even milled lumber.
  • It's just one joist. The load of the drywall and hardware it carries is spread across many joists.

Repairs needn't be complex.

One option would be to simply slather some construction adhesive in the cracks and run long timber screws or light-gauge lags down through the joist every foot or so to bind it back together. Pilot properly to prevent new splits, especially in the portion of the joist above the crack--it'll be quite brittle.

I can't tell with certainty how much clearance you have for more elaborate repairs, but I get the impression that you could slide in a new member alongside the cracked joist for sistering. Even if you can get something in there that spans from the end to a few feet past the primary cracks, that should be adequate. Here are some suggestions.

  • Use either solid, small-knot lumber of roughly the same size as the original joist, or use modern engineered lumber such as OSB of at least 1" total thickness. This could be stair stringer material (1" to 1¼") or two layers of 8' or 10' sheathing.
  • Plywood only offers roughly half the strength because every other ply is crossgrain. I wouldn't use it if you have other options. Absolutely do not use any form of pressed particle material, such as particle board or fiberboard.
  • Whatever lumber you use, fastening is critical. You don't take advantage of the repair unless the patch is rigidly bonded to the old joist.
  • While construction adhesive isn't rated as a structural component, it's worth using. It will add significant bond strength to the system.
  • Suitable fasteners will allow tight connection without requiring impacts that may damage your ceiling finish. Consider 2½" construction screws or lags, carriage or hex bolts, or ~3" pneumatic cement-coated or ring-shank nails. Hand-driven nails will likely result in damage to the drywall below.
  • If using screws or lags, consider piloting through the new member to allow the screw to slip, increasing clamping force. You could also use half-thread screws to accomplish the same.
  • The old joist will be very hard. You'll want to pilot properly into that as well if not using self-drilling fasteners.
  • If you're not able to achieve a tight connection with screws alone, use C-clamps or other devices to temporarily tighten the joint.
  • I would still try to screw the upper portion of the existing joist down into position, even if with just a few shorter screws. A large gap reduces its effectiveness, and it's just good workpersonship to get that tight before locking everything in place.
  • I updated the post with the (nearly) final result based on your advice.
    – Eric
    Commented Mar 19, 2022 at 1:37

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