Garmaine Staff asked 2 years ago

I have a vaulted ceiling drywall joint crack that extends across two adjacent sides of a 4'x8' sheet of drywall and runs into another 1' section, across & perpendicular to the vaulted peak. The long side is a hairline. The short side crack runs up to the peak and is 1/8" wide & puckered out a little. I started removing the old tape and got to the sheetrock next to a vertical wall and found a butt joint with a >1" gap, and the drywall was cracked at a corner because the original construction was shoddy. The truss above this damage is 1" above the drywall so when they nailed it, it crumbled the DW corner. They just mudded it.
How do I properly repair this so the crack wont come back? Wished I could post a pic. I'm thinking of adding 2×4 to truss in crawlspace. I have about 3' access on scissor truss. Suggestions?