Drywall, also sold as plasterboard or gypsum board, is a sheet of set gypsum between two paper faces. It is the dominant interior wall and ceiling finish in North America and much of the world because it is inexpensive, fast to install, fire resistant and easy to finish. It has one weakness that every site engineer and finishing contractor learns quickly: it cracks.
The sheet is rigid and brittle, the joints between sheets are filled with a compound that is harder and more brittle still, and the whole assembly is screwed to a frame of timber or light-gauge steel that moves with moisture, temperature and load. When the frame moves, the board cannot follow, and the stress is released along the weakest line.
Most drywall cracks are not structural. They are, however, a record of movement, and reading them correctly separates a thirty-minute cosmetic repair from a problem that belongs to a structural engineer. This article classifies the causes, the common crack patterns and what each one indicates, the repair method that suits each type, and the detailing that prevents most of them in the first place. Readers who want a refresher on the material itself can start with our guide to the types of plasterboard and where to use them.
Why Drywall Cracks: The Mechanics
Three material facts explain almost every crack.
The board has Very Little Tensile Strain Capacity
Gypsum board fails in tension at a strain far smaller than the movement a timber frame goes through in a single year. Manufacturers publish its thermal movement at roughly 9 millionths of its length per degree Fahrenheit (about 16 millionths per degree Celsius) and its hygrometric movement at about 7 millionths per percentage point of relative humidity. Over a 15 m (50 ft) ceiling run and a 40-point seasonal swing in humidity, that is about 4 mm of free movement. Restrain that movement and the board cracks.
The joints are the weak path
Sheets are joined with paper or fiberglass tape bedded in joint compound. A finished joint is the thinnest, stiffest and most brittle part of the surface, so stress concentrates there. Inside corners, the junction of wall and ceiling, and the corners of door and window openings are the places where joints and stress coincide.
The frame moves and the board does not
Framing lumber is commonly delivered at up to 19 percent moisture content and dries to 6 to 12 percent inside a conditioned building. Wood shrinks across the grain as it does so; a deep floor joist or a roof truss chord can lose several millimeters of depth in its first year. Light-gauge steel does not shrink, but it expands and contracts with temperature. Foundations settle. Floors deflect under load. Every one of these movements is transmitted to the board through the fasteners.
Causes of Cracks in Drywall
Shrinkage of framing lumber
The most common cause in new construction. As studs, plates and joists dry, joints open slightly and fasteners lose their grip. The symptoms are hairline cracks along taped seams and nail pops, the small bumps or crescent-shaped breaks where a nail or screw head has pushed through the compound. These appear in the first one to two years and then stop once the lumber reaches equilibrium.
Differential settlement
When one part of a foundation settles more than another, the frame racks. Door and window openings interrupt the wall plane, so the racking stress concentrates at their corners and a diagonal crack runs from the corner into the wall, usually at about 45 degrees and wider at the corner end. The mechanism is the same one familiar from masonry and concrete; see our note on cracks in concrete for the parallel. Settlement cracks are progressive: they grow in one direction and are often accompanied by doors that bind and floors that slope.
Thermal and moisture movement
Long, uninterrupted runs of wall or ceiling with no control joint accumulate the seasonal movement described above and crack somewhere in the middle, typically along a seam. Unconditioned spaces, attics and rooms with wide humidity swings are the usual locations.
Truss uplift
A specific and widely misdiagnosed case. In cold weather the bottom chord of a roof truss, buried in warm attic insulation, stays moist, while the upper chords in cold, dry air give up moisture and shorten. The truss arches upward and lifts the ceiling with it, by 6 to 25 mm (1/4 to 1 inch). Interior partitions do not rise, so a gap opens at the ceiling-to-partition junction in winter and closes in summer. The truss is behaving as designed; the crack is a detailing problem, not a structural one.
Deflection and vibration
Ceilings hung from undersized or overloaded joists, or from long-span trusses, deflect enough to crack the board. This is why building codes limit the live-load deflection of members that carry a brittle ceiling finish, typically to span/240 for roof members and span/360 for floors: the finish cracks long before the member is at risk. Vibration from machinery, traffic or heavy footfall produces the same cracks over a longer period.
Poor installation and finishing
Installation faults account for a large share of the cracks in otherwise sound buildings:
- Joints placed at the corners of openings, where a taped seam lands exactly on a stress concentration.
- Butt joints (the cut, untapered ends of sheets) left unsupported between framing members.
- Tape not fully bedded, leaving voids behind the paper that later lift.
- Fiberglass mesh tape used with ordinary drying-type compound on joints that move.
- Compound applied in thick coats, which shrinks and crazes as it dries.
- Fasteners driven too close to sheet edges, or sheets forced into place with no gap at the perimeter.
- Board hung before the building was dry or the framing had acclimatized.
Water and moisture damage
Water is a separate category. A leak softens the gypsum core, delaminates the paper and invites mold. The result looks like cracking, sagging or bubbling, but it is a material failure: the board must be replaced, not patched.
Types of Cracks and What They Indicate
| Crack pattern | Typical location | Likely cause | Structural concern |
| Hairline crack along a straight seam | Any taped joint | Compound shrinkage, lumber drying, unbedded tape | None |
| Diagonal crack from the corner of an opening | Door and window heads | Racking from settlement or frame shrinkage; a joint placed at the corner | Possible, if progressive |
| Horizontal gap at the ceiling-wall junction that opens in winter | Interior partitions under a trussed roof | Truss uplift | None |
| Long straight crack across a ceiling | Mid-span of a long ceiling run | Movement with no control joint; deflection | Low, unless the ceiling sags |
| Nail or screw pops | Scattered, or in a line along one member | Lumber shrinkage; a fastener that missed the framing | None; a line of pops can indicate a deflecting member |
| Fine map or spider cracking | Within a sheet, over thick compound | Compound applied too thick or dried too fast | None |
| Crack that lines up with a stepped crack in the masonry behind it | Finished basements, walls on masonry | Foundation movement | Yes: structural assessment first |
| Sagging, bubbling or stained board | Below roofs, bathrooms, plumbing walls | Water damage | None to the structure, but replace the board and find the leak |
When a Crack Is Structural
A useful first screen is width, measured rather than estimated. The BRE Digest 251 classification used for low-rise buildings treats cracks below 1 mm as fine and aesthetic, cracks up to 5 mm as easily filled, and anything wider as needing investigation. In drywall, three further signs move a crack from a finishing question to an engineering one:
- It is tapered, wider at one end than the other, which indicates rotation of the structure rather than uniform shrinkage.
- It is progressive: measured at a marked point, it has grown across more than one season and never closes.
- It is accompanied by corroborating evidence in the same part of the building: doors and windows that bind, floors out of level, gaps opening at the baseboards, or cracks in the exterior masonry.
When these signs are present, the finish repair comes last. Any compound applied before the cause is corrected is on a countdown.
Repair Methods
The correct repair depends entirely on the category above. The procedures below are the ones professional drywall repair contractors use every day, and the first covers the large majority of cracks.
Hairline and joint cracks
- Cut the crack open into a shallow V, about 3 to 6 mm wide, with a utility knife, and remove any loose compound and paper. Filling a closed hairline achieves nothing, because the compound has no key.
- Apply a thin bed of setting-type compound (the chemically hardening type, which shrinks far less than drying-type compound) and press paper tape into it, squeezing out the excess so that no void remains behind the tape.
- Build two or three thin coats, each feathered 50 to 75 mm wider than the last, and let each set before the next.
- Sand lightly, prime and paint. The primer is essential: paint applied over bare compound flashes and shows the repair.
Paper tape is preferred over self-adhesive fiberglass mesh on any joint that moves. Mesh elongates under tension and, combined with drying-type compound, gives a joint with markedly less strength across it. Where mesh has been applied over a painted crack and has failed, the repair begins by stripping it back to bare board.
Recurring and moving cracks
A crack that returns along the same line after a correct repair is reporting movement, and refilling it is pointless. The options are to remove the restraint or to hide the movement. Removing the restraint means a control joint in a long run, or a floating corner at a truss-uplift junction, with the ceiling board left unfastened within about 400 mm (16 in) of the partition and carried on clips fixed to the wall plate. Hiding the movement means crown molding fastened to the ceiling only, so that it slides against the wall. Both involve more work than another coat of compound, once.
Nail and screw pops
Do not drive the original fastener back in; it will return. Set a new screw into the framing member about 40 mm (1.5 in) above and below the pop, drawing the board tight, then set or remove the original and fill all three points in thin coats.
Structural cracks
Correct the cause first: underpinning, drainage or strengthening of the member. Monitor until the movement has stopped, then repair the finish. Where a sheet is cracked across its field rather than at a joint, replace the sheet.
Water-damaged board
Cut out the damaged area back to sound, dry board and to the center of the nearest framing members, fix the leak, allow the cavity to dry, and install new board. Patching over a softened core fails within months.
Preventive Measures
Most cracks are avoidable at the design and installation stage:
- Install control joints at the spacing recommended in the Gypsum Association’s GA-216: about 9 m (30 ft) in partitions and in ceilings without perimeter relief, and up to 15 m (50 ft) in ceilings that have perimeter relief, plus wherever the structure has an expansion joint or the framing changes direction.
- Let the framing dry to 19 percent moisture content or below, and let the board acclimatize on site before hanging.
- Keep the building between about 10 and 35 °C (50 and 95 °F) at a stable humidity during taping and finishing, and until the compound has fully dried.
- Avoid joints at the corners of openings; lay out the sheets so that each opening falls within the field of a sheet.
- Stagger and back-block butt joints, or use tapered-edge joints wherever possible.
- Fix with screws at about 300 mm (12 in) centers on ceilings and 400 mm (16 in) on walls, driven just below the surface without breaking the paper.
- Detail the wall-to-ceiling junction under trussed roofs with floating corners or clips rather than fastening the ceiling board to the chord next to the partition.
- Size ceiling members to the deflection limit for a brittle finish, not merely for strength.
- Apply joint compound in thin coats and let each dry; use setting-type compound for the first coat on joints and repairs.
- Ventilate attics and bathrooms, and fix roof and plumbing leaks promptly.
Drywall cracks because it is a brittle sheet fixed to a frame that moves. Nearly all cracks fall into a few recognizable patterns, each with a known cause, and the pattern says more than the width: a straight seam crack is a finishing matter, a seasonal gap at the ceiling line is truss uplift, and a tapered diagonal from the corner of an opening that keeps growing is a structural question. Matching the repair to the cause, and detailing new work with control joints, floating corners and dry framing, keeps the finish intact for the life of the building.