Drywall cracks and nail pops: what's normal and what isn't

Almost every house has a few drywall cracks or nail pops. Most are cosmetic. They come from wood framing drying out and moving a little, and a patch and some paint takes care of them. A few cracks are different: they are a sign that the house itself is moving, and patching them only hides the problem for a while.

This guide explains what causes the common ones, how to tell the two apart, and when to call in a structural engineer. For what the patching costs, see drywall and ceiling repair.

What a nail pop is and why it happens

A nail pop is a small round bump or crack over a nail or screw head in the wall or ceiling. Sometimes the paint flakes off and you can see the nail.

The usual cause is the wood behind the drywall. Framing lumber holds moisture when it's installed, and it shrinks as it dries. When the stud shrinks, it pulls away from the back of the drywall, and the nail that held them together pushes out through the surface. [1] Canada's national housing agency notes that longer nails actually make the problem worse, and that drywall screws resist this seasonal shrinking and swelling much better than nails. [1]

That's why nail pops often show up in the first years after a house is built or an addition goes on, and why they can appear in clusters. They are not a structural problem on their own.

How they're fixed: the loose nail is set or removed, a drywall screw is driven next to it to pull the drywall tight to the framing, and the spot is patched and painted. [1] See the findings for wall nail pops and ceiling nail pops.

Cracks that are usually cosmetic

What you see	Common cause	Usual fix
Thin crack running along a drywall seam	Small framing movement or shrinking joint compound [1]	Retape, fill, sand and paint
Short diagonal crack from the corner of a door or window	Stress at the opening, including vibration from opening and closing doors [1]	Tape and patch
Crack where the ceiling meets an interior wall, worse in winter	Truss uplift (see below) [1]	Patch, or cover with moulding fastened to the ceiling only
Tape bubbling or peeling at a seam	Tape not fully bedded in compound when the drywall was finished [1]	Cut out and retape

Truss uplift catches many homeowners by surprise. Many houses have roof trusses, the triangle-shaped frames that hold up the roof and ceiling. The bottom of each truss is buried in the attic floor insulation, where it stays warmer and drier than the top. The bottom piece shrinks more, so the truss bows upward and lifts the ceiling off the top of interior walls. The crack can open in winter and close again in summer. [1] It looks alarming, but it is a normal behavior of the framing, not a failing foundation.

The findings for a minor wall crack, minor corner cracking and peeling drywall tape cover these.

Signs a crack may mean the house is moving

Foundations move when the soil under them settles, or when clay soil shrinks in dry weather and swells in wet weather. The American Society of Civil Engineers' guide to these soils lists the signs to watch for inside and outside a house: [2]

Cracks in walls or ceilings, especially at wall corners and above doors and windows
Doors and windows that start sticking or won't latch
Cracked ceramic or vinyl floor tiles
Floors that slope, or walls that lean or bow
Stair-step cracks in brick or block on the outside of the house
Gaps opening between window frames and the wall, or between siding and trim
Driveways, patios or walks pulling away from the house

Notice that cracks above doors and windows are on both lists. One hairline crack by itself is common. The guide says the chance of real movement goes up with the number of these signs, how often they show up and where they are. [2] A crack plus a door that suddenly sticks, plus a cracked tile in the same part of the house, tells a different story than a single crack.

Dry spells matter too. North Dakota State University's extension service notes that sticking doors and windows and wall cracks can be signs that a building is shifting as clay soil shrinks during dry weather. [3]

These are the findings HomeCloud reports flag separately as a notable wall crack or major corner cracking. See foundation and structure for that side of the house.

How to keep an eye on a crack

The ASCE guide recommends watching cracks over time for changes that keep growing or that come and go with the seasons. [2] An easy way to do that:

Mark each end of the crack with a pencil line and write the date next to it.
Take a photo with a ruler or tape measure held next to the crack.
Check it again every month or two, and after a long dry spell or a very wet one.

A crack that stays the same size for a year is usually fine to patch. A crack that keeps getting longer or wider is worth having looked at before anyone patches it, because a fresh patch erases the history.

When to call a structural engineer

Have a licensed structural engineer evaluate the house if you see:

A crack that keeps growing
Several of the signs listed above in the same area
Doors or windows that have started sticking along with new cracks
Floors that slope noticeably or feel soft

The engineer can tell you whether the movement is normal settling or something that needs repair, and what kind. Foundation repairs often need a permit, and the rules differ from city to city, so check with your local building department before work starts.

Keeping water away from the foundation helps in clay soils. The ASCE guide recommends sloping soil away from the house, running downspouts at least 3 feet out, and watering evenly around the whole foundation during droughts rather than soaking one side. [2]

Before you sand or patch older walls

Two health cautions apply to older homes:

Asbestos: Patching and joint compounds and textured paints made before asbestos was banned in them in 1977 may contain it. Sanding, scraping or drilling them can release fibers. [4] Have older textured walls or ceilings tested before anyone disturbs them.
Lead: Homes built before 1978 may have lead paint. The EPA recommends hiring a lead-safe certified contractor for work that disturbs paint in those homes. [5]

Cracks next to water stains

A crack with a brown stain around it, or drywall that feels soft or sags, is a water problem first. The EPA's cleanup guidance says wet drywall can be dried in place only if it isn't swollen and the seams are intact; otherwise it should be removed and replaced. [6] The leak gets fixed before the patch. See moisture staining at the ceiling, and the roof and plumbing guides for the usual sources.

Once the walls are patched, they need paint. Our guide to choosing interior paint covers sheens and when a patch needs primer.

HomeCloud is a licensed general contractor that evaluates homes and prices and does the repairs, including drywall patching and painting.