Plasterboard cracks and nail pops in new build homes

A new home is built with a lot of water in it. Timber, plaster, mortar and concrete all shrink as they dry, and NHBC says drying out generally takes around nine months to a year. Small cracks while that happens are a normal part of a new home settling in.

NHBC states that most homes will crack at some point, however well they are designed and built. Heat speeds up shrinkage, so cracks often show once the heating goes on. Seasonal changes in temperature and humidity keep the materials moving slightly after that.

For the first months, NHBC advises warming the home gradually and keeping an even temperature. Keep windows or trickle vents open so moisture can escape, and run the extractor fan for about 20 minutes after cooking or bathing.

Where a crack sits tells you most about its cause. A fine straight line along a board joint or a corner is usually movement. A raised disc or ring on a wall or ceiling is a nail or screw pop. Cracks that are wide, tapered or stepped are a different matter and go to the builder.

NHBC names the joint between an external wall and an internal plasterboard wall, and the joints between ceiling boards, as common places for movement cracks.

A nail pop or screw pop is a fixing head pushing through the finish. It shows as a small raised disc, a ring of cracked filler or a round shadow on a ceiling. The usual cause is the timber stud or joist behind the board shrinking as it dries, which leaves the board loose on the fixing.

The fixing matters too. The NHBC best practice guide says boards should not be over-screwed, with the screw just below the surface and the paper intact. The Knauf Wallboard data sheet places screws 10mm from a bound edge and 13mm from an unbound edge. A screw nearer the edge can break out.

NHBC guidance states that a crack of 2mm or less is considered cosmetic and will not affect the structural stability or safety of the home. It can be filled. NHBC adds that a filled crack may return after a year or so, which is no worry unless it keeps widening.

Under the NHBC Buildmark policy, the first two years from completion are the builder warranty period. If you tell the builder about a problem in that time, the builder must put right, within a reasonable time, any failure to meet the NHBC requirements. Buildmark does not cover shrinkage that did not result from such a failure. Cover depends on the policy version for your home, so read your own booklet.

Developers registered with the New Homes Quality Board must give at least two years of after-sales service and put right snags and defects in that period. Its Code says that in most situations an issue must be settled within 30 days, or the delay explained with monthly updates.

NHBC asks homeowners to contact it about a crack wider than 5mm at any point, wider at one end, diagonal or stepped at any width, or constantly more than 2mm wide. The same goes for a crack seen inside and out, one with sticking doors or windows, or one that has grown.

Those signs call for the builder, and possibly a structural engineer, to look at the home. Report it to your builder by email or letter, as the Buildmark booklet recommends, and keep a record of who you told and when.

Photograph the crack with the date and a ruler or coin beside it for scale. NHBC notes that a £1 coin is about 3mm wide. A second photograph weeks later shows whether it has changed.

Most avoidable cracks and pops trace back to when the boards went up and how they were fixed and jointed. The NHBC best practice guide says boarding should not start until the building is watertight. It checks screw numbers, spacing, edge distances and the staggering of boards over doorways.

These are the common causes on a housing site, each with what prevents it.

• Boards fixed to wet timber, or before the plot is weathertight. Board once the plot is dry and keep boards dry in store
• Screws overdriven through the paper or set too near an edge. Set heads just below the surface at the manufacturer's edge distances
• Too few fixings or centres too wide. Fix to the spacing the board maker publishes
• Board edges with nothing behind them. Fit noggings where edges need support, and beside stairs
• A board joint in line with the side of a door opening. Stagger the boards so a joint falls over the head
• Joints filled without tape, or cut edges butted without preparation. Tape and joint every joint to the system's method

A hairline shrinkage crack is raked out lightly, filled with filler or jointing compound, sanded and painted. NHBC says small shrinkage cracks can normally be put right with ordinary filler and paint at routine redecoration.

A nail or screw pop needs the board refixed first. The usual repair drives a new screw into the timber close to the old one, then sets the old fixing below the surface or removes it. Both are filled, sanded and painted. Filling over a pop without refixing tends to leave it to push through again.

A joint crack that keeps reopening may need cutting out and re-taping. The builder decides that. On our own sites, every plot is photographed and recorded before handover, and a customer care administrator answers requests within 24 hours. Defects are dealt with inside the client's customer care charter timelines.