Cracks commonly appear above doors and windows. This is because they are the weakest part of any wall. Cracks here are not necessarily cause for concern. Consult a qualified structural engineer if cracks are severe or worsening.
Cracks are common in new property. This is not usually indicative of any serious problem. It is due to drying and shrinking of construction materials. Fill cracks and redecorate.
Consult a structural surveyor if new cracks have appeared in an older home. The building may require stabilising. Surveyors can place special equipment over the crack to monitor changes.
Weakened lintels---horizontal beams supporting the tops of windows or doorways---can cause cracking of the bricks above. In older homes, wood lintels may have rotted. Wood lintels without a waterproof barrier between them and the brick may swell. Brick arches over windows frequently shift.
Subsidence and Upheaval
Stair-shaped cracking in brick walls, including severe cracks from corners above doorways, indicates problems with the foundation. Possibly the ground beneath the house has shifted. This is common in clay soils, especially after drought. Leaking drains, tree roots, building over old mine workings or in earthquake-prone areas are other causes. Monitor cracks to see if they are actively worsening.