Banrach Consulting Engineers · House Subsidence · Dublin

What Are the First Signs of Subsidence in a House?

By Banrach Consulting Engineers

The first signs of house subsidence are: diagonal cracks running at approximately 45 degrees from the corners of door or window openings, wider at the top than the bottom; cracks wider than 3mm, roughly the width of a 10 pence coin; doors or windows that suddenly stick or jam where they previously operated normally; gaps developing between skirting boards and the floor, or between door and window frames and the surrounding wall; and a floor that has developed a perceptible slope. Not all cracking is subsidence; most cracking in Irish homes is cosmetic plaster shrinkage. A Chartered Structural Engineer can assess the significance of cracks you are concerned about.

The First Signs of Subsidence: A Detailed Guide

• 1
  Diagonal Cracks Near Door or Window Openings This is the most characteristic early sign of foundation subsidence (The Institution of Structural Engineers ). When one part of a building's foundation drops relative to another, the wall structure distorts, and the weakest points in the wall are at the corners of door and window openings. Diagonal cracks run from these corners at approximately 45 degrees. Key features include a diagonal orientation, a crack wider at the top than the bottom (indicating the foundation beneath has dropped), visibility on both the inside and outside of the wall, a width over 3mm, and cracks that may appear on both sides of the same opening simultaneously.
• 2
  Cracks That Reappear After Filling A crack that has been filled, plastered over, or decorated, and then reappears particularly in the same location and with the same diagonal orientation indicates ongoing movement. This is one of the clearest indicators that the cracking is not cosmetic. Cosmetic plaster cracks typically do not recur precisely in the same location after being properly repaired.
• 3
  Sticking or Jamming Doors and Windows When a building's frame distorts due to foundation movement, door and window frames distort with it. A door that is suddenly difficult to close sticking at a corner rather than along the whole edge may indicate that the frame has racked, changing from rectangular to parallelogram. This is a structural sign of foundation movement, not wear or humidity. If a door that operated normally for years suddenly begins to stick and this coincides with the appearance of diagonal cracks in the same area, the probability of subsidence as a cause is significantly increased.
• 4
  Gaps Between Structural Elements Relative movement between a building's elements creates visible gaps: between the skirting board and the floor, where the floor has dropped relative to the wall; between a window or door frame and the surrounding masonry, where the frame has moved relative to the wall; between a ceiling and the top of a partition wall, where the structure beneath has dropped; and between a wall and a fireplace surround, where the external wall has moved relative to the internal structure.
• 5
  Sloping Floors A floor that has developed a perceptible slope where it was previously level particularly at the junction with an external wall may indicate that the foundation beneath that wall has dropped. In older Dublin properties, floor slopes can accumulate over years before becoming clearly perceptible.

How to Distinguish Subsidence Cracks from Cosmetic Cracks

When Should You Call a Structural Engineer?

You should contact a Chartered Structural Engineer if you notice:

• 1
  Any diagonal crack near a door or window opening that is more than 3mm wide
• 2
  A crack that has reappeared after being filled
• 3
  A door or window that has suddenly started sticking where it did not before, combined with visible cracking nearby
• 4
  A floor that appears to have developed a slope
• 5
  Visible cracks on both the inside and outside of the same wall
• 6
  You are buying a property and the surveyor has flagged cracking as requiring further investigation

You do not need to call a structural engineer for hairline plaster cracks with no associated structural signs. But if you are in any doubt, a professional assessment is worth the cost. It either gives you reassurance or identifies a problem before it worsens.

Frequently Asked Questions

• What are the first signs of subsidence in a house?

  The first signs are diagonal cracks wider than 3mm from the corners of door or window openings (wider at the top), doors or windows that suddenly stick or jam, and gaps developing between skirting boards or frames and the surrounding structure. These signs warrant a Chartered Structural Engineer's assessment.
• Can a 3mm crack in a wall be serious?

  Yes, if it is diagonal, located near a door or window opening, and wider at the top than the bottom. A 3mm crack, approximately the width of a 10 pence coin, in this context is a structural, not cosmetic, crack and indicates differential foundation movement. A Chartered Structural Engineer should assess it.
• How do I know if my house has subsidence or just normal cracks?

  Normal (cosmetic) cracks are hairline, random in pattern, and do not recur after repair. Subsidence-related cracks are diagonal, wider than 3mm, located near structural weak points such as door or window openings, wider at the top than the bottom, and may recur after filling. Associated symptoms of subsidence include sticking doors, sloping floors, and gaps at skirting boards.