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Common mistakes · Detail

Shrinkage cracks and seams in a dormer

New materials settle and move. If the finishing does not allow for that, cracks appear along seams and corners. The good news is that most of this is preventable.
5 min leestijd·Onafhankelijke informatie

Short answer

Shrinkage cracks are caused by timber and plaster drying after installation. Hairline cracks are common, but large or recurring cracks suggest poor detailing. Exterior sealant cracks can let water in and need prompt repair.

Causes

Wood, plaster and sealants all move slightly with temperature and humidity. A well-built dormer allows for this movement. A poorly finished one fights it, and cracks are the result.

  • Temperature cycles — the dormer heats and cools faster than the main house.
  • Timber shrinkage — new wood dries and moves for the first few years.
  • Settlement — the structure settles slightly after loading.

Interior cracks

Interior cracks usually appear along plasterboard joints, at corners, and around window reveals. They are mostly cosmetic but can be annoying.

Exterior seams

Exterior sealant around windows, cladding joints and flashings is the first line of defence against water. If it cracks, water can get in.

Prevention

  • Allow movement gaps in the design.
  • Use flexible sealants on exterior joints.
  • Fix plasterboard to reduce vibration movement.
  • Use breathable paint on new plaster.
  • Schedule a touch-up after the first winter.

The full checklist

Checklist

Crack and seam prevention

  1. 01Exterior sealant is flexible and suitable for the material.
  2. 02Window reveals are sealed properly inside and out.
  3. 03Plasterboard joints are taped and filled with flexible compound.
  4. 04Interior paint is breathable and suitable for new plaster.
  5. 05A touch-up after the first year is included or planned.
  6. 06I know how to report exterior sealant issues.

FAQ

FAQ

Veelgestelde vragen

01What causes shrinkage cracks in a dormer?
Wood and plaster dry and shrink after installation. If joints are not detailed correctly, visible cracks appear along seams, corners and trim.
02Are small cracks in a new dormer normal?
Very small hairline cracks are common as materials settle. Large cracks, or cracks that keep opening, suggest poor detailing or movement.
03How do you prevent cracks in a dormer?
Use flexible sealants, allow for movement in the design, fix plasterboard properly, and use experienced painters who understand settlement.
04Can cracks cause leaks?
Interior plaster cracks rarely cause leaks. Exterior sealant cracks around windows or cladding can let water in and should be fixed quickly.
Conclusie
Cracks and seam issues are usually cosmetic, but they are also a sign of how carefully the finishing was done. A good company plans for movement and fixes small issues promptly.