Doors, windows and glazing

6.7.3In-service performance

Doors, windows and glazing shall be designed and specified to ensure adequate in-service performance. Issues to be taken into account include:

  1. weathertightness
  2. fire safety
  3. thermal break
  4. strength
  5. resistance to movement, shrinkage and the effects of moisture.


Doors and windows should be installed correctly to ensure adequate in-service performance. Windows and external doors exposed to wind-driven rain should be constructed and detailed to ensure they remain weathertight, including at interfaces with the structure.

BS 6375 contains recommendations for the classification of window components according to their resistance under test to air and water penetration, and wind pressure.

Joints between multiple door and window frame assemblies should be:

  • part of an engineered system
  • formed using suitable materials in accordance with the manufacturer’s recommendations.

Vertical and horizontal DPCs should be provided around the frame in accordance with Chapter 6.1 ‘External masonry walls’ and Chapter 6.2 ‘External timber framed walls’.

DPCs should:

  • be correctly installed
  • extend approximately 25mm into the cavity
  • be continuous for the full height of the frame.

When placing frames for external elements in openings, ensure:

  • the head of the frame is protected by the lintel
  • throatings in sill members are not obstructed by the wall face.

Additional precautions include:

  • setting the frame back from the facade
  • building a projecting porch
  • providing a rain check groove to inward opening external door frames
  • fixing weatherboards and water bars to external doors, but ensuring the threshold is accessible where appropriate.

In Scotland, Northern Ireland and areas of very severe exposure, ‘check’ reveals should be used, and an appropriate sealant applied between door/window frames and the structure.

Fire safety

Fire-resisting doors and positive self-closing devices should be fitted where they are required by building regulations.

Thermal break

Metal windows should incorporate a thermal break.


Door frames, windows and their fittings should be adequate to withstand operational loads.

Structural loads should be carried on lintels, beams or appropriate structural elements. Where frames are required to carry structural loads, they should be designed accordingly.

Resistance to movement, shrinkage and the effects of moisture

Doors and windows should be designed to:

  • avoid significant distortion, such as twisting and bowing during use
  • take account of timber shrinkage
  • be moisture resistant, including window boards.