Replacement windows

Windows normally provide natural ventilation and daylight to a room and may act as a means of emergency escape in the event of fire.

Building Standards Approval is necessary for works which may involve alterations to a wall to incorporate a window - such as removal of load bearing mullions or enlarging a wall opening.

Building Standards approval

There is no need to obtain Building Standards approval to carry out window replacement.

However, if the replacement is by a window which is not of the same type as the one being replaced it must comply with the relevant sections of the Building Regulations. If the replacement window is of the same type as the one being replaced special care must be taken with such replacements to ensure that the new window design will not fail to meet the regulations to a greater degree.

Building regulations

The minimum statutory requirements for replacement windows include the following:-

  • Ventilation

    The total opening area of a window or windows of a naturally ventilated room must be not less than 1/30th the floor area of the room. A trickle ventilator may be incorporated within the window frame. The size of the trickle ventilator may vary between a minimum, per room, of 4,000mm2 to 8,000mm2 - depending on the type of room, providing that the overall average for the dwelling is not less than 6,000mm2 per room. Some part of the window opening, including a trickle ventilator, must be not less than 1.75 metres above floor level.

  • Day lighting

    The area of glass of a window or windows must be not less than 1/15th of the floor area of an apartment. If the apartment has an external glazed door then this glazing may be included.

  • Safety aspects

    • Where any part of a window in a dwelling is above 4 metres from ground level both external and internal surfaces of the window should be able to be cleaned safely from the inside e.g. without the use of a step ladder.
    • No opening part of a window should project so as to cause a danger to the public.
    • If any part of a window is less than 800mm from floor level the opening should be protected by a barrier (this may include an appropriate type of glass), suitably constructed to prevent anyone falling through the opening.
      The type of glass may vary depending on its height from floor level and consultation should take place with the installer.

    These illustrations are from BS 8213 : Part 1:1991 and are reproduced with the permission of BSI under licence no. PD\1998 0954.

Safety Aspects Safety Aspects

  • Emergency escape windows

    Emergency escape windows are intended to allow the occupants of a dwelling the option of unaided escape from the dwelling in the event of other escape routes being unusable.

    An emergency escape window should be provided in every apartment in an upper storey of a dwelling at a height of no more than 4.5 metres from ground level, unless there is more than one way out of the apartment excluding the window.

    An emergency escape window should also be provided in any apartment which is an inner room, unless there is an alternative route out of the room.

    Satisfactory dimensions of an emergency escape window would be a clear opening of 850mm. in height and 500mm. in width, providing unobstructed exit. However, it is recognised that alternative dimensions may still be acceptable, and advice should be taken from the Building Control office.


  • Apartment:

    Means a room not used solely as a kitchen, store, utility room, bathroom or toilet.

  • Dwelling:

    Means a unit of residential accommodation occupied (whether or not as a sole or main residence)

    (a) By a single person or by people living together as a family; or

    (b) By not more than six residents living together as a single household (including a household where care is provided for residents).

  • Inner room:

    Means a room, other than a kitchen, bathroom or toilet which does not have a direct access to an exit nor direct access to an enclosed circulation area (e.g. hall) having an exit.

  • Trickle ventilator:

    Means a closable small ventilator which can provide minimum ventilation.


(a) Exemption from Building Control Approval is not exemption from other forms of permission such as Planning Consent, Listed Building Consent, etc.

(b) The installer of replacement windows should be advised of the need to comply with the relevant Building Regulations prior to commencement of installation.

(c) This guidance gives a broad view of the requirements for replacement windows in dwellings and if more detailed information is required it is necessary to refer to the Technical Handbooks to comply with the Building Standards (Scotland) Regulations.

For further information please contact the Building Standards office.