Guide to the design of balconies and terraces

BS 8579:2020 pdf free.Guide to the design of balconies and terraces.
In a temperate climate such as the UK, balconies in proximity to windows have environmental effects upon the interior of the building. These include:
a) providing beneficial shading on certain facade orientations from detrimental high and medium angle sunlight in summer, thus offering an aid to passive cooling of the interior spaces;
b) providing too much shading on certain facade orientations that would benefit from low angle solar gain in winter;
c) providing too much shading from beneficial daylight to the interior spaces; and
d) providing beneficial acoustic buffering to the internal spaces (see C1aue1Z). Enclosure of balconies can result in the following additional environmental effects upon the interior of the building:
1) detrimental overheating in the internal occupied space connected to an enclosed balcony on certain facade orientations due to the restriction of ventilation to the adjacent interior space and entrapment of incident heat;
2) beneficial passive insulation of adjacent interior space by the thermal buffering effect of the enclosed balcony space in cold weather; and
3) detrimental condensation forming on the inside of a single glazed outer weather screen.
The design of the facade, windows, balconies and weather screens should take these factors into account in reaching an optimum balance for interior comfort and energy efficiency.
A well-designed enclosure to a balcony can facilitate its use by occupants for a greater period of time during the year than an open balcony, due to the weather protection it affords.
An enclosed balcony should not be designed as an internal room for full occupation, which is not the role of a balcony. The important exception to this is classification for fire purposes, where the volume of an enclosed balcony is considered as an inner room and, therefore, occupied. Therefore, targets for airtightness and thermal transfer performance for the outer weather screen should not be set. Targets for acoustic separation from adjacent balconies through the party wall may be set to reduce the risk of acoustic nuisance from neighbouring spaces. Targets for acoustic reduction from exterior to the balcony through the weather screen may be set, but should not be as stringent as those for internal living areas. The buffering effect of the outer weather screen can be taken into account in both thermal and acoustic calculations for the thermal envelope of the building.
Where a balcony is enclosed, the outer weather screen should incorporate both controllable openings for purge-type ventilation (such as openable windows) and uncontrollable fixed openings for background-type ventilation. The controllable openings in the outer weather screen for purge-type ventilation should have effective free area calculated based upon the requisite percentage of the combined areas of the balcony pedestrian surface and the inner rooms being ventilated.
The fixed openings in the outer weather screen for permanent background-type ventilation of enclosed balconies should have effective free area to external air of at least 8 000 mm:. This would ideally be distributed evenly along the external perimeter at the base and top of the weather screen by continual gaps of a minimum 4 mm. Other arrangements for fixed ventilation can be adopted but might require greater free area.
NOTE I This ensures that on enclosed balcony remains a sheltered exterior amenity space, not to be confused with habitable space. lithe space occupied by the balcony Is to be sealed from exterior air, it Is not classed as a balcony and therefore does not fall within the scope of this British Standard.
NOTE 2 An enclosed balcony is not to be confused with a conservatory, which can be fully ci osed from outside.
Where an adjacent interior room relies upon trickle ventilators for background ventilation via the enclosed balcony, the fixed openings in the outer weather screen providing permanent background- type ventilation should provide at least 5% more effective free area than the trickle ventilators serving the room.
In addition to self-shading and ventilation, overheating can be controlled by coatings on the glass. Alternatively, either fixed or moveable shading devices, such as blinds, louvres or shutters, can be used. Detrimental solar gain can be controlled by moveable shading devices with little effect on beneficial daylight, if well designed and operated. The use of shading devices on the inside near the glazed weather screen creates a layer of hot air which, if fixed ventilation openings are provided at the base and top of the glazing, can create a convection current that expels hot air at the upper opening and draws fresh cool air in to replace it at the lower opening. This is the basic principle of a double-skin facade. Glass coatings and fixed blinds are less adaptable than moveable shading and care should be taken to ensure a balanced solution for ensuring interior thermal comfort in all seasons.
Drainage considerations
The design of an enclosed balcony should prevent ingress of water into any adjacent internal spaces or structure. An enclosed balcony requires a drainage strategy. as the weather screen is likely to be left open by the occupant during hot weather. An assessment should be carried out to determine risk and the amount of rain ingress and effect when windows in the weather screen are open. Piped or edge drainage should be provided with sufficient capacity. See Clause 15 for further guidance on weathering and hydraulic design.
Fire considerations
The enclosure of balconies triggers additional risks relating to fire, smoke and means of escape. Where balconies are enclosed on buildings containing dwellings, residential units or specialized housing, the guidance in BS 9991 should be followed. See also guidance related to fire in Clause 12.
No active heating, cooling or mechanical ventilation, including MVHR (mechanical ventilations with heat recovery) should be connected to the volume of an enclosed balcony which, as a sheltered exterior space, should rely on natural ventilation only. Electrical fttings should be suitable for use in exterior locations. Surface finishes to an enclosed balcony should be exterior-grade materials that do not discolour or degrade in moist external air.BS 8579 pdf free download.Guide to the design of balconies and terraces