Image - Typical balconies
The following considerations should be taken into account when designing or constructing roof terraces and recessed or projecting balconies, including all associated members like supports and guarding.
Dead and Imposed loads
Ensure the relevant Eurocodes and the requirements of the building regulations are followed when designing for dead and imposed loads.
I.S. EN 1991-1-4 should be consulted and followed when calculating wind loads appropriate to the site. Design should prevent uplift of the structure. This can be achieved either by fixing/anchoring the structure to the main structure or by making the structure sufficiently heavy so as to resist uplifting. Where required, provide holding down fixings.
Timber should be limited to secondary elements in projecting balconies. These timber elements should be supported by members that are not timber.
Where roof terraces and balconies also function as roofs, they must resist the passage of moisture into the building. Only an agreement certified or some similarly certified roof covering should be used and this covering should be laid in accordance with the manufacturer’s instructions. Specialist contractors approved by the manufacturers may be required to lay some proprietary systems.
Image - Roof terrace
Ensure that timber decking systems are of a type and design that prevents a build-up of standing water and that they only use compatible preservative treatments. In order to prevent damage to the waterproofing membrane, the underside of the bearers should have large, smooth contact areas with no sharp corners or edges.
Where concrete paviors are used as a surface finish in warm roof construction, ensure that the rigid insulation that is fit for purpose is used to provide sufficient support to the paviors.
To ensure that the finished fall is not less than 1 in 80, a fall of not less than 1 in 40 should be used unless a detailed analysis of overall and local deflection is undertaken. If tapered insulation systems are incorporated to provide a fall, the manufacturer’s design and instructions should be followed.
Image - Typical balcony drainage
Outlets to provide adequate rainfall disposal should be provided. I.S. EN 12056-3 outlines the expected rainfall intensities that should be designed for. Where roof terraces and balconies are contained by parapet and upstand walls, roof drainage overflow should be provided in case the outlets become blocked. These overflows should be located such that they prevent water from entering the building.
Guards should be designed to prevent the risk of accidents when the balcony or terrace is in service. Materials suitable for guarding include a wall, a screen (glazing), a railing, or a balustrade. It is important that if a balustrade is incorporated it will not be climbed easily, and also that any glazing consists of toughened or laminated glass in accordance with BS 6262-4:2005. Ensure that, when fixing guarding, the fixings do not penetrate the waterproofing or the damp-proof courses.
All screens, parapet walls, railings, and balustrades must be at least 1100 mm high and designed to resist horizontal loading to ensure stability and prevent overturning. Refer to relevant tables and Technical Guidance Document K of the Building Regulations.
Image - Recessed balconies
In situations where a roof terrace or a balcony forms part of the roof construction for the space beneath, insulation that complies with Technical Guidance Document L of the Building Regulations should be provided.