BS 6229:2003 'Flat roofs with continuously supported coverings Code of practice' and BS 8217:2005 'Reinforced bitumen membranes for roofing Code of practice', state that all weatherproofing upstands occurring around the roof area; including doorways, openings, rooflights, smoke vents, plinths etc must have a minimum height of 150mm, measured from the finished surface of the roof, if unwanted water entry into the building is to be avoided.

On exposed membrane roofs the upstand height is measured directly from the membrane surface. Where gutters’ are located alongside an upstand, the finished roof level is measured from the adjacent main area of roof, not the sole of the gutter. In ballasted/green roofs the upstand height is defined as being measured from the upper surface of the finished roof covering i.e stone ballast.

The implications of the requirements of minimum 150mm upstands should be considered at design stage, especially when designing balconies, as it might be necessary to allow for a cranked floor slab at the external walls, so when the insulation, membrane and surfacing of the balcony are installed, it does not compromise the upstand height.

In cases where disabled or wheelchair access is required, this is best achieved by constructing ramps, preferably with a porous or perforated surface, which not only allows rainwater to drain through, but provides a surface with grip.