Cladding should not fit tightly onto the horizontal surface of any apron flashing; it will retain moisture and collect dirt and debris. It should have a minimum clearance of 25 mm.
Apron flashings should be in position before any parapet cladding is installed. The vertical leg of apron flashings should be a minimum of 100 mm high and hemmed or hooked, unless this would cause difficulty in fixing. This dimension provides 25 mm clearance between the apron and the cladding; if a hook or hem is not possible, the apron height should be increased by 25 mm.
To avoid capillary action, a break should be made between the capping and the vertical-fixed surface using 'birds beak' or similar break on the flashing edge. No down-turn into the pan of the profile should have a clearance of 2 – 5 mm from the pan. (See 7.2.2B Scribed Flashing)
Where the finish above the apron is plaster or the durability of the cladding is 50 years, the hidden apron flashing is also required to have a 50-year durability. It can be achieved by using a non-ferrous material for the flashing. Alternatively, a two-piece apron should be used where the over-flashing has a 50-year durability and the apron flashing can be renewed independently. (See 7.4.4F Two-piece Apron.)
Any stiffening edge should not be turned inwards, as not only will this scratch the cladding when it moves, but it can also be the cause of roof noise.
When the parapet walls will be plastered or when other trades are likely to follow the roof cladding installation, the roof cladding and flashings should be protected from damage. Provision should also be made for working and walking on the roof cladding during this time.
It is the responsibility of the roof fixer to make this requirement known to the contractor, and the COP recommends photographic and documentary evidence to avoid any future claims for damage caused by others.
Where an apron abuts a block, brick or concrete wall without any cladding above it, the apron flashing can be weathered by a step or a continuous chase flashing. These flashings can be made from aluminium, stainless steel or zinc when used with metallic-coated steels, and should extend 25 mm into the wall. They should be hooked or mechanically wedged and should be sealed with a compatible, flexible mortar or sealant. (See .) 7.4.4 Apron Flashings
Waterproofing, release from curing agents or the moisture content of the concrete slab can inhibit adherence of the sealant to the concrete. This area should be primed to ensure the sealant bond.
7.4.4A Chased Apron and 7.4.4C Angle Diverter are not the preferred installation methods for apron flashings. 7.4.4B Vertical Cladding (Parapet Flashing and Detail)shows a better method that provides more positive weathering by covering the wall with vertical metal cladding up to the capping.
Where the roof sheeting stops short and does not extend to the wall, the unsupported apron flashing can have a transverse fall back towards the internal angle of the apron flashing. It is not possible to ensure that all the water discharged from the apron flashing will be collected by the spouting at this junction, unless special provisions are made including:
For clarity, the spouting has been omitted from these drawings. Spouting should be fitted after the wall has been finished and should be 10 mm clear of the wall cladding.
Aprons should be stop-ended and turned down to weather and bird-proof the end of the apron at this junction.
When flashing a cavity parapet, the apron should be in place before the cavity batten as it is not possible to retrofit the apron. The apron material should have a 50-year durability unless the parapet cladding is easy to replace.
When a chase or reglet (7.4.4G Chase-fixed Flashing) is not provided, a pressure bar flashing can be used to weather an apron flashing into a concrete tilt-up slab wall.
One method of obtaining a seal without cutting a chase is to screw-fix a rigid angle to the wall with an EPDM foam or butyl strip behind, as shown in 7.4.4H Pressure Bar with Butyl Backing. This method gives the advantage that the flashing can be easily replaced and it can be the same material as the roof cladding. Take care seal the junction at the chamfered edge of the slabs with a 'make-up' piece of backer rod or something similar.