Flashings

Although only a small component, it is often the flashings which have the greatest impact on the overall appearance of a building. Paying close attention to detail in flashings can make a difference and deliver well executed building. Most weather tightness issues on modern, pre-finished steel-clad buildings are the result of poor flashings. It is essential that close attention is paid to the specification, manufacture and fixing of flashings. Here we assess the specification of flashings. The MCRMA Technical Paper, ‘Flashings for metal roof and wall cladding: design, detailing and installation guide’, provides a good source of more detailed information.

• Where possible, it is always better to specify factory-fabricated flashings.
• Flashings can either be in the same colour as the main cladding or in a contrasting colour. In the latter case, careful colour choice is important.
• It is important to specify flashings in the same material as the cladding, to ensure that they weather at the same rate.
• As flashings are often sourced separately to cladding, the material should be specified by name. The unique Scintilla® emboss of Colorcoat HPS200® Ultra make it easy to identify whether it has been specified and used.
• Where accurate colour matching is important, it is good practice to source flashings from the same batch as the main pre-finished steel cladding.
• Flashings should be specified in minimum 0.7 mm gauge pre-finished steel.
• Open flashings (those which nest) should be designed to have a 150 mm overlap at joints.
• Long edges should be formed so as to improve rigidity and appearance.
• Closed flashings (those which do not nest) should be jointed with butt straps of minimum 150 mm length.
• It is important to always consider the specification of fasteners and sealants, to provide the full solution.
• The shapes of flashings are dictated by junction details.

For the fabrication of flashings, there are a number of things to remember. It is important to specify the following:

• Girth (width).
• Length (typically 3 m, but others available).
• Quantity.
• Thickness (e.g. 0.7 mm).
• Pre-finished steel specification (e.g. Colorcoat HPS200 Ultra).
• Colour (e.g. Colorcoat HPS200 Ultra Ocean Blue).
• Packing instructions (i.e. batching, if required).
• A sketch of flashing shape (profile) including dimensions, angles, colour-coated surfaces, welts.
• Butt straps.
• Any special considerations, e.g. tapering in length, radius for curved flashings etc.

• Flashings must be well secured to the structure or sheeting at maximum centres of 450 mm (or alternate profile crowns whichever is the closer).
• Large, unsupported areas of flashing greater than around 200-250 mm wide should be avoided, since these are prone to distortions. However, where such widths cannot be avoided, they should be stiffened, for example, with stiffening folds or by bonding boards or stiffeners to the reverse.
• Edges of flashings should be welted to provide stiffness and to hide cut edges.