COP:flashings; purpose

7.1 Purpose 

The purpose of a flashing is to divert water away from any point of entry and to make a building weatherproof.
Flashings are not only required to weather the many junctions on a roof or wall structure, but are also a visible part of the roof and wall cladding design. It performs an important role in the aesthetic appearance of the building.
The words weather, weathering, weatherproof and watertight used in this section and in the Code of Practice are used as nouns, verbs or adjectives. See 2.1 Definitions.

Experience is required to design, cut, and fasten flashings that will last the lifetime of the roof or wall cladding. Specialist assistance should be sought when such experience is not available.

It takes longer to make and install flashings than fixing roof or wall cladding, and roofing contractors are obliged to allow for acceptable trade practice, as described in this Code of Practice, when they tender.

The standard of workmanship on straight or curved flashings and accessories will determine the overall acceptance of the workmanship on a building. That is why both designers and roofing contractors should know the requirements of this section of the Code of Practice.

Roofing contractors must be competent to design, make and install the flashings as described in this Code of Practice.

Flashings include all folded metal sections required to make metal roof and wall cladding weathertight at:

  • the building periphery;
  • roof and wall junctions;
  • changes in direction;
  • intersections with other buildings;
  • any roof or wall penetration; and
  • junctions with other materials.

All flashings must comply with the lap, cover, expansion, and compatibility provisions of this Code of Practice. Flashings that cannot be seen and are not easily replaced, must have a 50-year durability.

The initial cost of good flashing design and the time taken to install flashings to good trade practice is repaid, not only by their appearance, but also because repair, replacement, and maintenance are minimised. Replacement of flashings can require the costly replacement of cladding; often it is not possible to remove one without the other.

All flashings must be designed to prevent ponding of water or build-up of debris

Flashings must be designed to weather the roof or wall cladding without reliance on sealant as the prime means of weathering.

Successful installation of flashings requires planning before any roof or wall cladding is installed. Both scheduling and sequencing are necessary to deliver flashings on site when they are needed and to provide the correctly dimensioned cover required in 7.3 Flashing Cover of this Code of Practice.