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Flashing a Bottom of Wall
last updated 25/07/16
Summary of this page

Flashing a bottom of wall provides an effective solution for the prevention of water entering between the bottom of the wall sheet and the footing (concrete, timber or steel).
When designing flashings you should be aware that manufacturer's folders may have different tolerances for folding flashings and the flashing length available may be restricted, for example 3 metre lengths. There are many variations to flashings, the following details represent a sample of suitable solutions.

 
Bottom of Wall Flashing - Type 1
Download CAD versions of this flashing

Typical sizes for bottom of wall flashing type 1

  • A = 150mm - 200mm (typical)
  • B = to suit the application (to outside of footing)
  • C = 10mm-15mm break @ 135 degrees (typical)

With a bottom of wall flashing it is important that the angle between A & B is sufficient to ensure good water drainage, a 15 degree break from the horizontal line would be sufficient. To maximise the life of the wall sheeting, the sheeting closest to the flashing should have a 'drip edge' and be sufficiently clear so as not to allow debris to build up.

Key Design considerations:
Extract from Corrosion Technical Bulletin CTB 16 - Immersion

"Moisture or moisture retaining materials should not be permitted to remain in intimate contact with ZINCALUME® steel, COLORBOND® steel or galvanized steel. Such contact will ultimately result in perforation of the material."
Read more in Corrosion Technical Bulletin CTB 16 - Immersion

Flashing a horizontal corrugated wall sheeting with a bottom of wall type 1 flashing

click to enlarge

click to enlarge

Download CAD versions of this detail
Technical Resources
  1. Corrosion Technical Bulletin CTB 16 - Immersion
  2. Acceptability of Drainage from an upper surface to a lower metal surface
  3. Material Selection
For a complete list of BlueScope Steel Technical Bulletins click here

 

Bottom of Wall Flashing type 2
Download CAD versions of this flashing

Typical sizes for bottom of wall flashing type 2

  • A = 150mm - 200mm (typical)
  • B = to suit the application (to outside of footing)
  • C = 50mm (typical)
  • D = 10mm-15mm break @ 135 degrees (typical)

As with type 1, it is important that the angle between A & B is sufficient to ensure good water drainage, a 15 degree break from the horizontal line would be sufficient. To maximise the life of the wall sheeting, the sheeting closest to the flashing should have a 'free drip edge' and be sufficiently clear so as not to allow debris to build up (refer key design considerations above).

Measurement C gives the flashing greater strength than type 1 and greater protection from water entering under the walling. This type of flashing would be suitable where footing height is available. It would not be suitable if concrete pathways were to cover the flashing (refer key design considerations above).

Flashing a horizontal corrugated wall sheeting with a bottom of wall type 2 flashing

click to enlarge

click to enlarge

Download CAD versions of this detail
Technical Resources
  1. Corrosion Technical Bulletin CTB 16 - Immersion
  2. Acceptability of Drainage from an upper surface to a lower metal surface
  3. Material Selection
For a complete list of BlueScope Steel Technical Bulletins click here

Resource Acknowledgements
Source: SteelSelect - author Richard Michael

Publication Details: November 05

Authors Disclaimers:  The information and advice contained in this article is of a general nature only, and has not been prepared with your specific needs in mind. You should always obtain specialist advice to ensure that the materials, approach and techniques referred to in this article meet your specific requirements. SteelSelect makes no warranty as to the accuracy, completeness or reliability of any estimates, opinions or other information contained in this article, and to the maximum extent permitted by law, SteelSelect disclaims all liability and responsibility for any loss or damage, direct or indirect, which may be suffered by any person acting in reliance on anything contained in or omitted from this document.