COP v3.0:installation; fixing-aluminium-sheeting

14.19 Fixing Aluminium Sheeting 

Aluminium is a naturally durable material with proven performance over a long period.

Most metals compatible with Galvanised and Aluminium/Zinc coatings are compatible with aluminium. However, to acquire the required fastener durability, use aluminium or stainless screws rather than painted steel screws.

Aluminium has approximately twice the thermal expansion of steel, therefore, expansion provisions must be executed as for steel of twice the length.

Being soft and frequently requiring oversize holes for expansion, aluminium is typically fastened with fasteners equipped with load spreading washers, as is typically reflected in published span tables. Installers must adhere to published fastening systems to meet design load/span expectations.

 

 

14.19.1 Painted Aluminium 

Painted aluminium products perform differently than uncoated aluminium as the paint coating affects reactions with the atmosphere, and reduces the aluminium surface area that can be sacrificed to defend against localised corrosion.

Pit corrosion can result from damage to the paint coating and exposure to corrosive substances. It is necessary to protect against wet contact with concrete, treated timber, steel, stainless steel, and butyl rubber.

14.19.2 Recommendations for Fixing Aluminium 

  1. The front edge of the spouting or gutter must be higher than the crest of the roofing profile.
  2. Eaves flashings of painted or unpainted aluminium must be used. Underlay should terminate on the top of the eaves flashing.
  3. When re-roofing with aluminium, the existing support members must be inspected to ensure all staples, wire netting, nails, or other materials likely to damage the aluminium have been removed.
  4. Galvanised netting or mesh must not be in contact with the underside of aluminium roofs. If present, it must be separated by a 5 mm barrier of inert non-absorbent, non-reactive material. Alternatively, self-supporting underlays may be used. Plastic strapping can be used for supporting underlays, stapled with stainless steel staples to the vertical face of the purlins.
  5. In a wet environment, aluminium must be separated from a corrosive surface such as concrete, butyl rubber, or CCA treated timber by using a 5 mm rigid strip of an inert non-absorbent material, an open woven geotextile layer, or PVC netting. Plastic coated steel netting is not recommended under aluminium sheeting.
  6. The design of the ceiling cavity must prevent the saturation of support members from internal or ground moisture. (See 10 Internal Moisture.)
  7. All screws should be fitted with a profiled or bonded washer. Fixing screws shall be aluminium or Grade 304 stainless steel. Stainless steel screws must be fitted centrally through pre-drilled oversized holes (9 mm) for roofing and walls, regardless of sheet length.
  8. For sheet lengths over 10 m, the capacity to allow for thermal expansion must be in accordance with the tables in the MRM COP v3.0.