Metal Roofing Alliance

1. DEFINITIONS

The 2015 IRC (pg. 20) gives the following definitions:
Metal Roof Shingle: An interlocking metal sheet having an installed weather exposure less than 3 square feet (0.279 m2).
Metal Roof panel: An interlocking metal sheet having a minimum installed weather exposure of 3 square feet (0.279 m2).

2. MINIMUM SLOPE

Metal Panels:

(IRC) Lapped, non-soldered seams, no lap sealant: 3&12
(IRC) Lapped, non-soldered seams, with lap sealant: &12
(IRC) Standing seam: &12

Metal Shingles:

(NRCA) 4&12
These limitations are general standards. Minimum slope for metal panel and shingle roofs may be manufacturer specific. Do not identify any installations as improper unless you know that they are improper. If you suspect that they are improper, recommend confirmation of proper installation by a qualified contractor.

3. GALVANIC CORROSION

To avoid galvanic corrosion, flashing and fasteners should be of the same metal as the roof-covering material. In the presence of moisture different metals in contact with each other will suffer galvanic corrosion resulting in deterioration of the least noble metal.

4. FASTENING

All fasteners should be corrosion resistant and compatible with the type of metal roofing used. Fasteners are often manufacturer-recommended and may consist of nails, screws, or clips. Nails or screws should extent at least through roof sheathing panels, or at least into wood board roof sheathing.
Metal panel roofs with exposed fasteners and alternating high/low profiles should have fasteners installed in low sections. Fasteners installed in raised sections will back out over time.

5. OFFSET SIDE JOINTS

Metal shingles are typically installed with offset side joints

6. FLASHING

Flashings are often profile specific, provided by the manufacturer, either as pre-formed flashing or as pre-finished flat stock used for onsite fabrication.

7. Manufacturing Problems

 Oil-canning (cosmetic);
 Tension bend staining (at bends/creases from manufacturing process).

7. Installation Problems

  •  Lack of seam sealant;
  • Fasteners of different metal (galvanic corrosion);
  • Loose/protruding/missing fasteners;
  • Underdriven/overdriven fasteners
  • Improperly placed fasteners;
  • Inadequate structural support;
  • Minimum slope:
    • Panels: &12
    • Shingles: 3&12
  •  Missing closure (bird stop);
  • Improper penetration flashing;
  • Improper sidewall/headwall flashing;
  • Improper repairs;
  • Exposed substrate;
  • Gaps at ridge/rake trim;
  • Impeded drainage;

AC condensate drains onto roof.

Weathering Problems

  •  Batch problems (different panels aging at different rates);
  • Coating deterioration;
  • Corrosion;
  • Evidence of ponding;
  • Deteriorated caulking;

Delamination of stone-coat.

Metal Roof Damage

  •  Wind damage;
    • Damage from uplift;
    • Loss/damage/displacement of seam caps;
  • Damage from foot traffic;
  • Hail damage;
    • To stone-coat
    • To manufacturer applied coating
    • To seams

Note: Hail damage to metal roofs is often cosmetic rather than functional damage.

Functional damage:
1.  Shortens expected service life
2.  Reduces ability of roof to shed water