Jerry Peck - Codeman wrote:I'll check the code for anything specific in it, however, the shingle manufacturer's installation instructions would be one direct and specific source that the code will refer to.
From the 2018 IRC (I used the 2018 IRC to allow for both a 'not new roof covering' and a 'not real old roof covering') (bold and underlining are mine)
R903.2 Flashing.
Flashings shall be installed in a manner that prevents moisture from entering the wall and roof through joints in copings, through moisture permeable materials and at intersections with parapet walls and other penetrations through the roof plane.
R905.2.8 Flashing.
Flashing for asphalt shingles shall comply with this section and the
asphalt shingle manufacturer's approved installation instructions.
- (Jerry's Comment: this is where the code refers to the "manufacturer's installation instructions", with a specific additional word: "approved": "Section R202 Definitions [RB] APPROVED. Acceptable to the building official." which means that the manufacturer's installation instructions shall have been submitted to the building official for approval - this would typically be done by the contractor submitting the manufacturer's installation instructions with the permit application, and "approval" of the of the permit application and issuance of the permit would be the "approval" of the manufacturer's installation instructions.If the installation instructions are not submitted and "approved", the manufacturer's installation instruction would not be applicable, in which case, installation of the asphalt composition shingles would not "be in compliance with the code".)
R905.2.8.2 Valleys.
Valley linings shall be installed in accordance with the manufacturer’s instructions before applying shingles. Valley linings of the following types shall be permitted:
1. For open valleys (valley lining exposed) lined with metal, the valley lining
shall be not less than 24 inches (610 mm) wide and of any of the corrosion-resistant metals in Table R905.2.8.2.
2. For open valleys, valley lining of two plies of mineral-surfaced roll roofing, complying with ASTM D3909 or ASTM D6380 Class M, shall be permitted. The bottom layer
shall be 18 inches (457 mm) and the top layer not less than 36 inches (914 mm) wide.
3. For closed valleys (valley covered with shingles), valley lining of one ply of smooth roll roofing complying with ASTM D6380 and
not less than 36 inches wide (914 mm) or valley lining as described in Item 1 or 2 shall be permitted. Self-adhering polymer modified bitumen underlayment complying with ASTM D1970 shall be permitted in lieu of the lining material.
- (Jerry's Comment: "shall be not less than xx inches (xxx mm) wide" does not allow for a penetration through that material as that would not meet the "shall be ... wide" requirement.)
P3103.1.1 Roof extension.
Open vent pipes that extend through a roof and that do not meet the conditions of Section P3103.1.2 or Section P3103.1.3 shall terminate not less than 6 inches (150 mm) above the roof or 6 inches (150 mm) above anticipated snow accumulation, whichever is greater.
- (Jerry's Comment: "Section P3103.1.2 or Section P3103.1.3" are not applicable to the vent terminal in question.)