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Does the 12/2 minimum pitch rule for shingles still apply if peel-n-stick is first applied to the roof deck? Why would I have to put down a membrane on 12/1 pitch above the porch, instead of shingles, if there is peel-n-stick? And then can't I just install the shingles right over the peel-n-stick? I just want the whole roof to look the same. I live in FL.

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As an aside, the typical expression of slope is rise-over-run: 2/12 or 2 in 12 – HerrBag Aug 29 '13 at 11:58

If there are not asphalt shingles and it meets the manufacturer specs for install, I can't find why not but you may still need to get it approved.

All from Florida Building Code 2004



R905.1 Roof covering applications. Roof coverings shall be applied in accordance with the applicable provisions of this section and the manufacturer’s installation instructions.

R905.2 Asphalt shingles. The installation of asphalt shingles shall comply with the provisions of this section.

R905.2.1 Sheathing requirements. Asphalt shingles shall be fastened to solidly sheathed decks.

R905.2.2 Slope. Asphalt shingles shall only be used on roof slopes of two units vertical in 12 units horizontal (2:12) or greater. For roof slopes from two units vertical in 12 units horizontal (2:12) up to four units vertical in 12 units horizontal (4:12), double underlayment application is required in accordance with Section R905.2.7.

R905.2.3 Underlayment. Unless otherwise noted, required underlayment shall conform to ASTM D 226 Type I, ASTM D 4869 Type I, or ASTM D 6757. Self-adhering polymer modified bitumen sheet shall comply with ASTM D 1970.

R905.2.7 Underlayment application. For roof slopes from two units vertical in 12 units horizontal (17-percent slope), up to four units vertical in 12 units horizontal (33-percent slope), underlayment shall be two layers applied in the following manner. Apply a 19-inch (483 mm) strip of underlayment felt parallel to and starting at the eaves, fastened sufficiently to hold in place. Starting at the eave, apply 36-inch-wide (914 mm) sheets of underlayment, overlapping successive sheets 19 inches (483 mm), and fastened sufficiently to hold in place. Distortions in the underlayment shall not interfere with the ability of the shingles to seal. For roof slopes of four units vertical in 12 units horizontal (33-percent slope) or greater, underlayment shall be one layer applied in the following manner. Underlayment shall be applied shingle fashion, parallel to and starting from the eave and lapped 2 inches (51 mm), fastened sufficiently to hold in place. Distortions in the underlayment shall not interfere with the ability of the shingles to seal. End laps shall be offset by 6 feet (1829 mm).



104.11 Alternative materials, design and methods of construction and equipment. The provisions of this code are not intended to prevent the installation of any material or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability and safety. When alternate life safety systems are designed, the SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design of Buildings, or other methods approved by the building official may be used. The building official shall require that sufficient evidence or proof be submitted to substantiate any claim made regarding the alternative.

Note: Also be aware of local amendments and declaratory statements

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@richardraustad the 2/12 slope merits Double underlayment. As Jason mentions, you will need the manufactures specs showing asphalt shingles over 1/12 are even allowed, to start. – HerrBag Aug 29 '13 at 12:09
@HerrBag, yes double underlayment if felt, but I hope I would not have to double the peel-n-stick, it seems pointless and would be costly. I'll call the code enforcement office. Thanks. – Richard Raustad Aug 29 '13 at 13:46
These codes are rock bottom minimums to assure safety; they're not trying to legislate excellence here. So it's a cautionary tale: shingle roofs struggle to function properly on a 4:12 roof angle or less. I would go with a different roofing system. Metal roofs work fine at much shallower angles, and rubber roofs work literally flat. – Harper Mar 24 at 17:22

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