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    FBC, Existing Building 611.7.2

    FBC, Existing Building 611.7.2

    New postby RobShepp on Tue Dec 02, 2014 4:27 pm

    Jerry, I'm looking for clarification or an explanation on FBC, Existing Building 611.7.2. What I'm understanding is the #1 lists two application for use within the HVHZ,
    a. a 4" wide tape at the seams and joint
    b. entire roof deck shall be covered with 30# felt or approved synthetic underlayment, fasteded in place.

    Are these applications for ALL types of roofing systems, or is one specifically for tile and the other for shingle/other? I have to admit, this section is a little confusing for me as I try to determine what does and doesn't qualify for SWRB. As you know, wind mitigation forms ask if the roofing system has a SWR...being as these types of systems qualify, i want to make sure i have a proper understanding of the code.

    Thank Jerry

    611.7.2 Roof secondary water barrier for site-built single family residential structures.

    A secondary water barrier shall be installed using one of the following methods when roof covering is removed and replaced:
    1. In either HVHZ or Non-HVHZ regions:
    a) All joints in structural panel roof sheathing or decking shall be covered with a minimum 4 inch (102 mm) wide strip of self-adhering polymer modified bitumen tape applied directly to the sheathing or decking. The deck and self adhering polymer modified bitumen tape shall be covered with one of the underlayment systems approved for the particular roof covering to be applied to the roof.
    b) The entire roof deck shall be covered with an approved a sphalt impregnated 30# felt underlayment or approved synthetic underlayment installed with nails and tin-tabs in accordance with Sections R4402.7.2, R4402.7.3, or R4402.7.4 of the Florida Building Code, Residential. (No additional underlayment shall be required over the top of this sheet.) The synthetic underlayment shall be fastened in accordance with the manufacturer’s recommendations.
    2. Outside the High Velocity Hurricane Zone:
    a) The entire roof deck shall be covered with an approved self-adhering polymer modified bitumen sheet meeting ASTM D 1970 or an approved self-adhering synthetic underlayment installed in accordance with the manufacturer’s installation instructions. No additional underlayment shall be required on top of this sheet for new installations.
    b) An underlayment system approved for the particular roof covering shall be applied with the following modification:
    (1) For roof slopes that require one layer of underlayment, a layer of approved asphalt impregnated ASTM D 226 Type I or Type II underlayment or approved synthetic underlayment shall be installed. The felt is to be fastened with 1 inch (25 mm) round plastic cap or metal cap nails, attached to a nailable deck in a grid pattern of 12 inches (305 mm) staggered between the overlaps, with 6-inch (152 mm) spacing at the overlaps. The synthetic underlayment shall be fastened in accordance with the manufacturer’s recommendations.
    (2) For roof slopes that require two layers of underlayment, an approved asphalt impregnated ASTM D 226 Type I or Type II underlayment shall be installed in a shingle–fashion and lapped 19 inch (483 mm) and fastened as described above. An approved synthetic underlayment shall be installed in accordance with the manufacturer’s installation instruction. (No additional underlayment shall be required over the top of this sheet.)

    Exceptions:
    1. Roof slopes < 2:12 having a continuous roof system shall be deemed to comply with Section 611.7.2 requirements for a secondary water barrier.
    2. Clay and concrete tile roof systems installed as required by the Florida Building Code are deemed to comply with the requirements of Section 611.7.2 for Secondary Water Barriers.
    RobShepp
     
    Posts: 22
    Joined: Sat Oct 04, 2014 8:56 am

    Re: FBC, Existing Building 611.7.2

    New postby Jerry Peck - Codeman on Tue Dec 02, 2014 9:48 pm

    Ah, trying to understand the incomprehensible, huh? (Really, I'm not kidding, it makes no sense - I will explain.)

    You are looking for guidance in building code requirements to address insurance requirements ... and those two don't mix any better than oil and water, nor was there any intent to have the two mix.

    One, the building code requirements, is based on the minimum consensus codes developed for a minimum level of safety. The other, the insurance requirements, is based on actuarial assumptions of risk, not on minimum safety standards.

    To qualify for the insurance discounts the roof is required to have a secondary water barrier, i.e., the "minimum 4 inch (102 mm) wide strip of self-adhering polymer modified bitumen tape" applied to the roof sheathing seams (not duct tape - although some tried to use duct tape for this when the requirements first came out) or "an approved self-adhering polymer modified bitumen sheet " which in effect sealed the entire roof and not just the roof sheathing panel joints.

    The above is for insurance discounts.

    For building code requirements, there is a different set of rules which are based on minimum levels of safety (and property damage to some extent in this case).

    You noticed that in the HVHZ peel-n-stick underlayment over the entire roof is not one of the permitted options - no, the HVHZ knows that roofs will be replaced and that the peel-n-stick will not be removed easily at all (said with a sarcastic tone) and therefore the peel-n-stick may only be applied to the mechanically attached underlayment, thereby making the underlayment easier to remove at the time of re-roofing (or at the time of a high wind event such as a hurricane ... more sarcasm).

    The rest of the state recognizes that, at the time of re-roofing, if the peel-n-stick underlayment is not easily removed ... then it is stuck in place ... and just go back over it with either a new roof (reusing the stuck in place peel-n-stick) or put another layer of peel-n-stick over the existing peel-n-stick (setting aside the requirement to remove the existing roof down to roof sheathing, this is readily allowed under alternate materials and methods in the rest of the state).

    Thus, getting the insurance discounts for the secondary water barrier in the HVHZ is, basically, asking for the roof to have been installed in non-compliance with the code.

    However, if you ignore what the insurance companies are asking for (what they want versus what the form asks for) and go by what the form asks for (a "secondary water barrier" if I recall correctly), you can read the code which calls 30" felt underlayment or an approved mechanically fastened synthetic as meeting "A secondary water barrier shall be installed using one of the following methods ... "

    Yes, there it is in the code: "A secondary water barrier ... " and, if method 1. is chosen, then the 30 pound or synthetic mechanically attached underlayment is a "secondary water barrier" - and it that is the wording on the insurance form, you would not be incorrect in marking "Yes" at "secondary water barrier" for 30 pound felt as you have the Florida Building Code to support your call.

    Unless the insurance form specifically calls for something other than a mechanically attached underlayment, you would be code-correct in marking a secondary water barrier is present on basically any roof installed or replaced with a permit in Florida. Whether or not the insurance company accepts it would be up to their wording as to what they define a "secondary water barrier" to be.

    Now, the reason for Exception 2:
    - 2. Clay and concrete tile roof systems installed as required by the Florida Building Code are deemed to comply with the requirements of Section 611.7.2 for Secondary Water Barriers.

    That would typically be a 30-90 hot mop system or other sealed underlayment system and is deemed to comply with the requirements of a secondary water barrier (the tile being the primary water barrier).

    Likewise, even unsealed System One tile roofs with the flashings on top of the tile, where the tile is the one and only "water barrier", the unsealed or sealed underlayment beneath it acts as a secondary surface over the roof sheathing to shed water, i.e., a "secondary water barrier".

    Now, if someone were to install tile over a plain roof deck with no underlayment, no, that would not meet the secondary water barrier requirement - plus it would never be approved at inspection time (I hope).
    Jerry Peck - CodeMan
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    Re: FBC, Existing Building 611.7.2

    New postby RobShepp on Wed Dec 03, 2014 8:28 am

    Thank you Jerry, that's what was puzzling me...the 1802 seemed to be non-code compliant.
    RobShepp
     
    Posts: 22
    Joined: Sat Oct 04, 2014 8:56 am


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