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Original Request
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Request ID:
8544
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Date Submitted:
June 29, 2021
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Requested By: Phillip McClure
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Code:
Residential
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Edition:
2017
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Chapter:
Chapter 9 Roof Assemblies
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Section:
R905.1.1, Table R905.1.1, Table Notes 1 & 2
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Topic:
Starting point of the eave.
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Question:
As used in the 2017 Florida Residential Building Code, in section R905.1.1, Table R905.1.1, underlayment notes 1 and 2, does the term “Eave” mean the lowest edge of the roof that includes the roof deck and other elements, such as furring strip, that extends the roof deck and are capable of supporting and/or mounting underlayments, drip edges and roof coverings?
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Comments:
I have a 5V crimp metal panel roof on my house. While observing the water runoff characteristics of the roof panels during a rainstorm, for the purposes of validating a quote for the installation of gutters, I observed water running out from between the underside of the panels, and the surface of the underlay. I also observed water seeping between the fascia and furring strip.
From observation of other houses being built in the community, the construction diagram of figure 1B was drawn. This has several other best-practice violations, but those are not the subject of this request. I noted that the felt underlay was applied unevenly, and not parallel to the edge of the roof. In most cases, the edge of the felt roughly lined up with the edge of the roof deck, not the edge of the roof. That left most of the furring strip uncovered by underlay. That makes the wooden elements at the roof edge; the roof deck, fascia and furring strip vulnerable to saturation from any water that seeps under the upper drip edge flange.
With the assembly of components depicted in figure 1B, the logical water flows of figure 1C were deduced. Note that in order for water to be dripping out from in between the furring strip and fascia, water first had to be seeping between the drip edge and underlay felt. This hypothesis was verified to be occurring by building a small, full size section of a roof edge, with the construction of figure 1B and an accurate 5.5:12 slope and applying water at different rates to the felt above the drip edge. In this configuration, the edge of the roof deck, back side of the furring strip and upper edge of the fascia will be kept in constant state of wetness, since Florida is a region of daily rainfall throughout most months of the year.
The issue that had resulted in the gross “undesirable water flows” shown in figure 1C has been partly resolved, but there are other sources of water flow under the metal panels. Metal roof manufacturers - including the one that manufactured the paels for my community - recommend that sealing tape and end closure foam be used to ensure a watertight roof system. However, since the manufacturers do not mandate the use of these waterproofing items, roofing company’s - including the one that is installing metal roofs in my community - chose not to use them. Minus the seam sealing tape and end sealing foam, metal roof coverings, like fiberglass and metal shingles and roof tiles, do allow incident rain water to leak between side seams in adjacent panels, and at peak and ridge caps, and at the open bottom ends when wind driven. The water will eventually drain to the roof edge. In addition, condensation forms on the upper and lower surface of the panels overnight on most nights. The condensation from the upper surfaces drips harmlessly from the lower edges of the panels to the ground. The condensation from the lower, inside surface however, drips onto the felt underlay, runs down the felt and finds its way to the roof edge.
This constant wetness will eventually cause the roof deck, fascia and furring strip to rot, which will compromise the holding power of fasteners in this area of the roof, which is critical to windstorm uplift resistance.
While still not optimum, if the felt underlay was trimmed at the outer edge of the furring strip, versus at the edge of the roof deck, this would keep water from seeping into the vulnerable surfaces of the roof deck, fascia and furring strips.
Section R905.1.1, Table R905.1.1, Underlayment Attachment Note 1 states, in the applicable sentences one to three; “Roof slopes from two units vertical in 12 units horizontal (17-percent slope), and less than four units vertical in 12 units horizontal (33-percent slope). 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-inchwide (914 mm) sheets of underlayment, overlapping successive sheets 19 inches (483 mm), end laps shall be 6 inches and shall be offset by 6 feet.”
Section R905.1.1, Table R905.1.1, Underlayment Attachment Note 2 states, in the applicable sentences one and two, “Roof slopes of four units vertical in 12 units horizontal (33-percent slope) or greater. Underlayment shall be applied shingle fashion, parallel to and starting from the eave and lapped 4 inches (51 mm), end laps shall be 6 inches and shall be offset by 6 feet.”
However, there is no definition for the term “eave” in the building code, and several architectural glossaries variously define an eave as a roof edge or a portion of the roof that overhangs and shades the walls. That lack of definition will result in felt applied as I have noted, and will allow room for debate amongst builders, roofers, local building inspectors and owners as to what constitutes an eave.
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Attachment 1: Download
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Attachment 2: Download
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