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Old 05-26-2009, 05:01 PM  
cittyguy
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Join Date: May 2009
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Default A hip roof without soffits or insulation

Hello.

I am in the process of purchasing a home built in the forties in Charleston, South Carolina. Thus, wind-driven rain and mold build-up are potential problems. The house is single story and about 1000 sq feet. The ceilings are all flat. The home has a hip roof with no rafter overhang and thus no soffits but a slight decking overhang of ~3-4 inches. There is currently NO insulation in the attic . Fortunately, none of the rest of the house appears to have been well insulated either as the attic appears dry as a bone and the wood very nice (all real 2x6). The roof is asphalt shingle over plank decking.

Assuming my insurance and mortgage companies will permit me to purchase the home in its current condition (sold as is), I will want to address issues of insulation, water runoff, and hurricane preparedness when I re-roof the place. I have some questions and hope more experienced DIYers can provide some answers .

1. At the time of roof replacement, should OSB be put down over the existing plank decking or should the planks be removed? Would it be better to hotmop the joints between each of the existing planks and forgo the use of further decking altogether?

2. Given the absence of soffit vents, I am thinking about installing something like the newfangled SmartVent (produced by a company called DCI) that install right along the edge of the roof and work in conjunction with ridge vents. I haven’t yet decided whether or not I will use a powered fan / ridge vent combination or use standard ridge and hip ridge vents in combination to permit exhaust. I am concerned about each of these products allowing wind-driven rain into the attic although the companies suggest they’re rated to protect against such. What do you think of these ventilation schemes given the absence of soffits? I haven’t found any clear instructions as yet detailing the means by which hip ridge vents are properly installed. Can you suggest a good resource (a book or web resource would be appreciated)?

3. I have heard that some planners in places that have seen substantial hurricane activity recently (especially Florida) are advocating that attics be sealed entirely (no ventilation) with expanding polyurethane foam sprayed directly on the underneath sides of the decking between the rafters. In conjunction with a reflective roof shingle, this is supposed to prevent mold buildup in the attic. I dislike the expanding foam option for a number of reasons (it certainly won’t be a DIY project) but dislike mold and potential damage caused by wind-driven rain entering my attic vents even more. Given that my rafters are only 2x6 can I even use the spray foam approach? Do you have a better suggestion for insulating this space? If I use the SmartVent and ridge vent systems, it seems like I could install vent baffles and then start shooting in fiberglass insulation (cellulose doesn’t seem like a good idea in this climate). What do you think?

4. Although the rafters do not extend beyond the outer walls of the house, the roof line extends approximately 4 inches beyond the wall. The overhanging decking appears to be supported in part by a piece of decorative trim attached to the fascia on the house. Can I simply trim the roof edge back, decking and all, so that it is only 1.5 inches from the fascia to permit gutter installation? Note that this house sits on a pier foundation and I have observed pooling after recent rains suggesting water runoff from the roof shouldn’t continue. I’ve attached a photo to show the roof overhang but fear I may need to return to the scene if I am to provide you with something better (the house in question is that with the EXTREMELY attractive asbestos shingles ).

Please let me know if you need further details to address the questions I’ve asked and thank you in advance for any assistance you offer (And if I sound naïve regarding this roofing project, I am, but I am also not planning to start the project without a substantial amount of research and a practice run on a shed I plan to construct in the backyard ). Thanks for your time!





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