Zero eave roof in Florida
aluna
| Posted in General Questions on
Hello, I’m an architect working on a single family home in South Florida with a steep roof slope and a zero eave roof design. Can anyone assist in providing any details for both waterproofing and attic ventilation. Since it’s a zero eave design, there are no soffits for intake vents, so I’m wondering what the alternatives are?
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At the risk of being snarky, the way to provide good waterproofing and eave venting is by using actual eaves, especially in FL with its torrential rains. But now that I've gotten that out of my system...
There are several manufacturers of eave edge vents that install under the eave shingles, over a gap in the sheathing. These work, but I question whether they are well suited to your climate. They are screened, but I doubt that they provide much resistance to wind-driven rain. Water can pile up on the eaves when driven uphill by wind, and I would expect that to enter the vents.
An alternative solution would be to go to a conditioned and unvented attic. These are very popular in FL these days. Install batt insulation in the attic rafters, and use vapor ventilation ports at the ridge. Or spray foam the attic rafters and skip the vapor ports. With a sealed attic, you can waterproof the eaves using adhesive underlayment like Ice and Water shield wrapped from the roof sheathing down over the wall WRB
Aluna,
Peter has given you good practical advice on how to proceed, and I don't want to pile on... but when you make design decisions like not using eaves, you are behind the eight ball from the beginning. I have a list of features I simply will not design into a project. They include things like decks over living spaces, low sloped roofs - and houses with no eaves. Setting those boundaries in advance, eliminates the complexities and fragility they bring to projects.
I'll add another option to Peter's 2.
Batt insulation between the rafters and continuous exterior foam insulation over the roof deck.
A good "belt and suspenders" approach would provide a second sheathing on top of the exterior insulation, covered by your roofing underlayment, battens, and your roofing.
The gap created by the battens would help establish a zone of still air under the roofing, facilitating drainage of any water that gets under the roofing.
This would be an unvented attic approach. In climate zone 1A I would do R10 exterior foam and R20 batt. In zone 2A bump the batt up to R30.
What are the roofing and exterior wall finish materials you have in mind?
Gutters? (I hope so.)
A sketch of the overall finished appearance you're after would help.
Thanks guys, understood that the most effective solution would be to add the soffit vents, however owner is adamant about having the more modern look to the design. We may have found a product for intake within the roof shingles by GAF, but still exploring. Would you guys have any suggestions for vent products to check out?
The IRC does not require soffit vents. Without them, it requires that 1/150 of the floor area is vented at the upper part of the roof, which can be through a combination of ridge vent and gable end vents. I'm not saying it's best practice, but it's an option.
I have also used venting drip edges, and on many occasions I have slipped roof venting behind a frieze or fascia board where the wall meets the roof.
For waterproofing, especially in a high-wind area like yours, I think the entire house should be waterproof before any cladding is applied. That can be achieved through a variety of membranes and rigid products.
Agree with Antonio above that a sketch or two would be helpful.
Aluna, I might be misreading your reply #4 above, but I assume you're not looking at shingles on a flat roof?
I'm in a somewhat different climate, but flat roofs are similarly risky here (CZ6, mega snow country). Concrete pandeck sloped at 1/8" or 1/4" per foot with all insulation on the exterior is a decent starting point to minimize as much risk as possible (given an inherently risky design choice).