Extending Roof Overhangs
I’m in the process of residing my house in central Vermont (zone 6) and am taking the opportunity to add external insulation. The house has pretty small overhangs (less than 1′). After residing the overhangs will be in the 6-8″ range. I’ve been scouring this site and have read many of the relevant articles and discussions. I understand in particular their benefits in terms of keeping water off the house.
My challenge is it still seems awfully expensive (in time and/or money) for the benefits. I should say my roof will need to be replaced at some point and that would be the time to extend the overhangs. In particular it seems to me there would be less of a benefit to extending the overhangs on the gable ends (north/south). Aesthetics aside maybe I should starting paying attention when it rains to the places that get wet and extend the overhangs there.
Am I crazy to consider extending overhangs as part of a re-roofing project? Am I crazy not to?
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Replies
Elias,
I'm a huge proponent of deep overhangs in almost every climate, but if you are adding exterior insulation which includes a rain-screen cavity, I wouldn't be half as worried as I would on an older house with poor exterior wall detailing. It may well not be worth the effort to deepen the overhangs.
Elias, I am somewhat more comfortable with having no overhangs than Malcolm (and most building science pros) but ONLY when all of the details are well-designed and executed. Overhangs can make it tricky to create a continuous air control layer, and don't help much (and can even cause problems) in high-wind areas, but otherwise the larger the overhang, the safer the structure.
I also think large overhangs are very cost effective, low tech details on a structure that can provide huge benefits, especially if your location is prone to lots of rain and/or wind driven rain. Without the large overhangs your detailing for windows, flashings, penetrations etc. needs to be bang on because your walls will certainly see bulk water.
6-8" is much better than the zero to 1 inch range that some modern designs aim for. I'd focus on getting the details right otherwise: a rain-screen gap, excellent air sealing underneath that, and careful choice of siding and paint (if paint is used). Note that you have the opportunity to get white cedar siding directly from mills in northern Vermont if that appeals to you.
Also, if you don't have gutters, consider adding them. That will give you some extra overhang, and divert water that would otherwise get on the siding. People in this region (I'm in NH) often avoid them thinking that bad things will happen with ice, but if you have your attic air sealing and insulation done well you will avoid ice dams. With the possible exception of a standing seam roof where snow avalanches might tear gutters off.
Thank you Malcolm that is reassuring. I am adding a strapping depth rain screen cavity.
Michael that brings up another rabbit hole I'll have to dig into when its time to re-roof. That is how to connect the wall's air control layer with the roof's. This is an old farm house. The original section was built by 1848. My residing project is adding the first real air barrier the house has ever had. I'm using R-12 Thermaltight, which is neoprene with a water/air barrier pre-attached. The attic was long ago turned into living space with some spray foam on the understide of the rafters. I expect without massive amounts of work there is no great way to connect air control layers. I have considered adding rigid insulation on top before putting a new roof down that might make connecting to the walls somewhat easier. Though I bet having foam above and below the roof could be a moisture disaster.
Bob thats my worrie. I do my best with all the detailing but I'm no expert its certainly a learning experience.
Charlie the local mill has quartersawn red spruce or white pine. I went for the spruce, white cedar would have been better. I wanted to go unpainted by my wife vetoed. We settled on a Vermont Natural Coatings semitransparent stain. I'm staining all sides before installing. Maybe that will wear off without chipping much and my wife will let me not re-coat it.