View Full Version : Gable Overhang Construction
We build in Grand Rapids, MI. Most builders overhang their roof plywood or OSB past the gable truss 12" and then nail a 2"x6" to the subroof to make their eaves. No other supports are put in place, so the only thing holding up the eave is the roof plywood, plus the fascia at the bottom of the eave. We typically nail 2"x6"x9 1/2" blocks 2' on center on the outside of the gable sheeting, then nail a 2"x6" eave to the blocks and the roof plywood to form the gable overhang. My question is, is our method adequate for a 12" eave overhang?
Builders in my area build a ladder frame 12-16" out from the gable and sheathe over the top. Their belief is the sheathing will have to stretch before the overhang will bend with the frame work below it. I suppose there is a little truth to it for a small overhang. The reason for doing this is for the ease and speed of it. Its only been done around here for about the last 8 years or so. I would like to see what these overhangs look like after about 20 yrs. I still use a dropped gable truss with 2x4 or 2x6 cantilevering on edge and fastened to the first or second truss in, and placed every 16”-24” o/c depending on the overhang length and snow loads of the area.
Bay Shore Building & Design, Inc. (http://bsbad.tripod.com)
Justin B. Jensen
03-13-2003, 12:10 AM
I see builders "floating" the rake overhangs as Mark describes in Salt Lake all the time. I personally will have nothing to do with the practice. In just a couple years of exposure to snow loads, you can visibly observe the rakes begin to droop, creating an un-planned swale in the roof. As far as I'm concerned, this is a failed experiment that caught on (how does that happen?)
Mark, I'd call your practice a reasonable "compromise". I guess I'm old fashioned; I order my gable trusses "held down" 5 1/2 inches and we build a ladder of outlookers to carry the rake eave. It doesn't take any longer than building the ladder frame and "planting it on" the sheathed gable end and you get the benefit of having a true cantilever to resolve the forces acting on the eaves across the top of your gable end wall.
If only we could put an end to some of the poor practices that have become commonplace.
03-15-2003, 10:07 AM
Mark we do ours much the same as you do: Extend the OSB 12", build 2x6 return boxes, then cut our barge rafters to sit on top of the return on bottom and nail it to the ridge on top. Nail through the OSB into the barge. We don't have any snow loads though.
03-16-2003, 01:19 PM
As to the OSB or ply holding a fly rafter by cantilever, this is a bad practice. with a 12" overhang, the sheathing only has to stretch 1/32" of an inch in order for the rafter to drop 7/8". One can imagine getting this much play just between the side of the nail hole in the sheathing and hte nail itself. For a 1/4" drop of the fly rafter, a "stretch" of 2.5 thousandths is all that is necessary. Obviously, if you want a rigid overhang, this method doesn't work.
P.S. I used the pythagorean thereom to come up with these numbers.
Justin B. Jensen
03-16-2003, 11:24 PM
You've mathematically proven what I've seen time and again.
I still can't understand what's so hard, time consuming or expensive about ordering gable end trusses held down and framing a proper ladder up the respective pitches.
03-18-2003, 11:58 AM
Not very Building Science oriented though.
Out here on Puget Sound, our overhangs are typically a minimum of 2ft. Soffits are very rare here. There is typically only a fascia secured to the ends of the rafter tails. Trusses are manufactured with an extended upper chord, so the tail supports the eaves and there are usually lookouts let into the tops of the gable end truss and the second truss that support the rakes. The rakes are usually secured to the ends of the lookouts and the underside of the roof decking. Some high-end builders will build 'craftsman' style homes and use large 4 X 4 or 6 X 6 brackets that support the rakes instead.
It is very common around here to see the gable ends of a roof drooping 1 to 2 inches, especially on very old homes where the brackets have been removed at the eaves or are pulling loose from the side walls. I recently inspected a 20-year old low-end home where no lookouts had been used at the gable ends. At one corner, the plywood decking has splintered and drooped where some fellow had stood on it while cleaning the roof and the entire rake was separated from eave to ridge and hanging from one nail.
They definitely don't build 'em like they used to.
ONE TEAM - ONE FIGHT!!!
Huh!? pythagorean's thereom isn't science?
03-27-2003, 10:47 AM
Sorry it's taken me so long to respond. Being retired military, I've found the TV to be irresistable over the past 7 days and have been staying up pretty late.
I'm not dissing pytagorean's thereom, but I consider that more of a mathematical equation solving process than Building Science.
When we refer to building science in the title of this forum we are referring to things such as vapor diffusion, heat transfer, ventilation and the like, and those aspects of construction that deal more with building technology and theory than they do with construction practices. That's why there are forums for framing, finish carpentry, etc..
ONE TEAM - ONE FIGHT!!!
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