question about gable overhang framing

10252 Views 11 Replies 6 Participants Last post by Gary in WA, Apr 9, 2009

wombosi

Discussion Starter · Apr 7, 2009

Been researching this quite a bit, seems there are two options:

My b uilding is a 10X12 with an 11-12 pitch, with rafters spanning 5' 11 1/4".

I would like to have exposed eaves and rakes, the rafter tails are already overhanging by 12" and I'd like to do a 12" overhang on the gables.

Is my only option to frame some 2X4 lookouts, notched through the end gable rafter? Or, can the OSB support the 12" overhang, simply by dangling, and have the top of the rafter face nailed into the end grain of the ridge board?

Also, if I cover up the end of the ridge with my overhang rafters, won't that mess up the way the sheathing lies? Assuming all the other rafter butt to the ridge, leaving a square top? ....

Thanks.

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Scuba_Dave

· #2 · Apr 7, 2009

I would say you need to support it with more then OSB
I have a 6" overhang that is supported by sheathing & brackets
I wouldn't trust 12" to OSB

I have always measured out any overhang & included that when running my rafters

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wombosi

Discussion Starter · #3 · Apr 7, 2009

so, should i just build the dang lookouts, and live with the strange look?

should i gut the ridge pole flush with the framing, and just go with lookouts so that i don't have issues with the overhang rafters?

thanks.

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Gary in WA

· #4 · Apr 7, 2009

Are you putting on a fascia board at the tails? I always run that wild on the gable, at least the overhang distance, plus some.

Your ridge should be: top edges flush with the ends of rafters, or held down to allow 1" air space above ( for ridge venting). I extend the ridge board past (through) the gable wall, then narrowing the width to be smaller than the barge rafter.

Cut ridge to O.H. width minus barge thickness. Install barges tight, face nailing and rake boards ( which cover ply end grain edge). Or, no fascia - install a sub-fascia, cutting the gable rafter tail off the thickness of that material. Nail sub through side of first common rafter back, face nail into gable rafter, and be nailed into through barge rafter.

Rip the osb to the width of your gable overhang, install it running up and down the roof plane. With a 12" O.H., strength grain running with the rip, it will be fine. Add a dummy block, flat, either: in line with the wall/rafter blocks; or towards the top- 8' up from the tail overhang. Be safe, GBR

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woodlake

· #5 · Apr 7, 2009

Yep, what GBR said.

The ridge will support the top of the barge rafter and a fascia board will support the bottom.

This will make the 12" overhang on the OSB negligible since the top and bottom of the barge is then supported, the barge is now basically a rafter.

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Wildie

· #6 · Apr 9, 2009

Here's a good site that shows various framing techniques!

http://tinyurl.com/cv2tvw

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wildcat

· #7 · Apr 9, 2009

schmolze said:
... have the top of the rafter face nailed into the end grain of the ridge board?...

Never, never ever use nails into end-grain if you are connecting a load bearing member. I don't recommend using wood screws either, and only lag screws when it is the only option.

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Scuba_Dave

· #8 · Apr 9, 2009

wildcat said:
Never, never ever use nails into end-grain if you are connecting a load bearing member. I don't recommend using wood screws either, and only lag screws when it is the only option.

and that leaves.....? :huh:

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wildcat

· #9 · Apr 9, 2009

Scuba_Dave said:
and that leaves.....? :huh:

You've got to find a way to the dowel type fasteners (nails or wood screws) into shear only. Thus your friend the Simpson catalog.

The National Design Specification (based on testing, research, etc.) says you can't load nails or screws "in withdrawal from end grain of wood." It also says that when placed in the end grain, lag screws can only carry 75% of their rated load.

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Gary in WA

· #10 · Apr 9, 2009

Wow, that's a new one for me! All I've EVER seen is nails, I use galvanized 16d. Considering that barge rafter is carrying itself and 6" of osb and snow load, what- 45# per---= 12' at 1.1 for span. This span is only 9'. 3-16d nails at the top, 2-16d nails at the bottom, what's the shear on that? 16d x 2= ? There won't be any withdraw force as it's top nailed. Plus they are butted to each other at the ridge. I know it holds me up, I'm 180#, because I've built like that for 35 years, and haven't had one break. What is the shear on a 16d common? 200#? 150#? I've seen gable overhangs sag, when there wern't enough supports present, but never because of nail shear failure. I think we need something written in the code books if this is such a complete failure problem. And educate all the citys' and counties' plan check engineers. Be safe, GBR

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wildcat

· #11 · Apr 9, 2009

GBAR in WA said:
Wow, that's a new one for me! All I've EVER seen is nails, I use galvanized 16d. Considering that barge rafter is carrying itself and 6" of osb and snow load, what- 45# per---= 12' at 1.1 for span. This span is only 9'. 3-16d nails at the top, 2-16d nails at the bottom, what's the shear on that? 16d x 2= ? There won't be any withdraw force as it's top nailed. Plus they are butted to each other at the ridge. I know it holds me up, I'm 180#, because I've built like that for 35 years, and haven't had one break. What is the shear on a 16d common? 200#? 150#? I've seen gable overhangs sag, when there wern't enough supports present, but never because of nail shear failure. I think we need something written in the code books if this is such a complete failure problem. And educate all the citys' and counties' plan check engineers. Be safe, GBR

In the case of a properly constructed barge rafter the rafter is restrained from putting withdrawal force on any fasteners in end grain if the barge rafter is properly attached to the roof sheathing (this connection takes the lateral shear).

I have seen people count primarily on the end-grain attachment to the lookouts and, for what ever reason, forget that the overhanging sheathing is still part of the roof diaphragm and needs to be attached accordingly (typically 6" perimeter and 12" field ea sheet). When its not installed properly wind and shrinkage/expansion can cause the barge rafter to pull away from the lookouts over time (nails just wiggle lose from end grain). This lets in moisture and bugs and over time the barge rafter gets warped and sags and makes the roof flashing in effective...more moisture issues with sheathing follow.

I guess I should have been more clear on this. But, yeah you see people put nails in end grain w/ withdrawal loading all the time and nobody catches it until you go for a site visit/inspection.

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Gary in WA

· #12 · Apr 9, 2009

Thank you, wildcat, for more info. I realize now that I have to be more precise in my directions. I did skip "nail the osb 6"o.c., with 8dgalv. into the barge rafter", then the rake board will cover the end grain. With much involvement on the forum, it makes one more exacting in his reply. (butchered sentence) I can't imagine the things you've seen in bad construction, but I'll bet you have some stories to tell! I apologize if I sounded harsh last night, it was way past my bedtime. Be safe, GBR

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