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jklingel 10-15-2013 01:59 AM

Gable ladder (fly) rafters, or lookouts
Whatever name you prefer, I have a question on how far they are allowed to extend out vs how far they extend back into the attic. I am of the understanding that the ratio is 1:1. A "normal" gable end stick-out is often 2', so the first truss, to which said ladder rafters abutt, should be inset 2' from the gable truss. It is my understanding that this "balance" will prevent lifting of the first truss if, say, the ladder rafters instead stuck out 4' and back in only 2'. (Gable truss is the fulcrum.) If 1:1 is the recommended ratio, how far can you push that if you assume a 30-40 psf snow load? 1.5 out to 1 in? 2 out to 1 in? We will assume that the supporting member (fly/ladder rafter) is strong enough to hold the load. All I am concerned about is the ratio of stick-out to stick-in. Thanks.

cortell 10-15-2013 08:31 AM

Unfortunately, I don't think code gives specific guidance for lookouts.

The rule of thumb ratio for cantilevering is 2:1, but for rafter lookouts, you typically you just go back to first common rafter (assuming it's at normal spacing from gable wall). Typically, lookouts don't extend more than 2', and I would caution against exceeding that. If you're going 2' and with that much snowload, I would do so only with 24" OC rafter spacing, and install the lookouts on edge, not flat. That latter, however, requires the gable rafter/truss to be sized accordingly (3-1/2" below common rafters profile).

If you can't install the lookouts on edge, I'd stick with 1' max overhang.

jklingel 10-15-2013 01:05 PM

Code, believe it or not, allows 2x4, 24" OC, to stick out 2' even if the 2x4 is flat. That does not rest well w/ me, but the truss guy said it is acceptable. I have no use for a 2x4 on its side. I used 7' x 2 x 6 on my shop, sticking out 3', 2x6 on edge, and a drop gable and drop first truss. That is apparently good for 4'. I am nervous about exceeding 1:1 on the stick-out vs stick-in, but I hear a "little fudging" is OK. Dunno. Thanks for the opinions.

cortell 10-15-2013 02:07 PM


Originally Posted by jklingel (Post 1253766)
Code, believe it or not, allows 2x4, 24" OC, to stick out 2' even if the 2x4 is flat.

Perhaps local code. I just double checked the 2012 IRC. I see no guidance on lookout construction.

jklingel 10-15-2013 05:10 PM

i erred when i said code, to be brief. the truss guy, in agreement w/ a few others who build, is what i meant by "code". sorry about that. thanks for looking it up. j

Gary in WA 10-15-2013 09:02 PM

Check for local rules in addition to the IBC you follow. Certain areas are stricter for snow, high wind, etc.; e.g.- R4506.7;


jklingel 10-16-2013 12:10 AM

very good info gary, thanks.

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