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Birdsmouth question (s)

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#23 ·
OOOOOHHHH! Drive-ins in the '55 Roadmaster!

Let's get back on topic here. I'd love to see a fellow engineers viewpoint on this. All of the construction of this type that I have ever seen end up with the walls bowed out and a sagging ridge.
 
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#24 ·
Teetorbilt said:
OOOOOHHHH! Drive-ins in the '55 Roadmaster!

Let's get back on topic here. I'd love to see a fellow engineers viewpoint on this. All of the construction of this type that I have ever seen end up with the walls bowed out and a sagging ridge.
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I think were cool on this one Teetor and am certain I could get my PE. to put his stamp on it. I think my PE is the best in the country but that is just my opinion and maybe the opinion of at least a couple of the building dept. around here.<P>

I don't get the "less facia" idea but what the hay.
 
#25 ·
Doesn't a rafter, on its most basic level, consist of a plumb and a level cut? Isn't every other cut theoretically just fluff? This may sound odd, but stringers are no different. In any event, "tails" as we call them up here in Mass, are technically just an extension of the imaginary plumb cut at the line of the wall (as opposed to the ridge obviously)Just because a bird'smouth or seat cut looks like a locking device of sorts, doesn't necessarily mean it is holding the building together. Collar ties and Ceiling joists keep walls from blowing out, and thus ridges from sagging, in my opinion.

Will somebody please explain deadrise to me? thanks.

-old
 
#27 ·
First of all it has been 4 days since this post originated, so my guess is you have done what you want to do. Perhaps I am not understanding all the posts, but do understand (at least I think I do) that you are not happy with only having that size fascia? Explain to me what the collar tie has to do with the size of this? This is the result of the size of rafter that had to be cut to acquire the desired pitch. I would think had the builder used a wider rafter, you would have ended up with a wider fascia. The reason for the birdsmouth was to accomplish the desired pitch of your roof, and a nailing surface along your top-plate. Here is what the layout and purpose of a collar tie is: http://www.tpub.com/content/engineering/14069/css/14069_213.htm
 
#28 ·
:furious: Ireally hope someone reads this. First, when we were typically hand cutting roofs, there was no hardware== H 2.5, H 1, etc. so if you stacked a rafter without a "birdsmouth" on a flat plate what would hold it? The plumb portion of the "birdsmouth" is incidental. Making a "level" cut allows the weight of the rafter to bear on the wall, yes very much like the stringer. second, this guy is talking about making "level" cuts with a recip. saw. RED FLAG. Ceiling joists hold the walls together to SUPPORT THE RIDGE WHICH IN TURN SUPPORTS THE RAFTERS, COLLAR TIES CREATE A SITUATION WHERE THE RAFTERS WOULD HAVE TO SPLIT APART LATERALLY FOR THE RIDGE TO SAG. There are many occasions when you will have a seat cut where the plumb portion rises above the plate rather than extending below. If yo want to run rafters without a "level" cut you need an engineer to call out very special hardware.
 
#31 ·
rob 53, thank you for making me reevaluate the question. when i saw the part about fascia size, and level cut, i assumed he was talking about reducing the plumb cut tail size by level cutting it. after all he had someone frame it that had to have some rafter knoweledge, if they cut and stacked. so again i assumed that they would have done the best the could. i see no problem whatsoever with a totally level seat cut extending to the over hang.:thumbup: as long as i dont have to walk on it.:cheesygri also the main problem i had/have is that no one explained what a "birds mouth" is for. sorry for any ill feelings not intended to anyone
 
#32 ·
Nailbanger,I think your right that probably a few more details needed to be considered regarding the original post but there is only so much that can be done on a forum without detailed drawings.<P>
Regarding the purpose of a birdsmouth. I think there are a couple of threads on that subject around here but you could always start another. probably get some response. <P>
No ill feelings that I know of.
 
#33 ·
"dead-rise"

In my experience a dead-rise is, after the rafter is installed, the height of the rafter at the outside point of the sheathing on the wall. In my ten years I have not cut any two rafter tails the same. It all depends on what and if you are matching some other roof. It also depends on the size of the rafter.
 
#34 ·
2nd generation said:
In my experience a dead-rise is, after the rafter is installed, the height of the rafter at the outside point of the sheathing on the wall. In my ten years I have not cut any two rafter tails the same. It all depends on what and if you are matching some other roof. It also depends on the size of the rafter.
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So is that the same as the H.A.P.??
 
#36 ·
2nd generation said:
In my experience a dead-rise is, after the rafter is installed, the height of the rafter at the outside point of the sheathing on the wall. In my ten years I have not cut any two rafter tails the same. It all depends on what and if you are matching some other roof. It also depends on the size of the rafter.
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Ridge is set correctly most all your cuts should be the same for the most part.

Can you tell me what RT=:thumbup: Gee I woner if thats ridge thickness.


Grap a line set your perimeters and smooth sailing from there.
 
#38 ·
bird mouth

The bird mouth notch should be a run cut called a seat cut the width of the top plate . So if you have a 5 1/2 top plate you should make a 5 1/2 seat cut . You'll have a " maximum bearing stacking point " resting on the top plate . The point of the bird mouth is the outside of wall which determines total run and rise on the rafters on most shed or ridge systems . Tji's have a method that suggests that the seating of the tji rafter must be center on center , that is center of the bottom cord of tji rests on center of top plate
 
#39 ·
Dave Y Crockett said:
The bird mouth notch should be a run cut called a seat cut the width of the top plate . So if you have a 5 1/2 top plate you should make a 5 1/2 seat cut . You'll have a " maximum bearing stacking point " resting on the top plate . The point of the bird mouth is the outside of wall which determines total run and rise on the rafters on most shed or ridge systems . Tji's have a method that suggests that the seating of the tji rafter must be center on center , that is center of the bottom cord of tji rests on center of top plate
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I'd have to disagree with you on the 5-1/2" seat/level cut. On a 12/12 with a 2x6 rafter, (for say a short shed roof etc.), you would have 2" left on the rafter to hold the overhang. I personally see very few reasons for large birdsmouths. Leave the lumber on the rafter instead of putting it on the ground and then in the dumpster. Well that's my opinion anyway.
 
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