# Birdmouth height question



## glkirk (Nov 27, 2011)

Acting as a designer, I want to draw this project with the rafter birdmouth up on a 2x flat on top of the ceiling joists.
I would like to learn all the ins and outs of this procedure.
I am using 2x4 walls and probably 2x8 ceiling joists and at least 2x8 rafters.
It will be a 12/12 pitch with a 1' overhang.
Is it appropriate to use a flat 2x6 up there?
Do some set the ceiling joists up like a floor with a rim/band?
How does the rafter tie in system work? Do you at least block between the joists and then sheet, then normal hurricane clips?
Thanks!
Gary


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## CarpenterSFO (Dec 12, 2012)

Maybe I'm misunderstanding, but why not make your studs taller, do it conventionally, and get the extra headroom inside? What advantage are you seeking by doing it differently?


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## kiteman (Apr 18, 2012)

*Brdmouth Height Question*

Sometimes we have had to "raise the roof"
To get a certain look for frieze/crown/soffit/brick pocket. Maybe it's like an energy heel. I've done this with a rim, rim with 2x4, blocking, etc. I see no need for a 2x6 plate. When using either 2x6 joist and rim with no plate or 3 blocks each bay I've used an h8. 

Andy will be along to tell us what you need on the coast.


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## TJDavis (Apr 19, 2015)

CarpenterSFO said:


> Maybe I'm misunderstanding, but why not make your studs taller, do it conventionally, and get the extra headroom inside? What advantage are you seeking by doing it differently?


Making the studs taller instead of the top plate would give less chance of racking wouldn't it?


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## superseal (Feb 4, 2009)

If i'm reading you right, I've done this many times and tend to call it raised rafter framing/energy heel.


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## CarpenterSFO (Dec 12, 2012)

superseal: Is additional insulation the purpose of that approach?


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## superseal (Feb 4, 2009)

To prevent rafter splay/thrust, you can notch birdmouth over the 2x4 plate and in addition nail twist strapping under the plate to catch the rafter in tension.

Generally you'll want a continuous rim for your ceiling/floor joist and vented blocking between the rafters.


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## Dave in Pa (Oct 10, 2009)

Are you trying to hit a certain window height? To many factors, not givin to help out here!


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## glkirk (Nov 27, 2011)

Thanks for the images Superseal!
The flooring/sheathing on top o the C. joists? Is this a one and a half story structure?
Not sure exactly why or if I may draw it this way or that.
Revit, the modeling program, tends to keep the roof/rafters up high off the plate. So the elevations show a good distance between the tops of windows and frieze/cornice. And that is the impression I get that I need to duplicate from the photo I was given.
I had seen this technique years ago on home where (I think) the acchy was trying to achieve a good Frieze and space above the 6'-8" header height.
As only a Class A builder for 30 years, and not an licensed arcy or engineer, I feel it behooves me to research this to the fullest before I draw it to be presented to a building permit office.
Still wondering about the hurricane anchor (typical) anchoring. How, I wonder, would that be expected by the plan reviewer?


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## kiteman (Apr 18, 2012)

It would be on your section detail


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## superseal (Feb 4, 2009)

CarpenterSFO said:


> superseal: Is additional insulation the purpose of that approach?


Primarily yes, and in addition, will elevate the rafter height for a many different variety of reasons...e.g. aesthetics, window and door clearance, larger overhangs, etc...


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## Rio (Oct 13, 2009)

Out here in California the frieze blocking (the blocking between the rafters at the plate) is one of the important load transfer areas (it's obviously a load transfer area everywhere but with the emphasis on seismic and carrying those loads to the ground is looked at closely as it's where the roof load is transferred to the walls). 

Anywhoo, that's why there's A35s at the plate to frieze block at that location and that's where the roof nailing schedule is tightened up to 6" on center. That's also a really common place for the building inspector to check the nailing. 

With that in mind I'd probably do some LTP4's at the rim to top plate and possibly lower top top plate and then A 35's on the upper rafter to plate as well as the C.J. to plate. The same holds true of the uplift hardware, just make sure that every place it can go flying off(the roof) it's firmly attached to the structure below all the way to the foundation.

As insulation regulations continue to tighten raised heel construction techniques will become more and more common even in temperate climates.


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## Calidecks (Nov 19, 2011)

Rio said:


> Out here in California the frieze blocking (the blocking between the rafters at the plate) is one of the important load transfer areas (it's obviously a load transfer area everywhere but with the emphasis on seismic and carrying those loads to the ground is looked at closely as it's where the roof load is transferred to the walls).
> 
> Anywhoo, that's why there's A35s at the plate to frieze block at that location and that's where the roof nailing schedule is tightened up to 6" on center. That's also a really common place for the building inspector to check the nailing.
> 
> ...


Yep, I have the low man put an A-35 on each block before they are installed. Then we have someone walk the plate with a strap nailer and back nail them. Seems to be a pet peeve with all inspectors.


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## superseal (Feb 4, 2009)

Forgot to mention the ease of stick framing your rafters whilst pouncing on a tightly locked floor...whether it be the attic or living space for that matter.


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## Philament (Dec 9, 2014)

superseal said:


> To prevent rafter splay/thrust, you can notch birdmouth over the 2x4 plate and in addition nail twist strapping under the plate to catch the rafter in tension.
> 
> Generally you'll want a continuous rim for your ceiling/floor joist and vented blocking between the rafters.


What is the spacing for the twists straps you used? Every fourth rafter?

Did you have to cut the birdmouth with a jigsaw for that detail?


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## superseal (Feb 4, 2009)

Philament said:


> What is the spacing for the twists straps you used? Every fourth rafter?
> 
> Did you have to cut the birdmouth with a jigsaw for that detail?


Yep, 4ft o.c. for the straps and the jigsaw for the notch...you nailed it!
Easy for one man to do as well. I do like to upsize the rafters one dimension as not to weaken the tails.


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## wallmaxx (Jun 18, 2007)

glkirk said:


> Acting as a designer, I want to draw this project with the rafter birdmouth up on a 2x flat on top of the ceiling joists.
> I would like to learn all the ins and outs of this procedure.
> I am using 2x4 walls and probably 2x8 ceiling joists and at least 2x8 rafters.
> It will be a 12/12 pitch with a 1' overhang.
> ...


I've done it as follows:

2x4 or 2x6 wall
2x8 / 2x10 / 2x12 / TJI's whatever for joists.
2' rip of subflooring or ¾" ply flush to the outside face of the wall
then a 2x4 or 2x6 plate also flush outside
Then rafters,

BUT

we had to use long twisted Simpson straps MST 16s or longer to connect the rafters to the joists and wall plates below.............it wasn't spec'd but the inspector said he "knew" it would be required. The problem is that the code book shows rafters being connected to joists (face and back nailed) and also to the wall plates. The on top method throws a wrench in that.

It gives you the joist height more vertical space in any sloped bonus room walls for example.


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## superseal (Feb 4, 2009)

Here's several different approaches as well when it comes to raised rafter plates...wanted to post them, but couldn't find them in my files til now.

Credit this to JLC, circa 2002


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## FrankSmith (Feb 21, 2013)

glkirk said:


> Acting as a designer, I want to draw this project with the rafter birdmouth up on a 2x flat on top of the ceiling joists.
> I would like to learn all the ins and outs of this procedure.
> I am using 2x4 walls and probably 2x8 ceiling joists and at least 2x8 rafters.
> It will be a 12/12 pitch with a 1' overhang.
> ...


If you run your plywood up to the 2x4" that your rafters will set on your full wall system will act as one including the ceiling joist and added rim board. At that point install your framing bracket from the exterior. Nothing to fancy or difficult about it.


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## glkirk (Nov 27, 2011)

I would like to thank you all for your input.
It has been very helpful!


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