Rafter& stair basic's. Photo's, beware dial up .

[PEG688]

So here's some photo's that will show how I put together stairs and install rafters.

If you have questions about a detail just ask I'll try to answer but the photo's should teach more clearly than typing about it.

 The garage /  loft area 24'x32' , 10/12 main roof , dormer 3 1/2 / 12





Collar tie nailing pattern the old 2 /1 /2/1 on a 2x6 /8 / ona 2x 10/ 12 the 3/2/3/2/pattern .



 Window header with 2x6 S/R bottom nailer installed,



Thsi view shows anti rotation blocking in , double rafters at dormer, and the elavated 24' 2 x10 collar ties/ ceiling joist in the dormer area .



  This is a strongback , a 2x4 , 2x8 L that is nailed together on the floor then slid into the attic . It is then nailed to the top of the ceiling joist / collar ties to stiffin the joist and provide some strenght / anti sway back to those almost max span joist. The S/B is long enought to sit on top of a 2x10 short collar ties nailed to the dbl dormer rafters.

 

 

 Good shot of the short ballon framed knee wall , DBL dormer rafter, blocking .



Typ. rafter to ridge cut's   YMMV



 DBL'S , typ. Note the 2x4 sub ridge board is not yet installed . The main ridge is a 2 x12 the rafter are 2x12 so the angle cut is longer than the ridge , code , or inspector's here require the whole ridge cut must be supported / filled in a 2x4 under the main ridge did this for us here.
 

 Stairs  platforms , post dapped for  shoulders, OSB ledger that the stair horse's are nailed to before they are lifted into place , the OSB is then nailed to the platform rim joist. You have to allow for this on your platform nosing over hang.

The 1x4's on the lower edges "hold off" the yet to be framed partion walls , this allows a 3/4" slot for the drywall to slide behind / beside the stair horse and partion wall.  

 

The above photo shows the 1x6 ledger the floor joist sit on and the 2x4 blocking at the break / top of the exterior sheathing.  









 There ya go   G/L PEG


 

[FrankInWI]

Hey, looks like you end up with some useable space upstairs!  Are those colar ties from rafter to rafter low enough to work?  How do you determine maximum height they can be at.  Are the lower ends of the rafter tied to that lil stub wall any certain way?
Thanks!

[PEG688]

The collar ties are 8' 5/8" off the floor  , for a 8' ceiling height. They will work fine in tension if the roof load ever requires it .

The stub wall is really a knee wall, a continuation of the lower wall. So it much like John's storey and a 1/2 ballon framing , with let in ledger.

The space above the collar ties will be full of (all most) insulation so it is not usable space.

As far as max height on a collar tie , IMO, they could be as high up as right up and touching the underside of the ridge board . These collar ties are 115"( 9' 7")  long point to L/P. It's the tri-angling effect that provides the anti spread strenght of a collar tie , again IMO.

The seat cuts are toe nailed in 2 ea 12 d gun nails or 16 d sinkers each side and they will have H-1 hurricane ties on each rafter SOP for PNW.  Along with the anti rotation blocking which is also toe nailed to the top plate and to each rafter.  

PEG

[Karl]

I hope bumping an old post doesn't bother too many of you.  Really useful stuff that could nearly be a sticky.

I do have a question though - I thought "collar ties" went in the top third, "rafter ties" in the bottom third, and that floor joists don't really act as rafter ties with a knee-wall separating them from the rafters.  Is that right?  Is there an exception I'm missing in this case?


I've dug up the links to the pictures since most had succumbed to link-rot:

[MountainDon]

I do have a question though - I thought "collar ties" went in the top third, "rafter ties" in the bottom third, and that floor joists don't really act as rafter ties with a knee-wall separating them from the rafters.  Is that right?  Is there an exception I'm missing in this case?

You are correct in your understanding of collar tie and rafter placement.  

Strictly speaking there is no exception to the rule when the roof is a standard set of rafters with a ridge board.

[Karl]

I'm starting to figure it out.

Since it's balloon framed, the stud is essentially a simple beam with a concentrated overhanging load (figure 20 AWC DA6-BeamFormulas.pdf).  It may not be covered in a standard but it is designable.  The knee-wall is only a foot high the moment load wouldn't be terrible but I wouldn't do it without getting an engineer to run calcs and sign off on it.

This would be terrible if platform framed.  Little 8 inch studs wouldn't react anything.

-Karl

[MountainDon]

A balloon frame as illustrated in the IRC differs in that there is a full second story that has rafter ties as ceiling joists.


Another method would be to play around with the kneewall height with the rafter ties raised to the limit of the lower third. That can get sufficient headroom in the central area of the upstairs.

Or go ridge beam or scissors truss or attic truss.