Cutting in Ledger or alternative

Started by beckhamk, May 01, 2011, 03:51:03 PM

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beckhamk

Had a few questions regarding the ledger for the loft floor.

1) If not doing a loft across the entire cabin, then we will only need to ledge the portion that is actually used for the loft correct?

2)   I did a dry run at the house by getting 4 or 5 2x6's clamped together and used a circular saw to cut slits and then used a chisel to knock them out.  Is this really the best and fasted way?

3) Is it best to cust the ledger after the wall is raised? or is it ok to mass cut these before the wall it put up?

4) Lastly, i want to see if this option could work and be acceptable, al be it more expensive.  Instead of having to cut for the ledger, couldnt
we just cut 2x6's to size and nail then to the 16 oc stuff and have the joists sit on this 2x6 instead?  I saw this done on one of the owner builders here, so i was curious if that would work well or not.

thanks in advance!


MountainDon

#1
A router makes the best cuts. Saws can result in overcut which weakens the stud even more.
Sometimes this is not an advisable method.
The main issue is there is no effective rafter tie in the loft section of the roof.

This is an intended topic in the IRC and best/good practices thread... but we're not there yet.

Variables that can make a difference between okay , maybe and No are...
Width of building?
Snow load?
Roof Pitch?
Height of side wall above ledger?
Just because something has been done and has not failed, doesn't mean it is good design.


rwanders

1. Yes----correct

2.  As long as your ledger will rest fully on all the studs----none left hanging in mid air.

3. This is how I would do it. Just snap a chalk line across the studs after the wall is raised for the top and bottom of the ledger cutout. Make several cuts using desired cut depth then knock out with hammer and chisel. Make sure ledger board will bear fully at each stud.

4.  Not correct----if you do it that way your loft joists will be dependent on the nails only----they need to bear on the studs directly to transfer the load correctly.
Rwanders lived in Southcentral Alaska since 1967
Now lives in St Augustine, Florida

Don_P

4) I was reading this differently, maybe wrong. If you were talking about running a shorter stud from floor to the underside of each joist, alongside of the tall balloon frame stud then yes this might work and would be stronger.

astidham

instead of a ledger, I put studs under my loft floor joist, from the bottom plate to under the joist, and nailed the studs and joist to the framed stud.
I have 10' sidewalls and I put the bottom of the joist at 7'6"
I would think this alternative would be superior.
"Chop your own wood and it will warm you twice"
— Henry Ford


rwanders

Quote from: astidham on May 01, 2011, 07:53:31 PM
instead of a ledger, I put studs under my loft floor joist, from the bottom plate to under the joist, and nailed the studs and joist to the framed stud.
I have 10' sidewalls and I put the bottom of the joist at 7'6"
I would think this alternative would be superior.


Definitely a viable alternative which provides superior results and avoids technically violating code on allowable notching of studs when you use 2x material for the ledger board.  Personally I prefer the method described above though it does cost a few more $$.
Rwanders lived in Southcentral Alaska since 1967
Now lives in St Augustine, Florida

Don_P

You're still not back inside of the warm loving arms of the code, but this is certainly better than notching the tension edge of studs.

beckhamk

Don_P was spot on!  I saw astidham actually do this in his and liked the simplicity of it compared to all of the cutting. I also felt it was stronger and superior solution.

astidham - when you did this did you just cut all of your studs to 7' 6"  or did you measure each one individually because of the slight differences in dimensional lumber?


One other question I would like to add. Assuming we kept the studs (normal framing stuffs) 16 oc, when a loft joist lands above a header I assume we would just add a shorter cripple stud next to the 16oc cripple studd for the same effect?

astidham

Quote from: beckhamk on May 02, 2011, 10:16:28 AM
Don_P was spot on!  I saw astidham actually do this in his and liked the simplicity of it compared to all of the cutting. I also felt it was stronger and superior solution.

astidham - when you did this did you just cut all of your studs to 7' 6"  or did you measure each one individually because of the slight differences in dimensional lumber?


One other question I would like to add. Assuming we kept the studs (normal framing stuffs) 16 oc, when a loft joist lands above a header I assume we would just add a shorter cripple stud next to the 16oc cripple studd for the same effect?

I cut my studs (from floor up) 7'6"
when we landed at a header, I just shimmed, it was only ~1/4 of an inch.
I did use composite shims, they are not supposed to squish, expand or anything.
"Chop your own wood and it will warm you twice"
— Henry Ford


Don_P

If the sidewall is subjected to bending you would look at the stud similarly to a beam. One of the first things to look at in bending is the section modulus of the piece of wood being bent, a way of representing the qualities of the geometry of the beam. An unnotched 2x6 has a section modulus of 7.56"^3 while the notched 2x6 is only 4"^3. Unnotched the stud is considerably stronger in bending.

PEG688


There are hundreds of thousands of houses in the USA that have 2x4 walls with cut in ledgers , they've been standing for about 100 years. Re-invent the wheel if you must. But you're wasting wood in doing so.   
When in doubt , build it stout with something you know about .

Don_P

The wall above those houses supports a vertical load of the roof above. The rafters on those houses are tied together across the building by ceiling joists, typically at the top plate but they can be as high as 1/3 of the roof height above the plate. If the tie is above that level the rafters can be trying to spread, thrusting against the walls, this is where you step outside of prescriptive code. The unnotched stud is stronger than the notched stud, if the tie is too high this all is rightfully an engineer required situation.

archimedes

Quote from: Don_P on May 02, 2011, 05:46:57 AM
You're still not back inside of the warm loving arms of the code, but this is certainly better than notching the tension edge of studs.

Why would this not be up to "code". 
Give me a place to stand and a lever long enough,  and I will move the world.

MountainDon

Because it does nothing to address the issue of the rafter ties. Rafter ties need to be at the rafter to wall connection or in the lower third of the 'rafter triangle' in order to count as a rafter tie.

Just because something has been done and has not failed, doesn't mean it is good design.


archimedes

Maybe I'm missing something.

If you replace the ledger board with a "cripple stud" (I think that's the term) under each loft floor joist,  don't the floor joist act as rafter ties?  And the cripple stud doesn't create any of the issues with notching the stud wall.

Or am I missing something?  ???
Give me a place to stand and a lever long enough,  and I will move the world.

MountainDon

You are missing something. The loft joists act as joists; possibly somewhat as wall stiffens, but not as rafter ties. They tie one wall to another wall but they do not touch or tie the rafters together. The rafter triangle is not complete. The rafter tie could be placed someplace in the lower third of the wall top to ridge height. That is not likely going to provide the wanted headroom in the loft for most of the buildings this is done in. If the rafter ties are placed higher than 1/3 their effectiveness as a rafter tie is reduced and they may place extra stresses on the rafters themselves. (As the rafter ties are moved up in the triangle correction factors should be applied; the rafters become deeper)

The section of wall stud from the loft floor joists to the top of the wall now has the full force of the rafter thrust bearing on it. That includes the horizontal component as well as the obvious downward component. The wider the building, the shallower the roof pitch, the worse it gets. The wall stud was never meant to resist those horizontal forces like that. If you have read the lumber grades topic you may recall that stud grade is very weak in bending loads when compared to #2 or better grades of lumber. Using better grade lumber would increase the upper wall strength. Not having the notch makes it better, but it is still not within the realm of the prescriptive methods in any building code.

Just because something has been done and has not failed, doesn't mean it is good design.

rwanders

I couldn't find mention of whether the poster was building with a ridge board or ridge beam----using a ridge beam would, I believe, change the load picture and therefore could be compliant with both code  and accepted practices without rafter ties?



Rwanders lived in Southcentral Alaska since 1967
Now lives in St Augustine, Florida

archimedes

Thanks Don.

I was working under the wrong assumption that the ledger board method would be code compliant,  and I couldn't understand why the cripple stud method would not be code compliant since it seems stronger.  But I now understand that neither method is code compliant.  Even thought the cripple stud method probably would be stronger,  it still doesn't meet code requirements.

Give me a place to stand and a lever long enough,  and I will move the world.

MountainDon

Quote from: rwanders on May 03, 2011, 04:06:16 PM
I couldn't find mention of whether the poster was building with a ridge board or ridge beam----using a ridge beam would, I believe, change the load picture and therefore could be compliant with both code  and accepted practices without rafter ties?

My assumption (always a bad idea  d*) was that this would be a simple rafter roof. It is the more common scheme. RW is absolutely correct, using a structural ridge beam along with proper load trace down to the foundation eliminates the outward horizontal thrust of the rafters on the wall tops. And therefore works. The catch is that ridge beams and their supports is not prescriptive either. The ridge beam would be sized by the beam manufacturers engineer from the information supplied by the owner-builder. That info does not usually come with how to carry the load down to the foundation.
Just because something has been done and has not failed, doesn't mean it is good design.

MountainDon

#19
Quote from: archimedes on May 03, 2011, 04:14:01 PM
Thanks Don.

I was working under the wrong assumption that the ledger board method would be code compliant,

A ledger board can be code compliant. As Don_P pointed out those instances also include proper rafter ties. It is really a rafter tie code 'thing' more than a wall stud or ledger 'thing'.
Just because something has been done and has not failed, doesn't mean it is good design.


MountainDon

Another sulution to the combined issue of ledger boards inset into notched studs AND kneewalls AND rafter loads (horizontal thrust) would be to use manufactured roof trusses such as those astidam used.
http://countryplans.com/smf/index.php?topic=8931.msg119734#msg119734

Those provide headroom and reduce the horizontal forces on the kneewall stubs.



Just because something has been done and has not failed, doesn't mean it is good design.

MountainDon

#21
A tip that was handed to me by PEte....
When we have a nice neat banded stack of trusses like this, now, before we cut the banding, is the time to mark any layout measurements.


And another note related specifically to a scissors truss...
With the scissors trusses, if you look very carefully on the design paper work which comes with the truss package, someplace you will find a lateral (horiz.) deflection at one of the truss bearings, and you must consider and tolerate that at the top of the walls, likely split btwn. the two walls. DonM's (aka MtnDon) comment "reduce the horizontal forces on the kneewall stubs," is truly the operative phrase here. Their design program assumes a vert. & horiz. reaction at one brg. and a vert. reaction and a roller at the other truss brg., thus they get a horiz. deflection at the roller, and it is real. But, at least it is an engineered system, with some real control which I can try to design around. The same thing happens with the gambrel trusses, they call them bonus room trusses in some areas.

But, the lateral deflection issue goes away with a truss which has a horiz. bottom chord at the truss brg. level. They can also make trusses with raised bottom chords, but all of these things are somewhat non-std. and cost more money, than their stock designs.

PEte
Just because something has been done and has not failed, doesn't mean it is good design.