Ledger or jack studs

Started by RIjake, September 04, 2011, 07:50:19 AM

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RIjake

I'm getting ready to start framing the walls but have got to thinking about the support for the loft floor. 

We all know that the plans call for the loft floor joists to be supported by a continuous ledger let in on the wall studs.  My cabin will have a loft over the entire length.  I thought maybe doubled 2x6s standing vertically and sistered to wall studs might be an alternate way of supporting the joists.

My plan is to use doubled 2x12s with a layer of 1/2" plywood sandwiched in between for the joists.  They will be on 4' centers and 2x6 planking will be laid for the loft floor.

It seems to me that vertical jacks may be quicker to install than letting in every wall stud.  What do you all think? 

astidham

I used jack studs with my loft, I think jack studs are superior to the let in ledger.
as far as 2x12s doubled on 4' centers, I think this span would cause you problems
"Chop your own wood and it will warm you twice"
— Henry Ford


PEG688


How wide is your building Jake?   

Why add the 1/2" ply?  The main reason on headers to add the ply was to thicken the two 1 1/2" from net 3" to net 3 1/2" back when exterior walls where framed out of 2x4. It adds very little , if any thing , to the strength of a header or beam.

If your out near max span on the 2x12's you could have the lumber yard size you some LVL , or PSL which may work better. They can be ordered as 1 1/4 " , 1 1/2" , 1 3/4 " and so forth.


The thing I don't like about the jack stud method is,    UNLESS you solid block every stud bay to prevent the joist from rolling , you have the potential of that happening. 

So it's a wash IMO materiel and labor wise as you need to either solid block  the bays or let in the ledger.

I'll add that the let in ledger method has a proven track record of at least 200 years , AND from a insulation stand point if you jack stud the joist and solid block you get less R- value in every stud bay, remember woods R value is lower then insulation.


So there's a few things to ponder.

G/L PEG 


   
When in doubt , build it stout with something you know about .

RIjake

#3
The cabin is 20' wide.
I understand the plywood in the header is to get the proper thickness, that is not the same as what I am doing.  When you sandwich plywood between the 2x12s you create a much stiffer beam.  This beam will be plenty strong enough at this span and the 2x6 planking will be fine bridging the 4' space.  We are not trying to achieve a 40lb live load.  This is a loft that will strictly be used for bedrooms.  No bath, no appliances etc.

As far as the jacks, the insulation factor is one that I had not thought of.

astidham, why do you feel the jacks are superior? 

PEG688

Quote from: RIjake on September 04, 2011, 10:52:44 AM
The cabin is 20' wide.
I understand the plywood in the header is to get the proper thickness, that is not the same as what I am doing.  When you sandwich plywood between the 2x12s you create a much stiffer beam.  This beam will be plenty strong enough at this span and the 2x6 planking will be fine bridging the 4' space.  We are not trying to achieve a 40lb live load.  This is a loft that will strictly be used for bedrooms.  No bath, no appliances etc.

As far as the jacks, the insulation factor is one that I had not thought of.  astidham, why do you feel the jacks are superior?


I'd not say "much stiffer" , but IF it makes you feel good I guess do it. The thing that's going to "stiffen " those joist as the 2x6 T&G you're nailing down as the floor. The plywood sandwiched between is a waste to time and $$ IMO.

I'd like to know IF astidham did any solid blocking  between the joists and the next regular stud?



  I was looking at some photo of Vermont storm damage and saw quite a few homes that had so damage that was pretty incredible, and this is NOT directly related to your jack stud V. ledger issue but in a broad sense it's related. but these house's a noticed the floors stayed in place and the wall shifted right off at the bottom plate as the other end of the house settled into the holes the water washed away on the other ends  of the places.

Most of those houses where total looses , but it's interesting to see how they failed , and relating it to smaller shifts that may occur in  a normal situation.

  http://s3.amazonaws.com/mhi-flood/LG9_9268.jpg

I hope that worked ,    see how the floor stayed put but the walls dragged right off the floor system, had the sheathing tied the walls to the floor maybe it would have stayed.

I guess it's a moot point as the place would have been totaled anyway , so at what point is "enough , enough"???
When in doubt , build it stout with something you know about .


KWillets

Doubled 2x6 jack studs would have a vertical load capacity of over 10,000 lbs. (http://www.awc.org/software/protectedPDF/AWC-ASDSupplements2001-0602-unprotected.pdf ).

You may be overbuilding.

Don_P

In balloon frame with a ledger the joist must be firmly attached to the stud, do the same thing here and the risk of rollover is taken care of IMO. Blocking will make it stronger, I don't know that it's necessary.

Not notching the stud for a ledger makes the wall much stronger. The section modulus of a member used to determine bending strength is bd2/6... breadth times depth SQUARED over 6. Making something deeper pays off far quicker than making is thicker, conversely notching the depth on the tension face weakens a member really fast. The track record for balloon frame and the code provision for it, is for a building with properly tied rafters... no horizontal thrust delivered to the walls.

PEG look at the floor again, it drifted up and right in the picture off of the foundation exposing the basement. Line up the exposed bay of oak flooring with the bay in the foundation wall, not an anchor bolt in sight. I think it started breaking as the rear dropped over the back foundation wall. It looks to be pretty old.

Native_NM

If the loft is going to cover the entire "second"  floor, why not just build 8' walls, lay the beams across, and build a 4' wall on top?  Run 4x8 3/4" plywood horizontally around the perimeter between the first and second floor to tie them together.  Better, faster, stronger.
New Mexico.  Better than regular Mexico.

RIjake

Quote from: PEG688 on September 04, 2011, 11:30:03 AM

I'd not say "much stiffer" , but IF it makes you feel good I guess do it. The thing that's going to "stiffen " those joist as the 2x6 T&G you're nailing down as the floor. The plywood sandwiched between is a waste to time and $$ IMO.

It's similar to using sandwiched plywood between the (3)2x12s used as girders in many member's post and pier foundations here on the forum.  I agree that the 2x6 T&G will tie it all together, but for the minimal cost and time associated with ripping some plywood it's a no-brainer IMO. 

So back to my original question......

I guess I'll stick with the plans on this.  Jack studs are plenty strong but the thermal bridging is an issue.

It is interesting reading Don, about the loss in strength with a notched ledger.  I have a lot of experience with balloon frame construction being a firefighter in an old northeast mill city.  I have never seen a floor fail, even in fire conditions from a notched ledger.  And the triple-deckahs we have around here are mostly built using full dimension 2x4s for exterior wall studs not 2x6s like I'm using.
Blocking seems like a good idea to keep the joist from rolling though. ???


astidham

Quote from: RIjake on September 04, 2011, 10:52:44 AM
astidham, why do you feel the jacks are superior? 

I feel jack studs are superior because they continue the load to the bottom plate without notching, or changing the regular structure, and has a larger face for the joist to sit on.

Quote from: PEG688 on September 04, 2011, 11:30:03 AM
I'd like to know IF astidham did any solid blocking  between the joists and the next regular stud?

PEG, I did not block between the two, but the joist are decked with 3/4 advantech ply. is this not equal to blocking?


"Chop your own wood and it will warm you twice"
— Henry Ford

PEG688

Quote from: Don_P on September 04, 2011, 12:36:45 PM


In balloon frame with a ledger the joist must be firmly attached to the stud, do the same thing here and the risk of rollover is taken care of IMO.

PEG look at the floor again, it drifted up and right in the picture off of the foundation exposing the basement. Line up the exposed bay of oak flooring with the bay in the foundation wall, not an anchor bolt in sight. I think it started breaking as the rear dropped over the back foundation wall. It looks to be pretty old.



I guess you're right about the blocking as long as folks don't get complacent about attaching the joist to the stud properly.  My fear is people tend to forget things , more so IF they think they've covered themselves by doing it "another way", when if they'd just done it as it's been done for a few hundred years they'd be OK.

I see that in that photo, here's another instance:

http://s3.amazonaws.com/mhi-flood/LG9_9262.jpg


  This ski resort failed more in line with what I'd think it should , maybe a new building?

http://s3.amazonaws.com/mhi-flood/LG9_9547.jpg

http://s3.amazonaws.com/mhi-flood/LG9_9551.jpg


This ones holding or at least held , who knows by now,


http://s3.amazonaws.com/mhi-flood/LG9_9702.jpg



All the photo's :

  http://www.mansfieldheliflight.com/flood/



Pretty devastating storm!! Good luck  to the folks in Vermont. 



 

     
When in doubt , build it stout with something you know about .

PEG688

Quote from: astidham on September 04, 2011, 01:35:42 PM


Quote from: PEG688 on September 04, 2011, 11:30:03 AM
I'd like to know IF astidham did any solid blocking  between the joists and the next regular stud?

PEG, I did not block between the two, but the joist are decked with 3/4 advantech ply. is this not equal to blocking?





  I'd say no, and I hope you nailed the joist to the stud adequately. Rotation isn't something I tend to stress on , like you,  I think the sheathing  goes a long way to resist rotation, BUT the code likes that solid blocking. 

A lot of things in the code book are over built in normal use , but then what "normal use" means can vary depending on what hits ya.


As the photo's I linked to show , when things go bad,  all the things we do can be undone , no matter how we build things.     

  And some mentioned being a fire fighter, which brings back the when things go bad part.   A lot of the seismic things we attempt to build for out here may ,,,,,, MAY ,, let a house not totally collapse so people MAY be able to escape before it caves in. At what cost to home ownership , added dollars to cost of building , do we go to for this end game???

But I'm drifting you off your topic , sorry.

   
When in doubt , build it stout with something you know about .

Don_P

Quote from: Native_NM on September 04, 2011, 12:40:22 PM
If the loft is going to cover the entire "second"  floor, why not just build 8' walls, lay the beams across, and build a 4' wall on top?  Run 4x8 3/4" plywood horizontally around the perimeter between the first and second floor to tie them together.  Better, faster, stronger.

It depends, and we're wandering into areas outside of prescriptive code. The extended balloon framed stud has some capacity to resist thrust from the rafters above... damn little and I've seen folks really pushing the limits here. The older historic buildings did not in my experience ever thrust on those walls with the roof framing. An engineer has proposed an experiment that at some point I need to build and photograph. However, if you simply stack a kneewall on top of a floor and then install a poorly tied rafter pair on those walls it is very likely to fail by tipping the kneewalls over. But... If the kneewalls on the floor are 5' tall or more then the ties can be lowered to the lower third of roof height, the rafters can be adequately tied, and life is good again.

Native_NM

Quote from: Don_P on September 04, 2011, 05:51:43 PM
It depends, and we're wandering into areas outside of prescriptive code. The extended balloon framed stud has some capacity to resist thrust from the rafters above... damn little and I've seen folks really pushing the limits here. The older historic buildings did not in my experience ever thrust on those walls with the roof framing. An engineer has proposed an experiment that at some point I need to build and photograph. However, if you simply stack a kneewall on top of a floor and then install a poorly tied rafter pair on those walls it is very likely to fail by tipping the kneewalls over. But... If the kneewalls on the floor are 5' tall or more then the ties can be lowered to the lower third of roof height, the rafters can be adequately tied, and life is good again.

A 4' kneewall and some nice engineered trusses would be a lot easier than jack studs, notching studs, or many of the other variations I've seen discussed.  The scissor trusses they build now provide nice interior height on a 20' wide.  Even platform framing with an engineered ridge beam would be easier in the end.  Now that I think about it, 20' TJI's would probably be easier and cheaper than doubling 2x lumber, and he'd end up with less deflection. 

Just my thoughts...
New Mexico.  Better than regular Mexico.


MountainDon

Quote from: Native_NM on September 05, 2011, 07:05:37 PM
A 4' kneewall and some nice engineered trusses

The key to something like this is the engineered roof truss. A scissors truss can still exert some lateral load (horizontal and outward) I believe, but the engineer should take this into account with his design. Of course he should be supplied with all the info including how the sidewalls are going to be built.

Or a ridge beam, and that has some engineering behind it too, all the way down to the foundation.
Just because something has been done and has not failed, doesn't mean it is good design.

Native_NM

Quote from: MountainDon on September 05, 2011, 07:10:11 PM


The key word in either case is "engineered".  I'm generally pretty frugal, and pride myself on figuring things out when I can, but there are some cases where it just makes sense to call in an expert.  In many places, the guy who sells you a ridge beam can also do the engineering calcs for you.  For a few bucks more, he'll have his crane guys lift it in place.  It seems like short dollars. 

New Mexico.  Better than regular Mexico.

Don_P