Loft Floor Questions

[MTScott]

Being a man of little experience, this question may be annoying to some, but... that's how you learn right?  This topic has been brought up time and time again, so I apologize for yet another Loft floor question.

I've been trying to learn the details of each piece of the 20x30 loft plans step by step - I'm currently thinking about the loft floor.  The ledger boards seems like a fine solution.  I intend to use a true Ridge beam, and based on other threads I've read, platform framing would then be acceptable (vs balloon framing) so perhaps I can just go that route; that said, a single stud all the way to the roof still seems like a good idea.  This isn't really what my question is focused on though...

If you did use 12' studs and wished to put in a loft - rather than notch in a ledger board why not use an 8' stud installed parallel to your wall studs hold up the loft joists.  I suppose this is a perhaps a waste of material, and it'll narrow your stud spacing, but it seems like it would be an easy solution and most definitely transfer the load properly?? 

Thanks,
Scott

[DutchMo]

Hi MTScott, and 

I don't have any definitive answers for you, but I'm also very interested to see the answers you will receive.  I've been pondering that same question.

To my simple mind, it seems like supporting the loft joist on a shorter stud sistered to the main stud would provide more bearing surface for the joist (5.5 inches in the case of 2x6 studs).  But maybe once you've satisfied the minimum bearing surface, the extra doesn't help you at all?

Regarding using a ledger to support the joists, I found this very informative post from a few years back: http://countryplans.com/smf/index.php?topic=10068.0
In that topic, MtnDon recommends cutting a notch into the studs to support the ledger.  I've seen lots of pictures of that approach, so it seems to be pretty common.

However, I don't understand how that approach is allowed.  Per code, notches should not exceed more than 25% of the width of the stud.  But cutting a 1.5 inch notch in a 5.5 inch 2x6 stud yields 1.5/5.5 = 27%.  Maybe it is a case of close enough?

I'm curious to hear what others say.

[MountainDon]

The past posts are persistent, but not always 100% correct.  I know more with more certainty than I did years ago.

To keep within code the use of a 2x let in ledger in a 2x6 stud is not good.      Check out the relevant code section,  TABLE R602.3(5) .  Scroll the page down about 5/7 to the bottom.  Check the drawing below that table.  We can use a 1x4 let into the wall stud as long as we also face nail the joist to the wall stud. There is a nail size and number of nails recommended; I have to look for that.  Using nails long enough to permit driving through and then hammer clenching over increases the strength.

I'll be back later....

But, with the mention of using a true ridge beam in the roof construction I believe the best way to attack this would be to platform build each floor and use that ridge beam with proper support columns down to the foundation. That eliminates the fore blocking that would be needed with a balloon framed wall.  Also eliminates the second stud, jack stud, that would increase the heat loss through the wall.

[MTScott]

The past posts are persistent, but not always 100% correct.  I know more with more certainty than I did years ago.

To keep within code the use of a 2x let in ledger in a 2x6 stud is not good.      Check out the relevant code section,  TABLE R602.3(5) .  Scroll the page down about 5/7 to the bottom.  Check the drawing below that table.  We can use a 1x4 let into the wall stud as long as we also face nail the joist to the wall stud. There is a nail size and number of nails recommended; I have to look for that.  Using nails long enough to permit driving through and then hammer clenching over increases the strength.

I'll be back later....

But, with the mention of using a true ridge beam in the roof construction I believe the best way to attack this would be to platform build each floor and use that ridge beam with proper support columns down to the foundation. That eliminates the fore blocking that would be needed with a balloon framed wall.  Also eliminates the second stud, jack stud, that would increase the heat loss through the wall.

Thanks for the info.  You identified the negative I was wondering about, which is heat loss through the wall.  I suppose a guy could use a 2x4 jack stud to eliminate some of the heat loss, but I'm sure there is still a negative affect.  It sounds like platform framing is the ticket for me anyway.  It also leaves a bit of flexibility in how high i make that second wall. 

[MountainDon]

You could turn it into a full fledged 2 story...  As long as the foundation / soil will carry the weight.  A ridge beam would then not be required if the second floor walls are high enough to permit proper rafter ties at the top of the second story walls or at least within the lower one-third of the rafters.

[MTScott]

You could turn it into a full fledged 2 story...  As long as the foundation / soil will carry the weight.  A ridge beam would then not be required if the second floor walls are high enough to permit proper rafter ties at the top of the second story walls or at least within the lower one-third of the rafters.

Part of the design I like is leaving the great room area open to the ceiling.  I would then have 16' walls in the great room.  Even with 12' walls I figured the ridge beam was just a failsafe solution to ensure no bowing would occur and meet code without using regular trusses.  If I do rafter ties on 16 foot walls with rafters, would that be acceptable to prevent sagging/bowing?  I've considered also changing the roof pitch to be 8/12 over the loft to 12/12 over the great room... but running 10/12 over the whole thing at a full two stories sounds simpler.  Either way, I'm dealing with same situation in the great room.

In the area I'm building, there is no local building department (city or county), so it defers to the state building requirements, which defer to the 2012 international code:
http://publicecodes.cyberregs.com/icod/irc/2012/

According to R602.3(5), 10 foot is the maximum, but it makes exceptions in R602.3.1, which allow (as far as I can tell) 16' walls, 2x6, 24oc when only supporting a roof. 
http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_6_sec002.htm

In this situation, would rafter ties suffice (every 4 feet?) with only a ridge board?  Even with a beam, would rafter ties still be a good idea?

The truth is I could do whatever I want, as no building permit or inspection is required (when doing it yourself), but i'd prefer to do it right, and also within my skill level (most of which is being learned as we speak).  Over engineering it is my fail safe when faced with "maybe" situations.   Hence my choice for a beam, but the beam won't come cheap.

[Don_P]

Read the footnotes to the stud height table, that applies to a 12' or narrower building width. It's easy to hit "design required" with that table. I'd want 2x8's minimum in a wall that tall. The studs are no better thatn the end connections, as the wall gets taller the wind is working on the attachments at top and bottom harder.

[DutchMo]

MTScott, I found this just today on another site.  Another way to do a loft:



Rather than running the loft joists across the width of the building (20 ft wide), they installed a large beam (LVL, essentially 3 2x12s), and supported it with jack studs.  Then they hung the loft joists on hangers between the LVL on one side, and platform framed the gable end walls.  In this case, the LVL is also supporting a center catwalk, and there is a loft on each end of the building.  You wouldn't have to do both sides, though.

That same thread had another pic that illustrates the framing a bit better:

[MTScott]

Read the footnotes to the stud height table, that applies to a 12' or narrower building width. It's easy to hit "design required" with that table. I'd want 2x8's minimum in a wall that tall. The studs are no better thatn the end connections, as the wall gets taller the wind is working on the attachments at top and bottom harder.

Agreed.  On the 20x30 1.5 story plans, it does have 12' walls in the great room area, correct?  Or is that just what many people stretch it to?  I'm curious what was designed to accommodate that.  Perhaps I had better purchase the 20x30 1.5 story plans.  I'm struggling with doing a longer version of the 20x30, or a longer version of a 16' wide building.  I could probably do what I need with 16' wide, but... eh, you know how it is .

[Don_P]

I believe you're seeing a stretch of a 10' wall height in plan.

[MTScott]

Ah, okay.  Now that i look closer, I guess the versions that I have seen with 12' walls are actually building a mostly complete second floor.  So, they are supported, thus meeting code.

In a smaller home, i really like the idea of that cathedral ceiling great room area... it makes the house feel bigger to me.

Something I could do, is run the same ridge line for the whole house, but frame 10' walls in the great room area, with a 12/12 pitch, and then run something like an 8/12 pitch over the loft.  it'll add some complication in framing the roof, but I'm sure it can be overcome.  My idea is more or less to stretch the 20x30 to 20x40, but I wish to put 2 rooms upstairs over the master that will end up being about 9x12, with a smaller loft area in front, perhaps stretched over the kitchen.

Question on wall height code... guys around here build shops all the time, 12-16' high, unsupported... just a big box, with shallow trusses.  Some are even only 2x4 construction.  Is code not a concern with a shop?  Is it only an issue when it is space that will be "lived" in?

Here is an example of a plan, 40x50, 12' walls, framed with 2x4s!
http://www.cadnw.com/details.asp?plan=G4050A

[MountainDon]

Building codes are focused on residential construction. A shop, barn, shed does not have to meet the same standards as a habitable building. Also different jurisdictions may have additional restrictions, above and beyond the code. And there are places that officially have the code at the state level (all states have adopted a code, usually the IRC) but have no local enforcement in some areas.

Then, to complicate things, there is no rule that states that anything sold has to meet any standards at all. Some plans may be older designs that once did meet code. If we go solely by pictures of what others have done we may be repeating errors. If we look closely at plans and websites selling them we may find a disclaimer that cautions the buyer to check with local authorities for suitability. If there is no local inspection of plans before construction then the plans buyer is on their own.

[Don_P]

All true, a kid with a crayon can draw and market a set of plans. The residential code is concerned with habitable buildings. Ag structures in many states are exempt from building codes... and it can show. There are 4 barns on my list, I'm kind of hoping one collapses before I get there, and it appears to be agreeing. Another that 4 of us that I know of have said "It's done". All of those are unsafe buildings in a storm or heavy snow, I'm fairly ok on a pretty day if I can run, no way would I shut my eyes in them.
The table you pointed to in the codebook is prescriptive, it doesn't say you cannot go taller with a 2x6 wall, it says "design required". It stops at pretty much bulletproof design. And plenty of people find ways to screw that up  .

The design part is kind of tough. A load bearing stud in an exterior wall is a tall slender column supporting the weight that is bearing on it without buckling, makes sense, as a tall slender column gets taller it wants to turn into a noodle more and more... and it is doing this while also acting as a beam, the wind is hitting it from the side. This combined loading stresses the stud more than if it were resisting either load alone. As the stud gets taller the stresses on the stud increase pretty rapidly.
In a 110mph design (using the new classification system, this is the old 90mph lowest wind design category)
The induced bending stress (Fb) on a 10' tall 2x6 stud @16" oc =737 psi, max bending moment is 250 ft-lbs
At 12' Fb=1029psi, 350 ft-lbs
at 16' Fb=1729psi, 586 ft-lbs
The compressive load from above remains the same but as the length increases the column wants to buckle more and as you can see, the wind sure wants to help that along. When they get moderately tall the engineers usually spec 2x8's and tight nailing of the sheathing, if it's a glass wall and tall, pay the man  .

From my observations after building too many lawyer foyers and personal great cathedrals... people are not comfortable in too tall a room. We are no different than our dogs, they hang out under the furniture or under the porch... we do too. In a gathering we will use a large space but for daily living I've watched my clients avoid those rooms they thought of as Great and favor the normal ceilinged rooms... they don't do it consciously and I just quietly observe and smile to myself, YMMV.

[MTScott]

"bulletproof" is the area I want to be in.  My goal here is to figure out where those lines are drawn with the things I want.  If I'm asking things that require additional engineering and design... well, reckon I should just change my expectations.  8' walls with a vaulted ceilings would be fine with me... I was just trying to figure out how to get more space in the loft without complicating a roof.  I don't really want to mess with dormers or anything fancy like that either.  I figure a simple roof with one ridge and no valleys or changes is the best roof there is both for simplicity, and durability.

I may consider doing a single smaller loft bedroom, and fitting an additional bedroom downstairs by going longer.  I have considered the "cave" mentality you're referring too.  I've heard that same thing from other sources, and while it makes sense I do like a little additional  height with some higher windows.  2 stories of height plus 12/12 rafters topping out at 26 feet would be pretty ridiculous.  Back to the drawing board.

Great information guys, thanks for the help.