Post and pier framing without the beams?

[_JT]

So, I'm planning to build a small cabin at the entrance to my land (50 acres of off grid undeveloped timber property in west TN). I've been reading here for probably six months, but just now registered. I've read about a dozen of the longest owner-build threads on the other forum, and gleaned a ton of useful info. Consequently, I feel like I know you guys, but you don't know me.

Anywho, I'm planning a 12x16 1.5 story on a post and piers foundation. 10' 2x6 walls balloon framed to have a loft over half of the footprint. 2x8 rafters with 2x12 ridgeboard.

My question is on foundation/footings (gotta start at the beginning, right?):

I was initially considering 4x4 posts with 4x6 beams, and then structure on top of that. Like this:

[/spoiler]

I realize there's no lateral bracing shown, but it doesn't impact the question I have for you guys. Which is: is there any reason why I couldn't go to 6x6 posts, and notch them to accept the rim joists, then thru or lag bolt the joists to the posts, allowing me to bypass the heavy and expensive beams? Obviously as shown the rim joist isn't one complete member, but if I went this route I'd order 16' rim joists.

Educate me, wise folks, please.

[flyingvan]

Ooooh, don't let Don see this.  Some of the best advice on here is start your design from the top down, and it makes lots of sense when you think about it---a substandard foundation will limit your roofing options, but if you start at the roof you'll know how strong your foundation needs will be

  I'm not quite sure what you mean---how would your floor joists attach to the rim?  It sounds like they wouldn't be resting on anything, which is OK in some situations but I doubt a 2x rimjoist bolted to a notch would resist the flexing and would tend to bend out.  Do you ever play Jenga?

[_JT]

Ooooh, don't let Don see this.  Some of the best advice on here is start your design from the top down, and it makes lots of sense when you think about it---a substandard foundation will limit your roofing options, but if you start at the roof you'll know how strong your foundation needs will be

To be clear, even though I'm not required to be code-compliant, I certainly am not building a substandard foundation. That's why I'm asking the question. If there's a good reason to go with the beams tying the posts together, I've no problem doing just that. Just trying to come up with the easiest, safest, cheapest way to build remotely on my own.

I'm not quite sure what you mean---how would your floor joists attach to the rim?  It sounds like they wouldn't be resting on anything, which is OK in some situations but I doubt a 2x rimjoist bolted to a notch would resist the flexing and would tend to bend out.  Do you ever play Jenga?

Floor joists would attach the same in either case: joist hangers. I'm not sure I'm picturing the right thing when you're talking about flexing at the rim -- can you describe it?

[flyingvan]

I was talking more generally about designing from the top down---didn't mean to imply your design was substandard...

  Well, if I'm picturing your idea right (and I admit that's a big 'if')  you have a rim that's 2x material supported by some notched 6x6's.  Then you use that 2x to support walls, which are holding a roof, which might hold snow, (dunno where you're building) and will take some wind loads too.  Then your floor joists are hung from the same 2x.  I would think the rim would tend to flex down (between your 6x's) and out (away from the butt ends of the floor joists)
   There are some really good reasons to use beams to tie tour posts together.  (It's why I asked if you play Jenga)  Stacking lumber for compressive strength instead of relying on the shear strength of hangars is a good idea....Besides, I bet what you'd save on joist hangars would cover the cost difference between a 2x rim and a whole beam
    Another thought---if you really want to notch those 6x's, could you notch both the inside and the ouside and run two 2x's?  the outer one could be bigger...I'll try to send a sketch

[flyingvan]

   So your 6x6 is notched both sides, and the outside rim joist is taller than the inside one.  Then there's a filler between the two that also runs between each of your posts.  Now your floor joists and walls sit on something more solid.

  Does this make sense?

[_JT]

I understand the suggestion -- thanks for sketching it out. I don't know that that way offers any significant time or cost savings over just using a beam, though. :/

As for your concerns: you've given me some good food for thought. The weight of the structure above bearing down on the rim joists is worth considering, as is the cost of the beams vs the joist hangers (I have a hard time believing beam + hardware would be less than 20 joist hangers, but if I'm also factoring in the time to notch the beams, that could be the case).

Would love to hear other input, as this isn't my area of expertise. I imagine after the holiday weekend is over it'll be a less more traveled around the forums.

[flyingvan]

Did you see the thread where we were discussing sandwiching 2x's for framing?  Also I realized an amateur (which I am) mistake in my sketch--3 2x's do not equal one 6x, at least not since 1961... And I agree just using a beam would be just as good

[Don_P]

Too late, saw it 
Remember a joist or a rim is a beam... it's simply a problem of quantifying loads and sizing the beam... a single rim on this might be an adequate beam.

west TN, 10 psf snow? If so add 10 psf dead load for roof self weight so 20 psf roof load. I'm going to try to carry half of it with a structural ridge supported on each gable end. So the center strip 6' wide (3' on either side of ridge) X 16' of ridge length X 20 pounds per square foot self weight plus snow weight = 1920 lbs uniformly distibuted along the ridgebeam. In really nice yellow pine a double 2x10, otherwise a double 2x12 would do the job there. The end walls need to carry that ridge load down to the 12' rim, half at each end. A 2x12 rim on the floor is adequate.

We need to carry 1/4 of the roof weight down each side, so half of 1920 lbs = 960 lbs. If all 6 of the 6x6's run from footing to the top of the wall and are notched for a "rim" to carry the remaining roof load then the 16' span is broken in half, divide that 960 by 2, call it 500 lbs. A single 2x6 up on edge, beam fashion,  would carry the roof load on the posts and not transmit it to the floor below... we just bridged the roof load over the floor below.

The floor should be designed for 40 psf live load and 10 psf dead load, 50 psf.  at 6' x 8' x 50psf= 2400 lbs floor load on each 8' rim section. A single 2x12 works as the beam. Rather than joist hangers I'd nail a 2x4 ledger to the 2x12 under 2x8 joists.

Bridge the loft off the posts by notching a 2x12 ledger into the 6x6's as well.

Frame infill wall sections. When you sheath the box the 6x6 posts then become beams cantilevered out of a bracing wall structure, a much better way to laterally brace pier and beam... which is substandard  .

[_JT]

Whoa, Don! You're blowing my mind. I hadn't even considered using the posts as full height members -- I was still thinking of chopping them down like in a normal post/pier system. I need some time to build what you're talking about in sketchup for further consideration.

One thing: I wasn't planning on using a structural ridgebeam, but rather a 2x12 ridgeboard. That said, if (2)2x12s (of the right species) will get me the structural ridge, maybe that's worth looking into. Then I won't have to worry about rafter ties stretching over the main part of the floorplan.

[Arky217]

I built a 24' x 48' pier and post house recently, and I must say what you are proposing thus far seems to be less than adequate.

For example, the maximum span for #2, visually graded yellow pine 2x8's for a 40 psf live/10psf dead load on 16" centers is 12'10". Though your plan is barely within those limits, it is just makes good sense to exceed the minimum somewhat, if for no other reason than to not have a bouncy floor.

I don't have my beam tables handy, but as to spanning 8' with 4x6 beams to support 1/2 of those joists + the weight of the walls + the weight of the roof + any snow load, well, I certainly would go somewhat stronger than that.

As to the posts, 4x4's for a shed or a deck, well no problem, but for a house ?  By the time you finish the house, it is going to weigh a lot!   I certainly would up that to 6x6's.

That brings up another likely problem. With only 6 points for the entire house to rest on, you better have some super large diameter piers or some hard rocky soil for the house to rest on.

I don't want to sound discouraging, but I dare say the foundation is the most important part of a house. You would hate to finish the house and then start to have problems with the foundation.

Just as an example, this is what my foundation looked like. Admittedly, it may be somewhat overbuilt, but overbuilt is far better than underbuilt.

(The 6x8 beams span 6', the 2x8 joists span 8' (end joists are 6x8), the posts are 6x6's from the red heart of cedar, and the 36 piers are 10" dis. at the top and 18" dia. at the bottom which is 20" down in hard rocky soil.)






Arky

[Adam Roby]

Did you see the thread where we were discussing sandwiching 2x's for framing?

I believe flyingvan is referring to my thread.

I am planning to build up 2x6 dimensional lumber to avoid having to notch a 6x6 beam, and this way I can continue the beam from the pier to the roof line (or any length imaginable) simply because they are being laminated together.

[_JT]

I built a 24' x 48' pier and post house recently, and I must say what you are proposing thus far seems to be less than adequate.

For example, the maximum span for #2, visually graded yellow pine 2x8's for a 40 psf live/10psf dead load on 16" centers is 12'10". Though your plan is barely within those limits, it is just makes good sense to exceed the minimum somewhat, if for no other reason than to not have a bouncy floor.

I don't have my beam tables handy, but as to spanning 8' with 4x6 beams to support 1/2 of those joists + the weight of the walls + the weight of the roof + any snow load, well, I certainly would go somewhat stronger than that.

As to the posts, 4x4's for a shed or a deck, well no problem, but for a house ?  By the time you finish the house, it is going to weigh a lot!   I certainly would up that to 6x6's.

That brings up another likely problem. With only 6 points for the entire house to rest on, you better have some super large diameter piers or some hard rocky soil for the house to rest on.

I don't want to sound discouraging, but I dare say the foundation is the most important part of a house. You would hate to finish the house and then start to have problems with the foundation.

Just as an example, this is what my foundation looked like. Admittedly, it may be somewhat overbuilt, but overbuilt is far better than underbuilt.

(The 6x8 beams span 6', the 2x8 joists span 8' (end joists are 6x8), the posts are 6x6's from the red heart of cedar, and the 36 piers are 10" dis. at the top and 18" dia. at the bottom which is 20" down in hard rocky soil.)

Appreciate the feedback, and your structure certainly seems admirably well built. However, 12x16 is 196sq ft. 24x48 is 1152sq ft. So, no joke your foundation is a lot sturdier: your structure is going to weigh (at least) 8 times what mine is. But don't take my word for it: let's go to the math. 192sq ft x 70psf loading (20 for the roof [no snow load] and 50 for the floor) = 13440 lbs of total load. Divided by six posts = 2240 lbs per post. According to the axial compression load capacity from here, a 4x4 doug-fir of 4' length can be loaded to 15,793 lbs. Or roughly 7 times what I would be loading it at. And you say that's under-engineered? I have to respectfully disagree. According to the tables (provided I'm reading them right, which I certainly wouldn't swear to after three glasses of scotch), I could support the weight of my entire cabin on ONE 4x4. Don't worry -- I have no plans to do so.

2x8 floor joists is a no brainer on a maximum span of 12 ft. This is a cabin that will likely see occupancy 3 days out of every month. If some floor deflection means I don't have to dig extra footings in extremely unfriendly soil, I think that's a trade off I'm comfortable with. Most of the hunting cabins I see are, frankly, either mobile homes or just outright terrifyingly poorly slapped together. So I admit I'm building to a different standard than someone who's planning a 50 year full time residence. Were I intending to live here full time, yeah, I'd absolutely beef up the foundation to the point of over-engineering. I am an engineer, after all.

[_JT]

I believe flyingvan is referring to my thread.

I am planning to build up 2x6 dimensional lumber to avoid having to notch a 6x6 beam, and this way I can continue the beam from the pier to the roof line (or any length imaginable) simply because they are being laminated together.

Thanks for the link. I'd read your build thread, but not since reconsidering my foundation plans. That's more food for thought.

--------------------------------

I'm still a few months away from the decision, but more and more it seems like my initial foundation plan (4x4 posts, 4x6 beam, structure on top) is probably the venn intersection of cheap, safe, and fast. Is the preferred method here to confine questions to a build thread, or start new threads for each topic as they come up in the design phase?

[MountainDon]

Is the preferred method here to confine questions to a build thread, or start new threads for each topic as they come up in the design phase?

The General Forum (here) is a good place to use different new topics for questions on specific items; make a relevant topic for ease in finding at some later date.  The Owner - Builder Projects Forum is a handy place to document a projects progress, be that floor plans or the actual construction. There's no real hard fast rule; we try to use common sense.

~~~~~~~

One of the main deficiencies of a pier foundation is the lack of lateral support. The ground is relied upon to resist tilting of the piers. If the ground is not up to the task (sandy, or clay that is plastic when wet, etc.).  Each pier is an independent entity; even though the top ends may be tied to a beam the bottom ends are unrestrained. If the soil is lousy or gets soaked the piers can rotate about some point along its buried length. That is one of the big reasons piers are not a prescribed foundation by any building code. They can be used, but for code compliance need engineering approval.

With lateral resistance in mind, even though a 4x4 might have more than enough vertical load carrying capacity, larger piers are better. They present more surface area to the soil to better resist lateral forces. Bigger piers are better.

Each pier needs a good solid footing to spread the load. Load bearing of the soil varies a lot between soil types.  A pier foundation will seldom have loads equally distributed. If the footing is inadequate that pier may sink.


Back to lateral resistance; the greater the pier height above ground, with a beam and the cabin on top, the less the stability of the structure. The illustration in the OP falls into my category of too high to be practical. Don_P's suggestion of carrying the pier length from footing up to the wall top plates changes a pier foundation into a pole building of sorts. Once the walls are fleshed out with wall studs and then sheathed, the entire structure becomes a rigid box including the legs in the ground. That also removes potential weaknesses such as the joint from pier top to beam, then beam to joist. Anyhow, IMO, it is worth a serious look.

[UK4X4]

a 4x4 doug-fir of 4' length can be loaded to 15,793 lbs. Or roughly 7 times what I would be loading it at. And you say that's under-engineered? I have to respectfully disagree.

Just to play devils advocate, lets look at the weights again, ref the above statement......its not the compresive load on the post, its the load on the ground that you have to concider as well, like a tennis shoe V's a stilleto heel on a wood floor.

starting at the roof

ref Tennessee

"Use IBC 2003—10 psf-25 psf with Case Study Areas at higher elevations"

So depending on where your building - you should add the snow load, but we'll guess at a low lying area with no hills arround and just take the 10#.

Give this to 3 diferent engineers and they'll all give you a slightly diferent version....as you can even add "factors" for roof angle and materials....this is just basic

I'm presuming the roof does not end at the walls , so add 2 ft to each dimension for the roof loads
your now at 14 X 16 =224sq ft x 15+10SL=5600

ist floor is 12 x 16= 192sq ft X 40#=7680( taken as a lighter weight loft)

ground floor is 12 x 16 =192sq ft X 50#=9600

Total weight is 22,880#

22,880# divided by your 6 posts =3813# per post

You have 4" posts, or 16sq" per post =238psi of force on the ground

In PSF thats an equivalent of 34,272psf
which is actually quite high...

You now have to look at soils,,,,the weight is fine for the posts, but whats under them ?

If you look at this loading chart for big foots, you'll see the diferences per each type of soil
and the size you'd need to support that PSF........
http://www.bigfootsystems.com/include/docs/gravityLoadTable_US.pdf.

"that's under-engineered? I have to respectfully disagree"

so your right the posts are fine.......and wrong they are not enough to support the weight unless your on bedrock...

Being that its all area based, its pretty simple to add in lots of SQ inches under each post and bring those forces down.

Example add a 18" diameter pad under each leg....264 sq inches

Your psi drops from 238 to 15psi or an equivalent of 2,160psf

which brings you down to being just about able to build on the worst soil at 2000psf

and here endeth the maths lesson

I had 90# snow and 1800psi soil at my location....so you can imagine I quickly had to move away from posts

[_JT]

The illustration in the OP falls into my category of too high to be practical. Don_P's suggestion of carrying the pier length from footing up to the wall top plates changes a pier foundation into a pole building of sorts. Once the walls are fleshed out with wall studs and then sheathed, the entire structure becomes a rigid box including the legs in the ground. That also removes potential weaknesses such as the joint from pier top to beam, then beam to joist. Anyhow, IMO, it is worth a serious look.

(bolding mine)

The illustration in the OP shows the posts including the length that will be below grade. Otherwise I'd agree with you completely. I understand the drawback with piers, vis a vis the lateral shifting or twisting in weak soil. I read your entire build thread, including how if you had to do it over again you would do a poured or block foundation. My soil is hard enough that I'm not sure it'll even be possible to dig by hand, meaning I feel pretty good about the load the 4x4 post/concrete footer will apply to it. I may turn out to be wrong, or, even better, I may be able to find a good deal on 6x6s that makes it totally worth upsizing and over-engineering.

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Just to play devils advocate, lets look at the weights again, ref the above statement......its not the compresive load on the post, its the load on the ground that you have to concider as well, like a tennis shoe V's a stilleto heel on a wood floor.

Ok, devil's advocate, but I have to tell you right from the start that what you're doing is known in America as moving the goalposts. I was responding to a post saying 4x4s were inadequate for the weight of the structure; not that the footing area was too small to transfer that weight to the ground.

starting at the roof

ref Tennessee

"Use IBC 2003—10 psf-25 psf with Case Study Areas at higher elevations"

So depending on where your building - you should add the snow load, but we'll guess at a low lying area with no hills arround and just take the 10#.

Elevation: 748 feet. No snow load.

Give this to 3 diferent engineers and they'll all give you a slightly diferent version....as you can even add "factors" for roof angle and materials....this is just basic

My dad and I are both engineers (him civil, me electrical), and we've both come up with completely different versions! The image of herding cats comes to mind. That is to say of course you're right.

I'm presuming the roof does not end at the walls , so add 2 ft to each dimension for the roof loads
your now at 14 X 16 =224sq ft x 15+10SL=5600

Ok, good point. With the roof overhangs I calculate 252sq ft on the roof, or 5040lbs.

ist floor is 12 x 16= 192sq ft X 40#=7680( taken as a lighter weight loft)

It's a partial loft, so 8x10 ~ 80sq ft x 40psf = 3200lbs.

ground floor is 12 x 16 =192sq ft X 50#=9600

Yep.

Total weight is 22,880# 17,840lbs

22,880# 17,840 divided by your 6 posts = 2973# per post

You have 4" posts, or 16sq" per post =238psi of force on the ground

3.5 actual dimension, so 12.25sq in per post = 242.7psi

In PSF thats an equivalent of 34,272psf
which is actually quite high...

34,948psf.

You now have to look at soils,,,,the weight is fine for the posts, but whats under them ?

If you look at this loading chart for big foots, you'll see the diferences per each type of soil
and the size you'd need to support that PSF........
http://www.bigfootsystems.com/include/docs/gravityLoadTable_US.pdf.

Thanks for the link. I hadn't seen that one before.

"that's under-engineered? I have to respectfully disagree"

so your right the posts are fine.......and wrong they are not enough to support the weight unless your on bedrock...

No, you're wrong, actually. Because you're assuming that the plan is to set the post in the hole and backfill with dirt, which if you reread you'll see isn't the plan at all. The post footing will bear on concrete, which will bear on gravel, which will bear on soil. Now, where you're right is that I think it'd be beneficial to nail a 6" square 2x piece to the bottom of each post before pouring the concrete. Give it a slightly wider area to displace that weight.

and here endeth the maths lesson

I had 90# snow and 1800psi soil at my location....so you can imagine I quickly had to move away from posts

Thanks! I enjoyed it, truthfully.

Keep in mind that the specifics of your build don't all apply in other places. You built on bad soil at high elevation in an area with a wicked snow load. My site has very little in common with yours. Your house is also huge (by my standards), and so much heavier.

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Thank you guys for the responses, and for the education. If I disagreed with you, it doesn't mean I didn't read and seriously consider what you said. It just means my head is so hard I can play football without a helmet.

[Don_P]

Total weight is 22,880# 17,840lbs

22,880# 17,840 divided by your 6 posts = 2973# per post

It's a partial loft

We've got loft end w/ridgebeam, middle, and unlofted end w/ridgebeam, so each pair of posts really has a different design load.

What has been talked about so far is the post's axial load. If the posts run up to the top of the wall and act as cantilevered beams it is a bit more complex, a beam-column, or a member with combined bending and axial loading. The wind would provide the bending load, gravity is the axial load, one of those wicked interaction equations. Without a geotech I'd design it as if it were standing on a parking lot, count the soil as zero for design, anything it gives you laterally is gravy. I am biased, I've had enough 4x4's go squirrely to feel that their best and highest use is to support a mailbox. Most builders do use a 6x6 to support a deck.

[_JT]

I'm not opposed to going to 6x6, although when I think about going from (6) 4x4 posts (which, by all information I can find, is more than adequate support for the structure as designed and req'd by code) to (9) 6x6 posts (so that I have another center beam that can support a column which will in turn support a ridgebeam), it starts to seem dramatically overbuilt for a part time cabin in the woods. Not to mention twice as expensive, and significantly harder to build. Now, if it's harder and more expensive to do it right, then that's the price and I'll deal with it. But, so far, it still seems the initial design is legal and safe.

One note: the posts as shown in the OP do NOT go up to the top of the wall in a cantilevered beam fashion -- they're just post/piers with a beam on top of them, and then the rest of the structure built on that foundation.

Don, with all my bellyaching about overbuilding, I am reconsidering using a ridgebeam. I'm thinking it might size out as something I could get in place without another set of hands. Can you or someone direct me to a beam sizing tool? If it's not cost or weight prohibitive, I may make that change.

[MountainDon]

http://www.timbertoolbox.com/

[Don_P]

The initial design is neither legal or safe. It is outside of prescriptive code and would require the seal of a registered design professional working within the area of their expertise.... as is my proposal. A full perimeter foundation under a habitable structure is prescriptive. I've been debating welding up braced corners to show how to do this better... but that still wouldn't make it legal without that stamp.

I was proposing 6 posts @ 6x6. The 12'x 2x12 end rim can carry the point load from the ridgebeam... although it would certainly be a good idea to double that rim or best to carry the load straight down to a footing (8 posts) however the load path is there. We were talking about minimums. The single 2x12x16' rim supported midspan can carry the 12' 2x8 joists but again we are talking minimums. a bouncy floor is as much about girder deflection as joist deflection, girders should really be < L/600 but that is a serviceability concern rather than a strength issue.

The calcs Mt Don linked to are mine. The ridgebeam is a simply supported unifomly loaded beam, top one under "beam and columns". I don't think the point loaded canti is listed, I'll try to dig up a link, I believe it is in the file.

gotta run for the day

[_JT]

Thanks for the info, Don_P and MD (and others). I wasn't able to easily track down all the variables I needed to size a beam using your calculator, but that's primarily because I still have a lot to learn about different species and grades of lumber. Otherwise the calcs are just like the ones in my old structures book from college, a class I quite enjoyed back in the day.

If I'm doing 8 6x6 posts, I may as well do 9, and a third beam. That way there'd be no concerns about the 2x8 span, and the middle of the floor would be well supported should I decide to add a woodstove for heating. Good to know that a 2x12 rim is sufficient to support the point load of the ridgebeam.

I'll modify my design to show those changes, pending whenever I figure out what size the ridgebeam should be.

[Don_P]

awc.org ,their publications link, supplement (to the NDS) is a free download with design values for many species and allowable adjustment factors.

There is an easy way to get them for many situations.
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp
Run the calc for the closest scenario you can, this is a joist and rafter calc rather than a beam calc so it doesn't get into the dimensions or situations a more basic calc can.

Here is their calc set up to give the allowable design values for the ridgebeam in 2x10 SPF to give an idea of what I'm talking about. It is not giving the allowable span for the beam! scroll down to the bottom of the page and use those design values in my calc. It has taken base design value and adjusted for duration of load (I used snow rather than wind), repetitive member and size (2x10).
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Spruce-Pine-Fir&size=2x10&grade=No.+2&member=Rafters+%28Snow+Load%29&deflectionlimit=L%2F360&spacing=24&wet=No&incised=No&liveload=20&snowload=20&deadload=10&submit=Calculate+Maximum+Horizontal+Span

Behind their calc it has taken base design value for Fb, 875 psi and multiplied it by 1.15 for repetitive member use (this is considered to be 3 or more members within 2' by NDS, 2 or more members by others, I'm being less conservative in using the awc calc). Then multiplying by 1.15 for duration of load (10 psf snow) if you used wind it would multiply by 1.6, so I've gone more conservative here. Size factor 2x10 multiplies by 1.1 and there ya go, adjusted Fb= 1272psi
E is unadjusted
Fv is adjusted by duration of load... 135 base value x 1.15=155.25psi

Oh, right click on my calc, click "view source" and read the script at the beginning of the calc, it should read just like the equations in your old college text, I just wrote them into a script to avoid my typical dumb math errors.

[_JT]

So, I've revised my design to use 6x6 posts (9 of them) with 6x6 beams. A doubled 2x12 ridgebeam. The structural ridgebeam means I don't need to worry about rafter ties. I've also decided, in that case, to go from 2x6 24OC framing to 2x4 16OC.

Initially, I had ledger boards for the loft joists, but I've swapped them out for trimmer studs, I suppose you'd call them? Anyway, I remember Don_P saying somewhere that the proper way to frame the walls for a 1.5story like this is to platform frame the loft wall, so that there's no hinge point along the short wall (perpendicular to the roofline). Ok, done deal.



The question I'm wondering now is how do I frame the wall opposite the loft? 10' high like the side walls, and with a gable wall on top of it? Frame it straight up to the underside of the rafters (nearly 16' at the peak)? Mimic the platform framing heights from the loft wall, only with no loft? What's the prescribed way to do this?

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I was hoping to modify my OP to reflect the topic shift, but this forum (strangely, in my experience) doesn't appear to allow me to modify my posts. Ah well. Eventually perhaps I'll ask a mod to move it to the other forum and make it the thread for my build. For now this works.

[flyingvan]

I think I'd frame that wall to match the side walls, with the double plate lapping over the corners.  I'd have a break in that column (I don't think any of the compressive strength would be compromised, and any tendency for it to elbow in or out would be stopped by the shear of the roof decking and the column opposite)  Then just fill in the triangles left and right with gable frames

A real engineer could probably confirm or reject this, but seems to me having that continuous horizontal top plate would keep the walls past the loft from wanting to flex out.  True, the structural ridge will help keep things in place, but you're putting a lot of stress at the point where your rafters meet the plate.  The near side of your drawing looks OK in that regard since the loft floor joists are holding everything together.  The top plate would provide a firebreak to and make the framing a whole lot easier.  (Actually you could frame both walls the same with a column below and a column above the plates, and join the columns above a below with a couple of Simpson Strong Tie HDU's and a length of all thread to keep them together)

[_JT]

That's an interesting suggestion, but I personally hate the thought of building a lateral hinge point into my columns. Just seems like a weak point you don't need. But then, it's why I asked the question, so I clearly don't have all the answers on this one.

And I'm not the right kind of engineer to ask, but I don't a top plate that's a 12' 2x4 is going to be nearly sufficient to resist outward forces from the rafter tails, were it not for the ridgebeam carrying half of the roof load.