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Author Topic: How much weight can a cantilevered 2X12 support as a shelf for SIPS  (Read 6784 times)

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Offline mmhailey

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I am in the midst of designing a foundation for a 16X24 cabin. I plan on using 2x4 stick built walls to enclose the frame. I have read several times about building a ledge to support Insulated panels, and would like to use this to support my walls. The problem I am having is deciding on how much cantilever I can get without compromising the structure. For example: One of Chappell’s paragraphs mentions using a 4 ½"





shelf extending out past the concrete to support the SIP. It looks to me in the pic, that he is using a 2X12 on the sill.

Question?

How much weight can a 2X12 support laying flat across the grain?
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Offline Left Coast Chris

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #1 on: August 15, 2010, 03:44:42 pm »
Hi mm,

From a structural standpoint the answer is none.   There is no allowable load listed for cross grain tension in the code.   When ever you apply bending force to a board the wood fibers need to be running in the same direction as the bending will be occuring otherwise the board will easily crack accross the grain.  What you could consider is putting a ledger below the 2x12 with lag bolts into the top plates and studs below. 

The best way would be to have wider studs and sill below to allow full bearing for the wall above especially if you are in snow country. 
Home built cantilever head, 24 HP honda mill, Case 580D, MF 135 and one Squirel Dog Jack Russel Mix -- Crickett

Offline beenthere

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #2 on: August 15, 2010, 03:45:46 pm »
From the diagram, there is nothing to keep that 2x12 from splitting off under the load (any load) of the 2x4 wall above the cantilever.
south central Wisconsin
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Offline Jim_Rogers

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #3 on: August 15, 2010, 08:35:28 pm »
It is true from the diagram above there is nothing to prevent that 2x12 from splitting.

However most external wall enclosure system such as this are "hung" from the frame.
The frame supports the external wall system and the 2x12 is just to keep the bottom covered and prevent any bugs or animals from getting up into the external wall cavity from the outside.

I will post more about this later on this week.

Jim Rogers
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Offline mmhailey

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #4 on: August 16, 2010, 12:30:08 am »
Thanks Jim.

I like your term "hung from the frame".  That makes sense to me., especially with regard to a SIP panel. I guess you will discuss how this relates to hanging a stud wall to the frame.

To further complicate the question. One more point :D I'll be adding a river rock veneer below the " hanging" wall, so the shelf extension makes flashing the siding to foundation easier I think.
Give a man a fish, feed him for a day. Teach a man to fish, and turn him into a liar.

Offline jdtuttle

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #5 on: August 16, 2010, 06:49:01 am »
Add a 45 deg support from each post to the rim joist for additional support.
jim
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Offline shinnlinger

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #6 on: August 17, 2010, 06:58:34 pm »
What if you nailed/bolted a ledger board/cleat below the panel?????
Shinnlinger
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Offline jamesamd

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #7 on: August 17, 2010, 09:41:06 pm »
Install a 1/4" X 11 1/2" galvanized steel plate under the 2X12, add sill sealing bubble strip to make a tripple decker sandwich.
Jim
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Offline shinnlinger

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #8 on: August 17, 2010, 09:57:09 pm »
I built a timber frame for a straw-bale house on a conventional deck and that necessitated the posts being 19 inches in from the outside edge of the foundation.  I put doubled up 4x12 hemlock joist under each post.   

Since a SIP is much narrower, you could obviously put your post 6-8 inches (depending on the size of your panel) off the outside edge of your wall.  Since the foundation is probably 8 inches thick any way you probably don't need to do anything if you are building a low posted cape, but you could double up your joists like I did if you have any doubt or you could put gunstock posts in your basement  or frame a wall along the inside edge to finish things off and simplify wiring.

In all of your planing, make sure your finished siding will drain outside the foundation wall.
Shinnlinger
Woodshop teacher, pasture raised chicken farmer
34 horse kubota L-2850, Turner Band Mill, '84 F-600,
living in self-built/milled timberframe home

Offline witterbound

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #9 on: August 20, 2010, 12:47:20 pm »
Where is the floor in your drawing?  Typically the stem wall is set further out, so that it is in plane with the outside of the 2x4 wall, and the rim joists/joists/floor decking/etc. goes all the way out for the 2x4 wall to sit on.

Offline witterbound

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #10 on: August 20, 2010, 12:49:54 pm »
Another thought.  Your 2x4 wall won't hang on the frame.  It's got to sit on a floor. 

Offline mmhailey

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #11 on: August 20, 2010, 11:50:48 pm »
I admit my drawing is poor.... I promise to spend some time soon to redraw it to make it clearer. I wish I could take the time to learn sketchup, but I and my schedule are not seeing it right now  :P. So my old vector program will have to do it.  :-\

I had this thing in my head about the 2X4 wall( panel) being a SIP replacement.  I'll try and draw what I have in mind a bit better, as soon as I have the time ( see above)  ;D

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Offline witterbound

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #12 on: August 21, 2010, 07:07:42 am »
I used a 2x4 wall on my timber frame instead of sips.  My stem wall sits out in plane with the outside of the 2x4 wall.  My posts therefore are not fully supported by the stem wall.  I added blocking under the posts (for the gap that is created between the posts and the stem wall for the floor system) that sits on the stem wall, so that the post is fully supported, but the blocking is not.  I believe this is farily typical. 

Offline frwinks

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #13 on: August 23, 2010, 10:55:06 am »
As Jim mentioned, the 2x12 is only there to cover things up.
All the work is being done by spikes and/or panel screws. 
I'm using a 7" panel screw 18" OC to hold/hang the 2x4 curtain walls.  The PE had no problems with stamping the drawings.




Offline mmhailey

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #14 on: August 23, 2010, 11:36:03 am »
 The initial idea for this came from page 13 in "A Timber Framer's Workshop" by Steve Chappell. He states that the sub-sill is extended 4 1/2" from the sill to support stress skin panels.  My reason for wanting to try the curtain wall is to use some 2X12X16' floor joists I have stickered. The footprint of the frame is 16'X24' so extending the floor deck to accommodate the stud wall" would mean buying some longer 2X12s.  :o

Thanks for the great pics. That certainly helps. Now I don't have to draw the plan out.  8) When you erected the walls ( curtain walls) did you just build the wall, and set it up on the ledge till you got the spikes in? or did you put support under the ledge till you had the wall secured with spikes??



While your plan is obviously very well insulated, this is a summer guest cabin, and will have R15 fiberglass batts in the 2X4 wall.  The outside of the studs will be full 1" sheathing applied on a 45 with tar paper applied, then 3/4" roughcut cedar siding. While foam is great I think, transport here to the island makes it unbelievably expensive.

Thanks

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Offline frwinks

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #15 on: August 23, 2010, 01:20:52 pm »
built the walls on deck, hoisted and rested them on ledger until we got the screws in. 

Offline witterbound

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #16 on: August 24, 2010, 11:58:50 am »
frwinks, I take it you can only put a spike or timber screw in where you've got a timber to screw the 2x4 wall into.  And I assume on these timbers you're putting them 18" oc, is that right?  Just never heard of it being done this way, and I'm curious.

Offline mmhailey

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #17 on: August 24, 2010, 08:34:53 pm »
Wow I finally sat down for a couple of hours and got to play with sketchUp.  One of the things I was having trouble with is how to draw the river rock veneer.


 



Here is my proposed foundation plan. 8" stemwall, with the 2X12 sill overhanging. I have girts, and bottom chords of my Kingpost truss to fasten the curtain wall to. The bottom will be secured to the rim. My plan will be to drill each stud, which are at 24" centers and then spiking them to the frame.

Comments still welcome.  ;D

Thanks
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Offline frwinks

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #18 on: August 25, 2010, 09:55:44 am »
frwinks, I take it you can only put a spike or timber screw in where you've got a timber to screw the 2x4 wall into.  And I assume on these timbers you're putting them 18" oc, is that right?  Just never heard of it being done this way, and I'm curious.
yes sir, the curtain wall is screwed to posts, girts and plates... and rimboard.
Our PE wanted full post bearing on the 10" block foundation, so your approach wouldn't work in our case.  When I approached him with the current option, he very much approved of it. Happy PE = happy building inspector = happy life ;D

glad you had a chance to play with SU, great software, very dangerous in the wrong hands though... I've added many nights of work to my project from a few simple clicks of a mouse... :D 

Offline witterbound

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Re: How much weight can a cantilevered 2X12 support as a shelf for SIPS
« Reply #19 on: August 25, 2010, 01:34:43 pm »
I don't hink you're going to want to run your drywall all the way to the 2x12.  Where will your posts sit?  Will they sit on the deck, with blocking under them to the stem wall?  Or, will they sit on the stem wall with the floor system being built around them?  I'm assuming the latter.  If so, do you plan to reduce the outside edge of the post bottom so that the rim joist is flush with the outside of the post?