Wall sheathing design

[BigMish]

I am designing how I will lay out the plywood the sheath the exterior wall. Some specs about the house:
-      it's on a post and pier foundation using PT wood for the posts
-      the beams sit 8' above grade
-      the floor joists sit 1' 7 ¼" above grade

The image below depicts what I plan: vertically place a sheet and half sheet of regular ply followed by a 1' 1 ¾" PT sheet of ply to grade (really just above to account for frost heave). I'll then side the house with horizontally laid cedar siding to just above grade. That's why the PT ply on the bottom is necessary: to serve as a nailing surface for the siding to (just above) grade. I also plan make a small wall system with PT 2x4s for nailing the PT ply between the foundation posts.

Thoughts?

[scottb]

I like the additional plywood at the bottom. It breaks any type of water wick damage to the wall as well as you said providing nailing surface for siding. I don't like 2 seperate sheets of plywood or 1 and 1/2 sheets from mudsill to top plate. One continuous sheet is better.
With this tall wall the corners will need a shear wall design, diagonal bracing (like an open web truss) between studs.

[BigMish]

If I used a single sheet of plywood from mudsill to top plate that would be an 11' foot long piece of ply, do they even make such things? All the books I have show multiple piece of ply being used to span this distance. :-?

[scottb]

That's why I said you need shear wall design for corners. I know you have 11 ft walls, sorry for confusion. Do a search for shear wall design.

[scottb]

This website shows just blocking http://timber.ce.wsu.edu/Supplements/Diaphragms/diaphragm.HTM  Do not take one person's (me!) advice or one website. Look at simpson's http://www.strongtie.com/ as well. Keep searching then decide.

[scottb]

http://timber.ce.wsu.edu/Supplements/diaphragms/diaphragmconst.htm shows blocking hit 1 then 2 for diagram

[MountainDon]

-      the beams sit 8' above grade

8 inches ?? not feet ??

Your structural rigidity might be better if the bottom piece of PT plywood extended further up the studs, say  lay it horizontally, 4 ft tall x 8 ft wide. Then the plywood panel that runs across the top plates could be placed horizontal as well in order to proffer best racking resistance across the top. Offset it at least one stud bay from the bottom panel. Then in between the top & bottom sheathing panels you would fill in.   Just my thoughts.  :-? ... where's PEG?

[tc-vt]

Taking a quick scan at the 2003 international residential code for wall design

First, it defines maximum allowable stud lengths for walls according to seismic category and snow load of less than 25psf and wind speeds of 100mph or less and depending on whether a aroof or aadditoinal floors are supported. (602.3.1)  

Then the types of wall bracing which are acceptable for different seismic zones and the number of stories are defined (602.10.1)  1/2 inch plywood satisfies most conditions.

Plywood does offer more strength when laid with the long side perpendicular to the studs.  Gluing it to the studs increases strength tremendously.  I wood use PT full width for the bottom 4 feet.  Then you could do a full width  course over that and finish with a final course trimmed to width to fit to the top plates.  It looks like you have boxed framing at the top or is that a second floor?  If a final top course only 3 feet wide doesn't come down far enough onto the tops of the studs, use the cut width course in the middle and finish with a full 4 foot width course at the top.

If you want more details on the code, write back with your dimensions and exposures.

Tom

[PEG688]

Mis why not run as wide a piece of treated ply as you can , you can bury it so you'll have a PT plywood skirt / crawlspace .

From the top of that with the seam where your showing it run the 8' sheet vertically as shown , you should move that line of solid blocking down so it falls 1/2 way on that upper seam, then fill in to the top 1/2 way up the top plate . Nail all edges , top , bottom and boyh sides 6 "OC and you have a BWP. That should take care of you shear issues , it won't be a true BWP / for eathquake code , I doubt that could be achieved with a post and pier foundation system.

But for the cabin your building that sheathing setup would be fine , some shear wall require 4" OC , and 2" OC nailing schedule .

If that is rewuired in your specific area the code offical will let you know.


 On a personel note ,   I think , can't prove,  that a horzontal layed plywood wall, with the seams staggered and all seams . joint solid blocked would be stronger. I've framed close to 100 homes , maybe more ,  :-/ in my life time , and only in the past 10 yeras or so have the soldered / upright 8' way become "the right way" .   Mainly becauce , generally , you can do one less row of solid blocking if the sheets are soldered/ upright.

Thats my .02 cents .

G/L PEG        

[BigMish]

It looks like you have boxed framing at the top or is that a second floor?

Yes, that is a short knee wall for a loft

I
If you want more details on the code, write back with your dimensions and exposures.

Not sure what you dimensions you need: the knee wall is 2' 4" from the top of the ledger to the top of the top plate and the walls are frames with 10' studs.

Mis why not run as wide a piece of treated ply as you can , you can bury it so you'll have a PT plywood skirt / crawlspace .  

I thought that this would be an issue with frost heaves: either the expansion of the soil in winter will break the ply wood or would force the ply wood up which, in turn, would push the beams up. Do you think this concern is unwarranted? If I did this wit would need to be vented, right?

From the top of that with the seam where your showing it run the 8' sheet vertically as shown , you should move that line of solid blocking down so it falls 1/2 way on that upper seam, then fill in to the top 1/2 way up the top plate . Nail all edges , top , bottom and both sides 6 "OC and you have a BWP. That should take care of you shear issues , it won't be a true BWP / for earthquake code , I doubt that could be achieved with a post and pier foundation system.

I think I understand what you are saying. Please take  a look at the following image and correct my understanding where necessary. Some questions:
When you say "blocking" you mean the 2x6s I made red, right?
Those are fire blocks as the loft is balloon framed, if I moved them down here, I'd still want an other set where  they where before for that purpose, right? That is to say, there would be two sets, one to serve as nailers for the ply and one set to serve as fire blocks.
Those blocks would just be inserted in between the students and nailed in right?

That's why I said you need shear wall design for corners. I know you have 11 ft walls, sorry for confusion. Do a search for shear wall design.

I'm unclear what a sheer wall is. I visited the sites you mentioned and search the forum. Can any one give me any direction here?

Thanks all, Mischa

[PEG688]

Poor poor Misha  :'(, the last drawing you did , is off , we used to line up the horz. seams but stagger the 4' joint , ,,  like on sub floor,,,  think of it that way ,,,   so when I said stagger the seams  , I shouldn't have said [highlight]all seams[/highlight] you do pay attention , almost to well  

Again on the fire block if you can locate it to break up / meet the 10' code requirement as in no stud bay unblocked if it's more than ten feet, and have it land where your sheeting seam is you get a two for one , fire block / solid block , a win , win.

One of the knocks on ballon framing , in the past was the nice fire chase that in true ballon framing would run from the sole plate in the basement up along the floor joist and all the way to the attic . this created a great chimmeny effect in old homes , generally the wood stove , or coal burning furnace was in the basement , when fire started there the fire ran up those stud bays into the attic , generally burning the house down.

   
 Where are yo located for that frost heave issue ?? What I'd do is end may skirting framing a bit above grade , so it would be hanging down off the beam bottom or some such , but I'd extend the PT plywood down into the ground so the dirt would have less to push up on , only the 1/2 " plywood that would keep critters out and yes you'd have to vent it with some type of soffit vent strip on 8"x 16" grills around the place , think cross flow on placement.

G/L PEG

[scottb]

blocking fulfills shear wall requirement.

[tc-vt]

A shear wall is a section of wall that is designed to resist shear forces from wind blowing against the building or terrestrial forces like earthquakes shaking your foundation.

Studs which are nailed to the top and bottom plates have no strength by themselves until they are braced somehow.  Different ways of bracing are defined in the code, some stronger than others.  Some are:

Let in 1x4 diagonal bracing that goes from top plate to bottom plate

Wood boards (1x ) nailed diagonally to the studs

Structural panels like plywood or OSB

Drywall

Portland cement plaster

Hardboard siding


The code then tells you how much length of your wall needs to be braced according to your seismic category and wind exposure, number of stories and type of bracing used.  If you have a 20 foot long wall, not all of it needs to have one of the above bracing methods.

In a seismic category C, 110 mph winds or less for a wall in a one story or top of a two story structure just about all of the bracing methods above are sufficient.  Bracing needs to be located at each end of the wall and at least every 25 feet on center but not less than 25% of the braced wall line.  Braced sections typically are required to be 4 feet wide.  

Then the code tells you how much bracing is needed next your wall openings according to how tall the openings are.

Code is the minimum requirement.  Adding the most recent code book to your library is a good investment.  It serves as a how to as well as an excellent how not-to.  It is written by the International Code Council.  The stuff I wrote above is simplified as there are many exceptions and details associated with these design requirements.

For wall heights - a wall supporting one floor and a roof, 10 feet tall needs to be 2x6 for 24 o.c. studs and 2x4 for 16 o.c. spacing.  A 12 foot tall wall requires 2x6 for either 16 or 24 o.c.

Tom

[PEG688]

 

blocking fulfills shear wall requirement.

Part of it , but as tc pointed out there's more to it than that.

[Jens]

I may just be old fashioned, but in my opinion engineers have gone way too far into the residential field and should stick with bridges, machines, and skyscrapers.  That is not meant to offend anyone here who may be an engineer, but when a shear wall is calling for 2in oc nailing (as I have had to do as well), I just don't see how it helps to hold the building up and make it more stable, to turn it into a 2x6 bundle of splinters.  Building codes, and engineers have gone so far, in part due to the downturn in quality of build, and caring attention to detail that was born of the maximum return attitude of this society so based on capitalism that it overlooks the basic right of humanity to house oneself, to provide for oneself, and to make the best out of any situation presented.  Older houses definitely weren't perfect, but it is my opinion that the attention to quality, and the slower speed they were erected with, are paramount to the structural integrity without the use of shear panels, seismic panels, simpson strong ties (another huge, legal rackateering operation IMO), hurricane clips, and engineered lumber.

Hmm, hmm.  Excuse me.  I could wax on for hours, but not everyone is interested in a soapbox rant.  On the west coast, wall sheathing (in my experience), is begun at the mudsill (pt plate on foundation), and carried up as high as it will go, hanging the panels vertically.  then you have to flat block between the studs at the end of the sheet, carry on above from there, still hanging the sheets vertically.  The logic I was told for that, is that once the drywall is on the inside, the grains alternate like plywood creating a more rigid building diaphram (yes, sheetrock has a strength grain).  In New England, the sheets are all laid horizontally, offsetting the seams like PEG said.  In either place, fireblocking is required to retain a wall cavity of not more than 8", and the sheets should meet in the middle of rim joists, or studs.  The object is to solid tie all of the seperate pieces so that the end naild studs don't suffer pull out.  Then again, most hundred year old houses, even in earthquake areas, don't have any of this, and are still solid.  Maybe I will just never understand why things have to change so much, and that is ok too.  Not that eveything was so hunky dorry back in the day.  As Peg said, PT plywood to the ground would be nice, and then be sure to tie as many layers of framing as possible.  If you have to break your sheets at the bottom of a wall, better to do it in the middle of the bottom plate, or in the rim joist area.  

Hope I didn't just confuse the heck out of everybody

[glenn kangiser]

Careful, Jens.  You are starting to sound like me.  Other builders on jobs  have mentioned the splinter effect 2 million nails has on a 2x.

[tc-vt]

On the pressure treated being buried underground - be sure the PT is ok for such a purpose.  I recently came across somewhere that one of the 'councils', the Plywood council, maybe, no longer offers recommendations regarding Permanent wood foundations, I think because of the change in PT formulation.

Tom

[PEG688]

Hobbiest BROTHER   Loved the rant , hip hip horay hobbiest fer President , Amen brother !!!  What he said !! Ya bring it !! Wo whoo  , oh I already said that

I wouldn't advise a PT foundation as tc said , but we where or I was speaking to a skirting , a good solid one , not a PT Foundation , which I think we are agreeing on tc.

Just trying to be crystal on that.

Oh and " RIGHT ON !" Hobbiest, pretty much my opinion on the over use of engineering on residental housing as well.   Wait till these house's start to be remodeled all that crap we HAVE TO ADD we'll have to remove , adjust , modify etc .  And IF we get a ripe snortin earthquake those house's may fair a bit better but still IMO IF the quake is large enough we just be to damaged to be practical , read $$$ , to repair and the same dozer / trackhoe that rips down the pre engineered new code house will knock down the new special engineered place.    

[BigMish]

Ok, here is my third attempt at interpreting what you're all trying to get across to me.

I made the sheeting translucent so you could see where the seems where falling and to show where I was placing the blocking.

Notice that I now have the PT ply a foot or so below grade.

Am I any closer? :-?

[MountainDon]

Getting there.  But not quite. Wish I could use that program.

Looking at this from the right side of the wall.

Start the lower course with a 2 x 8 PT sheet laid horizontally. To the left of it another 2 x 8 PT sheet.

Above the first one (right) place a 4 x 4 panel. To it's left place a 4 x 8 sheet, horizontally.

And so on, like a concrete block wall or brick courses.

But when it comes to the uppermost row of panels it would be best if the upper panel was 4 x 8 horizontal or a 4 x 4 if a half sheet is required. The full sheet will stiffen the wall bestter than a 2' panel.

You don't have to stagger the joints the way you have in that last image as much as staggering them as in a concrete block wall.

[PEG688]

Mish go back to the vertical sheeting option , just move your blocking so it falls on the top seam of the regular CDX, put the lower seam lapped onto the box sill.


Sort of like this ,


 

notice the vertical sheets , there is a row of solid blocking at the top edge , of course your PT ply would be where the foundation is in this photo.  Also note how we tied the dormer plywood to the lower wall ply, this elimates the hinge point , the plywood is a gusset of sorts like John drew for those site built rafters .

Whe I talked about the horzintally  run sheets that was how we used to do it before all this blocking , shear wall stuff was invented to make Mr. Simpson rich , so fer get that part , focus on the present , that is [highlight]if you need to meet code[/highlight] for shear walls .

If not and you want to run the sheet horizontally line up the horz. lines / seams . If you have to do the blocking it will be more rows / more pieces.

That high a wall and the ballon framing lead this job to be  a vertcally ran sheathed deal anyway , so I'd recommend the vertically run sheets in this case , except the PT ply I'd run that horiz.  rip a sheet in half  24" wide and run it down into the grd. [highlight]IF you like the idea[/highlight] of a skirted crawl space  , thats what I'd do if it where my place , thats what I'd recommend to a client who was paying me for my opinion.  For you Mis , it's free  

 And no I still haven't played with scetch up   I will have to take more photo's to answer all these questions , I think

G/L PEG  

 

[BigMish]

OK, returned to running them vertically and I think I may finally have it.

Assuming I do have it, I've got a complicating question: if I raised the height of the knee wall (keeping the height of the 1st floor ceiling the same) I'd want to either:
a) keep the knee wall short enough that the seem between the PT ply and the first row of non-PT ply would fall on the header joist
b) make the knee wall as high as I want, run the top row of ply vertically and put blocking also behind the seem between the PT ply and the first row of non-PT ply
Right?


PEG, in answer to your question regarding frost heave: I'm in upstate NY, a bit south of Albany. And thanks for the free advise!  

[PEG688]

Now in the last horz. scetch up deal stagger the 8' joints by  starting the top  row with  a 32"sheet (1/2 x 32"  x4' sheet)  run the grain the same way , so your joints on the top row  are staggered/ not over the vertical (4')  seams .

As far as a complicated question , this easy one was hard enought :'( :'(

I'll maybe look at that hard one tonight   maybe Johm want to answer it , please John feel free/ go  ahead  

[glenn kangiser]

OK, returned to running them vertically and I think I may finally have it.

Assuming I do have it, I've got a complicating question: if I raised the height of the knee wall (keeping the height of the 1st floor ceiling the same) I'd want to either:
a) keep the knee wall short enough that the seem between the PT ply and the first row of non-PT ply would fall on the header joist
b) make the knee wall as high as I want, run the top row of ply vertically and put blocking also behind the seem between the PT ply and the first row of non-PT ply
Right?


PEG, in answer to your question regarding frost heave: I'm in upstate NY, a bit south of Albany. And thanks for the free advise!  

I'll give you a hand PEG - you can check me and make sure I'm right.

I wouldn't let the sheathing dictate the height of my desired kneewall.  I would do the kneewall then use the sheathing to my best advantage to minimize hinging and make the wall as strong as possible, which means standing the sheathing vertically so it laps what would be the hinge point at the second floor-- seems that is what you were asking -- soldiering I think -- right PEG?  Add the blocking at the bottom seam if needed for shear nailing.

There is something else I would personally not do, and that is, I would not platform frame the kneewall.  Looks like semi-balloon   is the way you show it in the picture.  I would semi-balloon frame it using a let in ribbon to support the second floor joists, and fireblock  and edge block as necessary -  that would prevent the hinging at the floor level and make the wall as strong as possible.

[BigMish]

Now in the last horz. scetch up deal stagger the 8' joints by  starting the top  row with  a 32"sheet (1/2 x 32"  x4' sheet)  run the grain the same way , so your joints on the top row  are staggered/ not over the vertical (4')  seams .

Like is pictured below?

As far as a complicated question , this easy one was hard enought :'( :'(

I'll maybe look at that hard one tonight   maybe John want to answer it , please John feel free/ go  ahead  

Ha, you got that right! No rush, I'm just now considering raising the knee wall

I would do the knee wall then use the sheathing to my best advantage to minimize hinging and make the wall as strong as possible, which means standing the sheathing vertically so it laps what would be the hinge point at the second floor-- seems that is what you were asking -- soldiering I think -- right PEG?  Add the blocking at the bottom seam if needed for shear nailing.

There is something else I would personally not do, and that is, I would not platform frame the knee wall.  Looks like semi-balloon   is the way you show it in the picture.  I would semi-balloon frame it using a let in ribbon to support the second floor joists, and fireblock  and edge block as necessary -  that would prevent the hinging at the floor level and make the wall as strong as possible.

Yes, that is what I was asking but there isn't a hinge point (and this is in reference to your second point) it is balloon framed: what may look like the plates for a platform framed knee wall are just a let-in ledger  for the second floor joists (just as you suggest). But seems like the answer is simply to make the top row of ply verticle (would I want to use blocking behind the additional seem?)

.M