Hey folks - another structural question: The IRC and most manufacturers list that the floor framing needs to be up before backfilling around the perimeter for lateral support of the basement walls. Well that makes sense, except that for the walls in which the floor framing runs parallel, there is not lateral support for the wall. Now, the IRC requires blocking between the parallel joist and the wall for conventionally framed floors, but most of us use engineered wood products and I'm not sure it actually gets done. But even if the blocking is installed between the wall and the first joist, there still isn't a load transfer path to the opposing wall except through the wood structural panels that are installed as subflooring, and I would think that doesn't add much compared to the pressure of the wall. Obviously no one's houses are falling down, but just curious if anyone has given this any thought. THanks.

Retaining walls are engineered differently. Basement walls take into account the support provided by the flooring.

I used open web 4x2 floor trusses and 1-1/8" Advantech for my flooring system. There is a 2x6 strong back run perpendicular through the trusses every 10' or less on center. In my case, the end of these 2x6 strong backs butt solidly against the walls parallel to the floor trusses. That and the 1-1/8" Advantech sub-floor is what transfers the load to the opposite wall in my case.

I asked this question over the past summer after reading the same code as you. After doing some googling on the subject, I found that many municipalities have not adopted that code. They literally have those statements struck out of their code.

The code you are referring to came from the 2006 irc:

http://publicecodes.citation.com/icod/irc/2006f2/icod_irc_2006f2_4_sec004.htm?bu=IC-P-2006-000002&bu2=IC-P-2006-000019

If you look at the current 2012 code, they've removed that language and simply state that unbalanced heights of more than 4' need to be laterally supported at the top and bottom. The refer you to table r404.1.2(9) which deals with rebar spacing.

I can see your concern if you are dealing with conventional construction, where there is an anchored top plate with floor joists nailed parallel to them. Sure there is a 3/4 deck (diaphragm) spanning the top of the foundation, but the foundation walls that travel parallel to the joists aren't receiving any benefit from the diaphragm. There really needs to be some sort of blocking in my opinion.

Regarding the blocking, the 06 irc states 

" Floor shall be blocked perpendicular to the floor joists. Blocking shall be full depth within two joist spaces of the foundation wall, and be flat-blocked with minimum 2-inch by 4-inch (51 mm by 102 mm) blocking elsewhere."

So, with solid blocking, there would be a transfer from the bottom of the rim joist to the actual floor diaphragm, albeit at an angle.  Then, of course, there's the flat blocked elsewhere???? what ever that means.  

If you are referring to a two story ICF build, the floor diaphragm is truly laterally supporting the walls, so long as you have ledgers that are anchored frequently to the concrete . Like Arkie, I have floor trusses, and I not only have the 2x6 strongbacks that the trusses require, but I also put in rows of 2x4s laying flat along the bottom cord of the floor trusses every 4' that span the building width. Yeah, it might be overkill, but it doesn't hardly cost anything, so it's cheap insurance.

Great post Jeepster. Glad to see you got what I was getting at. I'm thinking the same thing as you in that even though it isn't really spelled out in the code clearly (albeit there is reference to requirements), I think I might inject some common sense and just do SOME sort of support in that can transfer the load across the building width. If there isn't a way to transfer the load, then I would think there is no difference from a retaining wall and it should logically be designed and built as such.

And Arkie - you are right in that the "strongbacks" are providing that support, but I guess it just seemed a little on the light side for all the pressure that the backfill exerts on the wall at the top.

A basement is considered a retaining wall, but based on the diaphragm from the floor system it dictates it as a supported retaining wall. Once you have the sub-floor installed engineering does not consider the parallel joists an issue.

How about walk out basements that retain full height on one side, angled loads as the ground slopes on the 2 perp. sides, and then nothing on the 4th side? My plan is to use ICF for the full underground and stepping it with the grade on the 2 sides. The exposed side would be double stud wall. I would like to run my floor structure parallel with the full height ICF wall and exposed double stud wall.

Izerarc, My two cents are that you will need to look at this more like a retaining wall since you won't have the strength of the full concrete box. Why not just add that one wall and be done with it. Surely the double stud wall isn't going to save you much after you tie it into the concrete and insulate it etc. Regards.

It really inst for the construction cost savings, but rather for the energy savings. The double stud wall is north face exposed so it should perform considerably better. My engineer will obviously look into it when the time comes. I also have not ruled out ICF all the way up to the roof either even though my energy modeling will take a hit (as well as the budget). Storm, quiet, bugs, etc would be the reasons for it. Also an easier achievable tight shell.

Whats your double stud design if you don't mind sharing.

It is a basic double stud wall. For the basement section, exterior studs are 2x6 @ 24" OC, space, and interior 2x4 walls 24" OC. Plywood straps connect the 2 walls together at the top and bottom. (attached to the side of a stud, not the top/bottom plates). Overall wall thickness will be between 10-12" (undecided). Exterior is sheathed with ZIP sheathing. Cavity packed with blown fiberglass or cellulose. Upper floor wall switches to 2x4s at the exterior instead of 2x6. Air tight drywall on the interior.

Izerarc,

Why not two 2x4 walls instead of 2x6 and 2x4 walls?  Do you need the extra strength from the 2x6's in the outer wall?

If you want more R value than your standard ICF offers, you can easily install additional rigid foam board insulation over the outside of the wall after the pour is completed. Adding 1" of rigid polyiso will add about R6 to your insulation value. If you have a 3/4" or greater air gap under your siding or brick, you can also use foil faced polyiso board and gain additional R value. The foil facer facing the air gap will add an additional ~R3 to your overall insulation value. With this combination and a typical ICF using 5" of EPS, you would have a wall with a overall R value of ~30.

Yes, by going with 24" centers, I need the 2x6 bearing wall for the basement level.

Posted By arkie6 on 06 Jan 2012 09:47 AM
If you want more R value than your standard ICF offers, you can easily install additional rigid foam board insulation over the outside of the wall after the pour is completed. Adding 1" of rigid polyiso will add about R6 to your insulation value. If you have a 3/4" or greater air gap under your siding or brick, you can also use foil faced polyiso board and gain additional R value. The foil facer facing the air gap will add an additional ~R3 to your overall insulation value. With this combination and a typical ICF using 5" of EPS, you would have a wall with a overall R value of ~30.

Izerarc, I agree with arkie on this one.  Although based on the new ASHRAE report you may already be at a point of diminishing return.  Checkout the K12 50% solution for your climate zone.  Basically, it says that a mass wall with a lower R-value is equivalent to a low mass wall with a higher r-value.  

At any rate, if you decide to stay with wood you might want to go with 12".

Consider that your design is actually three walls

10 inch wall:

1)  2x4 with R 3.6/in plus
2)  1" of R3.6 plus
3)  2x6 with R3.6/in

If assume zero air infiltration and we assign a framing factor of 8 and consider the R-value of wood to be R-1/inch Then your R-value is: 

R-Value of 10 inch wall:   = 1/((.08/3.5)+(.92/12.6)) + 3.6 + 1/((.08/5.5)+(.92/19.8)) = 10.4 + 3.6 + 16.4 = 30.4

Obviously your 12 inch wall will have an R-value of 30.4 + an additional two inches of 3.6 = 37.6 

Your framing factor is probably a bit higher and your air infiltration is probably not zero.   Obviously if your framing factor goes up a little these number drop fast.
I don't think either of these walls will beat the archie6 wall and based on the new ASHRAE data I don't think the 10" wall will beat your your baseline R-22 ICF mass wall.    Regards.

where is the framing factor of 8 coming into play at? I have careful detailing of the walls and various connections such as rim board locations, etc that allows for a completely thermally broken interior wall. Also 3.6 is rather low especially with the new Spider insulations that are just above 4. Even dense pack cellulose is higher then 3.6. Climate zone 6 is where I am at. Any report I have read claims the mass effect of ICF walls is minimal in heating dominate climates. However if you must know, I would be using the Hobbs vertical ICF, which claims r30 (which is an average). however I realize it will be less due to flat wall requirements, etc. If I go ICF, it will be for more reasons besides efficiency. If efficiency is my main goal, I will not select full ICF. THe main issue about Arkies suggestion, while good and I have considered it, is it makes an already expensive construction method even more costly.

Posted By lzerarc on 07 Jan 2012 06:25 PM
where is the framing factor of 8 coming into play at? I have careful detailing of the walls and various connections such as rim board locations, etc that allows for a completely thermally broken interior wall. Also 3.6 is rather low especially with the new Spider insulations that are just above 4. Even dense pack cellulose is higher then 3.6. Climate zone 6 is where I am at. Any report I have read claims the mass effect of ICF walls is minimal in heating dominate climates. However if you must know, I would be using the Hobbs vertical ICF, which claims r30 (which is an average). however I realize it will be less due to flat wall requirements, etc. If I go ICF, it will be for more reasons besides efficiency. If efficiency is my main goal, I will not select full ICF. THe main issue about Arkies suggestion, while good and I have considered it, is it makes an already expensive construction method even more costly.

Izerarc,   Your 10" wall is composed of three walls.  (1) wood 2x4 @24" O.C. (2) foam 1" and (3) 2x6 @24" O.C. each of the wood walls have a framing factor of 1.5/(24-1.5) which is about 6% not counting headers or bracing etc. so I used 8.   Your foam wall has some framing factor running through it holding the other two walls together.  I don't know what it is so I left it at zero.   You do have a nice thermally broken system and I think it is a good idea to further thermally break the interior wall connections as you said.

I don't know about spider but will read up on it.  I used 3.6 because thats about as good as things get with any air infiltration at whatsoever.   

I don't buy the mass effect being minimal in heating dominated climates.   See ASHRAE K12 50% Solution or ASHRAE Commercial 50% Solution for  Zone 6  Mass wall of R19 c.i. (continuous insulation) is equivalent to wood wall of R13 cavity + R12.5 continuous.   I don't think you will beat a mass wall of twice the Heat capacity and R-22 c.i. which is typical on the market unless you go with your 12" wall and you get the extra 2" of continuous.  

I'm sure Hobbs is a fine system but average R value means almost nothing.   Consider 2x4 wall typical wall (R1 per inch wood) with framing factor of 20 with R100 in cavity (if you could find it).  

R-value = 1/((.2/4)+(.8/100)) = R17.24    but the average R-value is (.2*4) + (.8*100) = 80.8 !!   R valueis 17 but average is 80.

As you know based on your design the heat goes through the studs -- you can used R1000 and not improve things much.   Good luck with your building it sounds great -- I just wanted to call the new ASHRAE stuff to your attention.     R-value is not all its cracked up to be.   Regards.

I guess 8 would be about right. I havent calculated it out yet.

I have read through the report quickly. It applies direct to me as 80% of our work is schools. However while it talks about mass walls and ci, as you know that can be any type of mass walls. It actually discusses the advantage of internally exposed mass, which is how we do our schools. Typically the wall is 8-10" cmu, I now use 2.5" of close cell foam, 1" air space and then brick/metal panels, etc. I also call to foam the back side and tops of parapets as well. Our foundation design is still up in the air, however we are exploring using thermomass foundations and also double wythe block walls filled with closed cell. (outer wythe supports brick and protects below grade foam). Most of our new schools and additions use geo thermal heatings and cooling.

Forgive me as I did not study the report but rather read it though quickly, however it appears only one of the case studies used ICF construction. For a school, I can see the benefit as the hvac requirements are a lot different from a home.

Performance wise it appears the r25-30ish icf wall will be similar to the double stud 10", however the 10" comes at a lower price tag. As mentioned if I go full ICF, it will be for the other benefits as well to justify the price.

Sorry to hijack the thread....back to topic. If you use hangers direct to the ICF form and do not use a continuous wood ledger on the inside of the form for the floor structure, how do you typically support the bracing for the floor when the structure runs parallel to the floor? install hangers all around the perimeter?

Posted By lzerarc on 08 Jan 2012 03:48 PM
I guess 8 would be about right. I havent calculated it out yet.

I have read through the report quickly. It applies direct to me as 80% of our work is schools. However while it talks about mass walls and ci, as you know that can be any type of mass walls. It actually discusses the advantage of internally exposed mass, which is how we do our schools. Typically the wall is 8-10" cmu, I now use 2.5" of close cell foam, 1" air space and then brick/metal panels, etc. I also call to foam the back side and tops of parapets as well. Our foundation design is still up in the air, however we are exploring using thermomass foundations and also double wythe block walls filled with closed cell. (outer wythe supports brick and protects below grade foam). Most of our new schools and additions use geo thermal heatings and cooling.

Forgive me as I did not study the report but rather read it though quickly, however it appears only one of the case studies used ICF construction. For a school, I can see the benefit as the hvac requirements are a lot different from a home.

Performance wise it appears the r25-30ish icf wall will be similar to the double stud 10", however the 10" comes at a lower price tag. As mentioned if I go full ICF, it will be for the other benefits as well to justify the price.

Sorry to hijack the thread....back to topic. If you use hangers direct to the ICF form and do not use a continuous wood ledger on the inside of the form for the floor structure, how do you typically support the bracing for the floor when the structure runs parallel to the floor? install hangers all around the perimeter?

Izerarc,  I suggest you go over to the K12 50% thread I started a few days ago and check out the list pf school I put together by type and by consumption.  Ordering them by consumption certainly solidifies your decision to use mass walls in school construction.   Richardsville is the top performing school in the US utilizing only about 1/3 of the consumption of energy star target.    That said, it is actually more than "any mass wall" since heat capacity must be at least 7 btu/sqft F.  

What I find so interesting about the report is that mass wall with less R-value beats low-mass wall with higher R-value in most climates.

Regarding your question --- about hangers.   There is virturally no load on the wall running parallel to the load bearing trusses.   You might only have 10 inches of floor cantilevered over to the wall (if I understand you question correctly).   I usually just screw to the webs or red-head a 2x6 back to the concrete.   This is not possible with some commercial and they may still choose to weld embeds to the wall to tie into even with this condition -- this is done on multi-story to tie the wall into the floor even though the wall is not load bearing in this situation.   Regards.

P.S.  Don't know status of IECC 2009 in your state but it's law in Texas now.   Commerical wall section doesn't allow foam or insulation in CMU cavity to count toward R-value.   This is for the same reason as you are eliminating your thermal bridges in your wall design.   Because of IECC 2009 --- since insulation must still be added (usually externally) ICF is now usually less expensive than CMU in Texas.