We are planning to build a story-and-a-half icf home with a finished, walk out basement.  The icf will extend up to the roof line.  Here's the engineer's current rebar schedule:  Horizontal #4@16"on center, Vertical #5@12" on center.  There is no change in the schedule for the above grade portion of the home.  I have reviewed the engineering literature from Reward and Logix and they both allow for a reduction in rebar for the above-grade portion of the home (vertical rebar #4@30" o.c. or #5@48" o.c.).

How do you the experts in the field handle above-grade rebar?  Can you reduce the amount of rebar for the above-grade portion of the walkout basement?  Can you increase the rebar spacing for the main level?  Does vertical rebar #5@12" o.c. sound reasonable?  Thanks.
Dan

Too many unknowns (e.g. where are you?) to comment. That said i'll comment anyway. ;) I have never built any structure with less than 18 O.C. Horizontal (4 or 5) and 16 O.C. vertical (4 or 5). If it was my house i'd stick with the engineers recommendation.

Specifically regarding what you can "get away with" in terms local code etc. (e.g. minimum steel). You've opted to build the best structure possible and i would stay on that path. Regards.

Cook90,

I think you should ask your engineer to justify the steel schedule.  Are you in an earthquake or tornado area?  Your steel schedule is similar to the requirements for a tornado shelter.

When they built my home, which is still under construction, I doubled the amount a rebar that Nudura recomended. But then a belt and suspenders sounds like a good idea to me.

Home is located North of Charlotte, NC in seismic zone 2a (Low seismic probability) and is in the 90mph 3-second-gust wind zone.  The house has no unusual structural loads.  It will rest on soil with less than 45psf max equivalent fluid pressure.  It will be approximately 4000 sqft.  Basement level will have a 10'4" ceiling with 8' back fill and 11 inch Reward icf.  Main level will have 9' ceilings using 9 inch Reward icf.

Does your vertical rebar spacing above-grade remain the same as the spacing below-grade?

Re: "Does your vertical rebar spacing above-grade remain the same as the spacing below-grade?"

No. Below grade usually requires more steel somewhat in line with what you have. Your above grade steel is more than typical for residential. We don't use reward but typically use #4 18" oc horizontal and #4 (or #5) 16" oc vertical (residential) with (of course) extra steel above and below and around all opening as required by the lintel schedule.

Just curious why 10' 4" ceiling height in the basement?

In my ICF home which is located in Arkansas and which will have ~7' of backfill on one side of the walkout basement, I'm installing #5 rebar at 16" oc vertically and #4 rebar every 16" horizontally. My ICF forms have ties every 8" vertically and horizontally. Over windows / doors <4' wide, I will install 2 #5 rebar over the opening. Over windows / doors > 4' wide I will install lintel reinforcement equal to or greater than the prescriptive method which will generally include 2 #5 bottom bars, 2 #5 top bars, and #3 stirrups between them. My basement walls are 8" thick core and 10' high (open web 18" deep floor trusses will hang inside the basement walls).

One the main floor which will be 6" thick core and 9' tall, I will be dropping back from the #5 verticals to #4 since there will be no load from the backfill. Otherwise, everything else will be essentially the same as in the basement walls.

And I'm using Grade 60 rebar rather than Grade 40 since I can get the GR 60 for ~ same price as the GR 40 at the local home supply, I just have to go pick up the GR 60 from a rebar specialty shop (CMC Rebar)

Thanks for the above info. 

Here's our reasoning for 10'4" ceilings (if we're out in left field, please let me know):  During the design phase our goal was 10 foot ceilings in the basement.  The architect recommended using 10'4" since standard stud lengths come in 124" (10'4") lengths.  It also worked out that our original icf plan was to utilize 9 courses of 16" icf (144") with internal brick ledge as the 9th course.  Open-web trusses (18") would rest on the top-plate/brick-ledge and hang 15" below the top of the 9th course.  Subtracting a 4" basement slab and 1" rigid insulation below the slab we get 124" floor-ceiling height (144"-15"-4"-1"=124").

Is this reasonable?

Our current icf installer (who entered the picture after the architect drew up the plans) plans to use Simpson Strong Ties so the above scenario can be altered, if necessary.

Is there a better ceiling height that I should be using?  Let me know.  I've done a lot of reading but have no field experience.

Alton,
I plan on calling the engineer today.  He's already voiced his dislike of icf construction to the architect so it may be an interesting conversation. 

Here's a possible explanation for the extreme rebar schedule....... I believe the engineer used a design wind load of 90psf to calculate the above-grade rebar schedule.  90psf is off the charts for both Reward and Logix icf (the charts range from 20psf to 80psf design wind load).  I think he might have incorrectly entered 90psf since we're in the 90mph 3-second-peak wind zone. 

Thanks,
Dan

As you imply, I don't believe there is a direct correlation here (e.g. 90 psf is not equal 90 mph etc). The kinetic energy or velocity pressure is given by the formula go=0.00256 V2 where go is pressure in pounds per square foot and V is design wind velocity in miles per hour. If this load formula is correct - which I believe it is then the square root of (90/0.00256)=187.5. Basically, 90 psf is approximately 188 mph. This is an oversimplification. See - http://www.arraysolutions.com/Products/windloads.htm. If you introduce gusts and drag and all that things get somewhat more complicated.

Back to ICF :) I suppose "Standard" stud lengths may vary (?) but here your standard is less than 10' -- see post on "Wall too short, is this a problem?)

A 10’ standard stud is 116 5/8” long or 3 3/8” shorter than one might logically expect.

Not that this makes all the sense in the world but then when you put down your bottom plate 1 ½ (2x material), add 116 5/8” standard “10 ft” stud” and a double top plate (for your interior walls) you will have a subfloor to ceiling joists height of 10’ 1 1/8” (this is 121 1/8”).

This allows for flooring and ceiling sheetrock to be added and depending on what you use a final height of very close to 10’ from finished floor to ceiling sheetrock.

Regarding the height of the ICF wall specifically, for a typical double top plate on top of the ICF wall you will need an ICF wall height of 10’ 1 1/8” (121 1/8”) minus the three inches of top plate or 118 1/8”.

BTW: This magic number (if you will) for an 8’ ceiling is 8’ 1 1/8” and 9’ 1 1/8” for a 9’ ceiling.

I can’t tell you how many times a builder has told me to build the walls 10’ high (120”) for a 10’ ceiling when he really means 118 1/8” (9’ 10 1/8”). If you don’t help step him through this he will have to cut each larger non-standard stud to fit and he won’t be happy. Regards.

Just found this on another site: "For flat surfaces with the wind perendicular to the surface (worst case).. F (lbs/ft^2) = 0.0046V^2 where V is the velocity of thewind in mph.For semi circular surfaces then:F (lbs/ft^2) = 0.0026V^2 where V is the velocity of the wind in mph.And V^2 is "wind velocity squared..." Looks like i may have (incorrectly) provided the semi-circular approximation in previous post. If you do some searching you can find equations that include wall height etc. YOu might check out "http://www.eng-tips.com/viewthread.cfm?qid=25358&page=6" REgards.

TexasICF has the basics pretty well stated. However, the "older" codes were much too simple, so the code writers, in particular, ASCE 7, had to make it much more complex than that. It's a nightmare now.
But back to your main point, Dan. Someone said to ask the engineer for an expalnation as there are too many variables. That's a good point. An accurate design may reduce the amount of steel for one thing, but something else may drive it up. As the Client, you certainly have a right to ask, but if he's done his job correctly and stands by it, you're probably getting the services you paid for.

If I'm reading the post right, he's using a 6"block for the basement and a 4" block for the main floor. This may be the reason for the rebar as proposed

I plan on calling the engineer today. He's already voiced his dislike of icf construction to the architect so it may be an interesting conversation.

To me this in itself is a problem. Although an engineer should design in an unbiased manner and should simply by the math of it all arrive at a correct conclusion, that does not have to be the case. His comments to the architect belie his mistrust of the product right off. It has been my experience working with mechanical engineers in plant construction this type of person may then look at every decision point in the calculation process and take the absolute most conservative interpretation, resulting in belt/suspenders/many times over. Now, please, this is about a certain type of engineer, not to bash enginers in general as without them, we'd live in teh stone age. I would look at getting a second opinion

As per previous post - I like a lot of steel myself - more than the minimum in the prescriptive method anyway. However, one question i've pondered in commercial work is "if this hotel is 10x stronger with #5 18" oc horizontal and #5 16" oc vertical than the wood hotel (that meets code) that is directly across the street - why must we increase the steel to make it 12x stronger?"

If you are looking for and engineer you may want to seek an engineer that understands vertical concrete as it's a pretty small step from there to ICF.

I spoke to the engineer today; however, he was out of the office and didn't have access to my plans.  We'll talk tomorrow (Wednesday).  I'll update the thread then.

Per the stud length comment I made in an earlier post.......stud length is not the reason for 10ft 4inch ceiling heights.   I misread my notes.

Dan

engineer tried to save me money on a house i built in calif in the high earthquake zone. He used every size of hold down in the simpson book and different number of bolts in different locations By the time you spend verifying every thing is done right the savings in material did not match all the headache and time spent. I told him it would have been cheaper to have all the hardware the same and vary locations to get the strength he wanted. On the last job My step son ( an elect contractor) bought all the left over and misordered rebar left on the job for 10% of reg price so we used a lot of # 5 wher # 4 was speced.

I can see where the above method wouldn't be cost effective.  However, in my situation, I'm wondering why the engineer has specified #5 @12"oc for the entire structure (below ground and above ground) when the icf manufacturer's engineering tables allow for above ground spacing of #5 @48"oc for our specific design. 

By the way, the engineer says, "It's only a preliminary design."  I suspect the final design will be in accordance with the icf manufacturers engineering specs.  The engineer doesn't want to commit to a design until he's fully paid.  The architect doesn't want to pay until the engineering is complete.