My NuDura Basement walls will be 10" thick. I was planning on having Form-a-drain footers, 10" thick, maybe 2' wide. I was planning to put some rebar in the footers themselves, but was contemplating the vertical rebar which will stick up out of the footers. I would place the ICF forms on top of these rebar and they would provide lateral strength for the basement wall, so that the wall couldn't move on the footers. The installation manual just says: "Local codes". Nothing about placement frequency and size... So here is my thinking, which I welcome input to... I was planning to use 3/4" (#6) rebar every 4', sticking up out of the footer 30" or so. I was also planning on driving this rebar into the soil about a foot before the pour of the footer and hanging the other rebar (which runs along the footer length, lets say, 5" above the ground, i.e. in the center of the 10" thick footer) on these vertical pieces... in a "ladder" configuration. (Difficult to describe, but let me try. .. at each vertical post which is driven into the ground, I would wire a little piece of rebar, say 16" long perpendicular to the length of the footer. On this piece, which I would suspended about 5" off of the ground, I would place two long pieces of rebar running along with the footer... thus the ladder. By driving the rebar in the ground, I can get a stable placement of these vertical pieces, and I have something wire the "ladder" to, helping me place the footer rebar in the middle of the pour. Is there any negative to me driving the rebar into the ground before the pour?) So here are the main questions, but feel free to add more input, as if I don't know what I'm talking about! Q1: What size rebar should I use? For the vertical (lateral strength) and horizontal 3/4"and 1/2? Q2: How often should I place them? every 4'? Q3: Is there any negative to driving them into the ground before the footers are poured? Thank you, Chessie

I would be concerned that driving steel rebar into the ground will expose the rebar to water that can lead to rusting. Rust can transfer from the vertical rebars to the horizontals. This can cause the concrete to spall. Consider using plastic rebar chairs to support the bottom horizontal rebar layer. Tie bent vertical rebars to the horizontal rebars to hold the verticals upright above the ground to avoid the potential rust problem. I think smaller verticals than #6 could be used at a closer spacing for better reinforcement. An alternative to the above is to drive non-rusting basalt rebar into the ground to support the horizontal rebars. (Paragraphs not working - everything runs together.)

Best practice is to space the dowels coming out of the footer at the same distance as the vertical wall rebar schedule. You should try to overlap the two. As Alton said do not drive the rebar into the soil.

Where are you located? Nudura's North American Tables (C-1) specify Footing Dowels as 1-15M (#5) x 20" long @ 48" o/c OR 1-10M (#4) x 20" long @ 24" o/c.

(Paragraphs weren't working for me either! Thanks for reading through the run-on!) Very good, thank you! I'll consider how to proceed. I'm familiar with metal "chairs" that you purchase to support rebar off of the ground before a pour.. these often sit on a plastic layer.. I put down plastic for moisture control both during curing and afterwards, to prevent wet floors.... The foundation should be dry, rust would still happen, but certainly not standing water (Thus the Form-a-drain, and a gravity drain away from the foundation.) Driving the verticals into the soil is tempting because it would be secure, and no additional worry.... making for a sturdy foundation for the horizontal rebar....

Basalt... hmmm, not familiar. Most likely more expensive, but maybe worth it... I could weld the verticals to secure them to the ladder.. .and place the entire thing on 5" spacers to place it in the middle of the pour of the footer... make them ahead of time in 10 and 20' lengths... I'll ponder and perhaps make them over winter. Again, thanks all!

- Chessie

I should note that National Building Code (Canada) also permits a keyway in place of the footing dowels to provide lateral support (based on the way you reference rebar size). I can't say if your local code permits the same.

Regarding rebar into the soil - I agree do not do it this way. You want to have the rebar fully encapsulated in the concrete to avoid contact with soil/moisture. Either wet set dowels after footing concrete is placed or tie the dowels to your footing rebar which will be lifted into the center of the footing.

When in doubt - ask your ICF supplier! They should be able to answer these questions (or at least know who to contact to get an answer) as it applies to your area.

ICFBdr -- I'm in US - Maryland. I had not seen that table, thank you! Perfect. -- Chessie

We would always do BOTH a keyway, created using 2x4s, AND footing dowels, placed and spaced as described by Smartwall. The keyway eliminates any cold joint gap between the footing and lower wall interface to help prevent insect and water intrusion. We would also put a 2" length of 1.25" diameter PVC pipe over the footing dowels after the footing pour that would subsequently be used to capture the wall vertical rebar. Doing all this results in much stronger wall. There are photos of this done on our place on our website. We are mostly retired these days.

Posted By Chessie on 13 Aug 2021 02:25 PM
ICFBdr -- I'm in US - Maryland. I had not seen that table, thank you! Perfect. -- Chessie

In the Maryland Residential Building Code book (Maryland uses IRBC) there are specific requirements for rebar sizes and spacing in concrete basement retaining walls. You can read it in chapter 4 -here> https://codes.iccsafe.org/content/IRC2018P4

This is great, AWWarn, thank you. I have been assuming that NuDura meets or exceeds any building codes, and that I would be safe to use their guidelines. However, I will go see if I can decipher the specs in Chapter 4, and make sure that I am meeting or exceeding these.

Sailawayrb - you said: "We would also put a couple inch piece of 1" PVC pipe over the dowels....." I like this idea, but I have a question as I think about it...

I was planning to place the vertical rebar in the footer in the center of the "soon to be placed" wall. However, the horizontal and vertical rebar of the wall gets placed a lot off center in the forms..... there are "rebar holders" in the plastic spacers of the forms that hold the rebar, and you use the "closest to foam" slot for the odd number layers of the foam forms in your wall, and "2nd closest to the foam" slot for the even number layers of the forms. Then, when you have set the required number of foam form layers (in my case, 9' walls will be require six, 18" forms) you thread a piece of rebar down in each cavity in between these, alternating, horizontal rebar. The rebar is placed on the "tension" side of the wall, which for my basement wall will be closest to the interior, to best strengthen the wall with dirt on the outside of the wall. SO (!) with all of that explanation, a centrally placed footing rebar will not line up with the vertical rebar that is placed from the top down. My options are to: 1) Ignore this 2) attempt to angle or bend the rebar to reach over to the middle and line up with the "vertical footer rebar" which I placed in the center of the 10" "soon to be poured wall" or 3) move the "vertical footer rebar" so that it lines up much closer to the edge of the foam form, and that I can set my vertical wall rebar in line with this.. and *then* catch a PCV ring or two to attach these two (vertical) rebars together. Is this what you would do? Place the footer rebar in line with what will be the position of the vertical wall rebar? I can make that calculation and do this... I just have to be careful when I setting my reinforcing in the footers.... Additionally, in my mind, the strongest location for the lateral wall support from the foundation footers would be at the 5" location of a 10" wall, not on the inside edge. Comments? Thanks all for these awesome tips and links...

Check with your local code official to determine if the vertical rebars in the wall have to be perfectly aligned with the vertical rebar dowels in the footer. I may be wrong, but I understand that the vertical rebars and the dowels do not have to be tied together or even touching each other provided they are close to each other and overlap 24 inches. Let us know what your code official says.

I don't see any benefit to making sure the footing dowel and vertical rebar are aligned or in contact. These are serving 2 different purposes: footing dowels provide laterally support for the footing/wall connection against the force of backfill (further supported after basement slab in placed), while vertical rebar provide lateral strength against the bending moment of the wall. Allowances are also provided (per Nudura's Tables) for overlapping bar to be spaced out by a certain amount (max rebar spacing is 1/5 the rebar lap length or approx 4" separation for a 20" rebar overlap).

There is no requirement to align the footing dowels with the vertical rebar. There is no requirement for a footing keyway either...and if you do a footing/wall monopour, you wouldn't do the footing keyway. Smartwall was the monopour expert here and he can explain best practices on that if you are interested. Or just search this site as I am absolutely sure he fully explained it very well in years past.

We always did separate footing and wall pours and hence did the keyway. Aligning the dowels and vertical rebar just took a little figuring and then marking layout for each different block we used...BuildBlock and Nudura for most part. Aligning the footing dowels and vertical rebar and using the PVC sections worked well and made installation easier. Cost to do this is practically nothing too.

I doubt hardly any ICF contractors do both keyways and align the dowels and vertical rebar. But doing so makes for a much stronger building and allows meeting higher earthquake seismic design levels. We did ICF construction in Seattle area for most part and then some in Southern Oregon before we retired from doing it...unless my husband decides to do another one...

Thanks all....

(ICFBdr - I was thinking along these lines, but thought that I might ask and see if I was full of hot air or not! Your reminder of the "up to" 4" separation for a 20" rebar overlap will definitely fit my build... I was even planning on making the rebar 24" long, not just 20".... just because that's what I usually do, over build. I'm incapable of building things light and "just to code". That probably describes everyone on this forum, why else would we all be building IFC homes???)


I was thinking that "middle of the soon-to-be-poured basement wall" (5" for a 10" wall) would be best for strength. (Strength within the 10" wall, not necessarily in tying into the vertical wall rebar, which might be 3 inches away.)

I don't mind moving them inboard if that would be much better. If it's negligible, then maybe the middle, with a keyway is okay, or as good, then perhaps I'll pour a keyway.

For a keyway, do people just use a 2x4 in the concrete to create a square trough, and then remove it and pour the wall over it, creating a wall that would have a very hard time moving out of this through? I really like this idea, and I think that I'll do this.

I'm trying to plan ahead, and tend to think through all the steps, which leads to questions... it's nice to have others discuss it and provide feedback.

Chessie (The plan is to pour these footers next spring, begin the walls in June.)

As I wrote preciously, we use 2x4s to create footing keyways. Attached are some photos. Better photos can be found here:

https://www.borstengineeringconstruction.com/Borst_Shop_Construction_Photos.pdf

https://www.borstengineeringconstruction.com/Borst_Residence_Construction_Photos.pdf

Best wishes with your project!

Gayle

Just what I was imagining. Thank you much for the pictures.. perfect. Chessie