Regarding vertical bar reinforcement in a flat-core job (blocks such as Arxx, Logix, Amvic), is it necessary to have a footing dowel for each vertical bar?

I have seen techniques discussed and photographed in which a PVC "collar" is made using a 1" cut of 1" dia. PVC pipe, and when the verts are threaded down from the top, the bottom of the verts are captured by the collar.

We have some tall sections of wall to do, and cannot imagine hitting so small a target looking down through 6" of core at 13 feet of depth.  Like threading a needle in a hurricane.  How does this get best handled?

Good question. Lots of variation in play here :-)

I was just looking at the Varianthouse website ( German technology) and they use NO footing dowels.

That PVC collar thing is pretty tough to do when it's time to drop your vert from the second last course, or top course on a tall wall. Never tried it.

If the horizontal bars are offset back and forth in the center of the core, as you build, the vert is "captured" roughly in the center between them.

Your only problem then, is to center the vert laterally in the core.that's a pretty easy task if someone follows the hoseman on first pass, and plays with them for a second.

Also helps consolidation. You could also embed your vert after first lift. That method would depend on you and your B.O.

It will be interesting to hear how others handle this.

And here is another wrench in the works. Bear in mind that my first ICF project will be a basement, with most all walls having backfill against them.

The most effective reinforcement scheme for a backfilled wall is to have the bars AS CLOSE TO the inside face of the concrete surface, while still getting sufficient "bury" to allow the bars to adequately work in the composite assembly of crete and steel. Ideally, the crete cover would be about 1" and certainly no less.

The closer to the center of the wall, the less effective the rebar in resisting the bending force of the soil pressure.

For that reason, we will run the horizontals at the inside clips of the webs, and then weave the verts though, doing it before the pour.

The rebar doweling of wall to footing is just to add some shear strength into the assembly, hardly necessary unless you are building in wildly unstable soil, and if you are building there, you have much more things to address than this little piddly matter. We'll put dowels at 4' centers just to look like we're doing something, and they won't correspond at all to what we do with the vertical steel.

True, the horizontal rebar should be placed close to the inside of the wall. The chairs in your forms should keep them in place where you want them. The rebar in the footings should also be placed closer to the bottom. The dowells should handle any shear issues, and so will the poured slab. As far as the uprights go, I would try to get them as close to the center as possible for compressive strength. I would not worry about trying to line them up with the dowels. Just my opinion. Scott

The pvc dowel clip, for lack of a better word, is very easy. I use 1 1/2" pvc, cut them on a chop saw that has the rear legs elevated, so the cut pieces roll off the saw into a bucket.
Place all the pvc collars on a piece of plywood, and spray the ends with a bright paint color, I happen to use an upside down marking pain in flourecent pink. Dries in 5 min, and good to go. Then when you're 10' or so up in the air, you can see the bright paint in the bootom of the ICF wall. Yes, sometimes you need a flashlight...and yes, I remember using grey pvc and they simply blended into the footing and we had a terrible time finding them.

Gene
Review your code application before you only go at 4' centers! As much as I like to limit rebar, the wall dowels replaces the keyway and I have always used 24" o/c for dowels!

Jim is right this is the same way we do the verts with PVC, another thing on a tall wall is to put the verts in a couple of courses before you get to the top.

I've seen a couple of different ways, and I'm not sure most solutions improve the wall strength commensurate with the effort involved. It always seemed like a lot of effort for something that doesn't likely improve performance. The intention seems to be merely to "meet code."

My first exposure to the obsession with vertical placements was using a 2.5 " PVC pipe with a cone formed in one end and a hole just big enough to fit over the footing verticals. The inspector was concerned that the later added wall verticals wouldn't be within the code mandated proximity of the footing verticals. While the footing concrete was still plastic, we used the pipe (sort of like a seed planter) to form a divot around each vertical coming up from the footing. The verticals stuck up enough to meet the code overlap requirement. After the wall was poured, we dropped the main verticals (cut to the wall height plus the depth of the divot) and then could tell when they dropped into the divot. Maybe it was luck, but a couple of pokes and the majority fell into place. For the few that didn't, the extra inch or two was cut off. Maybe a code violation, maybe not, but how to know for sure??

In thinking about what, if anything, all that hassle accomplished, I now believe that the divot itself is probably the most useful feature. Most ICF walls lack a keyway. The keyway provides shear strength between the wall and the footing that just rebar lacks. Rebar with an inch of concrete on both sides of it (created by the "keyway" divot) provides additional shear strength.

The "code" wall might require a 20" inch rebar overlap at a minimum and one inch proximity at a maximum for #4 bar. We can build that code wall using plastic rings that allows us to look down into the form with a flashlight and place the verticals prior to pouring. If the vertical is simply dropped into a "bulls-eye" piece of pipe laying on top of the footing, you don't have additional shear strength, just a proximity target. All you are getting is the possibility that your vertical is within the 1 inch required by code for an overlapping rebar connection. My understanding is that the rebar has to be within one inch for the entire overlap, and you aren't really getting a guarantee of that, but most inspectors are happy.

I think a better wall would use rebar out of the footing with divots that produce a 1" concrete surround for each bar. On that wall, we expose the footing verticals 36 inches instead of the code minimum. It is poured and the verticals are added without trying to hit a 1 inch target, merely trying to place them properly depending on the direction of the wall load.

The "code" question would be are the second wall's verticals within 1 inch of the footing verticals? The real question is which wall is stronger? Which wall is easier to build? Which wall is cheaper to build? By "missing" the one inch proximity at the top of the footing, extending the upright footing verticals to 36", and placing the wall bar 1inch from the unloaded side, do we have a stronger wall? Do we need an engineer to answer these questions?

Little plastic target rings may meet code and miss the issue. Instead of putting little plastic rings over the footing verticals, maybe we should be more interested in the strength of shear and tensile connections. Instead of trying to show that we've met the code minimum, maybe it would be easier to extend the overlap length to the point that the rebar proximity issue is gone. Since the time/costs appear the same, why not build a stronger wall?

A bit of a rant, but I failed a plumbing inspection last week and I'm a little sensitive.

Mark Fleming

Regarding the dowels in footings, the following is straight out of the Prescriptive Method for Insulating Concrete Forms in Residential Construction:

6.1 ICF Foundation Wall-to-Footing Connection
No vertical reinforcement (i.e., dowels) across the joint between the foundation wall and the
footing is required when one of the following exists:
• The unbalanced backfill height does not exceed 4 feet (1.2 m).
• The interior floor slab is installed in accordance with Figure 3.3 before backfilling.
• Temporary bracing at the bottom of the foundation wall is erected before backfilling and
remains in place during construction until an interior floor slab is installed in accordance
with Figure 3.3 or the wall is backfilled on both sides (i.e., stem wall).
For foundation walls that do not meet one of the above requirements, vertical reinforcement (i.e.,
dowel) shall be installed across the joint between the foundation wall and the footing at 48 inches
(1.2 m) on center in accordance with Figure 6.1. Vertical reinforcement (i.e., dowels) shall be
provided for all foundation walls for buildings located in regions with 3-second gust design wind
speeds greater than 130 mph (209 km/hr) or located in Seismic Design Categories D1 and D2 at
18 inches (457 mm) on center.
Exception: The foundation wall’s vertical wall reinforcement, at intervals of 4
feet (1.2 m) on center, shall extend 8 inches (203 mm) into the footing in lieu of using
a dowel as shown in Figure 6.1.

So, in most cases, for ICF walls or concrete walls in general, you don’t need the dowels.

If you do need dowels, either required per the reasons above or because you or the owner just want them, a) they do not have to line up with, or splice to the vertical steel in the wall, b) they do not have to have the same spacing as the vertical steel in the wall, c) where dowels ARE required, the minimum is a #5 bar at 48” spacing and the dowel should have at least 8” embedment in the footing and 8” in the wall.

So don’t worry so much about using things like pvc pipe to keep your vertical steel close to your dowels!

Now, the places you DO need to worry about keeping the rebar splices close is where you have more than one level to pour and you have to splice the vertical steel in the lower level with the vertical steel you drop down into the second level forms. So, how close do you have to be?

The requirement for a non contact splice is 8 bar diameters, so for a #4 bar is ½ x 8 = 4 inches and a #5 bar is 5 inches.

All you need to do is; a) when you do the first pour, make sure the top end of the vertical rebar ends up centered between the webs – not hard to do, and b) make sure you drop the upper level vertical rebar down into the same web cavity that the lower level rebar is in. The webs will “force” the rebar into the non contact splice requirements unless the webs are more than 8” apart.

If the inspectors have problems, pull out your Prescriptive Methods book and show em! (You should keep a copy at every job site, it's very informative.)

Just to clarify my last post, the 8 bar diameters required for a non contact splice refers to the maximum distance BETWEEN the bars, not the lap splice distance. The lap distance is 40 bar diameters or 20 inches for a #4 and 25 inches for a #5. Hope I didn't confuse anyone.