Having completed excavation for my house project I'm now confronted with whether I should scribe my blocks and pin them directly to the ledge which is the entire subgrade of my foundation, or level first with a footing.

(As far as as engineering goes I can proceed either way.)

Seems that scribing and cutting the forms might be easier than plywood, and shimming and filling any small voids with low expansion foam might help things to go quickly. Though I'll be cutting and throwing away a fair amount of form material and that won't be economically wise.

On the other hand, having a nice level footing might make setting the blocks plumb and level quick work. I can insulate the footing before backfilling.

Anyone have experience working on ledge and can offer some insight?

Thanks!

Have you considered the Fastfoot Monopour system?

http://www.fab-form.com/fastfootMp/...erview.php

Looks like a nice system but I'm not sure that I'd want that fabric between the bottom of my footing and the bedrock.

not sure that the round edge footing would meet code required minimum widths

Chris,

You may be right about round edge footing not meeting the code required minimum widths.  However, Fastfoot can be wide as needed when you make your own forms and it has been used in GA in coded areas.  My opinion is that the upper corners of a rectangular footing are subject to shearing at a 60 degree angle so actually the rounded top corners resulting from Fastfoot are less likely to shear.  Make the footer wide enough to meet the code and it should pass.  Instead of trusting my opinion, everyone should check with their local code official before using any thing different in their area.

Using Fastform will do the same thing, no, actually better, than installing granular fill and compacting it to create a level surface. I changed to FF many years ago, and never went back to traditional framed footings.

The question of curvature at the edges not meeting code makes no sense to me?? The footing, in general, is a freestanding concrete base of a specific width based on what hgt it is supporting AND what the soil conditions are! In this case, it seems we are talking ledge material, probably up and down and pieces sticking up here, and something big over there...... putting a free-forming membrane to contain the concrete to make a level surface is a no-brainer!! You could pin it to the rock if desired!

The membrane, under your wall or footing helps keep water migration down! In simple terms....it's a great product!!!

By the way, you can always form up a footing without plywood sculpted to the rock, just pour very slow and very stiff, self-leveling doesn't cut it!

delprete, Maybe we missed something here but you really were asking about setting the ICF forms directly onto bedrock vs. setting them on top of a footer poured on top of the bedrock, right? Does the code for your area allow you to pour walls directly onto bedrock without using a footer? If so, then I think it would depend a lot on how even the bedrock surface is. If it's relatively flat I would think you could trim the bottoms of the forms with less labor and cost than pouring a footer, except for the Fast Form approach. But you've already stated you don't want the fabric between the concrete and rock.

As Jim says, pour slow and stiff concrete and whichever way you go you won't need to be tight to the rock, although you may have greater potential for the ICF forms to float on spilling concrete than would plywood forms.

Alton;

yes I guess my point was on a typical 16" x 8" footer,  it would need to be poured wider so that the flat bottom was at least 16" before the "round" starts. There is not a problem with that other than its a waste of concrete

I just had the same thing happened and we used rough cut 1x10's and scribed them into the ledge. The footing went from 10" to nothing in four feet. I used heavy gauge electric fence wire under the footing form to keep the bottom of the footing form from spreading where we could'nt stake the form. The 1x material was a lot cheaper than cutting forms. We didn't cut the footing form too close because we lined the form with Fab-Form to make up for the gaps.

Posted By dmaceld on 27 Sep 2010 12:22 AM
delprete, Maybe we missed something here but you really were asking about setting the ICF forms directly onto bedrock vs. setting them on top of a footer poured on top of the bedrock, right? Does the code for your area allow you to pour walls directly onto bedrock without using a footer? If so, then I think it would depend a lot on how even the bedrock surface is. If it's relatively flat I would think you could trim the bottoms of the forms with less labor and cost than pouring a footer, except for the Fast Form approach. But you've already stated you don't want the fabric between the concrete and rock.

As Jim says, pour slow and stiff concrete and whichever way you go you won't need to be tight to the rock, although you may have greater potential for the ICF forms to float on spilling concrete than would plywood forms.

Yes, I'm considering scribing the icfs directly to the ledge. I haven't consulted with the local codes officer who I'm certain will be in agreement with an engineer's determination in this since nys code doesn't have any reference to icfs on ledge. I was told by a local engineer that the footings are structurally unnecessary as the bedrock will effectively be the footer.

The bedrock surface is uneven. My thinking is that I can scribe the forms to be close then shim and fill any gaps with low expansion foam. The forms would then be tied to the dowels that are set into the ledge. This way the icf "footer" would be easier to secure than wood forms. I'd mix on site and pour a low course rather than a full 8'.

What waste I might have in icf I'm thinking might be equal to the waste and work in using lumber for footer forms.

I can understand the scribing of the wood forms but I can't get my head around securing the forms to the rock to prevent any movement at the time of the pour. I guess that once the forms are in place I can back fill around them to keep them secure. Wire them to the dowels? I just want to find the slickest way to get this base course whether it's icfs or a formed footing done.

The wire goes on the bottom of the footing form since you have no way to use grade stakes. This keeps the bottom of the footing form from spreading. You keep the footing form in place by using a 2x4 laid on the ground and staked wherever possible.

If the inspector agrees that no footing is needed and the height variation isn't too great I'd be tempted to set the first row of block level, screwing say 8" wide plywood strips to the outside of the block letting the plywood drop to the surface of the rock. If you are only pouring the first row half full with a stiff mix, the pressure shouldn't be a problem. You could always brace the bottom of the ply with crosswires, or any other suitable method if it seems needed.

I've since decided to backfill and continue in the Spring with a monolithic slab on grade. Anyway I looked at it the labor and materials expense wasn't justified by the limited "basement" that I would've ended up with. I'd originally hoped for a full basement with an insulated slab. Having ledge for the floor would be whole different animal. It's a bummer that I'll lose the investment in the excavation that I did and will have to spend some effort in establishing a well-compacted base, but I can at least look forward to the benefits of the insulated slab and radiant heat.

Thanks for all the advice. It was great being able to get intelligent input.

As a side note whenever we can't stake we use bailer twin at the same location as the strappings on top of the footer. Has been working fine since I can remember! Good Luck!
Backfilling to hold in place is not such a good idea for how will you keep the panels where there supposed to be while backfilling? Unless you have two loaders dropping @ the same time, the same amount of dirt, the same spot, the same.... you get the point.