Best way to handle large step footers (8' +)
Last Post 27 Mar 2015 09:51 AM by emmetbrick. 8 Replies.
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BoomstickUser is Offline
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04 Mar 2015 09:37 PM
Hi, My first post... I've gotten many answers to other questions here, so I figured this would be a good place to ask. We are getting ready to build a new ICF house. Finalizing the plans now. ICF Walls, hollow core plank roof. Single story ranch. I can't figure out the footer... the house is a simple rectangle... with a basement in the middle. So we need to step the footer down 108" (9'). See linked drawing. Footer Issue When we built our current house (2x6 wall construction on slab)... it had a couple of step footers... which we formed and poured continuous. While I've found some 5' tall or so step footers (formed / poured continuous)... I haven't seen any examples of really tall step footers poured continuous or otherwise. It seems like something that would be very common (where the garage meets the house and there's a full basement?)... but I can't find pictures / details. Pouring a 9' tall column (to connect the basement footer to the ground level footings) seems odd / questionable? Hopefully a general contractor can pop in here tell me what I'm missing... or someone can put my google-fu to shame... I just can't find an answer. There is one thread here from 2007 that sort of talks about it... but wasn't conclusive. Thanks!
arkie6User is Offline
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04 Mar 2015 11:01 PM
When I did my footers for my garage that connected to the main house and full basement, I extended my basement footing out ~3' at the corners where the garage connected. This footing extension took up the space where the basement over dig occurred. After the ICF basement was poured, I had cement block, i.e. CMU, placed on that footing extension, 2' wide x 3' long and brought up to grade height where the garage footing would be poured. I punched three holes through the block at the height where the rebar for the garage footing would lay. The garage footings were dug and rebar placed. The garage footing rebar was extended into the cement block column via the holes in the block. I used 5/8" rebar at this transition in the footing because there was a foot or so of compacted fill at the end of the block column to pass over. When the garage footing was poured, we also filled the cement block column adjacent to the ICF basement. This tied the garage footing to the basement footing and was essentially one big step in the footing. I haven't had any cracks or other issues since this was done a couple of years ago.
arkie6User is Offline
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04 Mar 2015 11:10 PM
Here is a link that shows my footing column for my front porch: http://www.greenbuildingtalk.com/Forums/tabid/53/aff/4/aft/81755/afv/topic/Default.aspx
dave111User is Offline
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05 Mar 2015 12:02 AM
We treated ours as a grade beam. We put both sets of footers on undisturbed soil, which left a 2 foot gap between them (horizontally, much bigger vertically). We then bridged over the gap with the ICF wall, closing the bottom of the bridge with a temporary wooden brace for concrete placement. After the bracing was removed we had a gap you could walk though, and looking up you saw the bottom of the concrete wall with the foam on both sides. From an engineering standpoint it is just a grade beam, of course I had an engineer involved. It was a simple solution, and the gaps made a great place to run utilities. I will note that I didn't want any settling issues, so I did back fill the gaps with a flowable fill (washed pea gravel).
BoomstickUser is Offline
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05 Mar 2015 02:13 AM
I liked the grade beam idea (if it's what I think it is)... but I read that it's only good for a 5' change in elevation. See Figure 11 at bottom of this page: Footing Fundamentals This seems like the best solution to me... I don't understand why they say it's limited to 5 ft. One would think the taller the better.
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05 Mar 2015 02:47 AM
I think I may have figured it out.. I was so focused the footer "hugging" the basement drop I wasn't think about stepping it up a couple feet at a time and starting my walls on those steps. I updated the image (just a quick photoshop job, not to scale or anything). That approach seems more sound / traditional to me.
Updated Footer Drawing Ultimately I have other details on the structure that an engineer will need to verify... I'm just trying to get the design roughed out and make sure we can afford the house / feel confident in the overall design.
smartwallUser is Offline
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05 Mar 2015 10:32 AM
I did a footing pour with an 8' drop about 20 years ago. We used concrete blocks. We cut the face off the bottom block facing the footer and the face off the top block facing the other way, ran rebar inside, filled around the edges at the bottom of the top block and poured the whole deal. Simple with a lot less labor trying to cut forms to fit the excavated walls which are never shear.
Chris JohnsonUser is Offline
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05 Mar 2015 11:57 AM
Do you have frost to be concerned about?

We do continuous footings for the entire structure, while building the house footings, we enter the garage area and step up our footings like stairs, our code allows a maximum of 2' rise and minimum of 2' run for step footings.

OBC 9.15.3.8 (1)(a)(b) So generally we make the step heights to match the height of the ICF we are using to eliminate horizontal cuts on the block

Chris Johnson - Pro ICF<br>North of 49
emmetbrickUser is Offline
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27 Mar 2015 09:51 AM
What arkie6 said.
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