lzerarc
Basic Member
Posts:423
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| 27 May 2011 08:51 AM |
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Has anyone done shallow frost protected footings for an ICF basement/build? In the final design stages of my ICF house (full basement and main floor). The site slopes so we would have a walkout to the rear. When I was planning on doing ICF/wood combination, instead of stepping the footing with the sloping grade I was going to keep the footing height the same and switch to SFP. Obviously the size of the footer for 2 levels of ICF walls would need to increase, and I was originally planning on stepping the foundation down maintaining 3'6 frost protection. Now I am back to considering using the SFP version. It would be a savings of about 70-80' LF of 4' ICF, the concrete, and the extra labor involved in stepping and digging the deeper footings. any thoughts? |
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jonr
Senior Member
Posts:5341
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| 27 May 2011 02:06 PM |
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I'd take a look at FPSF + monolithic, thickened edge slab (ie, no footings). |
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Chris Johnson
Advanced Member
Posts:878
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| 28 May 2011 06:24 AM |
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I have done it, because I could and wanted to see how it worked.
If the digging is easy and your not having to content with a high water table go down. The insulation is thicker and wider the closer you get to the surface, meaning additional prep work as you want the insulation to sit as flat as possible. And then you have the landscape issue, the closer the foam is to the surface no garden is going to work too well there. |
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| Chris Johnson - Pro ICF<br>North of 49 |
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smartwall
Veteran Member
Posts:1209
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| 28 May 2011 10:46 AM |
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You're doing a full Icf house but you want to do part of the foundation out of SPF. I'm confused. Pour the whole footing and walls with a mono pour even the step footing. This willl save you money and time and give a stronger foundation. |
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lzerarc
Basic Member
Posts:423
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| 28 May 2011 11:58 AM |
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the thought behind it was to save where you could. For our area, we would need to take the thickened edge down and have about 16" of ground coverage.
So it would save a few yards of concrete, icf forms, quite a bit of fill, additional digging, etc.
However I have also considered a monopour. We will be using Hobbs icf with form-a-drain. Was planning on 10x20 footings. I have not seen it done however. I assume we would install the form a drain, using some sort of wood strapping spanning the 20", place the icf tracks and screw to the wood? |
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eric monkman
Basic Member
Posts:262
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| 29 May 2011 11:28 AM |
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Monopour footing and walls.. can create issues with uplift on your foam forms and it is difficult to do complicated layouts with. The risk vs reward factor is quite high , not worth chancing imho. FPSF are getting to be commonplace in my area due to mandatory soils inspections and techs realizing the $$ savings. Builders save on excavation and backfill costs, water pumping, formwork and concrete and rebar costs. The $$ offset can be quite a saving for the builder. Dow Chemical used to publish info sheets on the subject, and our local Soils PEng are quite knowledgeable on the subject. Generally, walk-out footings are 18 to 24 inchs below finished grade, with 2 inch S400 density foam in the footing box and S200 to 4 ft or better beyond the footprint. Frost drives at a 45 degree angle from the edge of the foam, so the farther out past the footprint, the deeper your frost protection. Joints should be taped or foamed if butt edged, or shiplap. We see a lot of foam blocks on bridge approaches and backfill on weak soils also. http://building.dow.com/na/en/appli...hallow.htm |
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smartwall
Veteran Member
Posts:1209
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| 31 May 2011 08:30 AM |
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Eric,
The rewards a many and the risk, if you know what you are doing, are few . I've done thirty jobs with the mono pour and have taught others to use it. The first one does have a bit of pucker factor but once you've done it the response is always "no big deal'. As far as layouts, they are easier because you can move the walls on the metal cross braces anywhere you need them. No finishing the footer or doing a layout of the dowels coming out of the footing. The vertical rebar is dropped into the footing from the top of the wall. The best of all the footing takes about a hailf hour of pump time to fill. I've never done a regular footing pour in that time. I'm glad for skeptics they have a tough time beating my prices. I've even been able to beat a couple of regular form guys on different projects, including a 1525 ft frostwall job with 36 corners. |
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greentree
Advanced Member
Posts:587
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| 31 May 2011 08:33 AM |
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Isn't the question here not one or another but the combination of traditional footing below the frost line combined with a FPSF at the basement walkout portion above frost line?
I thought you couldn't combine the two, but I may be wrong. I'm also under a different code than you unless you happen to live in WI.
But, I have seen ALOT of walkout foundations and I have never seen the walkout portion as a FPSF, it's always a frost wall. Common sense would tell me if they could just switch to FPSF at the walkout they would, less digging, less crete and everyone wants to save a buck. |
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lzerarc
Basic Member
Posts:423
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| 31 May 2011 09:50 AM |
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Greentree-
IRC, section R403.3 talks about SFP and joining frost footings. If IRC allows it, now sure why yours would not. We are in NE Iowa. |
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lzerarc
Basic Member
Posts:423
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| 31 May 2011 09:53 AM |
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Smart- I have poured enough footings, but never monolithic. I can certainly see the point, plus it saves a full concrete delivery and pump charge.
However with the questioning brought up, how do you fix any lifting in the forms? Allow it to happen and just level the tops of the forms? |
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BrucePolycrete
Advanced Member
Posts:524
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| 31 May 2011 10:11 AM |
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Use a from that doesn't lift. Forms that feature steel wire cross ties generally don't lift. I can assure you that Polycrete Big Block does not lift. And you don't even glue or tie the courses together (except the top one). Those plastic cross ties have masses of surface area. Wire ties go from 11 gauge (ArxxSteel) to 4mm Polycrete. I don't know how strong Arxx form is, but Big Block can withstand 1600 lbs/sqft of lateral pressure. |
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jonr
Senior Member
Posts:5341
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| 31 May 2011 10:19 AM |
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I'm trying to picture this in a FPSF case. ICFs sitting on gravel (actually horizontal high density foam if you insulate underneath everything) and then one could fill them and pour a slab at the same time? How do the ICFs attach to the slab (there is a layer of foam between them unless you cut most of it out)? I see some references to the ICFs sitting up on top of some grid - that makes sense but requires wood forms (or perhaps foam strips on the outside, chairs on the inside and rebar suspended between them). A single pour and jointless concrete between the floor and walls is appealing. You also know if concrete is making it all the way to the bottom ICF block.
http://www.icfmag.com/how-to/ht_wet-setting.html |
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lzerarc
Basic Member
Posts:423
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| 31 May 2011 10:56 AM |
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If we do SFPF, I would not do a mono pour with the slab and wall. I would pour the slab (probably use a key as well) and then install my rbar. Edge of slab would be at the edge of the concrete inside the icf. ICF foam would then aling perfectly with the exterior foam on the thickened edge, thus eliminating the detail of mtl flashing and protection. I am right between 2000-2500F degree days, IRC says r of only 5.6, however I would go r10 and use 2" of XPS, or possibly 2" of EPS.
However I would prefer to not have a slab down for bracing since I intend to stain the basement concrete and use infloor ran off of the GSHP....
The one thing I need to look into more however is the detail of the drain tile/form-a drain being used on the full depth basement walls and how that transition works.
Def. some major pros and cons here..... |
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jonr
Senior Member
Posts:5341
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arkie6
Veteran Member
Posts:1453
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| 31 May 2011 02:56 PM |
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Posted By jonr on 31 May 2011 12:49 PM
Maybe this. Could even glue the ICFs to the horizontal foam to keep everything in place.
Where is the footing to support the weight of the ICF wall and the roof? |
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jonr
Senior Member
Posts:5341
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| 31 May 2011 04:08 PM |
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It's a standard FPSF monolithic slab - the footing and the slab (thicker at the edges) and interior of the ICF are all one piece (ie, brown is concrete and cream is concrete). OK, I updated it to be clearer.
See figure 9 in http://www.cs.arizona.edu/people/jcropper/desguide.pdf |
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