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Discussion Starter · #1 ·
Hello,
I have been looking into doing this type of pour for a 3 season room and was wondering if anyone had:

1. Any drawings and/or photos of it

2. How the rebar is incorporated? (is it just tied together and dropped in as the pour is going on?)

The village asked that there be a 12" "bell flare" at the bottom of the wall ans I wondering if I should do rebar there as well maybe on supports.

To save on time as well as labor, I was thinking of using machinery to trench down the tench wall and then do the rest by hand. The soil is mostly clay.
 

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Thom
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Steel goes in prior to pour and gets inspected. You will need to incorporate the placement of the steel into your plans. Type of supports for the steel varies by location/local practice. Width of bell at bottom is also a local issue. You really need someone who is familiar with local practices to draw this up for you.

I haven't used that type of foundation in many many years BUT, when I did every local jurisdiction (Chicago area) had their own interpretation of what was needed.
 

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Discussion Starter · #4 ·
Anti-wingnut
You know, I don't really trust any one of my subs until I have done/ had them do, every type of job for me I am quoting out. I haven't done this type of foundation before, so when it was suggested by one of my subs to save some money I wanted to do research to figure out the most reliable and common practices as well as the inherent problems that might occur.
 

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Monolithic pours are quite common, and are often left to the discretion of the subcontractor performing the work. Regardless of whether this pour goes monolithic or not, you may be required to give the sub a detail of the re-bar placement. This may be done by you, and your interpretation of the pertinent code(s), or by an engineer if required. Many, if not most, areas of high seismic concern, are starting to become very stringent on engineering. I am fortunate in that most commercial concrete work is engineered, and we just put our rebar where specified (it is actually not that easy).

I am not aware of what a bell form is, it has never come up in anything I have been involved with, and may be a regional term.

If you have a sub that does your foundations, he should be able to do a mono pour. Another detail which is becoming frond upon is the use of PT bridges atop your footer form to support the wall forms. Some places are requiring steel bridges.
 

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oweing,

If the 3 Season room is from a manufacturer, They should be able to provide you with a detail for the footings. Otherwise I would go to an:thumbsup: engineer who is familiar with your soil conditions in your area or to the building Dept to see what they will require. In NW Florida where I am, I have had to form a 20"H x 16"W with 2 #4 rebar in mono slabs I have poured. It is dependent on the loads the slab must carry. I prefer mono slabs my self but that is what I am used to and I have no one but myself to blame if it is wrong. Use a good laser build good box forms and brace every 2-4 feet and you will have a nice slab to work on.
 

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There seems to be a little confusion here. It sounds like your proposing to install a "frost" wall assembly, not the more typical "grade beam" or "turned down slab", which is built above the frost line typically. If the reasoning for the 42" depth is the frost line, this is a fairly complicated process to get right. I've seen it attempted once or twice, but never very accurately. The trench has to be dug perfectly, as there is no extra space in the trench, assuming you want to use the earth for the forms? Both walls of the excavation should be lined with something smooth also so frost cant "lift" at any imperfections in your frost walls. The material used on the interior wall will be lost behind the concrete permanintly. There are other factors to be concerned about as well, which is why you won't see "Pros" using a system like this regularily. It's just too much screwing around compared to a standard footing+block or poured wall+finish floor assembly.
 

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There seems to be a little confusion here. It sounds like your proposing to install a "frost" wall assembly, not the more typical "grade beam" or "turned down slab", which is built above the frost line typically. If the reasoning for the 42" depth is the frost line, this is a fairly complicated process to get right. I've seen it attempted once or twice, but never very accurately. The trench has to be dug perfectly, as there is no extra space in the trench, assuming you want to use the earth for the forms? Both walls of the excavation should be lined with something smooth also so frost cant "lift" at any imperfections in your frost walls. The material used on the interior wall will be lost behind the concrete permanintly. There are other factors to be concerned about as well, which is why you won't see "Pros" using a system like this regularily. It's just too much screwing around compared to a standard footing+block or poured wall+finish floor assembly.

This system is used by contractors quite often. If formed properly there will be no materials left behind under the slab. This system may not be used alot in your area, but it is used alot around the country.
 

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This system is used by contractors quite often. If formed properly there will be no materials left behind under the slab. This system may not be used alot in your area, but it is used alot around the country.
NJ, what is the interior formed with, foam insulation?
 

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Discussion Starter · #12 ·
Hello again - got busy and couldn't check back for a couple days. Great discussion so far! Couple of responses below:

Anti-wingnut: The 'bell flare' is the term the Village's plan reviewer used. This is where it gets tricky to me - the trench is dug 8" wide and then at the bottom it is supposed to flare to 12", forming a integral footing. This also answers jomama's concern, because with that kind of structure below ground it will not be lifted - more likely the ground will crumble. I guess you would call it a slab with a 42" downturn.

jomama - I walked through the process with my sub a couple times and it is an earth wall form with forms(above ground) around it. There is no form or material below ground and BTW - jomama too!

b-wilson - Thanks for the insight, but as this is an attached addition to a house and we have the freeze problem up here in Chicagoland I need to be below that with any supporting wall.

Anymore thoughts are appreciated - this is helping me to visualize the problem and process. I called the local rental shops and they have a digger that has a 8" bucket to make the walls of the trench pretty accurate and smooth (the labor vs. rental equals out anyway) and then go back with hand tools to make the flare.
 

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We pour monolithic floors all the time with no problems.Use a trencher for the ditch it will cut a nice smooth wall.We don't bell the bottom but it could be done easily by hand with a trench shovel.The fun part is laying on your belly reaching down the ditch to tie rebar to the verticals,we use 2 rows.No forming material is required in the ditch unless using radiant heat in floor in which case you would probably want ridgid foam around outside perimeter to isolate concrete from cold ground.Some people will pour the ditch first leaving rebar stick up to tie the floor in with later but I feel it is best to pour it all as 1 pour (monolithic) if at all possible, but sometimes the size of the pour won't allow it (not a problem around here but some codes may require a single pour)
 

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We pour monolithic floors all the time with no problems.Use a trencher for the ditch it will cut a nice smooth wall.We don't bell the bottom but it could be done easily by hand with a trench shovel.The fun part is laying on your belly reaching down the ditch to tie rebar to the verticals,we use 2 rows.No forming material is required in the ditch unless using radiant heat in floor in which case you would probably want ridgid foam around outside perimeter to isolate concrete from cold ground.Some people will pour the ditch first leaving rebar stick up to tie the floor in with later but I feel it is best to pour it all as 1 pour (monolithic) if at all possible, but sometimes the size of the pour won't allow it (not a problem around here but some codes may require a single pour)
What's your frost depth requirement?
Are you saying you can do this as an addition to a house that has full frost protection, or you use this system on a detatched structure?
 

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I would just dig the trench 1' wide and eliminate the bell at the bottom.

What little extra cost is in the concrete, you will save in labor. Or you could dig it 1' wide and pin 4" of insulation to the upper portion of the trench. Save some on concrete, get a little r-value.
 

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What's your frost depth requirement?
Are you saying you can do this as an addition to a house that has full frost protection, or you use this system on a detatched structure?
We have a 32'' frost line,while some towns would allow additions with this type of footing we use it mainly for detached structures.
 
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