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Information on basement dig

Martinex

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Joined
Dec 6, 2016
Messages
12
Location
missouri
first time digging a basement gotta do it some time. I have friends that are experienced and going to help out, I didn't plan on it but bid it and got it. Have questions about digging the footings and finding grade 9' walls, 6" floor. How deep does the footings need to be and how wide? It's a 41x46 any info will be appreciated they don't have any plans on grade or any surveyors going to be me and the concrete guy laying it out.
 

Shimmy1

Senior Member
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Aug 14, 2014
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4,258
Location
North Dakota
The concrete guy should know how thick the footings will be, here in ND they usually use 2x8 forms, set them a half-inch or so above the highest point in the cut. Then, after laying the draintile around the outside, along the center footer (if it has one; it should at over 40' wide), and placing the sump, 5-6" of pearock is placed on the inside and around the outside, and the floor is poured on top of that.

So, if you have 8" footings, and 9' walls, the top of your wall will be 9' 8". At this time, the future homeowner needs to decide how much of the basement he wants sticking out of the ground. If someone asks me to look at a site, I bring my laser and survey the entire property. I usually set the preliminary grade height for top of wall at around 6" higher that the highest point on the property, and go from there. Keep access roads and any nearby (closer than a hundred yards) highways or township roads in mind as well. You don't want your driveway to be a conduit for water right into the garage.
 

digger242j

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Oct 31, 2003
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6,628
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Southwestern PA
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Self employed excavator
The rule of thumb that I learned is that footers should be as thick as the block, and twice as wide, i.e., for a wall built of 12" block, the footer is 12 inches thick and 2 feet wide. (Here in western PA. block foundations are the most common. I do understand that in other parts of the country poured concrete walls are the norm.)

One builder I work for wants 3' of overdig outside of the walls. Any others I've worked for want 2'.

Similar to what Shimmy said, you need to figure out where the first floor deck is going to be, and measure down from there. Thickness of the floor doesn't really factor into the excavation, as generally the bottom of the floor slab will be at the top of the footer. (6" sounds pretty healthy for a basement floor. I've never seen one thicker than 4".)

One thing I'll add is that anywhere that the bottom of the foundation will be close to ground level (a walk out basement door, or basement garage, for instance), the footer must be trenched below frost depth. Locally that's 3 feet. I'm not sure what it is there.
 

Martinex

Member
Joined
Dec 6, 2016
Messages
12
Location
missouri
thanks guys. This isn't a walk out that's why I was kinda stumped on what depth it should be dug cause, if I look at a walk out they have been on good slopes, so I just find where the floor would be and just cut back from there. But this one with no plans and not having a concrete contractor to ask questions so i figured I would ask on here. I bid it at 7'-8" but I think prolly going to have to be 8' deep. Leave 18" above cause the road is higher and will have good run off towards house. And laying drain tile around center footer? House is designed pretty well a rectangle. Will they run a footer through the center or just around 4 corners? I appreciate the info guys. I'm 22 and got a skid loader and mini excavator buissness going and having to teach everything my self besides a couple old guys I have got in good with. Just trying to get my information right. Thanks again ben
 

Martinex

Member
Joined
Dec 6, 2016
Messages
12
Location
missouri
Also they call frost line in Missouri 22-24" the government does any way, I do quite a few cattle water systems for them. But if it's for some one else I try to stay 30-36" deep. Same thing for fence and setting poles. But that's what they call for and it's water line! Lol
 

digger242j

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Oct 31, 2003
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6,628
Location
Southwestern PA
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Self employed excavator
If there are no plans it's pretty difficult to make any hard and fast statements on what to do. What does the homeowner want as far as how many steps it is down from the front door to the front yard? If they only want one step, you're going to need to go deeper than if they'd like four or five steps.

Keep in mind too, that you're going to have plenty of dirt coming out of a hole that size. You might get away with digging 6' deep and grading up around the completed walls with 2' of dirt and still only have 1' of foundation sticking out of the ground when you're done.

A house that big will almost certainly have something running through the middle, whether it's a bearing wall on a footer, or some structural steel, which would call for posts resting on pads, but generally speaking those would all be at the same level as the footer around the perimeter, so once you're done digging they're the responsibility of the concrete guys.

One other thing to consider, and it may not be a factor here, but might be some other time, is whether you have to get into an existing sewer lateral. Sometimes you have to find the end of the sewer and calculate up from there. Sure, they make pumps, but if raising the house a foot makes the difference between flowing into the sewer by gravity alone, or pumping, it's worth figuring that out in advance.
 

Martinex

Member
Joined
Dec 6, 2016
Messages
12
Location
missouri
Okay I understand now. So pretty well up the home owner how he wants it. So I got some questions to ask now.
 

redneckracin

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May 19, 2010
Messages
574
Location
Western PA
Occupation
Civil Engineer
Good luck getting the answers from the homeowner. Very few know much about anything when it comes to building a house. I'd try and find out what type of walls are going up as well. Superior walls need extra depth for stone placement (potentially an extra foot and extra width to get the phi angle). Footers do not need as much depth. I've personally never heard of a 12" footer for a house buts its a dam good idea. I've always heard 21" or the width of the block plus a set amount. I think the IRC sets how wide its needs to be now if its in a permitted area.
 

movindirt

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Sep 5, 2013
Messages
672
Location
under a shady tree
Our area requires a 16" wide footing x 8" thick, with a 8" thick poured wall centered on the footing. I didn't see in the above conversation, is this house in the country or in a subdivision? If its in a subdivision they usually plan the heights out from the start so nobody puts a house in a hole, some I've seen have a top of foundation height off curb height.
 

old-iron-habit

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Nov 22, 2012
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4,233
Location
Moose Lake, MN
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Retired Cons't. Supt./Hospitals
Check your local codes for minimum sizes and depths. Allow enough of a over dig around the outside for the basement contractor to work, install drain pipe if required, and above all make sure your slopes are within compliance. Safety first. Our basements have to be 8 ft here unless 4" of foam is extended horizontal out 4 ft and the building is heated. There is no one size fits all. You will get your education on the first one. If you are doing the backfill make sure you know up front whom is bracing the foundation.
 

GrandpaScott

Active Member
Joined
Sep 22, 2011
Messages
25
Location
Minnesota
Occupation
Septic System Designer/Installer/Inspector
I'm in agreement with previous comments. I'm in northeastern Minnesota, so pretty much straight across from Fargo. We've been digging 5' 8" to 6' to bottom of footing, depending on concrete guy (8" or 12" is their preference). 5' walls in the ground is typical. Waterlines up here are 6', typically, when in a yard, 9' under driveways.

If bottom is wet, a couple of the concrete guys want 1-1/2" drain rock to walk on, and set their forms on. Helps minimize disturbing original soil (mud).

Some of the concrete guys swear by tile through the footings, while some absolutely don't want to create a potential conduit for water to get inside the perimeter.

What digger242j said, sewer line is a critical benchmark. On city sewer, it is what it is. I'm rural, and a septic system installer, and we keep those fairly close to the surface (tank with 2' - 3' cover, pipe invert 3' - 4' below grade, respectively).

The concrete guy is who you have to make happy (which I've found to be challenging, no matter what :p ). It seems that a crawl space, or half-basement excavation is okay with 2' of working room, while a full basement demands the 3' of space outside of wall.

If you like the concrete guys, digging a ramp, or stepping down an access for them is usually appreciated.

What old-iron-habit said - know who's doing the bracing! I'd add that you want to exercise patience, as well (allow curing time). A concrete guy that I work with, that I listen to the most, wants at least a week, in mid-summer, before he wants me doing any backfilling.
 

CM1995

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Jan 21, 2007
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13,248
Location
Alabama
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Running what I brung and taking what I win
Back when I was in the residential side of the industry I wouldn't backfill a basement until the first floor was framed - at least sill plate, joists and subfloor. By that time it would be over the minimum 7 day cure period as well.

Digger gave same great advice here -

One other thing to consider, and it may not be a factor here, but might be some other time, is whether you have to get into an existing sewer lateral. Sometimes you have to find the end of the sewer and calculate up from there. Sure, they make pumps, but if raising the house a foot makes the difference between flowing into the sewer by gravity alone, or pumping, it's worth figuring that out in advance.

One auto parts chain I've done several sites for has a note on the utility page that places the responsibility on the GC to locate the invert tie in of the san. sewer before construction is started. If they fail to do so they can be on the hook for the cost of a pump.
 
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