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Old 05-18-2010, 06:57 PM   #16
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Digging basement to add headroom space


Really, jomama45: No one knows where the bottom of the rockwall ends, and if there is a footer to begin with. The owner is just busting out thin cracked concrete with a sledge hammer, digging down 16 inches. The main concerns here is the base of the rock wall, and to hire in a structural engineer that will take him to the cleaners, and will go far beyond what is necessary to protect himself is what will happen. The way I see it is the house has been sitting for a hundred years on dirt and digging down 16 inches next to wall won't cause the building to fall in. Now if under the wall is like digging into face powder, we have a different set of rules to go by don't we. So I take you of a man of experience , sop would you share your thoughts and detail explanations on how you would do "the base of the wall area". Not trying to be sarcastic, just trying to help my fellow man thats not afraid of blood sweat and tears.

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Old 05-18-2010, 09:40 PM   #17
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Digging basement to add headroom space


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Originally Posted by bernieb View Post
Really, jomama45: No one knows where the bottom of the rockwall ends, and if there is a footer to begin with. The owner is just busting out thin cracked concrete with a sledge hammer, digging down 16 inches. The main concerns here is the base of the rock wall, and to hire in a structural engineer that will take him to the cleaners, and will go far beyond what is necessary to protect himself is what will happen. The way I see it is the house has been sitting for a hundred years on dirt and digging down 16 inches next to wall won't cause the building to fall in. Now if under the wall is like digging into face powder, we have a different set of rules to go by don't we. So I take you of a man of experience , sop would you share your thoughts and detail explanations on how you would do "the base of the wall area". Not trying to be sarcastic, just trying to help my fellow man thats not afraid of blood sweat and tears.

If your original thoughts & suggestions were only meant for very small, exporatory holes, thats one thing. But, if those were recommendations on how to underpin the entire basement, which is how I deciphered them, they are way off base IMPO.

As for the footing under a stone wall, I'd bet dollars to donuts there is nothing there but dirt.

As for the depth of the wall below the floor, I'd bet there's next to nothing additional buried, except some dirt. Any possible excess wall that could possibly be under the floor is likely so deterierated from moisture, I wouldn't put any faith into it anyways.

Taking a wall that currently has about 40" of unbalanced fill and adding an additional 16" of unbalanced fill at the toe of the wall, & having it last for any kind of duration, is no simple walk in the park.

I've been in this trade long enough to have a healthy dose of repect for the possible issues & risks that are present in a job like this. Afterall, I've been on jobs similar to this, as well as many other underpins, & am luckily still here to talk about it.

I can't give any solid advice on a situation like this over the web, as it would be pure speculation w/o seeing the house firsthand & doing some actual troubleshooting, so why bother?

You may feel that an engineer is overkill on a job like this, but are you willing to put your stamp on this project & assume the liability involved? I know I wouldn't, even if I was contracted to do the work. I've worked far too hard to get to where I am to risk losing it all over a few hundred dollars for an engineer. I'd hope the OP would feel the same, as it is his own property value on the line.
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Old 05-18-2010, 10:12 PM   #18
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Digging basement to add headroom space


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Originally Posted by LU'S BASEMENT View Post
I heard that we need to leave about a foot of space undug next to the walls to avoid disturbing the foundation.
That's even more dangerous than "I heard that she can't get pregnant the first time."




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Originally Posted by bernieb View Post
Not to give you something else to "worry about" but I would do a test dig where your main plumbing enters under the concrete floor and see that the lateral pipe is deep enough for the new height. When your house was built a hundred years ago the plumbing code was different than today, and I have seen underground plumbing using "orange burg" clay like pipe 6" diameter "last forever" go house to house then after 3 or four houses go to the main sewer in the street. I doubt if you have a footer under the rock foundation ,but again dig a test ditch. I'd forget about hiring a structural engineer as long as you don't have running mud. Once your confident that the house won't cave in (haha) and I don't think it will ,you can dig down your 16 inches flush with the rock wall, and if a roto-tiller works use it. Once you have your depth you can use the concrete board half inch thick that Low's or Home Depot has to slap up against the exposed dirt wall under the rock wall ,then using 2x4's frame in for a footer of mixed concrete that will jam the base of the concrete board in. Put a small belly in footer next to rock wall, to carry away any water to a designated area to be pumped out if need to be. You can use light weight 4x8x16 core block ,2 rows high to get above dirt wall if there is one that is. You can overhang you studded wall when you build it ,stripping in for the block area. Figure your footer so you have a concrete slab rest for the floor.
This one started out good but turned into "OMG are you &%%& serious?!?!"

I wouldn't be dumb enough to do that even if I was smart enough to dig holes for column footers near the walls and supported the load that the existing stone foundation supported with a carrying beam on those columns.

Get the engineer. Get it done safely whether or not it means someone else does it. If you can't afford to do it right, you can't afford to do it.
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Old 05-18-2010, 11:10 PM   #19
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Digging basement to add headroom space


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Originally Posted by stuart45 View Post
Extending a home by digging out a new basement has become quite popular here, especially in London where building space for extensions is really limited and land really expensive.
Most jobs can be done, depending on whether it's cost effective.
I was wondering, have you heard of adding basements underneath existing slabs? Essentially it's mining operation, but there is considerable mining expertise there!
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Old 05-19-2010, 06:11 AM   #20
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Digging basement to add headroom space


So, some professional opinions are coming about, and I'm sure Mr home owner is listening. With all that said, and taking into consideration that I have seen in my days three floors high above grade where a gapping round hole of brick was knocked out 12 to 16 feet in diameter and a piece of machinery lowered to the ground. With that said, the set up brick acts as a supporting beam. So why then couldn't an underpin of concrete a foot wide and 90 degrees out from rock wall still keeping the sought after 16 inches of height,and having it for the slab rest also. Doing this 10 feet at a time, but having 8 inches of concrete beam so to speak, going underpin to underpin, poured all at the same time. The 8 inch beam is where the framed interior wall will set and hold back the dirt under the wall. Possibly doing the same on opposite wall ,bracing between with the framing lumber...............you boys are getting me smarter.
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Old 05-19-2010, 08:01 AM   #21
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Digging basement to add headroom space


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Originally Posted by xxPaulCPxx View Post
I was wondering, have you heard of adding basements underneath existing slabs? Essentially it's mining operation, but there is considerable mining expertise there!
I have heard of it, but have never worked on such a job so my knowledge is fairly limited. This may help explain the method.
http://www.diydoctor.org.uk/projects/digbasement.htm

I have seen a TV documentary where it was done and the HO called in an SE as he was worried about how the house was being supported. The SE thought that the house was in danger of collapse and recommended that they move out. The builders said that everything was OK and that they had yet to lose a house, and so they stayed and the job got finished.
It is a relatively new idea in the UK.

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