crawlspace to fullbasement


  #1  
Old 10-25-22, 10:29 PM
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crawlspace to fullbasement

Hello Everyone ,
i would like to convert my crawlspace into a fullbasement ,
i dont want to lift the house , but just dig inside and build a retaining wall to contain the soil and leave the house where is.
as homeowner do i need a structural engineer plan ?
im asking because i just had a quote , and they asked 14k for a plan.

thanks
 
  #2  
Old 10-26-22, 12:45 AM
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Are you intending to dig below the current footings?
 
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Old 10-26-22, 04:06 AM
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My grandfather did what you propose to his old farm house. He dug down a couple of feet from the existing stone foundation, poured a footer, blocked it up about 4' and the poured a concrete ledge between the new block wall and the stone foundation. That was about 60yrs ago and no permit/inspections were required at that time. I'm sure permit would be required today. The odds are all the excavating would be hand done - a lot of work!
 
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Old 10-26-22, 04:35 AM
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Any permit or other requirement is based on local rules but I would definitely retain a structural engineer. If you don't, who else would you trust to determine what is needed?

 
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Old 10-26-22, 05:41 AM
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Yes , my intent is to dig next to the existing wall , and build another wall 8ft high to get to a height of 8ft total. The purpose of the wall is to hold the soil under the concrete that hold the house.
i dont wanna lift the house or move it ,
i know i need a permit for it , but ny question is if i need a enginner plan or i can just pull the permit my self.

I had an enginner and it cost me $500 just to come out for prepering the quote, and yesterday he gave me a 14k quote just for draw the plan
 
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Old 10-26-22, 07:55 AM
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Sorry to suggest it on this forum, but not everything is DIY and replacing the support under a house is among them. And the permit process is probably the easiest part. I believe the issue is finding the right engineer. At $14K, the guy probably didn't want to do it. Keep looking.
 
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Old 10-26-22, 09:39 AM
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I can't imagine any inspections department that will permit the work without professional Engineering. It is one thing to dig a hole in virgin ground but you are talking about removing soil that is CURRENTLY supporting the house. The soil and your specific circumstances need to be studies in order to come up with a plan that will work. If you just start digging there is good chance that the side of your excavation will blow out and the existing foundation will slide/fall into the hole.

In my county the inspectors roughly go by a 45 rule. They draw 45 lines outward from the BOTTOM of the footer. The soil under that cone is considered to be supporting the footing and cannot be disturbed. If you want to dig in that area it needs Engineering.

Then the second big issue is the construction of the new basement walls. They will not be simple walls just carrying a vertical load. They must support the side loads coming from the soil with the side pressure because of the weight of the house. It will NOT be normal "wall" construction.

This is why it is often better and cost competitive to raise the house. This allows the area underneath to be excavated and new footers and walls constructed. That work can often be done without professional Engineering since it's very similar to new construction.
 
 

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