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Question DetailsAsked on 4/15/2014

Cost to dig out and construct a 1100sft basement under a existing home on a crawl w 3 beds 3 window wells an bath

Would like to move furnace water heater and water softener down as well. Then also to add about 8ft out off of back off home w New basement under that as well finish off w New Windows and siding

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3 Answers

Voted Best Answer
8
Votes

For this type of job, you need plans and specs from an Architectural/Engineering firm before thinking about contractors - and to get a building permit.


Ben's method would work and done incrementally could cost well over $100,000 plus as he says, but this not really the most economic way to approach this big a job. A House Mover or Foundation Underpinning specialty company can usually slide your house onto a whole new foundation, or jack it up on steel beams and hold it there while a basement is dug underneath it, without any intermediate piers. The jacking/move cost would probably be on the order of $30-40,000, and a new basement probably about $40-50,000 - rough ballpark, though I have been involved in some 1000-1500SF single story jobs that went for under $70,000 total.


I have been involved in a fair number of these type jobs - and the way the numbers come out, if there is room on the property to move the house, it is almost always nearly as cheap or cheaper to build an equivalent square footage (basement plus ground level) addition rather than add a basement under the house, and that way your new footage is half above ground so worth more on resale, plus you do not lose use of the house for a month or two. Second cheapest is usually sliding house to a new foundation, if property is large enough to do this - though house is totally cut off from utilities for a week to three. Most expensive, and usually only done in tight city environments or with full 2 story or higher houses, is adding the foundation in place, though your utility interruptions should be on the order of hours at a time rather than days or weeks.


Talk to an architect - I think you will quickly lean towards the addition option rather than adding a basement - it is just too expensive to deepen foundations in most cases, plus you WILL get cracking in the house and possible water and sewer pipe problems in a move/underpinning job, which is not the case with an addition. This become more likely the case since you want to add 8 feet off the back of the home anyway - so why not just enlarge the addition and do it all that way - MUCH simpler, and MUCH less disruption of your life, and you get much higher resale return on your investment.

Answered 2 years ago by LCD

1
Vote

YOU are looking to spend a Pile of money .

Doing simple math , 28x40 =1120 sf .

In order to remove 1120 sf of earthen spoil from underneath an existing structure is going to require an enormous amount of temporary cribbing , using railroad size cross ties for cribbing or 6x8x4 timbers which cost about 20.00 each @4 foot lenght . To stack these 9 foot in height creating a Pier to rest your home on while removing the spoil ,and you'll need about 4 cribs every 8 feet ,rough math = 18 timbers x 4 = 72-timbers for each pier x 4 = 288 timbers, 288 x 6 peir sets= 1728 x 20.= $34,560 in timbers alone .These will be reset every 24 feet or so ,and then moved up successively as you Frame and pour foundation walls ,which will probably cost $60.00sf , pour 24x9 x 8"foundation each pour= 162 cf x $ 60.00 sf = $9720.00 or you could pour footers and set block walls under the home frame exterior, which would require you to pour footers on each side simultaneously and then set cement blocks to create a foundation wall on each side as you continue to excavate and reset your timber cribbing and so on and so on..................................The point being ,you are opening a can of worms attempting to remove the earth from beneath your structure and run the risk of the piers collapsing while attempting such a daunting Task.Of course we are NOT counting Architectual or Permit cost nor real labor costs !


Were we to run out the numbers completely , I would dare say and venture a quess between labor , material and equipment costs you would easily invest $ 150.000 to $185,000 in RAW costs ,much of which would be in material you could only resell to a Home Mover .


Your best investment , would be to relocate to a new home with a full basement

and give up the idea of digging out from under your home .

It is a grand Idea ,and as there are numerous contractors seeking work , I am sure you could find many wanting to accomplish the task,,,,,,,,,,,,BUT , The risks Out weigh the benefits ,unless of course ,You got a pocket full of money burning a hole through your pockets and creating enormous discomfort for You !

All of that being said ,It's YOUR Dream ,and if you desire , Follow IT !

Answered 2 years ago by BentheBuilder

8
Votes

It has been awhile (2000) since it was done to my 2 story house but it ran me $17,000 to have the house lifted, dug out, concrete poured and set back down.


I did do the electrical and pumbing and added a knee wall so my overall basement was 9' tall. 6' conctete with a 3' knee wall.


The original house (950 sq ft x2 for the second story) had a 6' partial basement under the front 1/3 of the house with the rest had a crawlspace under it.


Be aware that cracking of existing drywall WILL happen.

Answered 2 years ago by loghome

2
Votes

THIS JOB COULD BE DONE FOR 38,000,ANY QUESTOINS FEEL FREE


Answered 1 month ago by BENNYRED




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