# Cutting out a concrete basement floor



## DUDE! (May 3, 2008)

Not to bust your bubble but you may want to pay a contractor to come out and give you a ball park figure for what you are wanting to do, let him know ahead of time you don't plan to do the work right now, hense you need to pay him something for his time to come out. You are talking big work here, don't think you want to be carring out concrete peices, that'll get real old real fast. You bought a 800 sq. ft. house and want to convert it to double the size, nothing wrong with that. And by no means is there anything wrong about future planning.


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## AllanJ (Nov 24, 2007)

Don't forget, when you excavate your basement floor, you will go below the level of your foundation footings. This could cause the soil underneath and also the foundation itself to collapse into the excavation. Not sure how the foundation is shored up to prevent collapse.

And, if you had and needed a perimeter drainage system along the outside of the foundation, you would need to install another such system along the inside of the foundation below the level of your new basement floor.


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## jeffhoward001 (Jan 6, 2009)

Thank you for the replies guys... Agreed it's a formidable task, and we'll definitely have a contractor give us a quote on the different aspects of the project as we start to solidify the details. We're definitely still in the "information gathering" phase right now. 

I'm not too concerned about the labor of breaking out the concrete. It's no doubt going to be hard work, but it's something I've done before on an outside slab and I imagine it's the same principle. My main concern is having the concrete cut properly around the edge of the foundation and the footings for the beams. We don't plan to do anything without a contractor's approval on what we can/can't should/shouldn't remove with respect to the concrete floor. 

Any manual labor portions of the project aren't a concern since we're not on a tight time line (since we're not using the basement right now). I'm more concerned with doing everything right, making sure that the cost/benefit ratio is there, and that we take all the necessary precautions to protect our house in the process.

Edit: I did some research on the footing, and it sounds like we may need to reinforce while excavation. This is definitely something I would discuss with a professional before removing any soil.

- Jeff

Has anyone heard of this being done?

- Jeff


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## concretemasonry (Oct 10, 2006)

When you remove the slab from a basement, you are removing a necessary structural element. The slab should be on the footing and prevent the foundation walls from moving inward.

The reason the slab should be on the footing (a floating slab) is because the common practice of some contrectore (mainly poured wall contractors) to not put any reliable connection between the footing and the wall that can resist the soil pressure.

Going below the footing is especially dangerous.

If you are interested enough in the resale, you may want to make sure the replacement slab and modifications are done properly and have some design professional to assume the responsibility and help get the permit that will be required now or when you go to sell.


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## jeffhoward001 (Jan 6, 2009)

We're definitely going to hire a contractor to assess and plan before doing anything, so I'm mainly trying to get a picture of what we're up against before putting the time/money into hiring a contractor.

Thank you for the reply concretemasonry, that definitely helps. It makes sense that structurally the slab would be functional in keeping the footing in place (especially on the daylight side of the basement). It sounds like how we handle the footing is the most important detail. We plan on going down about 24" (2 ft). I've done a lot of reading online, and it sounds like other people have gone 12" down with a small "curb" where they left 6-10" of soil. We definitely would not want a 24" curb, so I would need to do something else.

Is it possible to cut out and excavate in the middle, keeping at least 24" of soil around the parameter, then dig out sections (e.g. 6’x6’ sections) and pour them individually? In theory, this would keep solid ground around the footing, and allow us to pour new concrete around/under the old footing.


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## Garasaki (Apr 14, 2008)

jeffhoward001 said:


> We're definitely going to hire a contractor to assess and plan before doing anything, so I'm mainly trying to get a picture of what we're up against before putting the time/money into hiring a contractor.


I think what you may be looking for is a structrural engineer. You could schedule a half hour meeting with one to answer specific questions you have. If you have the original plans for your house, it'll make your job a lot simplier. If you don't have the original plans, try to see if you can dig them up thru your local municipality. I'd guess it'll cost 75ish bucks and you'll walk away with real answers to your questions and that should allow you to speak to contractors to price out the work. (FYI it's not really a contractors place to design something. Architects/Engineers serve that role and also assume responsibility if the design fails. Contractors responsibility is to build and they assume responsibility if the worksmanship fails. Contractors will not assume responsibility if they design something and the design fails)

This can be done. Anything can be done to a building if you throw enough money at it. Perhaps you'd also like to replace all your copper wiring with solid gold wiring? It's possible. Wether it's wise (well cost effective, or adds value) or not is a whole different story.

Are there any posts in your basement? Where do the stairs come down? (on the "edge" or right in the middle?)

Chances are, if you go thru with this, you will have a section around the outside that remains at it's original


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## 4just1don (Jun 13, 2008)

Is there ANY way,given the current housing market,,,you can 'buy' a larger house WITH a deeper basement?? Trade up so to speak. Another idea would be to 'buy' another(with not alot down) and rent this one (for as much as your payments are)to a reliable couple that would take good care of it,,till the market improves,,then sell it?? 

After you do the due diligent homework of propsed work,and analyse THAT cost,,,it would be WAAAAAAY cheaper IMHO!!! The hardest part is going to be supporting center beams while excavating and pouring new footings and center support. As well as the outside ledge left over from footings area!!

Unless your in some sort of different market,,thre are some whale of a deals out there!!! 'Smartest' strategy would be to 'BUY' all the homes you can afford to,for now. Depending how your 'rental' markt is at this point in time!! This housing downturn and economy isnt going to 'last' forever!!! Easiest path to get where you 'wanna' go!!!


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## yesitsconcrete (May 11, 2008)

UNLESS you can find a pe who's also a contractor, those're separate vocations,,, i wouldn't use the former for conflict of interests but would CERTAINLY call in a pe ( structrural ) 1st,,, not sure i'd pick an arch but that's just me & my background.

design/bld contractors are very common.


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## Garasaki (Apr 14, 2008)

yesitsconcrete said:


> design/bld contractors are very common.


This is true. 

I think you will find many of the design/build contractors have someone else assuming legal responsibility for the design portion. This fact would be found very deep in the fine print.


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## losttool (Dec 2, 2008)

This is an engineering job, Civil or structural. If you mess up the foundation it's game over. I liked the suggestion above trade up to a bigger house.:thumbsup:


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## jeffhoward001 (Jan 6, 2009)

It seems people always make the suggestion of buying a bigger house, but (IMO) that discounts so many factors that go into buying a property. We all buy houses as a form of investing... yup, there it is... But on my list of "reasons" for buying our current home, the "as an investment" reason was roughly #6 on the list... We bought in a nice, older area of Portland Or where nearly all the houses are around 50 years old, all the lots are around 10K+ sq ft, and you're less than 10 mins for downtown. 

So the theory of "buying up" into a biggest house really doesn't apply unless you either a) aren't really in love with your neighborhood or b) Are will to put yourself another 100K in debt to buy a biggest house in the same area.

I'm not saying it's a *bad* suggestion, I'm just surprised people are so quick to make the suggestion, especially on a DIY forum!!

Maybe my family just gets attached to their houses, or have a stronger stomach for remodels/expansions, but we've expanded/remodeled every house I grew up in and significantly increased the value by doing the majority of the work ourselves (In fact my Dad is adding about 1000 sq feet to a house built in the 1920's right now...).

Most of my friends from college were engineers, so I'll call one of them tonight to recommend a structural engineer to come take a look at our place.

Sounds like concretemasonry is speaking from experience... Is anyone else speaking from experience in trying a project like this, or just throwing in their 2 cents?

- Jeff


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## yesitsconcrete (May 11, 2008)

raising hand - my own 1864 house in upstate ny :thumbup: + did several similar projects in nj & pa


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## jeffhoward001 (Jan 6, 2009)

yesitsconcrete -

Thanks for the reply. So we'll definitely be hiring a structural engineer to make sure all necessary precautions are taken, and that we do the project right. My thought is, if I (or "we", I have plenty of friends to help) do all the back-breaking labor (concrete extraction and excavation) would the project still be expensive? As long as a professional tells me exactly how to reinforce the foundation to prevent damage, it seems like a pretty straight-forward project, albeit ridiculously time-consuming with lots of back-breaking labor. But I'm not in a hurry to get the project done as it's currently unused space in our house, and the pay-off is huge as we'd be doubling our sq footage. 

Can you give me a few examples of how a project like this goes? Everyone seems (understandably) cautious about how complicated this can be, but can you give me a few examples of where it gets complicated? Is my idea of doing it in sections ridiculous?

Thanks,

- Jeff


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## yesitsconcrete (May 11, 2008)

my house was easy - 2 friends in competing house-moving biz's split the job & we only lift'd 1/4",,, took time to properly support everything ( fireplace, boiler room, downstairs bathroom, etc ) but actual ' lift ' was easy ( radios, observers, experienced guy on the hydraulic jack manifold ),,, our nj pe partnered w/us,,, his method was steel-rein piles bearing against existing footing,,, wasn't particularly difficult - lots of bull labor, many curses in spanish & english, & we wore out many, MANY 5gal bkts til we got a small bobcat w/tracks :thumbup:

sectioning the work might work but i'd have to think about it,,, our cruise boat leaves tomorrow from fl & there's a bid opening at 2 this afternoon,,, maybe dick's got some ideas that'd help.


even i can't get 5gal of wtr into 4gal bkts


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## seat o my pants (May 2, 2009)

Just a thought, but instead of digging down, have you thought about going up. It's possible to raise the house up a foot or two, install additional foundation wall block, and set the house back down...and bingo, 8 ft basement ceilings, no footing issues, and the add on basement will match up. Just a thought.


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## jwms (Feb 18, 2008)

*another idea*

I'm a neophyte here so to speak therefore just throwing out something that may be way way off base to your current question and plans. 

If you go through with removing the floor etc.. and in addition thinking of future expansion plans it seems you are really rebuilding the house. Therefore what about demolishing the home and building a new one? I am throwing this out because it keeps you in the same location which apparently is key in your case and you get a clean start vs working around alot of preexisting issues.


Just a thought based on knowing nothing about the cost associated with demo and new build in your area.


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## Knucklez (Oct 21, 2007)

there is no way a contractor is going to tell you how to do the job and then let YOU do it. if it fails (water, collapse, cracking etc.) and you sue him? the job you speak of is too critical.

the only person that would take such a liability is a structural engineer. it is 400 to 600$ for consultation. and you will need permits and city inspection. so get them involved early, let the city know who your engineering firm is that you hired. 

Knucklez


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## Trailcharger (Dec 2, 2009)

*Lowering basement floor*

Hi I have done this and gone down two feet in my basement. The best way to do it by yourself is with underpinning the existing walls. I excavated the perimeter of my slab around 1 foot in width and made a 2 and 1/2 by 7 foot form and did seperate underpinning pours by working my way around the complete basement. What is great about this method is you only remove the dirt between the slab and the wall just before you do each pour so at anytime only 7-8 feet of area is technically unsupported. It also allows you to use the existing slab as a brace for the concrete form. After working my way around the basement ( took me approximatley 4-6 yards of concrete that I mixed) I then removed the whole slab and excavated down a 16 inches. After that I had a 4 inch slab poured per code and I gained a foot of headroom and now have 7 foot ceilings which is great. I don't see much of a need to go 8 feet but if you wanted to gain 8 feet I would suggest a combination of he underpinning / excavation and possibly looking into sinking your first floor beams and joist hanging the floor joists if they haven't been done this way. Consider also you will need to remove a lot of material. The slab is a project itself but the dirt below is a complete other ball game and you need to consider the material you are dealing with. You could run into rock,clay old debris concrete footings, ledge etc. Your slab may also have wire mesh in it which will be a pain to deal with. You will also need to pour lower footing for new lally columns. It can be done but it won't be easy. I did it all myself with the exception of pouring the slab which was only 15x 32 feet. I started the underpinning and excavation in May of 09' and finished last month. All being done nights and weekends. So be prepared for the worst.


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## Peter Carpenter (Oct 16, 2010)

*Sections . . . absolutley*

Your project may already be underway but I want you to know that your job should only be done in sections. Depending on your area, time between sections could vary though it had always been my understanding that opposite sides can be done at the same time so a small job like yours might take three cycles.
Cheers
Peter


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## Knucklez (Oct 21, 2007)

Trailcharger, you don't happen to have pictures of this do you?


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## jdmc33 (Jan 18, 2012)

Hey Jeff, 

Just wondering if you ever tackled your basement project. I am considering breaking up my basement slab, digging out a bit, and repouring a new slab with radiant floor heat. I would like to see that someone else has done it successfully.

Dan


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