Digging out basement?

Submitted by MRMAGOOONTHE5 t3_11dnqfh in DIY

I've got a basement in a house I just bought but it's half poured concrete slab, half mounds of dirt and clay. The house was built in 1940 and is on a cinder block foundation. Some of the dirt half is at the same level as the concrete side, but then there are mounds of it that come just shy of reaching the floor joists, and then a massive pit underneath the main water drain probably 6 ft deep. No idea why it looks the way it does. I think I want to excavate and make it all level even if I don't pour concrete it would be nice to not have dirt mountains and be able to put down a proper vapor barrier.

My question is what are the odds of these being "load bearing dirt mounds" helping to hold the foundation in place. If I start picking these apart and flattening it out am I going to cause some problems? There is no exterior basement access so everything will be hand dug.

149

Comments

You must log in or register to comment.

Interesting-Past7738 t1_ja9pq89 wrote

You need to get an assessment from a structural engineer.

206

thecarpenter t1_jaa6fvd wrote

This is the way. I do this day in day out with geo's and structural firms. Depending on what finding they arrive at will determine the scope. This could turn out be a very costly build. Without any information of your situation I could loosely suggest that you wall off the slab edge with a standard exterior envelope if you can justify the that the slab square footage will benefit what you're after.

29

Internet-of-cruft t1_jaasz8h wrote

You absolutely cannot dig out that dirt on your own without some proper support. If you just try doing this on your own you might have the structure collapse on you.

A structural engineer can tell you if it can be done and specific methods for supporting the home during the dig out.

22

merc08 t1_jabf6in wrote

I have a crawlspace under my house instead of a basement. Is it theoretically possible to get it reengineered and dug out to a full height basement or is that just a recipe for collapsing the house?

3

AttorneyAdvice t1_jabvql5 wrote

yes, just make sure to watch some YouTube videos before you do

5

ClassBShareHolder t1_jacdwgl wrote

They move houses all the time. You can absolutely lift the house, put a full basement, and set it back. The question is, is it worth the cost?

5

Lord_Quail t1_jacisk8 wrote

Underpinning is generally the best option for that. But connect with an experienced contractor in your area.

2

Megas3300 t1_jae851h wrote

It can be done, basically lifting the house off the foundation, and rebuilding it(or just making the foundation taller).

On a smaller scale It’s been done to homes around me to get 1-2 more cinderblock layers in the basement to make it more habitable. I know of at least one case where somebody did this by themselves with a whole bunch of harbor freight bottle jacks.

I’ve also seen where an entirely new basement/foundation was installed adjacent to the home, the house moved on to the new foundation, and the old foundation then demolished.

2

Direct_Big_5436 t1_jacgvps wrote

You can back pour cement walls using a “shutter box” and have a full basement. It will take some engineering and I would hire a contractor that specializes in doing such.

1

javeryh t1_ja9s5tt wrote

I live in a house built in the 1920s. Had a (maybe) 6' basement made out of a mix of brick, cinderblocks and clay. Water down there every time it rained. I hired a structural engineering company to design a plan to dig down far enough to give myself 8' finished ceilings for my home theater. I had 2 choices - underpinning so I could dig right up to the foundation walls (basically use the full footprint of the house) or come in from the walls as far as I wanted to dig down and leave a ledge all the way around the perimeter. I went with the second option because underpinning was like 5x as expensive. The ledge ended up working out just fine because I left all of my utilities against the walls and then built interior walls with closet doors/fake countertops to hide the ledge. Looks like the whole room has 8' ceilings - you can't tell. Anyway, this was a very very complex and costly project.

Hire a structural engineer. Do not attempt this yourself.

EDIT: Here's a pic of the "ledge" and how we had to get creative to dress it up. The drawers work and the doors open but the lower cabinets are mostly filled with concrete. There is about 8" of space on top of the ledge and under the drawer for storage but from looking at it you would never know.

And here is a pic of my equipment closet, which has the ledge inside but it's a regular door that goes to the floor.

75

LogicBobomb t1_jaa9iwb wrote

Great solution to that problem, nice work

12

ntyperteasy t1_jaafbhb wrote

I would guess (only a guess, worth less than you paid for it) that someone had to dig out the main drain to replace/fix it and just left the "spoils" there when done. If that is correct, then there is no harm in putting it back (if you are convinced the drain is working correctly, not leaking, etc.) Loose dirt is not going to be doing anything structural. And, of course, if the mounds of loose dirt don't touch the joists they also aren't doing anything.

The proper path forward is to get a structural engineer out for an inspection and consult.

And definitely keep an eye on that drain - are you sure it isn't leaking or easily obstructed so that the previous owner wanted it easy to get to?

31

itman404 t1_jab15um wrote

Mine was like this. Made extension to house. Dug out footings and left old dirt.

3

NotAvailableInStores t1_jaatra8 wrote

Some years ago a guy in my neighborhood decided to dig out his basement without consulting anyone at all. House started to fall in due to foundation failure, it was a shut show. Get an engineer.

17

timetoremodel t1_ja9q0o3 wrote

You are really going to have a pro come and assess the situation and give you recommendations.

13

Horfire t1_jaak8j3 wrote

Do you have my house?

Seriously though I'm in the same situation. I've just decided that the cost to do it right is not worth it so I left it alone.

My neighbor is a contractor and ended up digging out his basement to put in a two room apartment. Was really nice until it rained and he had 2" standing water. Renters moved out.

13

meatpoi t1_jabb4t6 wrote

Licensed contractor here. Only saw "Digging out basement?" and "diy" and just wanted to stop by to say... No.

11

KitNumber17 t1_jaa3d3j wrote

Without seeing pictures, they don't sound like they're structurally integral, but Geotechnical engineering is a dark art. Definitely get professional advice before excavating anything on the underside of your house.

9

tigerCELL t1_ja9sldb wrote

Whatcha got there are some burial mounds in your basement and a sacrifice pit.

8

RL203 t1_jac9o27 wrote

My house was built in 1922. I could not walk in the basement without constantly ducking my head (I'm 6'-3" tall). I was always hitting beams or HVAC ducts or bare light bulbs (always fun when you are bent over for some reason, stand up and take out a light bulb with your head).

I underpinned my entire house coming away with a basement that now has 8'-6" of headroom.

It's a long story and if you are interested, I can tell you how I did it later as I have to get my ass out of bed and head out just now.

But I will tell you this, the pay off is worth it but it is dangerous if you do it wrong. Think stages. Lots of stages.

4

led76 t1_jacb6bv wrote

How expensive per square foot was it to underpin and dig out if you don’t mind saying? Or maybe just how expensive was the initial structural engineer consultation?

1

RL203 t1_jaczkja wrote

I am a licensed professional engineer (structural) in Toronto and I did my own design for both permitting and construction methodology. So it was free (figuratively speaking).

If I was to be asked to do a design for underpinning a basement my fee would be 10k to 15k which would include hiring a geotechnical engineer to do a borehole and give me a report on the soil I'm dealing with. Drawings would be signed and sealed, suitable for permitting and construction with all specs on the drawings.

As to the cost per square foot, I have no idea. I took a month off work and hired a foreman and two / three pairs of hands and paid them all by the hour. I also laboured / directed with the crew.

Work included new main sewer, new basement drains, some waterproofing, subdrains, excavation, new columns and footings, new concrete floor on 2 inches of SM, vapour barrier, crushed stone subfloor, new water service, plumbing work, and all new electrical panel and associated rewire.

100k to 125k (I didn't keep track of just the underpinning, it was part of a much larger renovation. I kept a spreadsheet of the entire project, which I'm still working on. So my price is an estimate.). Price does not include finishing the basement.

It's a lot of hand digging, staging, pumping of self compacting concrete, etc.

2

led76 t1_jad3uaf wrote

Thanks so much! That’s very helpful

1

Thoreau80 t1_jabhqys wrote

If the dirt mounds are “just shy of reaching the floor joists,” then they are not “load bearing.”

3

mdmaxOG t1_ja9wlz9 wrote

yea, basement walls and foundation walls are two different things. especially with cinder block. The dirt could very well be a factor in keeping that wall from bowing.

2

UncleLazer t1_jab3p22 wrote

I have had my basement dug out below me in a two story house while living in it with my wife and young kids.

So it is totally doable.

Step one is to spend a couple grand on a structural engineer. They will go from your attic down to see whats up and make sure whatever is done is safe.

2

q-bus t1_jab62vp wrote

You also probably want to get a radon test if there is a lot of exposed Earth in your enclosed basement

2

keyserv t1_jaareaw wrote

I wouldn't. If you take away too much dirt you could condemn the place.

Just leave it alone.

1

dickpickdan t1_jadfm13 wrote

This is a common project where I live in Baltimore. It usually costs at least 100k. Requires a structural engineer. If you have a local Facebook group for home improvement etc, you should ask around there.

1

beazzy223 t1_jadjk7e wrote

As others have said, get an engineer to come and scope it out. I hired one to check out a foundation on a rental property. $550 bucks saved me 50k in foundation work.

If you are really dead set on doing this without help make sure you build temporary over engineered structural supports around your work site. Do small sections at a time. I honestly wouldnt do it without an engineer.

1

surgycal t1_jadqxsc wrote

they took the bricks out to burry someone down there my man, that's just the extra dirt left

1

ComradeGibbon t1_jaemhvb wrote

I'm going to go out on a limb here and say the massive deep pit and the mounds of dirt almost touching the floor joists are related to each other.

1