# Underpinning Basement Standoff Jacks / Supports For Inside Acess Only?



## rsvp

About half of our basement sets on a 16" wide shaped limestone wall held together with mortar from the 1870s. It extends just over 4 feet and sits on undistributed compacted dirt. We are wanting to underpin the wall in this area of the basement to achieve full 8' foot tall walls by digging the existing wall out in 20" wide sections. Each section would first have a 8" x 20" x 16" reinforced concrete footer placed on the bottom. On top of this would be placed a reinforced 2 cement block wide and deep column which will be filled with cement. The remaining gap between the existing limestone wall and the block underpinning would be filled with expanding concrete.


 As a extra safety precaution I'd lid to use a temporary brace under the section of limestone wall section from which the dirt will be removed. Based upon years of driving forklift this could easily be accomplished by placing a single forklift fork under the wall section with an additional extension added to the fork to provide access (cribbing would of course be placed under the fork since hydraulics do fail). Using an actual forklift is; however, not an option due to cost and access issues.


 I've looked at foundation jacks; which are essentially piles with a "L" shaped lifting shelf attached to them; however, they are not an option as they are placed on the outside of the foundation and because they would provide no working access if placed inside. The shelf used on these jacks are also too shallow as we want support to extend under the full width of the wall.


 I've previously experience building our own four car garage and attached shop by hand including digging the foundation and basement entrance by hand. Its been over 10 years and no cracks, even in the sidewall, as build stuff to last and do the proper research beforehand.


 Anyone aware of a jack or lift that might work for such a situation. I've not quite found anything to date. About the only thing that might come close is a manual scissors pallet with an extension placed on one of the forks; however, one might have problems with finding the right fork and the fork would need to be able to support around 4,000 pounds as each section of limestone would weigh around 1,500 pounds. Of course each section of the wall is partially supported by neighboring wall sections but its better to be safe than sorry and one needs to account for the amount of leverage caused by focal point.


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## nealtw

Welcome to the site. Can you post photos of the wall.


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## slownsteady

My first thought is jack up the house and rebuild a whole new foundation. Why do you want to preserve the old foundation?


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## rsvp

slownsteady said:


> My first thought is jack up the house and rebuild a whole new foundation. Why do you want to preserve the old foundation?



One half of the house sits on 18" thick limestone foundation that is full height. The other half is of the same construction wall, but extends just over 4 feet to be below the frost line. The existing wall is massive, solid, and has never leaked unlike many modern walls which use hollow blocks.

There is no reason to replace the existing foundation when underpinning would do. The new basement entrance we put in, which connects to our attached garage/shop, is made from a group of older 3 chamber cement blocks recycled from a barn, which are reinforced in rebar and filled in with cement. Cement blocks with a footer would be the easiest method to complete based upon previous experience as the process could be completed in steps at any time.

The only question is developing a temporary adjustable height moveable brace as an extra precaution.


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## rsvp

nealtw said:


> Welcome to the site. Can you post photos of the wall.



We live in an area whereas the base ground layer under any dirt is limestone. Older houses are built with pieces of limestone taken from the ground and roughly shaped into rectangles and square of various sizes which are then joined together with mortar. This is not the finely polished blocks you see in say a county courthouse; however, nor is it a unstable rubble wall consisting of rounded field rocks simply stacked on top of each other.

Here is a quick illustration. The pattern seen on the limestone is a generic adobe illustrator pattern and not actually how it appears - its a series of roughly squared blocks of various sizes which are mortared together.

The plan here is so dig out 20" or so wide sections and to lay a 8" deep footer. On top of each footer is placed a cement block column that is 2 blocks wide and deep. The footers are tied into each other with rebar. Each column is ted to the footer with rebar. The columns will be filled with cement and reinforced with rebar.

The underside of the existing limestone wall is not perfectly horizontal thus the gap between the blocks and limestone wall will vary. What we are looking for is a jack or lift to place under the section of limestone wall above the column we are currently wanting to install. This jack support should contact the underside of the limestone wall at one or two points in a similar fashion to a forklift. It needs to extends the full width of the 18" wall, with any vertical bracing being positioned inside the basement and standing off from the interior of the wall to provide access to the wall.

The final gap between the limestone wall and block columns will be filled with expanding cement in two steps. First, areas around the jack support will be filled, but not quite touch the jack supports under the wall. The jack supports will be removed once that cement is cured and the unfilled areas where the jack supports were will be filled.

I am looking for a safe methodical approach here. Currently the areas where the blocks are shown is composed of undisturbed compacted earth which partially extends into the basement as a series of flat top earthen embankments covered with a thin coating of cement. The top of each embankment is around 18" with a wider base. The top "shelf" was used to store canning jars and other goods back in the day.


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## nealtw

rsvp said:


> We live in an area whereas the base ground layer under any dirt is limestone. Older houses are built with pieces of limestone taken from the ground and roughly shaped into rectangles and square of various sizes which are then joined together with mortar. This is not the finely polished blocks you see in say a county courthouse; however, nor is it a unstable rubble wall consisting of rounded field rocks simply stacked on top of each other.



So you will be digging down on both sides of the wall?
You are concerned about the blocks falling while you are working under there?
Would the stone be big enough to be one block reaching inside to outside?


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## rsvp

nealtw said:


> So you will be digging down on both sides of the wall?
> You are concerned about the blocks falling while you are working under there?
> Would the stone be big enough to be one block reaching inside to outside?



Here's a better illustration of what we are looking for in terms of a jack.

1. Remove a 20" wide top portion of the cement over the dirt to expose the bottom of the limestone wall.

2. Drill one or two holes in the dirt under the bottom of the wall.

3. Insert horizontal jack arms in the hole or holes.

4. Raise the arms using the jack.

5. Remove a 20" wide column of dirt.

6. Insert cement footer.

7. Build block column.

8. Fill in most of the gap between the underside of the limestone wall and the top of the block wall. This will require temporary spacer wood to be placed next to the horizontal jack arms so they are not cemented into the wall. 

9. Remove jack arms.

10. Remove temporary wood spacers.

11. Fill in the remaining space or spaces where the jack arms or arms were.

12. Repeat the process for the next section.

In regards to your questions:

We will digging from the inside only.

Yes, we are concerned about the bottom of wall giving way.

The limestone is of various sizes and are fit together like a 3D puzzle held together with mortar. There are no stones which would span the entire depth of the wall. There are no stones which would span the width of area to be excavated.


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## nealtw

I understood all of that, Weight dissipates from the load into concrete at a 45* angle so compacted dirt would have to be more like 60* well into the area where your jack apprentice is sitting.
A fork lift uses weight and leverage to lift a load. Have you considered the weight you will be putting on the foot print of that jack if you could get enough weight to counter the weight you are holding.
The one way you could get the balance is to prop back to the wall but that would be adding stress to the wall that you are holding.
Are you open to other ideas?


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## slownsteady

To be clear: if I understand the premise correctly, you will not be lifting the wall so much as digging additional basement space below it and adding a block wall (built in small sections) underneath at the new depth. And you want to do this all from the inside. Do I have this right?
I'm only trying to get a clearer picture of the project because it is sort of intriguing.
have you calculated any loads for each section?


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## rsvp

nealtw said:


> I understood all of that, Weight dissipates from the load into concrete at a 45* angle so compacted dirt would have to be more like 60* well into the area where your jack apprentice is sitting.
> A fork lift uses weight and leverage to lift a load. Have you considered the weight you will be putting on the foot print of that jack if you could get enough weight to counter the weight you are holding.
> The one way you could get the balance is to prop back to the wall but that would be adding stress to the wall that you are holding.
> Are you open to other ideas?



The illustration is just a quick mock-up of of how a jack would need to be positioned and not anything I've actually built. The actual jack would need a lot of extra support such as more extensive frame connected, a wider support base, and some type of counterweight.

A 20" x 16" x 48" section of the wall at 169.2 pounds per square foot of limestone weighs in at 1,504 pounds. Any of the gas powered forklifts I've driven in the past could do this easily with a fork extension; however, that not really an option.

Essentially what the original builders did in the 1870s was dig out a pan shaped depression in the dirt inside the basement for a root cellar and cover it with a cement-like layer. The dirt below the cement is undisturbed and still compacted from the thousands of years it has sat there. The floor in this area is only about 2" deep in this area as its essentially the same skim coat they placed on the walls.


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## rsvp

slownsteady said:


> To be clear: if I understand the premise correctly, you will not be lifting the wall so much as digging additional basement space below it and adding a block wall (built in small sections) underneath at the new depth. And you want to do this all from the inside. Do I have this right?
> I'm only trying to get a clearer picture of the project because it is sort of intriguing.
> have you calculated any loads for each section?



Yes that is correct.

Each 20" x 18" x 48" limestone wall section weighs 1,504 pounds based upon the cubic weight of limestone. I'd round it up to 2,000 to be on the safe side.

The mock-up of the jack was not intended as a actual plan of anything to be built but just to illustrate the requirements of some type of support system - its has to extend under the full width of the wall at one or two points and any vertical support has to stand away form the wall to allow access.

The last illustration included a quick mock-up of a jack sh


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## nealtw

My first thought was much like slownsteady but but hold the house up with temp walls or post and beam and take the wall out and replace it at full depth.
# 2 was to bolt a long channel iron across the lowest set of stone to stabilize them hence the question about the size of the stone.
The other thing we have seen is to dig out the basement leaving so many feet at the wall and build a short retaining wall to hold the dirt in place.

Your thinking about the dirt may be right, but there is dirt and then there is dirt.
When we build new houses a geo tech engineers inspect the soil for type and stability and drive a rod in to judge the resistance. And then they determine the size of the footing we put in.
House next door to each other in undisturbed soil can have very different footings.

We do know that the soil is carrying the weight  but then you have to consider the moisture, some soils get stronger when it drys out and others need moisture or a certain percentage.

So looking at your plan what if you dug it out like your plan  but were able to drive small I beams into the dirt  on the outside and and block up the inside.
The mortar should hold the wall together, you are just looking for insurance.


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## nealtw

There is one other consideration.
As you pointed out , they dug a trench and just built a wall there and the soil on both sides add support. the wall was never meant to be a retaining wall.


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## rsvp

nealtw said:


> My first thought was much like slownsteady but but hold the house up with temp walls or post and beam and take the wall out and replace it at full depth.
> # 2 was to bolt a long channel iron across the lowest set of stone to stabilize them hence the question about the size of the stone.
> The other thing we have seen is to dig out the basement leaving so many feet at the wall and build a short retaining wall to hold the dirt in place.
> 
> Your thinking about the dirt may be right, but there is dirt and then there is dirt.
> When we build new houses a geo tech engineers inspect the soil for type and stability and drive a rod in to judge the resistance. And then they determine the size of the footing we put in.
> House next door to each other in undisturbed soil can have very different footings.
> 
> We do know that the soil is carrying the weight but then you have to consider the moisture, some soils get stronger when it drys out and others need moisture or a certain percentage.
> 
> So looking at your plan what if you dug it out like your plan but were able to drive small I beams into the dirt on the outside and and block up the inside.
> The mortar should hold the wall together, you are just looking for insurance.



Thank for your input.


 When we built our attached 24' x 36' garage plus a small bump-out to contain a new basement entrance connecting the basement to the garage via hallway closed off by doors we used a 16" x 8" footer with just over 4 foot foundation walls under the main 6" floor slabs. This would be code in a larger city, put technically not required in this small town whereas a permit consists of drawing a crude outline of your addition on a paper and paying a $10 fee, LOL.


 We decided to build the entire garage ourself based upon what contractors wanted to do. The first foundation contractor that did ane stimate wanted to dig a trench pit in the ground and pour cement in for the foundation walls with no footer or rerod - all for $15,000. We opted for own custom built plywood and wood forms using screws and double-headed nails so that we could reuse much of the materials. We built the entire structure for less than that.


 This has not cracked in over over 10 years as its reinforced with steel. The soil appears to be rather uniform over the lot, consisting of undisturbed very hard black soil for the first 8 feet. At 8 or so feet one starts to see some small rounded sand particles and rounded stones which have been there since the glaciers deposited this material. Below that, although, we've never seen it, will be limestone. I do understand about soils changing though - one farm parcel sells for $8,000 an acre and the one nearby sells for $12,000 due to differences in the soil over a small area.


 I think a smaller I beam as you suggested might do the trick. A hole could be first drilled under the edge of the wall and the end of the I beam inserted into this hole. The I beam would be inserted into this hole and jacked up. The jacking part could be accomplished by building a steel frame and cage designed be picked up with a standard pallet jack. The interior of the cage could be filled with counterweight which could be a number of things such as extra rock chip base normally placed under the footings or extra limestone blocks I have. This also would allow the apparatus to be easily moved. My dad's a certified welder so that is a bonus.


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## rsvp

nealtw said:


> There is one other consideration.
> As you pointed out , they dug a trench and just built a wall there and the soil on both sides add support. the wall was never meant to be a retaining wall.



Here is a breakdown of the basement which uses the same 18" deep limestone walls. We've replaced the floor in the full basement area with a new 6" slab. The root cellar has perhaps 1 or 2" of old cement. The crawl space has no floor as is hardened soil - its black soil but you need a pick to break it up. Part of the crawl space at one time housed a rain cistern which was filled in with limestone debris probably when when they put the water lines in back in the 1930s.

 There is also a partial internal wall between the crawl space and root cellar but that does support anything - it was added to keep vermin from entering the crawl space and then entering the root cellar. This internal wall actually needs to be removed as its caused a joist to be pressed upward as the house has settled over the years, causing a small hump in the bathroom floor.

The full width of the basement is not shown to scale.


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## nealtw

All I know about soil, is that I don't know about soil, all I know is that engineers pick it squeeze it and look at it and say something like Hmmm, poke a rod into it a few times and go away and write a report on what they want us to build. And is some cases they want dirt to be removed and replaced with gravel. We worked one house , the hole cost 30 K before got in there. :help:

The tall walls in the full height basement are likely down some distance below the floor and and the floor joists add support to the top. that is what makes it a foundation and not a retaining wall.

So with your wall when done will have a bend factor in the middle as it will be or maybe hard to get the kind of joint you want.
And If you get a good joint then you are saying every joint in the old wall will withstand the force against it.
And maybe it will take that force but you don't trust it to hold together while you dig below.

There may be a reason we can't find a video on this job.

I am just trying to share all my fears so you can think about things you may not have touch on.


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## rsvp

nealtw said:


> All I know about soil, is that I don't know about soil, all I know is that engineers pick it squeeze it and look at it and say something like Hmmm, poke a rod into it a few times and go away and write a report on what they want us to build. And is some cases they want dirt to be removed and replaced with gravel. We worked one house , the hole cost 30 K before got in there.
> 
> The tall walls in the full height basement are likely down some distance below the floor and and the floor joists add support to the top. that is what makes it a foundation and not a retaining wall.
> 
> So with your wall when done will have a bend factor in the middle as it will be or maybe hard to get the kind of joint you want.
> And If you get a good joint then you are saying every joint in the old wall will withstand the force against it.
> And maybe it will take that force but you don't trust it to hold together while you dig below.
> 
> There may be a reason we can't find a video on this job.
> 
> I am just trying to share all my fears so you can think about things you may not have touch on.


 

 Thanks for the information as two heads are better than one!

I thought about your point about having a good bond between the old wall and any extension wall placed below as this will be the weakest area in regards to resisting any pressure placed on the outside wall by exterior soil.


 I think perhaps it would better to modify the current prototype set of plans per the following illustration. Keep in mind the old wall's block is a simply a generic pattern from Adobe Illustrator and not how it actually looks. The actual limestone wall is made of roughly squared blocks of various sizes layered in interlocking pattern.







 This plan would reproduce a portion of existing shelf that protrudes into the basement by extending each block column into the basement the width of a 8" block. A additional block wall would be added on the interior of the existing limestone. The block wall would be tied together with rebar. The block wall would be tied to the limestone wall using embedded anchors and rebar at various points. This should tie the entire structure together and prevent any failure and has the advantage of providing a flush interior wall.

In regards to our garage we removed the existing dirt down to a depth below the frost line. This was all done by hand with shovels and wheelbarrows, including the new basement entrance. We used a layer of what around here they call "3/8 fines", which is a mixture of rock chips up to 3/8", to form a base under the footers, which we added a couple inches at a time and compacted. After the footings and foundation walls were completed we filled in the area between the foundation walls with the same material, compacting every 2 inches in depth. We then let the material inside the foundation walls settle until the next spring and added a small amount of further compacted material before pouring the garage slabs over the top. This allowed the rain to further compact the material by washing smaller particles in between the existing micro gaps. We would in a similar fashion be placing rock chips under the footings, but not waiting until the next spring for each section to settle :0)


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## nealtw

I think the only way you can do it is with concrete a bigger footing may be another  10 inches and 10 deep with two rows of rebar bent to connect  to the new wall and drilled and tie into the blocks.

Like you picture coming up inside the block wall but only up about 8 inches above the bottom of the bottom of the block


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## rsvp

nealtw said:


> I think the only way you can do it is with concrete a bigger footing may be another  10 inches and 10 deep with two rows of rebar bent to connect  to the new wall and drilled and tie into the blocks.
> 
> Like you picture coming up inside the block wall but only up about 8 inches above the bottom of the bottom of the block


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## bud16415

I havent been following this thread until today and will throw in my 2 cents for what it is worth. Around here we have a lot of shallow field stone basements / crawl space. A lot are about 6 deep and because the frost line is about 4 and they were hand dug or with horses they went about 4 deep and then used what they dug out to raise the ground level around to about 6. People were shorter and basements were never intended as living space in the 1800s. Many are still like this, ours is. In the 40s and 50s when people didnt mind doing hard work and being farmers they had time in the winters and many dug them deeper and built the wall with the shelf to sit the canning jars. All the ones I have seen built a retaining wall in a couple feet out of blocks pinned and filled, and then a cap on top. I have seen a variety of shelf depths and I assume they went back as far as they could before they felt the stone wall would fall and then stopped. That would depend on the soil conditions or maybe how many canning jars they expected. I suppose some people are still doing this and hauling the dirt out a bucket at a time. I have one bump out in our basement that has sloped down dirt with a crawl space above and I plan on doing a retaining wall and a cap there (old school) but it is only about 6 wide. 

Anything I see getting hired done now labor would kill you doing it this way. They go in now and brace a long section and remove it all and lay or pour a new wall many times working from the outside in. 

I know you dont want to do that and are looking for a way to stabilize the wall for fear of a fall in and plan on doing this in really small segments at a time to minimize the risk, and at the same time maximize the floor space you will be left with. 

I wish I had an answer for you on to how best crib and support that section and allow to safely build under it but I dont and I know it was suggested you contact a professional to advise on soil specs and such. I doubt they would give you the go ahead with a process for doing this also. They would just tell you carry the weight on some temp beams and columns with steel plates to spread the load take it down a section at a time pour a footer and build a new wall up. 

If I think of anything I will post back. Good luck and it is really good you are putting a lot of thought into this.


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## rsvp

Here's what the a portion of the wall looks like. The full depth basement walls are the same material.


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## nealtw

[ame]https://www.youtube.com/watch?v=I9dQ4pl5Ii4[/ame]


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## slownsteady

Nice find. If there is a way to contact this guy, he may have some advice. But notice that he did not try to undercut his foundation.


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## bud16415

There are a million done just like Neal&#8217;s video around here. It is a matter of how brave you are how far you dig back and trust soil to hold the wall up. You always end up with a shelf. The OP wants to hold a section at a time up and slip a new wall and footer in below it.


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## nealtw

His wall is mortared, why would you not treat it like brick?


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## bud16415

nealtw said:


> His wall is mortared, why would you not treat it like brick?



Well it is 100 plus years old and lots of this mortar was pointed in from the inside and outside to seal it up. It is an unknown. 

The only way I would trust doing something like this DIY. Stay with me Im going to paint a mental picture here. 

First crib the joists and jack up and take the weight of the house mostly off the foundation in the area where you will be working. Then drive steel under the lowest stone and past the outside of the wall a good 2 feet. steel could be ½ x 2. After getting an area large enough to work on done then drive a piece 3 angle iron in on top of the steel. I would space the steel every foot. I would then weld the angle to the bars I have driven in. now I would build some 45 degree bracing to run from pockets in the floor backed up with a good foot and weld or bolt that to the angle. Now you have a section of the wall braced in place from falling and the rig you just built is only holding the stone not the house as well. dig out that section and place footing and build wall. move over 4 foot and repeat. 

The problem in doing this is you assume the bottom row of stone was laid flat. Every time I have ever worked on field stone I always found they found some bolder they put in first and who knows if they didnt dig it down a little to get that one set in. with stone there is no reason to start with a flat footing as you correct all the way up the wall and end flat. 

I have seen a lot of old places taken down and when they get to the basement walls they roll them in a bury the stone. It never looks like it is too hard to do.


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## nealtw

bud16415 said:


> Well it is 100 plus years old and lots of this mortar was pointed in from the inside and outside to seal it up. It is an unknown.
> 
> The only way I would trust doing something like this DIY. Stay with me Im going to paint a mental picture here.
> 
> First crib the joists and jack up and take the weight of the house mostly off the foundation in the area where you will be working. Then drive steel under the lowest stone and past the outside of the wall a good 2 feet. steel could be ½ x 2. After getting an area large enough to work on done then drive a piece 3 angle iron in on top of the steel. I would space the steel every foot. I would then weld the angle to the bars I have driven in. now I would build some 45 degree bracing to run from pockets in the floor backed up with a good foot and weld or bolt that to the angle. Now you have a section of the wall braced in place from falling and the rig you just built is only holding the stone not the house as well. dig out that section and place footing and build wall. move over 4 foot and repeat.
> 
> The problem in doing this is you assume the bottom row of stone was laid flat. Every time I have ever worked on field stone I always found they found some bolder they put in first and who knows if they didnt dig it down a little to get that one set in. with stone there is no reason to start with a flat footing as you correct all the way up the wall and end flat.
> 
> I have seen a lot of old places taken down and when they get to the basement walls they roll them in a bury the stone. It never looks like it is too hard to do.



The problem with cribbing or temp walls holding up the house is working room, dig it out first or after, getting beams in there. Taking the weight off the foundation may not be a good idea, if the wall has out side pressure leaning in.?????????

And with the best laid plan, do the corners first or last?????


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## bud16415

nealtw said:


> The problem with cribbing or temp walls holding up the house is working room, dig it out first or after, getting beams in there. Taking the weight off the foundation may not be a good idea, if the wall has out side pressure leaning in.?????????
> 
> And with the best laid plan, do the corners first or last?????



My opinion at first is really the one I feel strongest about and that is do it the tried and true way with the 3 or 4 foot shelf. You can still walk around when done and store things and it is next to impossible to make a stone basement into useful living area. It is great for storage etc and to walk around to service pipes and a place for the furnace and tanks etc. I would take the same amount of money and effort to do more than that and build a nice building at ground level if I had the room to use for other things.


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