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Deeper basement with stone foundation

Wrenovator's picture

My client wants to deepen the basement approximately 16 inches on a 1900 victorian with a stone foundation. The stone thickness measures approximately 20 inches. The current basement floor is concrete, believed to be a 2 inch thickness. The existing dimension from floor to bottom of joists averages around 6'-8", with the client wanting the ceiling height to become 8'-0". What kind of conditions at the footing am I likely to encounter once the excavation is started to remove the old floor and deepen the basement? I am thinking that a one-foot wide stem footing at the inside perimeter of the foundation will be needed to make sure it is stabilized. I've told the client he should also put in a perimeter drain and a sump discharge. Does anybody who's done a similar project have some advice?

(post #91457, reply #1 of 15)

It's always a challenge with these old homes.

It could be that you have no or little footings under the stone foundation to start with.

If I was looking at this job, I would have to dig a hole in one of the corners of the house BEFORE I would commit to anything. Dig it down at least 3 feet and leave overnight.

It will tell you the conditions of any footings, soil, water table and drainage.

THEN you can put together an informed and intelligent plan of attack.


(post #91457, reply #3 of 15)

Odds run close to a hundred percent that there is no footer. Destabnilizing the soils close to the bottom of the wall could be dangerous, depending on the soil type. I would want a soils engineer on hand when digging the hole.

Sometimes, the reason cellars were only dug so deep is because it wasn't easy work without modern equiptment but around here, they dug until the water appeared. That means that going deeper involves an underwater plan.

I have done this by entirely replaceing foundation walls in segments, twenty or more feet long at a time.

Crib up to support

Excavate wall and immediate area like for new.

Place steel adjustable posts under sill and on precast concrete donuts set below the level of the intended footer.

Pour footer over and around them.

Pour wall on footer with steel post remaining within wall. This concrete wall goes to sixteen iches below footer for me which is about ground level.

Then we lay concrete blocks up to sill. Exterior finish is either parge coat over the block or stone to match old foundation type.

Not easy or cheap.


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #91457, reply #2 of 15)

I should imagine that the stone will have a tendancy to want to crumble if you dig under it.. I tried to stabalize a barn once with a stone foundation.. what a disaster... I wound up digging a hole and pouring cement while I shoved the stones back in place.  The corner that had crumbled had a corner of a  barn dangleing in mid air.. . I spent a whole month digging holes and dumping cement.   Forget about adding rebar on some schedule,  if you get to the bottom under a few stones and none fall out,  quick pour cement.

(post #91457, reply #4 of 15)

In these parts, when deepening a basement within a stone foundation, the excavators will not remove soil within perhaps 6-10 inches of the wall, depending on the soil stability.  A  kneewall is poured around this remaining undisturbed soil to protect it and hold it in place.  Typically there is no wide footer to contend with, just stone laid on undisturbed soil.


Where are we going, and what's with this handbasket?

(post #91457, reply #5 of 15)

If I understood the story right, Andy C was pouring onme of those buttress walls and had the weight of it cave the rubble wall in. Rubble walls are so unstable. That's why I prefer to support the house before I start anything and then replace it entirely.


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #91457, reply #6 of 15)

The kneewalls used around here aren't poured against unsupported flieldstone foundations, they only cover and stableize the exposed soils, extending not far up the original foundation.  How high was Andyc's walls?  I bet that was a real drag.


Where are we going, and what's with this handbasket?

(post #91457, reply #11 of 15)

I had one small section of wall cave in "under a basement window". There was a huge flat stone that jutted out from under the window sill. I think the weight of the concrete on that stone toppled the wall. Was about a four foot wide section by about five feet high.

 Outside of knocking my new washer and dryer across the dirt floor everything was ok..actually I ended up with that room in the basement having a concrete floor now in our temporary laundary area. Blessing in disguise. I poured the entire side and front perimeters with no more problems.

   If the wall is rubble rock and not cemented I wouldnt mess with digging under it. What I did was pour a wall next to..on the outside of the rubble wall after cleaning out the dirt between the stones. After a section was poured up against the existing rubble rock wall I shoved a giant dil....I mean vibrator into the wet concrete and vibrated the cement into the existing stones. I think it did a great job of firming up those walls.

   If your willing to go to that expense (cost me almost six grand) as a first step and then putting house jacks under one corner at a time and a few more, maybe a four foot length at a time and poring concrete under the existing rock with rerods sticking out ready to tie the next section in, then you can probably do it. Dont think its worth the expense or energy.

  I only did it to keep my 1680 house up another 323 years.

Be a wall



"Attachment is the strongest block to realization"

(post #91457, reply #12 of 15)

Tadpole here is still looking for a reason why the simple solution, seen repetetively in 100+ year old homes (at least in these parts), is not a good idea.  Biggest disadvantage is loss of effective floor space around perimeter.  Advantage is low-tech and relatively low cost.  Last one I saw was dug out by hand over a summer by a home owner and sons, then had the contractor finish up kneewall and slab.

Please excuse crude drawing as illustration:


Where are we going, and what's with this handbasket?

crudedrawing.jpg24.03 KB

(post #91457, reply #13 of 15)

Nothing wrong with crudedrawing especially since this is crude work ;-)

You helped me to understand what you were saying. I was thinking in terms of what I show here. I'd probably think of what you demonstrate as a curb. It contains the soil that is acting as a footer to keep it from moving. Walls like this do fine when placed on undisturbed soil and compress from their own weight for all these years but once the soil next to them is disturbed, water moving through the base ground can move the fines with it and weaken the soil structure. Your curb retains the fines and prevents water movement to some degree.

What I show and describe as a buttress wall is poured with a one sided form and the concrete is vibrated into seams and opennings in the rubble to encapsulate it and brace it off. Not normally done when going deeper. Yours might work for a smaller home and decent soils. A three or four story house or masonry building on clay soils might challenge it.


Excellence is its own reward!



Oh Well,

We did the best we could...

rubblewall_buttress.gif3.84 KB

(post #91457, reply #14 of 15)

A few years back we were called to a 200 year old stone home that was having an addition installed by another contractor. The excavator had dug a hole for a full basement  in the addition next to the existing home. The existing home had a 6' basement ceiling, so during the digging process they dug about 2' below the botttom of the home's stone wall. They had about 30' of the stone wall exposed in this way when suddenly the entire stone wall three stories high shifted outwards about 3 inches. The excavator quickly filled the hole back in to save the house. We were called in to fix the problem and finish the addition  It took shoring the whole side of the house from the inside and then we had to tear down 3 stories of stone. The fact that there was a spring underground contributed to the problem.


carpenter in transition

carpenter in transition

(post #91457, reply #15 of 15)

Self disposing idjits - gotta love'um.

They were wroking hard to take care of their own execution and burial, complete with headstones


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #91457, reply #7 of 15)

Get a house mover and have him jack up the house now you remove the old walls and floor with a bobcat. With that gone you now pore a footing and walls to what ever hight the person wants. It will take a lot less time and be safer then working on one wall at time have to worry that the wall will collapse on you. You don’t have to go any deeper either just make the wall higher.

You may have to rent the beams from the house mover for 30, 60 days wile the concrete cures to a good strength.

(post #91457, reply #8 of 15)

depending on the site conditions, existing house and local ordinances, I agree it might be better done this way. Even possible to elevate house permanently.


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #91457, reply #10 of 15)

Did you see that program on PBS about Chicago  about 1840  they decided to deal with sewage instead of dumping it on the street.  They found out they had to jack up every house and building it town.  including a big hotel and restaurant. The hotel was 130 bed or some thing like that.  They used 1000 screw jacks and 250 people to do it.  They did not want to disrupt business.  according to program the people kept on eating in the restaurant while they jack it up. 

(post #91457, reply #9 of 15)

I had the same issue, 2 years ago in a restoration project. The existing foundation was good and it was on a footing.  The house was a big, brick, colonial style, built in 1910. The basement had about 6 ft. clearance. The job was to replace the floor, and install a new perimeter tile to a sump. The option of deepening the basement was considered desireable, if it was feasible. At the end of the day, the cost and implications of excavating below the existing footing were just too problematic. We did the work, and the basement turned out just great for its original purposes - support for the house, service access for utilities and storage. Now that its continually dry down there, the old place will probably last forever. enjoy the day, h.