I am considering building a workshop under my house. Have to dig out
the dirt.
I will be digging down anywhere from 3.5' to 5.5' under existing
foundation.

Plan to pour new wall under existing foundation. Will have house
resting on crib and beams.

Do not want to take out existing foundation. Walls are from 3' high
and go down to 18". Would prefer to make new wall under old
foundation.

PROBLEM: I will have to undermine the existing foundation. Remove
dirt. While this is in process, is there any way that I can support
the existing foundation? It seems that the weight of the foundation
will be to heavy for the crib and beams support system.

1) pour columns and footing with rebar in them. Every 8'. Columns
will then be hidden/buried in the TOTAL foundation pour. COLD
JOINTS? Leakage, Unstable foundation due to two pours?

2) Steel bar with plate on top and bottom? How thick would the bar
have to be?
Steel bar placed on footing. Bolted under old foundation?

3) I have looked up permajacks. To expensive to leave in the concrete
pour.

Was trying to dig out and have one continuous pour for the new
foundation.

The other thought was to pour the new foundation in sections. Jam
rebar 2' into dirt adjacent to new wall form. When wall is poured,
rebar will be exposed when digging out the next section. Attach next
set of rebar to new wall. Was advised that this may allow water
leakage in cold joints. Planning to us a meridrain system against the
dirt (outside of the new foundation wall).

Any suggestions?

Mark

wrote in message
ps.com...

Any suggestions?

Mark


You would have to be nuts to try and do this job yourself.

wrote:
I am considering building a workshop under my house. Have to dig out
the dirt.
I will be digging down anywhere from 3.5' to 5.5' under existing
foundation.

Plan to pour new wall under existing foundation. Will have house
resting on crib and beams.

Do not want to take out existing foundation. Walls are from 3' high
and go down to 18". Would prefer to make new wall under old
foundation.

PROBLEM: I will have to undermine the existing foundation. Remove
dirt. While this is in process, is there any way that I can support
the existing foundation? It seems that the weight of the foundation
will be to heavy for the crib and beams support system.

1) pour columns and footing with rebar in them. Every 8'. Columns
will then be hidden/buried in the TOTAL foundation pour. COLD
JOINTS? Leakage, Unstable foundation due to two pours?

2) Steel bar with plate on top and bottom? How thick would the bar
have to be?
Steel bar placed on footing. Bolted under old foundation?

3) I have looked up permajacks. To expensive to leave in the concrete
pour.

Was trying to dig out and have one continuous pour for the new
foundation.

The other thought was to pour the new foundation in sections. Jam
rebar 2' into dirt adjacent to new wall form. When wall is poured,
rebar will be exposed when digging out the next section. Attach next
set of rebar to new wall. Was advised that this may allow water
leakage in cold joints. Planning to us a meridrain system against the
dirt (outside of the new foundation wall).

Any suggestions?

You can jack up and use cribbing on anything...just maybe not your
personally. The sectional method of underpinning is more common for
shallower excavations.

I think you need to call in some pros. Your workshop probably
wouldn't be so useful with your kitchen sitting in the middle of it.

R

On Mar 24, 7:43 am, "RicodJour" wrote:
wrote:
I am considering building a workshop under my house. Have to dig out
the dirt.
I will be digging down anywhere from 3.5' to 5.5' under existing
foundation.

Plan to pour new wall under existing foundation. Will have house
resting on crib and beams.

Do not want to take out existing foundation. Walls are from 3' high
and go down to 18". Would prefer to make new wall under old
foundation.

PROBLEM: I will have to undermine the existing foundation. Remove
dirt. While this is in process, is there any way that I can support
the existing foundation? It seems that the weight of the foundation
will be to heavy for the crib and beams support system.

1) pour columns and footing with rebar in them. Every 8'. Columns
will then be hidden/buried in the TOTAL foundation pour. COLD
JOINTS? Leakage, Unstable foundation due to two pours?

2) Steel bar with plate on top and bottom? How thick would the bar
have to be?
Steel bar placed on footing. Bolted under old foundation?

3) I have looked up permajacks. To expensive to leave in the concrete
pour.

Was trying to dig out and have one continuous pour for the new
foundation.

The other thought was to pour the new foundation in sections. Jam
rebar 2' into dirt adjacent to new wall form. When wall is poured,
rebar will be exposed when digging out the next section. Attach next
set of rebar to new wall. Was advised that this may allow water
leakage in cold joints. Planning to us a meridrain system against the
dirt (outside of the new foundation wall).

Any suggestions?

You can jack up and use cribbing on anything...just maybe not your
personally. The sectional method of underpinning is more common for
shallower excavations.

I think you need to call in some pros. Your workshop probably
wouldn't be so useful with your kitchen sitting in the middle of it.

R

The reason I ask, is that I have been to two architects, two
engineers, 4 contractors.
Everyone speaks from their own level of knowledge. Each being very
informative and accurate.
But the whole picture is not spelled out unless one asks all the
questions.

Just trying to find solutions to as many questions that come up for
me. All the drawings have been approved by an engineer. Supporting
beams/footings. The final question is one that I started with. How
to support the wall when I am digging out. How to support the wall
during the pour. The best way to do the job without spending a
fortune.

Mark

wrote:

The reason I ask, is that I have been to two architects, two
engineers, 4 contractors.
Everyone speaks from their own level of knowledge. Each being very
informative and accurate.
But the whole picture is not spelled out unless one asks all the
questions.

Most architects would not know where to start with that sort of
underpinning. It sounds like you're still shopping around for a
design. No one is going to offer complete details until you cough up
some money. If you've already paid for the design, and it's not
spelled out how the work is to proceed, you've only gotten half of a
design. If you have hired the engineer and they have not provided a
preferred method of underpinning, and left it entirely up to the
contractor, I don't think very much of your engineer.

Just trying to find solutions to as many questions that come up for
me. All the drawings have been approved by an engineer. Supporting
beams/footings. The final question is one that I started with. How
to support the wall when I am digging out. How to support the wall
during the pour. The best way to do the job without spending a
fortune.

My car is misfiring - what's the correct timing?
You just asked a similar question. No one knows what your house is
like, different areas of the country mean different things when they
say "foundation", soil conditions, etc. You get the drift.

What sort of contractors have looked at your project in person? Local
foundation contractors will have their preferred way of doing things
and will be familiar with local practices, construction and soil
conditions. They'll also probably have an engineer on staff or a
business relationship with an engineer. They'd be able to provide one-
stop shopping for your job. No one on a a newsgroup can compete with
that sort of head start.

Smaller contractors will probably opt for the sectional method of
underpinning as it requires less equipment. Larger contractors and
house movers won't blink twice at jacking your entire house up. BTW,
unless you have faulty foundations jacking the house up instead of
digging down, might be a better way to go. Zoning, cost and
aesthetics would be the main concerns.

Again, only a local contractor would be able to make the definitive
determination and tell you what things would cost.

R