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Old 10-22-2012, 11:31 AM   #1
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Basement Lowering - Increase Height Info?


Hi,

There is a house I'm interested in purchasing; I'm just doing some research for future improvements I would like to make to the house.

The house has an unfinished basement, but the height is low around 6'3" by the joists and 5'9" by the beam that runs accross.

I did some research online and saw there are 2 methods that could be done to increase height: underpinning and benching.

1. If I wanted to increase height by 18"; what would be a ballpark figure of having this done to a 20x18 basement with "underpinngin" or "benching"?

2. I would rather use the "underpinning" method to not lose any space in the basement. However, I read that with "underpinning" it is a little more risky especially since you are messing with the foundation of the house.

Howe safe is "underpinning" if I were to hire an experienced contractor/engineer?

Thank you!

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Old 10-22-2012, 12:14 PM   #2
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Basement Lowering - Increase Height Info?


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Originally Posted by olimits7 View Post
1. If I wanted to increase height by 18"; what would be a ballpark figure of having this done to a 20x18 basement with "underpinngin" or "benching"?!
You likely won't get any useful answers on this site. Best to call a local contractor for a rough quote.

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2. I would rather use the "underpinning" method to not lose any space in the basement. However, I read that with "underpinning" it is a little more risky especially since you are messing with the foundation of the house. How safe is "underpinning" if I were to hire an experienced contractor/engineer?
Underpinning is done quite often and is as safe as the engineer/contractor are qualified. If properly designed and installed it is as safe as a newly constructed foundation. Make sure you hire people with documented and referenced experience with that type of work.

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Old 10-22-2012, 05:38 PM   #3
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Basement Lowering - Increase Height Info?


Underpinning refers to a technique used to temporarily support the foundation. There are numerous possible ways to underpin a foundation, one example would be to excavate beneath a relatively short length of wall, and install steel supports supported by soil beneath the foundation. There are many other ways to perform underpinning, however underpinning by itself is merely a support technique.

There are only two ways to raise basement height. One way is to lift the entire house up, and install new block or concrete around the foundation, then lower the house onto the new, higher foundation. Very pricey, very difficult work, should only be undertaken by very experienced contractors.

The other option is to excavate the floor deeper. This will create an unbalanced load on the foundation, which is prone to sudden and catastrophic failure in an unbalanced condition. The "benching" method you mentioned attempts to prevent foundation failure by digging at a slope from the foundation, or digging vertically but at a "safe" distance from the foundation. This is one way that open pit mines are constructed. A "benched" basement must be designed by an experienced engineer, and constructed by an experienced, competent contractor with lots of insurance, since mistakes can and do happen, which sometimes lead to catastrophic failure of the foundation.

The "underpinning" technique involves initial excavation underneath the foundation, temporary support of the foundation, and installation of a new foundation under the old foundation, typically concrete, but could be concrete block. After the foundation is extended the appropriate amount, the basement can be excavated to achieve the desired additional depth. This method is relatively common, but requires careful design, and a very experienced contractor with lots of insurance, since it is always possible for the temporary support to fail, leading to potentially serious damage to the house.

None of this is inexpensive. However, given the difficulty of the work, and the potential for catastrophic damage to the house, this is not the job you necessarily want low bid on.
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Old 10-22-2012, 05:59 PM   #4
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Basement Lowering - Increase Height Info?


Best to start by making sure your local building department will even allow this? Then you really should consult with an engineer, architect or building designer to see what you are in for. I suspect they will be willing to talk with you about the feasibility of the project for free or a minimal fee. If you decide to proceed, they should be able to refer you to qualified contractors that you might not find easily on your own. You are most certainly going to need drawings, load calculations, stamps, permits and inspections for this and they can provide invaluable help with such things.

What you hope to do is going to be neither a casual or inexpensive proposition and first thing you should probably ask is if it will be worth sinking the kind of money into the house. Assuming what you want could be accomplished. You might be better off looking for something with a more suitable basement if this is important to you.

This is a project where you really would not want to put much credence in price/cost estimates from even the most sincere of us. There are just too many variables and potential disasters hiding if this is not planned and executed correctly.

How old is the house and how sound is it structurally? Will the framing stand up to messing, even temporarily, with its foundation?

Last edited by user1007; 10-22-2012 at 06:03 PM.
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Old 10-22-2012, 08:22 PM   #5
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There are only two ways to raise basement height.



.
actually, there is 1 more way. completely replace the foundation.

i was looking at small ranch houses, with bad foundations. 2 contractors told us it would be around 40k to replace the foundation. so i figure it would end up costing over $50k.
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Old 10-23-2012, 02:39 PM   #6
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actually, there is 1 more way. completely replace the foundation.
He said that...
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Old 10-23-2012, 03:48 PM   #7
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Increasing your height can easily be done by underpinning the existing wall escpecially only 18". Small sections about 2' long aprx every 6' along the existing wall will be excavated and formed with a one sided form. Concrete will be poured in these sections. After they are cured the forms will be stripped and the areas inbetween these new finished supports will be excavated. 2- #4 rebar will be drilled in the newly placed concrete along with expandable water stop and one sided forms will be placed along the 6' sections of unpoured wall. After pouring and stripping the panels you will have a nice new smooth wall that will blend perfectly with your upper walls. On a building of your size I would quote aprx 16K. That would include all excavation and concrete work.
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Old 10-23-2012, 06:06 PM   #8
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Concreteman, I find it amazing that you would quote a price on a job you have not seen. For that matter, we don't even know where the project is located. There may be obstructions that would interfere with the underpinning operation. There may be ledge. Portions of the house may be built on incompetent soil. As a contractor, I would expect you to be very interested in the exact conditions, as they could drastically affect the cost of work. And as for saying the work is easy, well perhaps you have the required experience, equipment and understanding to make it easy, but from personal experience as a geotechnical engineer on many underpinning projects, my belief is it is never easy, it always requires an experienced contractor with local knowledge, and there are many ways to go horrendously wrong.
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Old 10-23-2012, 06:52 PM   #9
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I was not "quoting" anything. I am giving them a general guidline as to how much that project should cost on average with decent soil conditions and decent access. Nothing more.
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Old 10-23-2012, 07:44 PM   #10
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I might be off topic, but I'm curios about what is so special about this house that you are considering taking on this kind of a project?

Why not just keep looking until you find a house that suits your needs?
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Old 10-23-2012, 08:13 PM   #11
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He said that...
he said " One way is to lift the entire house up, and install new block or concrete around the foundation."

note "around". i take this to mean the existing foundation would still be there, wrapped by a new foundation. wrapped, not replaced.

perhaps just a wording thing.
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Old 10-24-2012, 08:28 AM   #12
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Underpinning for additional usable living space could possibly be the most expensive way to incur additional square footage. Why not consider a small addition, which would give you a full basement as well as first (maybe even second) floor space??
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Old 10-24-2012, 10:12 AM   #13
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note "around". i take this to mean the existing foundation would still be there, wrapped by a new foundation. wrapped, not replaced. perhaps just a wording thing.
Maybe just a wording thing. But "wrap" likely means adding to the top of the existing wall. If you are wrapping around with a whole new foundation then you'd just take out the old and install a new.

The hardest and priciest part of the option (either way it's worded) is lifting the house up. Once up whether you add to the top of the existing foundation wall or replace in its entirety is dependant upon the existing condition of the foundation, budget, and objective.
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Old 10-24-2012, 10:13 AM   #14
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Underpinning for additional usable living space could possibly be the most expensive way to incur additional square footage. Why not consider a small addition, which would give you a full basement as well as first (maybe even second) floor space??
Totally agree. Either bench it (basement) or build it (addition).

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