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Old 03-05-2010, 11:09 AM   #1
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Determining Depth of Existing Footer/Foundation


I have a 1930's DC brick rowhouse and will soon be adding onto it. It is necessary for me to ascertain the depth of my existing footer/foundation. Seems obvious to me that I should dig next to the foundation of the house until I reach the bottom.

Is this this right way to go? Are there any risks? I would assume I'd like to fill the hole ASAP, do I need to do anything special? Any suggestions, tips, warning would be much appreciated.

Also, any thoughts as to what I will find? What sort of footer/foundation was typically employed? Current min/req foundation depth is 30", is the current depth likely more or less than that? Thoughts? Wagers?

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Old 03-05-2010, 01:56 PM   #2
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Determining Depth of Existing Footer/Foundation


One of the easiest things to do is call L&I and ask them what they want to see. My inspector will let me shoot him some digital pics.

Please do not dig up anything without finding out from someone (i.e. Engineer / mason) of how far to dig wide and deep. In Philadelphia i have to clear it with utility companies before I dig, so look into that.

Your house is attached to others so any catastrophic failure will affect your joining neighbors.

If you have an architect/engineer they can walk you through the process.

Good luck

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Old 03-05-2010, 02:40 PM   #3
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Determining Depth of Existing Footer/Foundation


Lemon-

Thanks for the reply.

Please forgive the ignorance, but what is L&I?

My architect doesn't seem to know the answer to this and the nature of the project hasn't required an engineer, hence turning to this forum. I am really sensitive to doing damage to my home or others, but had envisioned a relatively small small hole for exploratory purposes. What do you usually do?
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Old 03-05-2010, 03:28 PM   #4
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Determining Depth of Existing Footer/Foundation


[quote=stubits;410124]Lemon-Thanks for the reply.Please forgive the ignorance, but what is L&I?quote]

I would take a guess on Licenses and Inspections.
Your codes are probably different to ours, but we would dig out the footings to the required depths for modern foundations regardless of how shallow the existing is.
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Old 03-05-2010, 03:30 PM   #5
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Determining Depth of Existing Footer/Foundation


Thanks! Here we need to match existing footings for certain applications.
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Old 03-05-2010, 03:31 PM   #6
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Determining Depth of Existing Footer/Foundation


In my experience on mostly commercial projects, we use a small excavator to dig a trench adjacent to the footing for exploratory purposes. However, as previously noted, it is essential that you obtain Dig Safe permission first, as there are likely to be utility lines in the area, and hitting a gas line will be the end of your happy day. You may also need a permit from DC since you may be digging in the sidewalk.

It is possible to do exploratory holes using small augers, however you are not likely to be able to determine the exact details of the foundation. There is absolutely no way I would hazard any kind of guess what you will find for a footing. Possibly someone expert in the practices of the 1930's could help, but personally I would not rely on a guess for anything more than a beer wager at the local pub.
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Old 03-05-2010, 03:38 PM   #7
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Determining Depth of Existing Footer/Foundation


Your advice is always great Daniel, I look forward to your well informed responses around here.

This will actually be at the back of my house, so no public property involved. Also, all the utilities, gas, electric, sewer, water enter through the front, so little chance of damage. Also, it is a walkout basement at the back of the house, so I would be surprised if the foundation/footing extended much more than 3' below grade. Frost depth is currently defined as 30".

I really just need to know the depth of the current footing/foundation, not much more than that. Would it be risky/dangerous/foolish/unproductive, to dig a 1'x1' (approximate) hole next to the foundation and go down until reach the bottom of the foundation? I figure I can do this relatively easily by hand if it is only 3', no?
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Old 03-05-2010, 04:45 PM   #8
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Determining Depth of Existing Footer/Foundation


As well advised above... Call be for your DIG. We can all be surprised by
where the Eminante domain Utilities stick things.

Stake out your addition and ask them to come check... you will need to do this anyway.

1930's every area was different as to how well codes if any were enforced. Rowhouses I have seen in Philly from the 1920"s look rock solid.

DC as I recall from history class, was built on or near marshland.

Start with a post hole digger 4-6" off the wall. Code folks may want to
know how wide your footer is also. ( Are you one or two story?) I would dig a min of 4' away from the bldg corner... away from windows above..( one side that is coming down anyway is easier to deal with than two incase ......it happens.) Dig only what you need to get the info required.

Always plan for the worst thing to happen and be happy when it doesn't.
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Old 03-06-2010, 08:40 AM   #9
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Determining Depth of Existing Footer/Foundation


Thanks! Will definitely call before I dig. The reality is that the addition is all within the basic footprint of the home, we are enclosing a small 5x10 "court" (as the code people call it). The addition will actually be 3 stories as our home is 2 stories plus a walk out basement.

I will be doing most of the work myself, but will be hiring out the foundation work. When they masons come to do the excavation, can they figure of the existing footer depth at that time? Or do we need this info in advance? Typically?

As far as digging 4' from the corner and avoiding doors and windows, that will be tough, the house is only only 15' wide and along the back there are 2 windows and a door on each of the first two floors.
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Old 03-06-2010, 10:20 AM   #10
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Determining Depth of Existing Footer/Foundation


Permit folks like to see that kind of detail in the plans so they know your design is based on sound practice. Your foundation contractor will need to know what he should be doing. Most contractors would not like to slow down to wait for plans and design change permit approval. Tie-in to existing foundation and a detailed foundation plan would be expected by most permit offices.

Buried unforseen and hidden obstructions can make for surprises ( why did they bury all the original construction rubble there? or I wonder in what ice age that monster bolder got left there.)

Pick a spot you feel is safe (follow the structural load) and dig only what you need to get the info required.
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Old 03-06-2010, 10:52 AM   #11
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Determining Depth of Existing Footer/Foundation


Get DIG to locate the buried utilities (gas water, power, cable, etc.).

Do not rely on the codes on something that old. You never know if they were followed. Also prescriptive codes usually give minimums, but the actual situation can be greater. On a construction site it is frequently necessary to go deeper for footings or wider if the soils (rubble, etc.) or water table dictate that.

Without reliable information, a contractor may bid more to cover the uncertainties.

Dick

Last edited by concretemasonry; 03-07-2010 at 08:53 PM.
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Old 03-07-2010, 08:45 PM   #12
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Thanks everyone!

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