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Phil, Mechanical Engineer
Category: Home Improvement
Satisfied Customers: 8769
Experience:  Retired contractor, 51 years experience
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This is a question on slope of trenches around an

Customer Question

This is a question on slope of trenches around an excavation. I'm putting in basement but I'm close to the property lines and there are also big concrete porches on front and back sides of the house. I wanted to dig straight down in those places and also I am close to the property line on the west side. City of Portland said I would have to have 45 degree slopes down to the bottom of the trench. Bottom will be 8 ft below grade, and 8 ft out, which I can't do. However I', building engineered concrete walls and the PR Stae Codes division told me that engineered walls would be a NON PRESCRIPTIVE application and they couldn't make me go by code. THIS IS THE QUESTION!!! Very important, and I also would have to have test pits dug if if I want to be steeper than the 45 degree, IF it is prescriptive under the soil classification tables. But State of OR says engineered walls would not be in a PRESRCIPTIVE CLASSIFICATION> Who is right, and what should I do?
Submitted: 2 years ago.
Category: Home Improvement
Expert:  Phil replied 2 years ago.


You cannot dig the hole without the required slope, depends on a soil analysis however, but a slope is always required.

If you can dig the basement out so that only one or two sides are vertical and the other two sides are open to a much larger space, so that you are not in a situation where a collapse of the vertical side can trap a persons if it collapses.... then you could use engineered concrete walls.

If the basement area is so small, and enclosed on all sides by vertical dirt walls, then if one side collapses it could bury a person, that would not be allowed.

This would be allowed for example.

Look that over, let me know if it makes any sense on your end or not.... there are other things you can do however such as fitting styrofoam forms inside narrow trenching too small for a person to enter, the pouring those forms with concrete that may or may not be permitted in this case. We can look into that option.

We can go from here without a time limit.

Customer: replied 2 years ago.
I just looked at another Victorian house in the neighborhood where a major contractor is putting a basement underneath it-----and they have some six foot vertical excavations, a few feet away from the building line, but the front is all opened up with a modest slope. I am NOT going to raise my house up: it is 1200 sq.ft. footprint and big (8x18 ft.and 7X24 ft. by 16inch concrete porches). I can have slope on the east and west side, but it's still very tight: I would like to do something like go up four feet vertical, and then 45 degree slope. If worse comes to worse, I could just do a half basement, and then down the center I would have a framed wall, with the soil just sloped away whatever they required. I can also have about a 45 degree slope in the frontyard---where it has bay window. But a half basement is kind of a waste. This is typical of old Portland OR houses----they are on separate lots (not rowhouses) but often they are little more than a few feet apart. So when the foundation is bad it's tough---but most smaller houses can be picked up in the air but I don't want to do that. At least in my case I have a 50x100 lot, but on the west side I am 1.5 feet from the property line; and that is the part that is really hemmed in on the front and back, also, and then they want me to put in an added stairway somewhere, in the back corner I guess, in order to have livable space as per new code. On the west side I could probably excavate into my neighbors "driveway" which is really just dirt and patchy asphalt. (all it does is keep his tires out of the mud, that's it). I could work things out---he is a pothead Buddhist and very passive.Now you are saying that a soil engineer is an absolute must? So I have to have two engineers then? Also the engineer I have seems to think this is a complex problem; whereas I see it as a hodgepodge bunch of junk foundations (this house had two major additions) and all this junk needs to be replaced with something normal. But the engineer has to analyze everything (even if it looks like junk) and figure out what it is "accomplishing" and then exactly how to replace it? Sheesh---I am a commercial carpenter and have done all kinds of big stuff and concrete work and I see the most probable solutions----but getting this to engineer is a Gordian Knot. AND I have told the City that all new partitions in the basement would go to actual footings, not just rest on the concrete slab. And I told them I could put in solid timbers and 4x6 framing---not studs. But the engineer may still not be able to figure it out?? This is like Alice in Wonderland. Aren't there civil engineers around who know how to deal with Victorian houses? Maybe I will call the contractor doing the one closeby---but that house was not added on to, like mine was. Pretty crazy.
Expert:  Phil replied 2 years ago.

Hello again, your last idea is the best. Talk to the contractor doing the house nearby about the engineering and permit issues he faced.

The city is not going to want to accept any verbal descriptions from you the owner, they will rely on your own simple (to scale) pencil sketches for simple work, such as $1,000 worth of plumbing in some cases, but will require an engineered drawing for this kind of extremely heavy foundation work.

If there is a problem and they are found to not be strictly enforcing the building code, the people involved could loose their job... so these can be quite cautious.

A structural/ civil engineering firm will have no trouble figuring it out...but it could easily result in a project that is not cost effective... one of the reasons for that, is that a structural engineer by some reports, and in some states, can be sued even after he dies and his estate made to cover the damages, which can be in the millions of dollars if anyone is killed.

Stay in touch, I will be interested in how this situation unfolds.


We are on the honor system here. Please remember to rate my service, the company only pays me if you rate my work. It is how I earn a living, and does not increase your charges.

If you need anything else, just let me know. You can continue asking follow-up questions at no additional cost.


Customer: replied 2 years ago.
I think you missed my early point, where I said the State of Oregon Building Codes Division told me that since the foundation itself was already being engineered this would be a NON-PRESCRIPTIVE APPLICATION-----in essence, their codes are moot. With an earlier question he had told me that the official policy is that in order to be binding they have to "cite it and write it." Therefore when you move into a situation where a wall is engineered you throw out things like table R405.1. And we discussed this at length last week----looking through Chapter 4 in the Residential Specialty Code--- after City of Portland told me I couldn't have straight up excavation.To illustrate his point, however, there are homes built on steep upward slopes from the street, and they have an engineered retaining wall and obviously they can't dig 45 degrees out from the footing.Conceivably, OSHA could come and fine me for not having a safe trench. But I am pretty much going to be the only person down there setting the footings and pouring them. I will hire help for rod busting, and especially for the pours. But, there is a building frenzy right now and the likelihood of OSHA showing up is nil. The risk would be that some city inspector sees something and stops the project. The house up the street is being lifted by Emmert Industrial Corporation which is a well established house moving company. I sort of know the owner, from a political group. (He probably runs into all sorts of issues with the DOT's and State Patrol, etc. when they move houses.)So, the State expert on Residential Building Code says that the codes are moot because it is engineered and non prescriptive. The other pertinent point is that I want to do this basement project in phases. 1200 sq ft. total, but I could start with a 300 sq, ft utility and bath area, in one rear quadrant. And that would have interior walls, which I would put on to footings anyway. Then I could move to the next quadrant, and have both side access and front access. And in doing both of these I would also be putting a wood framed load bearing wall running from back to front, more or less down the center of the house. Thus there is no real danger of the house collapsing and of course I would used shoring methods (union carpenters do a lot of shoring). This does mean the city inspectors would have to come a lot more. Then for the third and fourth quadrants---roughly 600 sq ft. I will have a fire rated wall with two windows inset two more feet----so I could even do that wall in three pours. Where I get to the vertical digging is in two places: the inside line(which is the front building line) of a large concrete front porch, 8 ft by 18ft; and along the back wall, where there is a covered concrete porch that also has the present access stairwell. Also there is a little storage room, more or less along the building line, and the building line jogs a bit. Overall it works out pretty well architecturally, but it is sort of complex to deal with. And the engineering is really tricky.I have owned this for four decades and was not planning on doing anything with the foundation. However, City of Portland did make me do something years ago when they observed that the west wall was low in the dirt. Had to replace the old fashioned perimeter beam with cement block and dig a small trench. But now. I have to correct numerous plumbing and wiring deficiencies, the foundation has been leaking, and I know there is dry rot in places, so a basement makes sense and is not that hard to do, practically speaking. If I don't do these things it would get killed in a purchase inspection and might not even meet muster for bank financing. So this is really an important matter for me to handle. I know how to do all of this work, and don't need to hire a contractor and pay $100,000. But jumping through all of the procedural hoops is another matter.
Expert:  Phil replied 2 years ago.

Hello again, I am not a civil engineer and you should not rely on me at all to advise you on this very complex and high risk project. Getting into an 8 foot deep trench to dig footings yourself however would be a real risk to your life in most cases. I cannot comment on that intelligently without seeing the job.

I can't say that I understand all of the potential aspects of 'non prescriptive application' issue, that is something a person would almost have to be there to relate to accurately.

I have taken some very serious risks in my career so I understand your motivations... looking back however, and even at the time, I knew that my entire approach was wrong.

I just got lucky is all.

If you take that approach shoring the trench would be in order for sure. Digging footings inside the trench would involve your touching the unsupported sides of the trench and that could easily result in a collapse.

You might want to consult a civil engineer about the potential for pilings so that you not have to expose yourself to such a potentially fatal situation.


Expert:  Phil replied 2 years ago.

The building codes are only *minimum standards.... any person or building official is to do only what is safe and proper, regardless of what is printed in the code manuals, and it says that in the introduction section of each manual. I would look into the use of deep pilings if digging the footings personally presents any risk to your safety at all.