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Old 03-23-2012, 05:20 PM   #1
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Pitfalls of building a root cellar below the footing level of adjacent house?


Here's the plan for a new construction: I'd like to build a thermally isolated root cellar, concrete with a barrel vault roof, buried under 6' of soil, adjacent to my house, and accessible through the basement.

My concern is the stability of the footings for the house if the root cellar's footings are below the level of the home's footings and the cellar structure is within a few feet of the home.

-Am I right to be concerned?
-Is there a way to achieve this scenario? (without stepping the home's footings down to the same level as the cellars. - I want to avoid having a 16' high foundation wall at that part of the foundation.)
-Is there engineering best practice which specifies distances between footings for adjacent structures, depending on soil conditions of course?

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Old 03-23-2012, 10:47 PM   #2
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Pitfalls of building a root cellar below the footing level of adjacent house?


See and engineer who can look at it, test the soil, see the foundation, footer, etc. If you access through the basement (I assume knocking out for a door), then you have a header/footing for that issue, too. If this is a small place, you are probably OK, but.... reread the first sentence.

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Old 03-23-2012, 11:08 PM   #3
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Pitfalls of building a root cellar below the footing level of adjacent house?


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Originally Posted by jklingel View Post
See and engineer who can look at it, test the soil, see the foundation, footer, etc. If you access through the basement (I assume knocking out for a door), then you have a header/footing for that issue, too. If this is a small place, you are probably OK, but.... reread the first sentence.
Thanks for responding.

Rest assured that an engineer will be signing off on this. My concern right now is the integration into the design for the new construction. Here, let me post a pic to show you where I'm coming from:




What would be most convenient is for me to use the space under the basement stairs and step down the foundation and put in another flight of stairs leading towards a door in the basement wall. That space under the stairs is dead space otherwise.

The space for the root cellar would be between the driveway and the foundation wall which has the front porch designated. The front porch would be built over top of part of the root cellar.

My concern here is that the root cellar footings would be below the footings for the house and very much below the footings for the garage.

Is there a rule of thumb that has more success than failure that I can use in the design phase before an engineer vets the design for feasibility? What I want to avoid is a wholesale redesign when the engineer looks at the plan and declares "What ever possessed you to put your root cellar so close to your foundation. No one in their right mind would do that. It should be at least 10 feet away."
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Old 03-23-2012, 11:34 PM   #4
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Pitfalls of building a root cellar below the footing level of adjacent house?


OK. I see better what is planned now, but I can not advise one iota on any specs. It is a gut feeling that if this root cellar is fairly small, the footings, etc, for it can be whatever will support it, and I see no reason to attach it to the house if it is buried that deep. That is purely GUT, though. If the project falls apart and the engineer says to build your bunker above grade instead, enclose the area under the stairs and put in shelves, etc. It ain't ideal, but my area is storing a ton of paint and other BS. Let us know what the engineer says, if it is printable.
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Old 03-23-2012, 11:50 PM   #5
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Pitfalls of building a root cellar below the footing level of adjacent house?


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Originally Posted by jklingel View Post
OK. I see better what is planned now, but I can not advise one iota on any specs. It is a gut feeling that if this root cellar is fairly small, the footings, etc, for it can be whatever will support it, and I see no reason to attach it to the house if it is buried that deep. That is purely GUT, though. If the project falls apart and the engineer says to build your bunker above grade instead, enclose the area under the stairs and put in shelves, etc. It ain't ideal, but my area is storing a ton of paint and other BS. Let us know what the engineer says, if it is printable.
I'm not much worried about the footings for the root cellar, I'm worried about the effect that a root cellar would have on the nearby footings/foundation of the home, the very big ticket item. All the loads in the house are coming down, ultimately, to those footings and then into the earth.

What effect would a "concrete bunker" type of root cellar, on its own footings, have on the load paths coming from the house, especially if the soil near the home's footings is disturbed and that disturbance was characterized by digging 5' deeper?

If all of this disturbance happens before any home construction begins does it become a wash? How about if I build and then backfill around the root cellar two months before I start on the house - does the settling of the backfill stabilize the ground around the home's footings? Does it not matter what loads are coming from the house onto it's footings if the root cellar work is at least X feet away? What soils should be avoided?

I know that some of these are very specific questions that I can't get answers to without a soil test and engineer looking at everything, but I'm hoping that someone could shed some light on the principles I should be thinking about for this aspect of the project.

Right now I have a pretty short path from the kitchen, down the stairs, and into the proposed root cellar. If this design doesn't work I'd rather begin anew and incorporate any insights I pick up from this thread and design another floorplan with a short path between kitchen and cellar.
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Old 03-24-2012, 06:17 AM   #6
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Pitfalls of building a root cellar below the footing level of adjacent house?


Typically the zone of influence of a foundation is taken to be approximately 45 degrees acting outward and downward from the footings. No digging can occur in that zone without special underpinning techniques. In some soils, the zone extends out at a flatter angle (more restrictive condition). You are correct to be concerned about undermining your house foundation by placing a root cellar immediately adjacent to the footers.

You should get your engineer involved at the planning stage. Engineers do not bite, at least not very hard. It makes little sense for you to develop a plan, only to find out it is dangerous, excessively expensive, or could have been better. Get the engineer to look at the site and give you some ideas on how to make it work.
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Old 03-24-2012, 12:21 PM   #7
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Pitfalls of building a root cellar below the footing level of adjacent house?


Assuming you haven't built the house yet it should be very simple to do what you are talking about. What basically should be done is extended the footings of the home just in that one small section so the bottom of those footings are at the same depth as those of the root cellar.
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Old 02-10-2013, 06:24 PM   #8
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Pitfalls of building a root cellar below the footing level of adjacent house?


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Typically the zone of influence of a foundation is taken to be approximately 45 degrees acting outward and downward from the footings. No digging can occur in that zone without special underpinning techniques. In some soils, the zone extends out at a flatter angle (more restrictive condition). You are correct to be concerned about undermining your house foundation by placing a root cellar immediately adjacent to the footers.

You should get your engineer involved at the planning stage. Engineers do not bite, at least not very hard. It makes little sense for you to develop a plan, only to find out it is dangerous, excessively expensive, or could have been better. Get the engineer to look at the site and give you some ideas on how to make it work.
Hi Daniel. I'm also interested in building a small root cellar under my crawl space. I was thinking of digging 3 feet from the inside of the footing. Only about 2.5-3 ft deep. 6ft x 6'6 space accessed by hatch above. Will disturbing the filling of this size affect the foundation? Thanks
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Old 02-10-2013, 07:19 PM   #9
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Pitfalls of building a root cellar below the footing level of adjacent house?


Any time you dig deeper than the foundation, adjacent to the foundation, you have to analyze the conditions very carefully. This cannot be done over the internet, it requires a hands on investigation, unless you are putting something really small in, for example a flower pot that will be a foot or so deeper than the foundation base would be OK. But from your description, best to have it looked at, either by an engineer or perhaps the person who will do the digging. It is always a bad experience to have the foundation fail during excavation, very expensive, harsh experience.

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