Concrete Slabs & Root Heaving

janenc7bSeptember 9, 2008

I love shade trees. Our condos currently have large Bradford Pears shared between neighbors. When these have to be replaced, the rules require it to now be more of a dogwood, redbud type to prevent root heaving of the concret slabs.

It is my hope to make a case for a larger shade tree. After searching on the internet, I still don't know which trees have roots that will go vertical and not impact the building. Someone said that Pin Oaks are good (I'd love an oak)but I have not verified that is true.

Can you give me some direction? Thanks...

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lou_midlothian_tx(z8 DFW, Tx)

I've read that bald cypress won't do it ('Nanjing Beauty' might work the best as it is more of columnar type for tight spot). Shantung maple probably won't do it and it's much tougher than dogwood or redbud. 25-35 feet over time.

    Bookmark   September 9, 2008 at 6:21PM
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heptacodium

There is no hard answer for this question.

The first question what is the space between the slabs. If insufficient space is allowed, it doesn't matter what you plant, you are going to have problems. I live in a community that thinks a two foot hole cut in concrete is enough to allow a shade tree to survive and grow, and then gets outraged when the tree grows to it's mature size and does what it does. The fault is not of the tree, it's of small minded people who like to think they can control all factors.

The greater pity is this...as expensive as it may be to remove and replant, it's still a meager fraction of the cost of replacing a slab. No matter what your information, good luck getting around one.

In a practical sense, what you are looking for will determine what you find. Want to see problems with concrete heaving due to tree and root growth? Look aorund you and that is what you will see. However, if that were such a major problem, it's safe to say there would not be a tree planted in any city in America, nor even in many of the small towns.

There are other answers. Structural soils are available, designed to limit compaction, allow penetration and growth of roots under structures and slabs. However, they are expensive and require that consideration of such factors be taken into account before construction began. Usually, they are only used in government jobs or other projects that require plants units per density.

The best answer I can give? Information is a powerful weapon. I do have some info regarding value of trees and landscaping around, it all came from internet sources. I'll try to locate it and get back with the highlights. Otherwise, start searching under tree value and landsacaping.

    Bookmark   September 11, 2008 at 10:02AM
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gardengal48

Are these foundation slabs or more in the nature of patios/driveways/pavers? Foundation slabs have footers that make tree root issues no more problematic than they would be if it was an excavated foundation - if the foundation is in good condition and structurally sound, you should have no worries unless shrinkage/heaving of clay soils is present in your sitation.

As to the root structure of trees, almost without exception, roots travel horizontally, not vertically. Some tree species will develop tap roots at an early age only to outgrow them as they mature - the majority of any tree roots will be located in the top 12-16 inches of the soil and will extend laterally, often as much as 3-4 times the height of the tree. Otherwise, trees with deeper root systems are generally only found in very arid/desert areas where soil moisture is held deeply underground.

    Bookmark   September 11, 2008 at 12:36PM
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janenc7b

Thank you for the responses. The local Extention Service said Willow Oaks are good in this application. I throw that in the discussion as a idea.

The slab I am concerned about is the foundation slab under four condos and maintained by the association. We are 4 single level units and we share the foundation slab forming a square. Two opposite sides have Bradford Pear trees. They are currently good size trees and about 8 feet from the structure. They are pretty trees and very brittle so replacements are likely.

Appreciate your help as I make a case for my tree. The fact mentioned about foundation slabs having a "footer" preventing tree heaving was very interesting. What is a footer?

    Bookmark   September 12, 2008 at 3:16PM
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gardengal48

A footer (more accurately, a 'footing') is a supporting base for a structural element like a wall or foundation slab. It is placed/poured vertically into the soil to a specified depth to anchor the slab or other structure. Typically, all footings are reinforced concrete and the depth of their placement is determined by the both the weight of the structure and the depth to which soil in that area freezes. 36-48 inches is pretty common.

You can imagine how difficult it would be for tree roots to damage a structurally sound foundation slab when it is necessary for them to travel 36-48" down underneath the footing and another 36-48" back up to the slab. Just doesn't happen :-) Free-standing slabs (lacking any footings, like is typical with storage sheds, patios, driveways, etc.) are another story.

    Bookmark   September 12, 2008 at 5:33PM
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freshair2townsquare(z7/8, D/FW)

7b: but what part of the country? where are you?

    Bookmark   September 12, 2008 at 10:46PM
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janenc7b

Great information! I am in the Winston-Salem area of North Carolina. I wonder if there is a building code on "footings"? If there is, then I can use that as my standard. It does make sense that that would be one determined root to go down a yard and then back up again. LOL I do love shade trees and hope I can make a case for a larger tree. Thank you for the help.

    Bookmark   September 13, 2008 at 10:57AM
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davidandkasie(Z8 MS)

You can imagine how difficult it would be for tree roots to damage a structurally sound foundation slab when it is necessary for them to travel 36-48" down underneath the footing and another 36-48" back up to the slab. Just doesn't happen

i beg to differ but it does happen. around here footings are generally only 18-24" since we have no frost line, but even with a 48" footing it is possible. it just depends on teh type tree it is growing and how close to the structure it is. tree roots will also find any crack in the footer and force their way thru. in reality the ONLY way to guarantee no tree roots under a slab is to not have any trees even remotely close to it. my grandmother's house has a pine tree root heave her front walk. the closest pine was behind the house, about 60 ft away! and this root ran straight back to it under the house slab.

    Bookmark   September 13, 2008 at 2:19PM
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janenc7b

DavidandKasie, please expand on your comment - "It just depends on the type tree it is growing and how close to the structure it is." Are you aware just which trees are better to be close to a sturcture and if so, that answers my question?

I would rather beat this out in this forum than address our board and get called up short by a local expert in the condo group. Thanks so much for the details.

    Bookmark   September 13, 2008 at 9:10PM
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