Pouring a Concrete Patio Over Tree Roots: 4 Things You Should Know

It is not uncommon to find tree roots that grow on the surface rather than downwards like a normal situation. Roots that grow on the surface get in the way of many projects, and humans find it hard to choose what to do when they need to use the space.

Building a concrete patio over existing tree roots is not easy, but it is not impossible either. Because roots need a constant supply of water and oxygen, placing concrete to sit on top of it will hurt them, if not kill them. If you intend to pour a concrete patio around an existing tree, you’ll need to make provisions to allow space for the tree to grow and receive water. Keep in mind that as the tree matures, the concrete will likely crack.

Trees are meant to grow free and wild. In any direction, anywhere, everywhere. Around homes’ unlike in the wild, trees face challenges of sharing the limited space with humans, and because they do not have a say, humans do to trees what they deem fit and according to their plans.

The Ins And Outs Of Concrete Patios (Detailed)

To know if building a concrete patio on top of tree roots is possible, you must first understand how the space set aside for a concrete patio is prepared before concrete is poured on it. 

One thing to note is that all patio spaces are paved, and concrete patio slabs rank high among the available choices as it is the easiest and most efficient of them all. That is given that there are two other types of paving materials for patios: bricks and tiles.

The advantage concrete slabs have over their counterparts is that concrete does not make it easy for weeds to sprout through its floor as it is also easier to maintain.

There are tree roots on spaces where you want to install your patio becomes a challenging situation because as much as you want to go on with your project, you also want the best for the trees.

Trees bring life to a dull environment; they purify the air, shield your home from outside view, provide shade and a relaxed atmosphere in hot seasons as well as muffle noise coming from the outside world.

Tree roots are the life link of the tree, and when they are brutally handled, the tree’s life is at stake.

The question is, do you chop off the roots, abandon the project, or find a way to go about your project while doing the best you can to ensure the tree survives after all the trauma.

Concrete is a mix of sand and cement, and when mixed in the correct ratios, it produces a challenging mixture that can last for long and withstand harsh conditions when laid down. 

Will Concrete Hurt Tree Roots?

The work of tree roots is to supply the tree with water, nutrients, and oxygen, but they do need to be alive themselves to carry out their designated job.

Did you know that tree roots breathe? Every bit of a tree lives to stay alive? Roots, leaves, branches, the trunk, name them, they all breathe. They breathe in oxygen and breathe out carbon dioxide just like animals do, and just as humans do. 

If tree roots breathe, how do they breathe, you ask? They do breathe through specialized cells that are located on the surface of the root. In the forest, or generally where most trees and plants grow and are not interfered with by human activity, you will find that the soil is loose.

That is so because the soil contains air that is oxygen in its composition, which is meant to supply roots and animals that burrow the ground with air(oxygen) to breathe as they go about balancing the ecosystem. 

As they breathe, they live, feed, and grow. 

The question now becomes, will tree roots be able to breathe with a concrete slab sitting on top of them? The truth is that the tree’s roots get caught in the crossfire and, if not careful, will suffocate for lack of air to breathe.

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Will concrete hurt tree roots? 

Yes, the concrete slab will hurt the tree roots in two ways:

  1. The first and the most crucial is that a concrete patio will cut off the usual supply of air and water, which the roots are accustomed to and which is beneficial to the life and growth of the tree. We eat to live, goes the slogan.
  2. The second is that a concrete patio and all it comes with it is heavy. The roots that were once free are now burdened with the weight of the concrete slab. Roots are accustomed to growing where it is accessible to penetrate, but they will be affected already.

Note: Unless the tree has other sufficient roots from the surrounding circumference (the patio project does not impact that) to supply it with food and water, the tree will stagnate in growth and might eventually give up on life.

The good news is that tree roots extend in all directions. The more room they colonize, the greater the tree’s chances of thriving in every sector, be it in height or diameter. 

How The Space Of A Patio Is Prepared (A Rough Picture)

Most patio spaces are built with a depth of 4-8 inches, and the areas that are meant for the project must be cleared of debris, grass, and soil, including making sure that the surface is as flat as possible.

There are two ways of excavating the soil from the designated area in a typical situation;

  1. Manually digging up the area and shoving the soil out into a wheelbarrow, either carried out on your own or by a hired hand.
  2. Letting an excavating machine do the work, most of these machines are hired because many of the people who have them are involved in excavation work.

But now that your project is intruding in the way of tree roots, it means that you have to go the manual mode and at a slower pace, having enough patience and being mindful of the roots.

Even so, some roots will not escape unhurt or displaced. To minimize damage, whoever is responsible might have to use gloved hands when cleaning and excavating soil, as tools like shovels will hurt the roots.

The truth is that the whole process will be painful, slow, and time-consuming.

It is one thing to suffocate the tree roots and another to hurt them. Tree roots consist of secondary roots, a network of smaller sources diverting from the main legume to speed up the search for water and nutrients.

Given all that, it will be outrageous to be not mindful of them intentionally.

How big is the patio? With this in mind, the project kick starts with marking out the boundaries the deck is set to cover, excavating and leveling up the area, constructing a four-wall unit that will hold the concrete, dividing up the inner space, and finally pouring concrete on it.

But before concrete is poured to cover the base of the patio area entirely, gravel or more giant stones that have been crushed are laid on the bottom; this is for two reasons;

  1. It is to level out the surface below so that it will not consume too much concrete.
  2. To allow the concrete to drain off the water.

The idea of paving the patio base with gravel or crushed stone is the break we have been looking for all along. It is the proverbial “casting one stone to kill two birds.”

When patio creators think of ways to ensure that the patio survives all weather and nature-related challenges, they solve significant issues, especially tree roots covered in concrete problems.

Two things in this scenario kill tree roots;

  1. Lack of air to breath
  2. Stagnant water is not draining away

The primary purpose of laying gravel on the patio base is to allow water to drain so that concrete does not break or sink.

As that happens, the tree’s roots benefit as they still get to breathe and get supplied with water draining from the concrete.

It is a genius idea and a win-win situation for everyone.

Will Pouring Concrete Near A Tree Kill It? 

The human activity that is concentrated under or around a tree is the most cause of tree mortality. 

Trees need food and water, while roots need to breathe to grow and be competent in their activity. The focus here is on the soil maintaining air spaces to allow roots to breathe.

That aside, we see big trees every day in towns and cities along boulevards, sidewalks, and footpaths thriving amidst concrete pavements.

How is that possible? The trees in urban settings that continue to grow unabated have root barriers installed adequately around the tree’s stem.

Root barriers are sensitive enough not to infringe on the growth and the needs of the tree. Pouring concrete near a tree and not around a tree will not kill if done right. 

Trees die all the time, especially when they lack water and oxygen, but if they are left with enough room and their water supply is not interrupted, a tree can survive anywhere. 

Trees don’t die quickly; they fight a good fight and maximize all they have and the little they get. Here is how trees in towns and cities survive.

In a typical scenario, tree roots travel downwards in search of food and water. Still, once in a while, we see tree roots protruding and growing on the surface around the tree. Whatever they seek is found in abundance on the surface more than deep down the earth.

In urban areas, tree root barriers work miracles. The idea is to deter the roots from breaking through the concrete surface but still get to breathe and feed.

Just like in patios, footpaths and pavements are shallow. The depth of an 8” in most patios’ while the root barrier goes down 18”.

The thing is that the tree’s stem is given an allowance of 12” on both sides. It allows the roots and the stem to breathe and enable the roots to take in water.

After the 18” depth, the roots are set free where they can now set their course. It is not the best scenario, but it is better than nothing.

Pouring concrete near a tree will affect the tree one way or the other but chances of it killing the tree are slim.

Can Tree Roots Lift Or Break A Reinforced Concrete Slab?

Tree roots are wired to go where the supply of water and nutrients are available. 

But it again depends on the type of tree that is growing near a concrete slab. If the tree belongs to a smaller species, then its roots pose no danger. However, more enormous trees have more extensive roots that would defer structures to get their way.

When was the concrete slab installed? Was it when the tree was younger? Did you consider the type of tree and the size it will grow into in full bloom?

But rarely do tree roots break through the surface of a compact concrete slab not unless the slab was broken or cracked already. Cracked floor leaks in the water; when roots pre-existed under the concrete slab, they will find an avenue to breakthrough in the pursuit of water.

But as the tree keeps on growing, its root network expands, trailing behind larger and stronger roots. As they expand in size, they demand more space to occupy, and they end up pushing away the soil to make more room.

The survival and steady growth of the tree are dependent on the further the roots can spread and explore. The bigger the sources, the stronger the tree.

But the vigorous growth of tree roots can be disastrous to concrete floors and slabs. Because trees can not break through a barrier, they tend to manor our—the bend where the end of a concrete floor or slab could suffer the consequences. 

The roots will exert pressure as they grow in length and size, and the once comfortable curve is now squeezed. The corner of the concrete slab will lift.

Final Thought

As said earlier, building a concrete patio over existing tree roots is not easy, but it is not impossible either.  

More often than not, the only time tree roots come to your mind is when they are growing on the surface and standing in the way of projects such as patios. You want to build a deck for your home, but you find the space allotted has tree roots scavenging on the surface.

It is a tough decision because the roots and the tree will get hurt one way or the other. But to beat the odds, laying out gravel beneath the concrete slab will solve more than the lack of oxygen problem.

When you have a pool of water staying in one place for too long risks sealing or occupying the air spaces present in the soil, suffocating the roots; when the surface of a project can drain water, it becomes a big win for sources as they will be able to breathe.

Sources

DO TREE ROOTS DAMAGE SIDEWALKS, FOUNDATIONS & PLUMBING?

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.

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