Where does a tree root barrier go?
It depends on the layout. Most barriers protect paving, so they run straight along it. The other layout is a ring around the tree.
| Layout | Where it goes | How far from the trunk | How it sits |
|---|---|---|---|
| Straight run along a sidewalk, curb or driveway | Along the paving edge, on the tree side, centered on the trunk | Set by the paving edge, not by a distance rule | Vertical. A lean of about 10° is optional where there is room. |
| Ring around a tree | A full circle around the trunk, in open ground | At least half the distance from the trunk to the mature drip line | Vertical |
If your project plan or city detail differs, follow the plan. Next to an established tree, talk to an arborist first, because the trench cuts the roots on that line.
Where does a straight run go along a sidewalk or curb?
Right along the edge of the paving you want to protect, on the tree side. Set it vertical and center it on the trunk. That's how city details draw it:
| City detail | Where it goes | Length | Depth |
|---|---|---|---|
| San Diego regional drawing L-06 | Along the paving, not around the root ball | At least 10 ft each way from the trunk | 24 in |
| Washington County, Oregon, 4010 | Paving side, centered on the tree | 10 ft in planter strips | At least 36 in |
| Bremerton, Washington, 3351 | Curb and sidewalk sides, centered | 8 ft | 24 in |
All three draw the barrier vertical. In a planting strip, the paving edge can be close to the trunk. Iowa State University Extension puts small trees in strips 4 to 10 ft wide, so a trunk in the middle is 2 to 5 ft from each edge. The run still goes along the edge. With paving on both sides of the strip, a city detail may call for a run along each one, as Bremerton's does.
How long should the run be?
Use the length on your plan or city detail. With none, make it about the mature canopy width plus 2 ft, centered on the trunk. That carries it about 1 ft past the mature drip line on each side.
The mature canopy width, or spread, is the full width of the grown tree. It's on the nursery tag or in a tree guide. For a full-grown tree, measure it.
| Mature spread | Run length | Order (5 ft steps) |
|---|---|---|
| 15 ft | About 17 ft | 20 ft, our minimum |
| 20 ft | About 22 ft | 25 ft |
| 30 ft | About 32 ft | 35 ft |
| 40 ft | About 42 ft | 45 ft |
| 50 ft | About 52 ft | 55 ft |
Example: a tree that will spread 30 ft. 30 + 2 = 32 ft. Order 35 ft, the next 5 ft step, and center it on the trunk: 17½ ft each way.
Should the barrier be vertical or angled?
Vertical, by default. That matches the city details above. Where there is room, you can lean it about 10°, top edge toward the tree, so roots that reach it are guided down.
Room means space between the top edge and the paving. At 10°, the bottom edge sits closer to the paving than the top: about 3 in on the 18 in barrier, 5 in on the 30 in and 6 in on the 36 in. Keep the top edge at least that far from a slab, so the bottom doesn't end up under it. Right at the paving edge, set it vertical.
Bamboo Shield tilts the other way on purpose. Its top leans away from the bamboo, so rhizomes turn up where you can see and cut them.
How deep is the trench, and how high does the top edge sit?
Leave the top edge ½ to 1 in above finished grade. Iowa State University Extension says the top must stay above the soil and mulch to work. Dig the trench to the barrier depth minus that.
| Barrier depth | Top edge above finished grade | Trench depth |
|---|---|---|
| 18 in | ½ to 1 in | 17 to 17½ in |
| 30 in | ½ to 1 in | 29 to 29½ in |
| 36 in | ½ to 1 in | 35 to 35½ in |
Backfill in 6 in lifts, firming each one, so the barrier stays where you set it. Call 811 before you dig. The tree root barrier install manual covers each step.
How far from the trunk does a ring go?
At least half the distance from the trunk to the mature drip line. The drip line is the circle on the ground under the tips of the outer branches, once the tree is grown.
- Find the mature spread, the full width of the grown tree.
- Halve it for the distance from the trunk to the mature drip line.
- Halve it again. That's the closest any part of the ring should come to the trunk.
A ring is usually for a new tree with paving on more than one side. Set it vertical: a leaning ring is a cone, and a flat strip won't sit evenly on one. Keep it out of the planting hole. A barrier tight around the root ball can turn young roots sideways, so they circle the trunk.
A ring doesn't hold the roots in. Roots grow under and past it. It is designed to turn roots down and away from the paving.
Around an established tree, a ring cuts roots on every side. Talk to an arborist first.
How much barrier does a ring take?
Multiply the ring's distance from the trunk by 6.28. A ring has one joint per piece, even a one-piece ring, where its ends meet. Add 12 in per joint and round up to the next 5 ft.
| Mature spread | Ring at least this far out | Ring length | Order at 18 or 30 in | Order at 36 in |
|---|---|---|---|---|
| 20 ft | 5 ft | 31.4 ft | 35 ft, 1 kit | 35 ft, 1 kit |
| 30 ft | 7.5 ft | 47.1 ft | 50 ft, 1 kit | 50 ft, 1 kit |
| 40 ft | 10 ft | 62.8 ft | 65 ft, 1 kit | 65 ft, 1 kit |
| 50 ft | 12.5 ft | 78.5 ft | 80 ft, 1 kit | 85 ft in 2 cuts, 2 kits |
Example: a tree that will spread 40 ft has its drip line 40 ÷ 2 = 20 ft from the trunk, so the ring goes at least 20 ÷ 2 = 10 ft out. 10 × 6.28 = 62.8 ft, plus 1 ft for the joint, is 63.8 ft. Order 65 ft and one connecting kit.
The 36 in barrier's longest piece is 70 ft. So a ring for a 50 ft spread takes two pieces and two joints: 78.5 + 2 = 80.5 ft. Order 85 ft as two cuts, such as 45 ft and 40 ft, with two kits.
What changes next to an established tree?
Talk to an arborist before you dig. The trench cuts every root it crosses on that line.
One research finding to take to that talk: in a study of young oaks, root cuts closer than 3 trunk diameters to the trunk made the trees easier to pull over. That's a research result, not a ProTech rule. Do root barriers hurt trees? covers what the research found, with a table by trunk size.
The strip between the curb and the sidewalk is often city right-of-way. Some cities need a permit to cut a street tree's roots, so ask your city forester too.
Which depth do I need: 18, 30 or 36 in?
Use the depth your plan, spec or city detail calls for. The city details above call for 24 or 36 in, so check your city's first. With no plan or spec, send us the tree species and the site, and we'll help you choose.
For background, Iowa State University Extension says a sidewalk barrier should be at least 18 in deep, and University of Illinois Extension puts over 90% of a tree's root mass in the top 18 in of soil.
| Depth | Thickness | Puncture (ASTM D4833) | Weight per ft | Longest piece |
|---|---|---|---|---|
| 18 in | 80 mil | 155 lbf | About 0.6 lb | 175 ft |
| 30 in | 80 mil | 155 lbf | About 1.0 lb | 100 ft |
| 36 in | 100 mil | 200 lbf | About 1.5 lb | 70 ft |
The 30 in reaches 12 in deeper than the 18 in at the same 80 mil. The 36 in adds 6 in more and is thicker.
Prices are on the Sidewalk Shield product page. For joints, 5 ft steps and the 20 ft minimum, see how cut-to-length ordering works.
My spec calls for 24 in. What do I order?
Use the depth the spec calls for. Sidewalk Shield comes in 18, 30 and 36 in, not 24 in, so don't swap in a depth on your own. Ask the engineer or city which depth they will accept, or contact us before you order.
If the spec says "or approved equal," get approval before you order. Send the engineer the depth, thickness, puncture result, material and joining method.
Who is Sidewalk Shield not for?
- A lifted slab on its own. A barrier won't flatten it. Put the barrier in while the panel is replaced, before the pour. See why tree roots lift sidewalks.
- A tree in a grate or small well, with no city detail. A ring needs open ground at least half the drip-line distance out, and paving all around leaves none. Follow the city detail, or ask us.
- Bamboo. Use Bamboo Shield, with its top tilted away from the bamboo.
Common mistakes
- Planning for today's canopy. Use the mature spread, for the run length and the ring distance.
- Using the ring distance for a straight run. A straight run goes along the paving edge. Half the drip-line distance is for rings.
- Making the run too short. About the mature canopy width plus 2 ft, centered on the trunk.
- Leaning the barrier right against the slab. At 10°, the bottom edge ends up under it. Set it vertical there.
- Burying the top edge. Leave ½ to 1 in above finished grade.
- Leaving out the joint overlap. Where two cuts meet, add 12 in to the order and one connecting kit.
FAQ
Can a root barrier go right next to the sidewalk?
Yes. That's where a straight run goes: vertical, along the paving edge, the way city details show it. Next to an established tree, talk to an arborist first.
Does the half-drip-line rule apply along a sidewalk?
No. It's for a ring around a tree. A straight run goes along the paving edge, wherever that is.
How far past the tree should the run go?
As far as your plan or city detail says. With none, make the whole run about the mature canopy width plus 2 ft, centered on the trunk, so it reaches about 1 ft past the mature drip line on each side. A tree that will spread 30 ft takes about 32 ft: order 35 ft.
What if my run is longer than one piece?
Order two or more cuts. Each piece is up to 175 ft at 18 in, 100 ft at 30 in and 70 ft at 36 in. Overlap the ends 12 in, clamp them with one connecting kit per joint, and add 12 in to the order for each joint.