If you are planning a patio, walkway, or backyard makeover in Cambridge, there is a rule you need to understand before the first shovel goes in the ground: the Tree Protection Ordinance. Cambridge protects the trees on private property harder than almost any city in the state — and if a tree is in the way of your patio, or even just near the work, it can shape your permits, your budget, and your timeline. Here is exactly how it works, in normal terms.
The rule in one sentence
In Cambridge you need a city permit to remove or injure any “Significant Tree” on your own property — and that is a lower bar than most people expect. A Significant Tree is any tree on your lot measuring 6 inches or more in diameter, measured at 4.5 feet up the trunk (what arborists call DBH, diameter at breast height). Anything 6 inches or thicker is covered. A tree of 30 inches or more is an “Exceptional Tree” and counts for even more.
Trees under 6 inches do not need a permit, and routine pruning does not need a permit either. But that mature maple shading the back corner where you want the fire pit? That one is protected.
The permit is free — the mitigation is not
Here is the part that surprises people. The tree removal permit itself costs nothing. But unless your tree qualifies for a “special circumstance” (more on those below), the city requires mitigation — you either plant replacement trees or pay into the city’s Tree Replacement Fund. And that payment is real money:
- $850 per inch of trunk diameter for most properties.
- $85 per inch (a 90% discount) for owner-occupied homes that carry the Residential Exemption.
Run the math on a common case: removing a single 6-inch tree with no replacements is $5,100 — or $510 if you have the Residential Exemption. A large 30-inch Exceptional Tree, with its 1.5× multiplier, can run into the tens of thousands. You can shrink or erase that payment by planting replacement trees on the property instead, which most homeowners do.
The permit is free. The tree is not. On a Cambridge lot, a mature tree in the wrong spot is a line item — and it is smart to know that number before you design the patio, not after.
When you owe nothing: the special circumstances
Mitigation is waived if the tree meets one of the city’s special circumstances. The most common are:
- The tree is 100% dead, confirmed by a Certified Arborist.
- The tree is dangerous, confirmed by a Certified Arborist.
- An emergency — for example, it has uprooted and threatens people or property.
- The tree poses a significant negative impact on an existing structure (this one requires City Engineer approval).
- Removing it would benefit other Significant Trees on the property.
One catch worth knowing: the city’s own arborists cannot sign off for you. For a dead or dangerous tree, you have to hire your own Certified Arborist (verified through the Massachusetts Arborists Association or the ISA) to file the assessment. Building it into the plan early keeps the project moving.
The part contractors get people in trouble with: Duty of Care
This is the rule most homeowners have never heard of, and it is where a bad crew can cost you thousands. Under the ordinance’s Duty of Care provision, any permitted construction project has to protect the Significant Trees on the property during the work. If a tree gets damaged during construction — roots severed by excavation, the trunk gouged by a machine, or the soil compacted over the root zone — the city treats it as a removal, and you owe the full mitigation, even though you never meant to take the tree down.
In practice that means the excavation, base, and grading around a protected tree have to be planned, not improvised. Root zones get fenced off. You hand-dig where you have to. You do not stack materials or run a machine over the roots. After 37 years building on tight lots, this is exactly the kind of thing we plan around before we start — because on a Cambridge property, protecting the tree is protecting your budget.
Where permeable paving comes in
Cambridge also cares a great deal about stormwater — the city’s Land Disturbance and stormwater regulations exist to keep runoff out of an already-stressed drainage system. Permeable paving is the move that solves two Cambridge problems at once:
- It keeps protected trees alive. A solid concrete or mortared surface seals the ground and starves tree roots of the air and water they need. Permeable paving lets rain and oxygen pass straight through to the root zone, so the mature tree you are required to protect actually stays healthy after the patio goes in.
- It manages the stormwater. Instead of adding impervious area that sheds water into the street, a permeable system soaks rain into an engineered stone reservoir underneath — reducing runoff and keeping you on the right side of the city’s drainage rules.
On a small Cambridge lot with a mature tree you are legally required to keep, permeable paving near that tree is often not just the nicer choice — it is the one that keeps the tree, and your mitigation bill, out of trouble. (For the full technical breakdown of how permeable systems are built, see our permeable paving guide.)
How this shapes a smart Cambridge patio project
Put together, the Cambridge playbook looks like this:
- Inventory the trees first. Measure anything near the work at 4.5 feet up. Six inches or more, it is protected — design around it.
- Price the trees, not just the pavers. If a Significant Tree truly has to go, know the mitigation number before you commit to a layout.
- Protect what stays. Fence root zones, hand-dig near roots, and keep machines and material off the critical root area — Duty of Care is not optional.
- Use permeable surfaces near trees so the roots keep breathing and the stormwater stays on-site.
- Line up a Certified Arborist early if any removals or assessments are in play.
The bottom line for Cambridge homeowners
Cambridge’s tree rules are not there to make your patio impossible — they are there to keep the city’s canopy alive as it gets denser. The good news is that the things the ordinance rewards — keeping a mature shade tree, using surfaces that let the ground breathe, managing your own stormwater — are the same things that make a backyard genuinely nicer to live in. Plan for them at the design stage instead of at permit time, and a Cambridge patio is very buildable.
Thinking about a patio in Cambridge? We build across the city — from Cambridgeport and Mid-Cambridge to the neighborhoods around Harvard, MIT, and Porter — and we plan around the tree rules so you don’t get surprised. See our Cambridge patio work or call for a free on-site look.
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Published July 11, 2026 · American Elm Landscape LLC, serving Cambridge, MA. General information, not legal or arboricultural advice — always confirm current requirements with the City of Cambridge before you build. Sources: City of Cambridge Tree Protection Ordinance (Municipal Code Title 8, Chapter 8.66); City of Cambridge Public Works “Apply for a Tree Removal Permit” (last updated Nov. 2025); City of Cambridge Land Disturbance & Stormwater Management regulations.