Trees and urban forests

Trees near foundations

Trees are often considered to be the cause of damage to building foundations, but trees are not always the source of the problem.

Damage is often a result of the behaviour of the soils under the foundation. Uneven soil shrinkage can lead to uneven settlement and foundation damage. In the Ottawa area, shrinkage of sensitive marine clay is a major contributor to building foundation damage.

The City of Ottawa is committed to protecting its natural environment and resource base. In an effort to preserve mature trees, the City has instituted a formal 4-phase assessment process to investigate the circumstances related to mature municipal trees that are suspected of contributing to foundation damage.

For program information call 3-1-1.

City of Ottawa infill tree conservation program

Tree conservation is considered an essential element in the growth and development of the City of Ottawa. Trees improve air quality, reduce heating and cooling costs, minimize our carbon footprint, and increase property value. The Infill Tree Conservation Program has been developed to maintain and enhance these benefits within the city.

These infill guidelines apply to all new single, semi-detached, duplex and triplex units built inside the greenbelt that are not subject to Site Plan or Subdivision applications.

Infill Tree Conservation Program brochure [ PDF 2.799 MB ]

Building permit application

For each building permit application for a new single, semi-detached, duplex or triplex within the greenbelt, the following must be included:

• Tree disclosure information on the grading plan submission - prepared by an Arborist identifying those trees that are protected under the Urban Tree Conservation By-law 2009-200 and the Municipal Trees and Natural Areas Protection By-law 2006-279. 
• Grading Plans must include:
  • A table listing the diameter at breast height (DBH), species, condition, ownership, and outcome (retain or remove) for all trees that are protected under city by-laws. This includes all city owned trees and distinctive trees (with a DBH of 50 cm or greater) on the subject property and on adjacent properties whose critical root zone (CRZ) falls within the area of excavation. For those on neighbouring properties, their location and DBH can be estimated.
  • The location of all trees listed in the table and the proposed zone of excavation overlaid on the grading plan. Where excavation is planned within the critical root zone of any of the trees listed in the table, an Arborist assessment of the impact of the work must be included. This assessment should include any mitigation measures that should be implemented for retained trees. 
• A $700 refundable tree planning deposit to ensure that trees lost to development are replaced, will be collected at building permit issuance.

Pre-construction requirement

• All trees protected under City tree By-laws shall have protective fencing (snow or metal) around them prior to construction. This protection zone shall be the maximum area available to the tree that will not have any vehicular traffic, nor be used for the storage of materials. A sign will be installed on the fence identifying those trees that are to be protected under the By-laws. Refer to the City’s Tree Protection Specification [ PDF 377KB ] for more information.
• The applicant shall contact the Forestry Inspector prior to construction to ensure that any trees protected under City tree By-laws have been properly protected according to City standards.
• If a neighbouring Distinctive Tree will be damaged, it is recommended that the applicant contact the neighbour prior to excavation to discuss mitigation measures.

If tree removals are required

Private trees

If the tree is 50 cm or greater in diameter (157 cm circumference), a Distinctive Tree Permit is required. Please visit How to Apply for a Distinctive Tree Permit for more information on the permit requirements. Please note that you can no longer apply for a permit at your local Client Service Centre. Visit Ottawa.ca/urbantree for more information, including how to measure a tree.

City trees

If removal of any City tree is requested, contact Forestry Services through 3-1-1 and a Forestry Inspector will contact you. If tree removal is approved, the compensation value of the tree will be assessed and this value must be paid to Forestry Services in addition to the $700 refundable tree planting deposit; the removal and replacement costs will be the responsibility of the applicant. 

Building construction completed

• Once a new building is complete, the applicant is required to plant a new tree in the right-of-way adjacent to the new dwelling. If there is no space to plant a tree in the right-of-way, the tree may be planted on private property. The tree shall be planted according to the City of Ottawa Tree Planting Specifications for Infill Properties. 
• Once the tree is planted, contact 3-1-1 and request an infill tree planting inspection. 
• A Forestry Inspector will visit the site to inspect the tree. If the tree has been planted successfully according to the City of Ottawa Tree Planting Specifications for Infill Properties, the $700 deposit will be refunded. If the tree has not been planted or does not meet the City specifications, Forestry Services will retain the deposit and either plant a tree on the right-of-way (space permitting) or elsewhere in the City.
• In the event there is a City tree in the right-of-way that is to be retained during construction, the refundable tree planting deposit will be retained to ensure that it is protected properly, and will be released only once the Forestry Inspector determines it has not been damaged through the construction. In the event the tree has been damaged, additional charges and fees may apply according to the Municipal Trees and Natural Areas Protection By-law 2006-279.
• If the removal of a City-owned tree was approved by Forestry Services prior to construction, replacement tree(s) will be required in accordance with the agreement made at that time.

Tree planting specifications for infill properties

Proposed planting locations and species must be approved by Forestry Services prior to planting within the right-of-way (ROW), usually through submission of a Landscape Plan. If the planting does not meet Forestry Services' specifications, the $700 tree planting deposit will not be refunded. Below are the guidelines; where space is limited to plant a tree, please contact the ward Forestry Inspector to discuss options.

Any trees planted within the ROW are immediately protected under the Municipal Trees and Natural Areas Protection by-law (2006-279) and cannot be moved after planting.

For any City-owned tree that is to be retained, the Infill Tree Planting Deposit will be held as a security to ensure that it is protected properly, and will be released once the Forestry Inspector confirms that it has not been damaged through the construction. In the event the tree has been damaged, additional charges may apply. Refer to the tree protection guidelines for more information.

Planning for planting in the ROW:

• Determine how much open (soft) space is available in the planting location. A minimum of 9 m² (1 m depth) of good soil is recommended to support one tree. If there is insufficient space to plant in the ROW, planting on private property will be considered.
• Note the locations and types of existing obstacles, above and below ground, using existing surveys plans, observations, and have utility locations marked by contacting www.on1call.com or 1-800-400-2255 (call before you dig). Use this information along with the setbacks listed below to determine a suitable planting location on the site, and the appropriate size of tree to plant.
• If there are overhead wires present, consult Hydro Ottawa’s tree planting guidelines. 
• If sensitive marine clay has been confirmed on the site through a geotechnical report, only small-growing, low-water demand species may be planted a minimum of 7.5m from the house. 
• Ensure no future conflicts with building projections, overhead or underground utilities that would pose future maintenance problems or impede full development of the canopy.
• Tree species must be appropriate for the site (size at maturity, salt tolerance, etc.). There are many resources online to help select the right tree for your lot. Keep in mind that often native trees are best adapted to the local climate but less so for high salt conditions.
• Planting must be done according to the specifications in Forestry Services’ tree planting detail.
• Trees must be watered regularly following planting to ensure proper establishment. Inspections will take place in the autumn at which point the City will assume maintenance responsibilities for trees planted in the ROW.

Key spacing (minimum distance) guidelines:

For deciduous trees:

• Minimum 50mm caliper stock
• 1m from utility boxes
• 1.5m from sidewalks, driveways, walkways, fences, sound walls, and old stumps.
• 2.5m from curbs, hydro transformers, or behind fire hydrants
• 4-7m from any part of an existing tree, depending on canopy width
• 10m from bus shelters and community mailboxes

For conifer (evergreen) trees:

Follow same setbacks as deciduous, but due to the widest branching being at the base of the tree, conifers need greater setbacks for ground-level obstacles.

• Minimum 200cm height stock
• 4.5m setbacks from sidewalks, walkways, driveways, and curbs.
• Do not plant on corners where sight lines will be compromised.

How to get your Tree planting deposit back:

• Once the tree is planted, contact 311 and request an “Infill Tree Planting Inspection”. Inspections will take place in the autumn of each year.
• A Forestry Inspector will visit the site to inspect the tree. If the tree has been planted successfully according to these specifications, the $700 deposit will be refunded. If the tree has not been planted, Forestry Services will retain the deposit and either plant a tree on the right-of-way (space permitting) or elsewhere in the City.

For more information call 3-1-1.

Key Definitions

“arborist” means an expert in the care and maintenance of trees and includes an arborist qualified by the Ontario Ministry of Training, Colleges and Universities, a certified arborist with the International Society of Arboriculture, a consulting arborist registered with the American Society of Consulting Arborists, a Registered Professional Forester or a person with other similar qualifications as approved by the General Manager;

Critical root zone (CRZ) - The critical root zone (CRZ) is established as being 10 centimetres from the trunk of a tree for every centimetre of trunk DBH. The CRZ is calculated as DBH x 10 cm

DBH” or “diameter at breast height” means the measurement of a trunk of a tree at a height of one hundred and twenty (120) cm

Newly planted trees

Newly planted trees require a regular supply of water to survive since they do not have a network of roots and are less able to absorb water. Always water the hole before planting and water regularly.

During dry periods, use a soaker or drip hose. The best way to ensure that the water reaches the roots is to maintain the earth ring or saucer around your tree. Place the soaker hose in the earth and water for two hours twice a week. If it rains for two or more days, watering is unnecessary.

Watering should be done in the morning before the heat of the day. If the water is pooling or running off to surrounding areas, either the flow rate is too high or the ground is saturated and you should stop watering. Use a hose water timer to ensure that you don't over water.

Mature trees

A tree that has been planted for 15 years or more may appear to be able to survive without your help. Its root system can reach water and nutrients even when surface conditions appear very dry. Trees of all ages suffer when there is a drought. Water does not reach trees planted in areas such as sidewalks, patios, or raised lawns where water naturally drains away. Be sure to pay extra attention to these trees. Extra water to all trees during a drought can prevent pests or disease.

Trees near foundations

During very dry weather, soil particles will “lock up” water molecules at a threshold level. This is especially true of clay soil particles, which have very strong electrical charges and hold water very tightly. This is the beginning of a battle between soil particles and roots for water uptake. Clay soils will actually shrink in volume due to water loss, which reduces the soil’s capacity to support adjacent structures such as foundations. Foundation damage from unstable clay soils may be avoided by ensuring that trees close to foundations are always well irrigated. Again, the overnight trickle from a garden hose will help maintain the water balance necessary to keep clay based soils stable. During drought conditions, water overnight weekly. Should you require additional information, please call 3-1-1.