Trees Near the House:
What Roots and Branches Do to Foundations, Sewer Lines, Roofs, and Paving

Branches, roofs, and gutters

This is where trees show up most in Russ’s reports. Branches that touch or hang over a roof rub the surface when the wind moves them. They drop needles and leaves that hold moisture on the roof and clog gutters. Shade and debris together are a big part of why moss does so well on Portland roofs, and the post on moss on Portland roofs covers what that does to shingles.

Overhanging branches also give squirrels and rats a path onto the roof and into gaps at the eaves.

The rule of thumb in Russ’s reports is to keep branches trimmed back at least 5 feet from the roof and the walls. He has also written up a tree trunk that was crushing the end of a gutter, and a large branch pushing down on the overhead electrical service lines to a house. That last one is for the power company or a certified arborist, not a ladder and a saw. The gutters and downspouts post covers what full gutters do to the rest of the house.

Branches near the power line to the house are a separate question, and the post on the overhead electrical service covers who usually handles that trimming.

Roots and the sewer line

Many older Portland-area houses have clay tile or cast iron sewer lines, and roots find the joints. A sewer line carries water and nutrients, and the joints in clay pipe leave small gaps for fine roots to enter. Those roots grow, catch debris, and can eventually block or break the pipe.

A home inspection can’t see a buried sewer line. A sewer scope can, and the sewer scope post explains how that works. Trusted Home Inspections recommends one on every house, and a big tree between the house and the street is one more reason.

Roots go after other buried lines too. On one inspection, Russ found the water meter vault packed with roots from a large tree growing right beside it, enough to get in the way of reaching the shutoff.

Roots, paving, and retaining walls

Concrete walkways, driveways, porch steps, and patios are thin and light, and roots lift them easily. Russ’s reports flag offsets over about 1/4 inch in a walking surface as a trip hazard, and tree roots are a common cause. He has written up concrete driveway slabs lifted by roots, an asphalt driveway cracked and heaved by the tree beside it, and a concrete retaining wall along a driveway that was leaning and displaced, most likely from the roots of the large tree next to it. That wall went to a structural engineer or landscape contractor.

In the City of Portland, the adjacent property owner is responsible for repairing a sidewalk, including damage from street tree roots. Pruning those roots needs a permit from Urban Forestry first.

Roots and the foundation

This is the one buyers worry about most, and it’s usually the least direct. Roots rarely push through a sound poured concrete foundation. They follow moisture, grow along the wall, and work their way into cracks that are already there.

The bigger effect is often on the soil. A large tree pulls a lot of water out of the ground in summer. On clay soils, which cover much of the Willamette Valley, soil that dries out shrinks, and that can add to settlement near the tree. The post on what Portland soils do to a foundation covers how clay moves with the seasons.

Russ’s reports use about 10 feet between a trunk and the house as a rule of thumb, and note trees planted closer than that. Stumps left against the house get noted too, because rotting wood near the foundation can draw wood-destroying insects.

Tree rules and what the inspection covers

A tree you’d like to remove after closing may need a permit, and that’s worth knowing before you count on it.

The home inspection looks at trees where they touch the house: branches on the roof, roots lifting paving, trunks against gutters or siding, vegetation holding moisture against the walls. It doesn’t judge a tree’s health or whether it might fall. When Russ sees a damaged or leaning tree, the report sends it to a certified arborist.

If you’re looking at the outside of a house before making an offer, the exterior showing checklist covers the rest of the lot. To set up an inspection, you can book online.