Roots busting foundation / slabs: Validate with reply

[M.D. Vaden]

I've read a lot of concern about tree roots busting foundations of houses, but have never been called yet to deal with a tree causing that, as most of my work is with medium and small trees.

But distributing flyers in Beaverton, Oregon, I did see a poplar that raised the foundation of single level home in one spot to crack the foundation concrete to about a 1/2" crack. Maybe a 1/2" to 1" lift in that spot. The tree was planted about 3 feet from the house.

Concrete driveway slabs - all the time. I see this every month, and removed a concrete driveway last summer, to install pavers. The driveway was demolished by Japanese black pine and Austrian pine root. Oddly, some grew under being 3" in diameter, but in the middle, farther from the trunk, a couple of them became 6" to 7" in diameter. Had to work hard with the backhoe to remove them.

Anyhow, its the building foundations that I'm very interested to hear validation of. I doubt that a root can do much when there are 2 or 3 stories of weight over the sidewalls. But what about the single story homes or slab foundations?

If roots can get underneath a driveway slab, it seems that they should be able to get under a house slab too. But I have not seen one in-person.

 

[clearance]

I have seen foundations cracked, with big trees as the culprit. I have also worked a lot of construction. If you don't want to saw down the close trees then put in lots of rebar. And I mean lots, 3/4" (20mm) in the footings and walls, it is pretty cheap and its amazing how many people don't want to use it, or skimp on it. Driveways as well, a matt of 3/8" (10mm) properly tied will do wonders, the concrete may crack after time, but the crack will be hairlike, not spreading forever.

 

[SilentElk]

It is an issue. Around here a ton of people have rentals around the college. The elms just sucker like weeds right at the found dation and some are too cheap to remove the tree when its very young. Instead they wait years until the tree is basically imbedded in the house when it's 60 ft tall.

 

[Toddppm]

I recorded a show on TLC I was watching about a Sweet Gum in CA that got under the slab of the house and caused it to crack. The worse room was about 1.5 " out of whack. They brought in engineers and contruction consultants that told them they need to gut the house and replace the entire slab, then rebuild etc. to the tune of $750,000.
The tree had been removed 2 years earlier and was 70 ft. away supposedly. What they didn't mention was who originally built the place and if the construction of the slab was the actual problem that the tree took advantage of.
What a crock of ????. The show is called "This house must go"

 

[Boa07]

We have some serious issues in Oz with legal precedents being set in this regard, I'll agree with Clearance in that almost all the potential for vegetation and foundation conflicts can be removed/remedied through appropriate engineering of the foundations at the outset. It can be even simplier in certain circumstances...through the construction of a barrier wall around the building foundations themselves, cutting off both the foundations and the subgrade beneath them from the influence of any roots at all...this does cost and unfortunately at least here it would seem the cost is viewed as being too great.

 

[John Paul Sanborn]

There have been some papers in JoA regarding heaving and fracturing of pavement from trees. The statistics confirm what was stated above about construction. Trees get blamed for a lot of problems stemming from poor design/construction.

We've been over this before, but... trees grow by putting on a thin layer of cells inbetween static "dead" layers. The root cap can push small particals of soil away, but will move around larger soil peds. I've moved large slabs and see flat topped roots that grew under them.

Another aspect is that the biggest limiting factor to root growth is O2 content. If the free O2 falls below something like 8% most trees will not establish roots into that soil, or old roots die.

So tree roots that have a plumb of moist, aerated soil will grow. Fine roots will invade and exacerbate the weakened condition of a structure; e.g. pools, ponds, sewer laterals, drain-tiles... Next, when backfill is done with dynamic clays, or a good gravel/sand base is not used, trees can exacerbate the seasonal hydraulic expansion and contraction of the clay soils.This can cause heaving of slabs and push in walls.

This all said, I would like to see someone take a look at Matthecks work with pipelines and see if large roots can exert sufficient heaving forces during heavy weather.