Excavating near a tree
yonyonsin
| Posted in General Questions on
Apologies if this question is beyond the scope of this forum. I’m trying to figure out how close to a tree I can excavate for a footing, without doing unacceptable damage to the tree. The attached drawing shows the basic situation. The tree is some sort of Asian elm, 40-50 feet tall, with two conjoined (inosculated?) trunks, each about 20″ in diameter.
I asked an arborist about it but he was very reluctant to give an opinion. (Makes sense — he has nothing to gain and a lot to lose by approving any kind of damage.) How do I go about figuring this out?
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I bet no matter which option you choose, the tree will be fine. Which is exactly the problem--it will have the last laugh. In short order it will be sending roots into your footer tile. I'm all for trees close to the house, but not that close. Two twenty-inch elm logs would yield a nice big dining table.
Ray,
there aren't many Elms left, so I appreciate your interest in saving it. I have a large sugar maple very close to my house. It cradles my deck and offers shade and comfort.I love having it there. I didn't have to excavate too close to it, however, except for a couple of post holes for the deck, and it has been very healthy for the 40 years it has been our companion.
I don't think anyone can tell you for sure, an arborist included, whether a tree will survive close by excavation. Some of the root system will undoubtedly be destroyed, compromising the trees ability to get water and nutrients. But, the will to live is tenacious, and the tree will likely survive, even if it struggles for the first few years. You can always help it out with watering if it appears to be struggling, but no guarantees. I usually go with the notion that it may live and is worth giving it that chance. Others don't want ANY tree anywhere near the house,
I built much closer to a tree than that--near a corner so we essentially took out 1/4 of the roots. It's only been 1.5 years since the damage but it's fine so far. Here are the tips we got for protecting it from our excellent arborist (who did not guarantee it would be OK):
1. Cut the roots with a saw rather then ripping them with an excavator. When they get ripped, follow them back to where they aren't damaged and saw them there. This make them much better able to heal, and make rot less likely to start.
2. Put a 6" deep layer of wood chips around the tree, where you are not excavating, to minimize compaction of the dirt around the tree, which would choke off oxygen to the roots, and reduce water filtering down to them. It's not just for machinery--foot traffic is just as bad for compacting soil and by the time the job is done, there will have been lots of foot traffic.
3. Rope or fence off around the base of the tree, so it doesn't become a spot to lean equipment, etc. If feasible, also much of the root area.
4. Be sure to have clear communication with your excavator, including not piling material in that area.
You can't expect your GC or excavator to agree to be responsible for preserving the tree--they can't guarantee anything. But you can put the protection provisions above in a contract.
I don't think the stepped footprint is necessarily better than the original. The roots aren't that predictable.
You may also want to install a root barrier between the root and your foundation and drainage system. Roots clogging drain pipes is more likely than roots damaging a foundation. There are plastic materials made as drain barriers, but we found the $20 4x8 "plas-tex" sheets at the orange big box store were easier to work with and cheaper.
Imo, the tree will be fine. Oftentimes on a healthy tree you can chop out nearly half of the roots and it will be fine. Keep a nice layer of mulch on it and extra water for the first year. Regarding roots in the drain tile, use extra clean stone in that area use solid pic pipe in lieu of perforated ribbed tile. Add a few more footing bleeders and you'll be fine.
Plan on cleaning your gutters frequently as well.
Ray - The least damaging foundation near a nice tree is concrete piers with a reinforced grade beam. I have built 2 such foundations within 3-6 feet of large trees that I wanted to keep. The trees and foundation have held up fine for the last 12 years, and 16 years respectively. I hand dug the holes for the piers that were near the tree, using a sawzall to cut the roots. The future roots have plenty of dirt to grow into rather than into the piers. The piers were 4-6 feet apart. No gutters! The other advice above from Howard, Charlie and Rick sounds fine given the distance of the tree from the building, even with the "preferred footprint". Good luck to you on your project.
While I am not the expert, landscape architects up here in Ottawa recommend no work within 6' from the drip line of the tree. Drip line being the projected surface area that the canopy/branches cover in the middle of summer. We work on large subdivision, and any trees that must be preserved during construction are to be protected with an orange snow fence, as a minimum delineation. Like others, my hunch is that the tree will survive if you encroach within its drop line a little bit and take a lot of care when dealing with the root system.