Harming Redwood Roots. From one that has "harmed" many.

I tried to answer this question in the "comment section", but wrote too many words. So, I put it here as a "Post".

"How close can a proposed building foundation typically be to an existing mature redwood tree without harming the tree and it's root system?"

First, you have to convince me that you have a very, very good reason for needing a building there. You should never build ANY kind of a building around a redwood. The redwood always wins!

I know this stuff is boring to the folks that don’t want to know anything about redwoods, but they “know that they love them”. But, please read! You WILL learn something, I promise!

I don't have nearly the experience that some have, but I have experience that not many have. I have cut and fallen redwoods, I have built roads with a Cat through them, I’ve dug out stumps. I’ve split every kind of a redwood split product that can be made out of redwood. I’ve built many structures from redwood. I’ve built many structures near redwoods. I have what is known as “Common Knowledge” about them.

Here's why you will lose if you build around a redwood: The common misconception about a redwood is that it only has a very shallow and weak root system. Nothing can be further from the truth. More later.

Fir trees usually have two major tap roots, that are usually found on the uphill side of them. They go deep down, and they anchor the tree very firmly to the soil. I know this from dynamiting them off of hillsides for road building. I dug a small hole between the roots, placed a small charge, and touched it off. That gave me a burrow between the tap roots, and under the center of the tree. Then I placed a bundle of dynamite under the tree, along with fertilizer and diesel fuel, I back-filled the hole with soil, lit the fuse and ran like hell. The tree would jump out of the ground about a foot. With its tap roots gone, it would fall right over.

Redwoods are not that simple. Even though they have “No tap root” they have dozens to hundreds of what I will call “anchor roots”. The anchor roots extend downward at a 30 to 45 degree angle, if the tree is on flat ground. They seek firm soil and they will extend downward until they reach it. These anchor roots can be found as deep as 12 feet, they quite commonly are found at 10 feet deep. On hillsides these anchor roots can extend almost straight down. That is why you can see redwoods growing above a cut road bank. You wonder how they stay there. I know from digging the stumps out of hillsides that they have the roots that seek the tight soil. In most all cases they have roots that go straight down on the lower side of a steep hillside. That may answer some peoples questions. Redwoods don’t have tap roots, they have MANY very sturdy “anchor roots”.

In combination with the anchor roots the redwoods have thousands of “feeder roots” that seek nutrition for the tree. These roots are very fine. From hair like, to pencil size. These are the roots that you see when you dig around the base of a redwood. These surface roots are what give people the misconception that “the redwood trees only have surface roots”. The feeder roots are very resilient and grow quite rapidly. They grow to where the food, and water is, in a very short time. (I was going to say a heartbeat, but we have enough anthropomorphizing of redwoods. Redwoods are not people, people. It‘s okay to love them, but they don‘t have toes) Redwood's feeder roots grow rapidly in the direction of needed nutrients. People just walk to the grocery store. Redwoods are much more adapted to where they live than we are. If the redwoods were people, I wouldn’t be surprised to find redwood roots coming up in the beer walk-in. They are not people, it does the tree a great disservice to think of them as such, please get real!

As I’m am sure you realize by now, the redwoods don’t make it to be thousands of years old without a sturdy and well adapted, and resilient, root system.

Now, to answer “Anon’s” question: Don’t cut into the plain of a thirty degree angle down from the base of the tree. Because that is the area of the anchor roots. On hillsides measure the angle down from the surface angle and add to it. On a 60 degree hillside you can dig straight down, if you are foolish enough to do that. I have! Stay without of that plain, and the redwood won’t even acknowledge your presence. You will not harm the tree even a speck! But you will be repairing your building a bunch. Don’t do it unless you need the building very badly.

I want to say that everything here is from my own direct knowledge. I have no education to rely on, so I would sincerely appreciate any corrections from the erudite.