Design of a tree as a structure / inspectors gone wild 15

[jwilson33]

A client of mine installed small light fixtures (12" arm, small single bulb light with about .5ft^2 of projected area. The trees are 40ft+ tall oak trees with 12"-18" trunks. The inspector is claiming that the trees become structures as defined by the IBC Code 2009 because of the addition of a fixture. He now wants full calculations to demonstrate the tree will not blow over in a 90mph wind event.
We have gone back and forth, but he has dug his heels in and told the client they have to file for an appeal through the zoning board of appeals. I have demonstrated by calculation that the load added to the tree is less than 2% of the current load on the trunk alone and therefore the added load does not warrant a structural upgrade. But he rejected that argument because this is a change of use and the tree must now fully meet the current Code.
I am looking for something in the Code that might demonstrate that the tree does not become a structure by addition of a light fixture, or some other slam dunk wording. I am sure he knows his argument is foolish, and the reasons for this probably have nothing to do with the lights on the trees.
A picture of the installed fixture is attached.

 

[SLTA]

"If you disagree with my decision you are welcome to go to the Building code board of appeals. You have 30 days to do so."

OH PLEASE OH PLEASE OH PLEASE do this. I would LOVE to hear what happens at this meeting.

Please remember: we're not all guys!

 

[SkiisAndBikes]

My office once received a review letter, similar in absurdity. The request was to provide calculations confirming how much the lake level would drop when running snow making pumps for the local ski hill at full volume. The lake was 15,000 sq.km (5,800 sq.mi.) with a volume of about 10350000000000000 cubic metres of water (directly connected to another much larger body of water). I recommended a very professional response containing the calculations showing how miniscule the drop would be .... something in the order of millionths of a millimeter.

 

[Spartan5]

While not a structural engineer, I regularly look at this forum and learn lots of interesting things here.

That said, and to play devil's advocate a bit; maybe the inspector and/or permitting agency desire that trees not be used for the mounting of lights or other structures. I think that the "full calculations" requirement is just the means to that end. Are there real chances that the light will increase the likelihood that the tree blows over? Not even a little bit.

On the other hand, in contrast to a treated wooden pole, this tree is a living organism. Though strong and sturdily mounted now, there does exist a measurable potential for the multiple puncture wounds to contribute to disease or insect infestations which could lead to the failure of the mounting of the light or trunk upon which it is mounted.

Just a thought.

 

[cvg]

long term health of a tree is certainly not within the realm of the inspectors or the cities jurisdiction. failure of the mounting might cause a light fixture to fall off the tree, certainly no a public safety issue. building departments are supposed to protect public safety. this is not a safety issue.

 

[hokie66]

I tend to agree with Spartan5. They don't have a law against mounting lights on trees, so they are using what powers they have. But I don't think trees are suitable as light poles, as they blow over and fall over. Oaks have shallow root balls.

Not often I support obstinate inspectors, so preparing for abuse...

 

[cvg]

so does mounting a single bulb, 12" security light on your garage require a permit? or on your backyard shed? or anywhere on a pre-existing structure or not? I fail to see why this is an unsuitable use. Not much larger than a medium sized bird house.

 

[TehMightyEngineer]

I see little to no difference between a wooden post and a living tree. They're both wood and both anchored into the ground and both susceptible to the same failures and damage (rot, insects, etc.).

Maine EIT, Civil/Structural.

 

[hokie66]

They may be more worried about the wires than the fixtures. If they were solar powered, maybe the issue would go away.

 

[TehMightyEngineer]

Maybe a good question for the inspector is what if the tree was dead? Then it's just unsawn lumber and should be no different than any other post supporting a light.

Maine EIT, Civil/Structural.

 

[RHTPE]

TehMightyEngineer -

Maybe a good question for the inspector is what if the tree was dead? Then it's just unsawn lumber and should be no different than any other post supporting a light.

Perhaps - but does the "post" have a proper foundation?

I would go the appeal route as soon as I received the letter from the inspector. However, if the inspector were to require annual inspection of the "post" and the light fixture's anchorage to said "post", I could support that.

Living in a rural area, I have used trees for the support of a variety of things. Long-term attachments to trees can suffer from one or more of the following problems:
- as the tree grows, the live portion may grow around the attachment making its removal difficult;
- depending on the size of the attachment, the growing tree can literally 'push' the attached item off its connectors, or;
- the attachment can facilitate the ability of rot and/or disease to enter the tree.

Structurally, I do not see a problem here. It really is a long-term performance issue, and from this perspective only the inspector may have legitimate concern. Otherwise, I think he's being a bureaucratic ass.


Ralph
Structures Consulting
Northeast USA

 

[jwilson33]

Well, it hasn't been confirmed in writing yet, but the client was told verbally that the inspector has backed off and is accepting the fixtures as they are. I was almost looking forward to seeing this debate go public at a town meeting but it seems that isn't going to happen. I will share any more insight, for whatever it might be worth, if I get any. Thanks to everyone for sharing in this post, it has been interesting reading all the comments and perspectives.

 

[TehMightyEngineer]

Raplh, those are some good points and I agree those should be considered.

Maine EIT, Civil/Structural.

 

[IFRs]

Call it a wood pile, there are easy calcs to copy and use. At this point you have spent more time fighting it than giving him a 3 line calc.

 

[bridgebuster]

I wonder how Tarzan got past the building inspector?

 

[oldrunner]

Although the comments are all over the place - the one thing that I would be looking for is the connection of the light to the tree itself. It might last a year. I would rather see a band of some sort around the girth of the tree with a positive connection. I don't know how long the screws are in the photo - but sometimes where the screws go in, there may be eventually rot. Others may have a different experience - and now there is a liability problem if the fixture drops off the tree.

But putting a band around tree presents a problem also - as the trunk will get larger and may grow over and around the band. (Have an example in my rear property where we put up a hammock and over the years got an ugly growth where the rope was present.) Probably have to adjust the band each year - or at least look at it.

Being a pole guy, estimating the size of the tree and the various shape and coming up with a structural analysis (which is probably only good for next year) is pretty easy. The real hard part is verifying the foundation or the roots. Are the roots spread out or does it go straight down? Then there's the problems of the Woodpeckers which in my area are riddling many of the trees. I've also got boles problems over almost all of my property - they kill the roses - but I don't think that will affect you. If the tree is a digger pine, then you don't know when they will come down. Had one on my property (about 200 feet) that fell across the road. The county cut it up and dumped it on my property and it took about a year to cut it up and burn it. (Tree was originally hit by lightning and lasted about seven years before it fell).

Come to think of it, the electric company and the telephone company put their lines on some of the trees on a property in the forest that I know about. Maybe they get away with this because they are utilities and don't have to conform to the building code. This area gets some big winds and sometimes the lines snapped off the trees and you lose your power. Then it might be tough when the telephone company gets the lines mixed up and your getting your neighbors telephone calls. And the telephone fix-it people swear that you have no problems because it says so on the computer in front of them. Looks like a bug in that computer program. You know, I don't think their computers programs are as good as Risa or SAP2000, but that's their problems and for us to sit through the night with no power. Which means that your light on the tree that the inspector has dinged you for, may be just for spite, might not go on.

Almost forgot - ground penetrating radar can probably show you where the roots are.

 

[malikasal]

The title reminded me of a project my company did a while ago,but it was a tree made of Steel sections, not a real tree!!!

Please go to the building code board of appeals i would really like to see how this goes .




“If you don't build your dream someone will hire you to help build theirs.”

Tony A. Gaskins Jr.

 

[RHTPE]

There are practical & durable ways to structurally attach to a tree trunk. oldrunner mentioned possibilities.

My experience has found the following:
[ul]
[li]Banding around the tree is risky - it may effectively girdle the tree and kill the portion above the band.[/li]
[li]The tree's living band (bark + sapwood) will grow around and embed some attachments, usually when the entire perimeter of the attached item is in full contact with the trunk.[/li]
[li]Items like signs and other broad surfaces tend to get pushed outward as the tree grows, straining and ultimately failing the fasteners.[/li]
[/ul]
In my opinion, the most reliable fastening method is through-rod(s) - and it causes the least trauma to the tree. This is what arborists use to strengthen a "Y" branch. Stainless steel is best for the long-term. The tree will ultimately grow around the edges of the attached item if its contact area is reasonably small - perhaps a width <= 15% of the tree's diameter. A large contact area runs the risk of the outward growth of the tree pushing with a force greater than the capacity of the fasteners.

My comments are based on first-hand experience over the course of my life. From tree-houses to running phone lines to attaching flood lights, I've been there, and I've seen the long-terms results of various fastenings.

Now, the engineering stuff aside, perhaps this is more of a liability concern for all involved. If the light and its attachment can remain secure, the falling fixture hazard is mitigated. But how is power supplied to the fixture and what is the associated hazard if a storm takes down the tree? Who is exposed should the unthinkable happen - the inspector or the owner or the designer? Probably all who were involved, since "accidents" and "acts of God" can still blamed on some specific person or persons. Common sense does not apply.

While the comments provide numerous opinions and suggestions, I look forward to what the final outcome will be.



Ralph
Structures Consulting
Northeast USA

 

[jvvse]

I had a blast reading this thread. Now I don't feel so bad about the inspectors I deal with.