View Full Version : Decks around trees

05-28-2008, 08:11 PM
Has anyone had experience with building decks around fairly large girth trees? I am looking at a project now where the homeowner wants to have a deck built (~550 sq ft) extending out from the house and around a large (42" diameter) tree such that the tree pretty much ends up in the middle of the deck. He is an arborist and really likes to look at trees, I guess. My big concern is no matter what you do there will be heaving of the deck as the roots start to encroach on the footings. We don't have a frost line to worry about but even by digging deeper you just destroy more roots, not good.

It is an evergreen, not sure what species exactly, similar to cedar but the drip line extends at least 8' beyond the trunk and apparently the root system is diverse and close to the surface. He wants an octagonal opening around the base of the tree which only adds to increasing the number of footings. Keeping the number of footings to a minimum is critical but with the the shape of the opening and low ground clearance I don't think I will be able to set joists on a beam. If I can't get him to change his mind I may end up begging out of this one. I would appreciate any feedback. Thanks.

05-28-2008, 08:39 PM
If code would allow it why not cantilever in towards the tree rather than have footings right up against it? Otherwise just tell the owner that the tree could very likely die if you build the deck around it like that and if he still wants to do it then build it. Just make sure you put it in the contract that its not your fault if the tree dies.

Joe Wood
05-28-2008, 08:54 PM
With old established trees it's sometimes better because you pretty much know where you can locate the footings because the major roots are already there, but then sometimes there's nothing but roots after you dig down a few ". Sometimes you need to be pretty creative with your footing locations, so that you can get even more creative with your beam/joist layout to make it all work :-)

Does the tree get only seasonal rain or is the area irrigated? If irrigated, you need to now cap it and install something like drip under the deck to keep the tree watered, but then you have increased under the deck moisture issues to deal with.

I'd say go for it, and use an all plastic decking that can take any moisture and staining from leaf/fruit drop.

05-28-2008, 11:59 PM
What is the span across the deck? It might be possible to design it to have two large beams spanning perimeter to perimeter & the rest of the deck hung off of them. That way you'd avoid needing any footings near the tree, and all your footings would be as far as possible from the main root section.

The beams might need to be fairly large, and they would have to be pressure treated.

Another thought might be driven pilings instead of poured. The disturbance would be much less than digging holes, less chance of damaging the tree also.

05-29-2008, 12:03 PM
Thanks for the replies, I appreciate that.

Let's see, it only gets seasonal rain no irrigation, although I was planning on using 4/4 x 6 Ipe. I predrill everything and use surface screw fasteners. There is only going to be maybe 10" of clearance under the deck, in this area, not enough room for a beam, as that would have let me place footings the maximum distance apart. My original plan was to build a joist framework that would be supported by concrete footing pads. Not possible to excavate any dirt because you would only be getting into the roots. I have advised the owner that you may get some cupping in addition to heaving, not to mention discoloration from the drizzle of resin tannins from the tree. Can't go any higher at this point because it would bring the outer end of the deck above 18" which means having to pull a permit and the owner is not too keen on that.

Maybe it is best to try and persuade the owner to pull a permit in order to get higher clearance so I can stick a beam under or to just stay away from the tree all together. Thanks again.

Bill Robinson
05-29-2008, 01:01 PM
Easier to think about with a pic.

What about raising the deck level near the tree, call it a seat, so you can add structural support?
Bill R

Joe Wood
05-29-2008, 02:21 PM
Maybe, extend it out level from the house, but raise it up around the tree?

S. Donato
05-29-2008, 05:18 PM
what about just flush framing your beams? with 18" you have plenty of clearance to do that. JMHO

05-29-2008, 08:33 PM
Thanks again. Here is one of my overview sketch renderings which I typically provide to homeowners as a way of offering different options to choose from (couldn't download pdf as it was too big). This one is based on his preferences. As I mentioned, he is an arborist and really wants to be able to directly visualize the base of the tree as it emerges from the ground. That's his thing.

The sidewalk is considered ground zero, 0" and the elevation change to just under the front door threshold is 25". That gives me four, 6 1/4" rises to the upper level. The area around the tree is 12 1/2" above ground zero but the area underneath is only about 10" as it bulges up from the roots. The outer most area nearest the retaining wall is where it is dropping off so it is about over 2' above grade, putting him into the 'get a permit zone'. The canopy or drip line and associated roots extend probably 8' beyond the trunk. The octagon opening allows for about 2' of clearance around the trunk which exposes the underlying soil/roots.


Dick Seibert
05-29-2008, 09:55 PM
I built a home on a lot with a lot of oaks, the owner was an attorney who said (half joking) that if I killed one tree he'd sue me for everything I was worth. I had the architect design the entire structure on 27 telephone poles, house and decks. Even the entrance was a bridge between telephone poles, but that was '73 before our earthquake codes came into play and I don't know if it would engineer at this point. We just drilled the holes and had the drill rig boom set the poles for us, we did have a pump there too and pour some concrete into the bottom of the holes for the poles to sit on, but they were backfilled with dirt.

It was quite spectacular and we didn't kill any trees, he was a party person and always invited me to the parties because people wanted to know about the house, there were parties with the governor and attorney general asking questions about the trees coming through the deck, we didn't attempt to let any grow through the house itself, although he wanted to do that if possible. Here's a book on the subject (http://www.amazon.com/gp/reader/0882661701/ref=sib_dp_pt#reader-link).

06-01-2008, 09:24 AM
what about just flush framing your beams? with 18" you have plenty of clearance to do that. JMHO

My thoughts as well. I am sure he knows as an arborist the dangers of putting footing in the root system. Betterheader makes a stainless steel flitch beam that I can imagine would span great distances.
I find more often then not in our rocky glacial till soil its far faster and cheap to install beams then it is to dig more footings

It seems you need to get more creative on comming up with solutions that work with in the customers specs.


bread and roses
06-06-2008, 03:29 PM
My first thought would be helical anchors, redi-footings, or the type of footings that use four soil nails in a pyramid- I looked for the recent thread that mentioned them, but all I could find was another thread from someone who, like me, had forgotten what they are called.

For what it's worth, I worked next to a deck built around a tree last summer- it looked quite old, at least 15 years, and the tree and deck were both doing fine (deck was cedar or redwood, tree was cedar). It was higher than yours, and the deck was scribed to the tree trunk, within about 2". I think your octagon plan is better.