View Full Version : Decks around trees
05-29-2008, 01:14 AM
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
05-29-2008, 05:29 PM
Bill, instead of placing the joists on a beam, what about using flush girders and hangers? If the budget allows, perhaps you could span most of the distance with some treated lams to minimize footers around the tree.
05-30-2008, 01:45 AM
Good idea but unlikely the HO will go for the additional expense of treated lams.
There is only going to be maybe 10" of clearance under the deck, in this area, not enough room for a beam & joist, 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. The octagonal opening is going to require a few more footings for support. Not possible to excavate any dirt because you would only be getting into the roots. I was planning on using 4/4 x 6 Ipe. I predrill everything and use surface screw fasteners. 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
06-29-2008, 03:02 AM
Under these circumstances I would keep the deep footings at the perimeter with intermediate 'floating' concrete pad supports...i.e: support the deck but allow natural movement.
I would let it float. If you are making a round deck,cut a cicle out of cardboard that goes around the tree and radius off that.
07-18-2008, 11:49 PM
We always build a square frame work around the trunk. The size of the square and how far off the trunk it sit depends on the tree's root structure. If you're close enough to the tree, you can then frame in closer to the trunk off your initial square by blocking inwards to create more of a circular framework.
You may have to keep the framework a couple feet off because of the roots. In this case set your framework down and cantiler your joists over the framework to close in on the trunk. I'd cut the decking in a radius a 3-4" away from the tree and finish up closer to the tree with a 1" think trim ring which you can make into an octagon. How far the framework stays away from the tree will determine its growth potential.
Hope this helps,
Dan Milford (DW Elite Decks)
07-24-2008, 03:44 PM
Have you thought about Bison deck supports for the deck? I think it would be a much easier job for you and a hero in the arborist community, besides that type of tree usually has very shallow roots and if they had severe weather I would be afraid the tree would go over and take the deck the ledger and the rim of the house and the arborist with it!! If you use the bisons YOU don't disturb the root structure and are off the hook for any blowover liability I would think.
Have you thought about building the deck frame up close to the tree and then using approved joist hanger screws from simpsons and making the deck so that every few years it could be expanded to accomodate the tree growth? Agan i think you would be a hero in the arborist and the "green' community
just my two cents
07-24-2008, 04:42 PM
Your getting a lot of good advice here and Dan makes good points about framing. I've built a number of projects with trees coming thru the decks. I may be the only here that doesn't know to stay away from them.
There's one shown in the May Issue of This Old House Magazine that I designed and built while with another company before I started my own company. It had 3 trees coming thru.
I would'nt rule out the pressure treated glulam if it solves the problem as you're probably only talking a bout a few hundred dollars at most.
When we've framed around trees close to the ground level we have framed in a way that allows for the main framing having at least 8" -12" of clearance and then added blocking to this that could be removed over the years as the tree grows. The decking itself we cut around the tree allowing some clearance with the understanding with the customer that over time that this would have to be cut back.
Most decking can float out slightly beyond the framing and by framing as Dan suggested you kind of round it out.
Footings kind of does depend on the type of tree and is a judgement call.
Trees coming thru elevated decks are more of a chaleenge and require allowance s for wind blow and in many cases should not even be attempted from a liabilty standpoint
Just thought I'd chime in.
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