Early next Spring I want to add on to my existing deck, which the previous owner framed around some moderate-sized (24-36″ diam.) oaks. The house sits on a steep grade. I’m read recently that, contrary to popular impression, most of a tree’s roots are actually pretty near the surface. I’d like to frame the new deck around other existing trees. I’m wondering how people deal with digging the post hole footings within a foot or two of a large tree–meaning, how they cut through the roots. I’m not sure I can get a Bobcat with a drilling rig up this hill. Two-man augers aren’t meant for anything but dirt, are they?
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I haven't had much better luck with the Bobcat augers than the two man augers. If your deck has gotta go where it's gotta go.....well you do what you gotta do. You could very well lose the tree when you cut those roots. No magic tricks for this stuff. Just axes, grubhoes, shovels and sweat. Be kinda sad to lose a big 'ole tree for a few more sq ft of deck. Look into using a larger beam to limit the number of footings necessary to support your new framing. Or consider sistering new joists to your old and cantilever the framing...just be sure it's properly engineered.
I'm hardly an expert on this, but here's what I think, or know, or think I know:
1. There are 'feeding roots' close to the surface, and 'structural roots' much deeper - they serve different purposes, obviously - the shallow ones will be finer and easier to deal with. As long as you don't tear up a large area, the tree should survive a few holes poked in around it.
2. I ran into this a month ago, hand digging footing holes near a couple of trees. The digging wasn't too bad (used one of those clam-shell post hole diggers). When I encountered roots (ok, all you serious craftsmen, cover your eyes), I just leaned into the hole, sawzall in hand, and cut through the roots. I'm sure there's a special place in hell for me for this tool-abuse, but it worked.
3. Are you sure you want to keep the trees? My dad built a deck 20 years ago around a nice oak - he left a pretty big area around each tree for future growth - so much that I used to worry that someone would step in the hole and break a leg. Now, the tree is tight to the deck, so we just went through a painful exercise to expand the hole. It wouldn't have been bad if it was just decking to cut, but we had to head-out framing members, etc, to fix it. At the very least, make sure the framing can accomodate future growth, so you can just zip around it with a sawzall (if that still works!)
Good luck ... Bill.
...contrary to popular impression, most of a tree's roots are actually pretty near the surface...
root distribution depends on species and soil types - - I'd encourage you to plan your posts so they aren't set within 4' of the trunk, and leave yourselve some flex to move a few inches to avoid major wood - - Bill's strategy with the sawzall is quite appropriate - try to avoid tearing roots out and minimize trauma -