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Building with green lumber

Ralph_Beaty's picture

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I am in the process of building a tree house for my sons and have access to three local sawmills that are now cutting white oak. I would like to use white oak for the foundation and support structure because of its strength and durability. The only problem is the sawmills only have green white oak.

I have gone to Lowes and Home Depot for pressure treated pine, and since it's stored outdoors, it's also wet.

In my opinion, both the white oak and PT pine are going to shrink once I secure them to the trees. Yet I fear either may pull out of square or level in the tree, making playing in it dangerous.

I am familiar with an early structure Frank Lloyd Wright built out of green lumber in the early 1920's, using it right on top of the dirt foundation. Of course, the structure is now in need of serious structural repair. However, for my purposes at present I'm thinking that if a green-wood built house can last this long, then surely a green-wood built tree house foundation would meet my needs.

Any input you can provide would be appreciated.

Thank you,
Ralph Beaty

(post #166569, reply #1 of 6)

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One of the earliest FH issues had an article on building with green lumber. You just have to simply anticipate shrinkage when spacing and fastening. Shiplap, nail only one side of a board. You also should take into account ring direction of boards, as boards will cup away from the center of the tree. Anticipate the possibility of refastening boards later after they've shrunk. A good reason to use deck screws intead of nails.
But, geez, it's only a tree house. A little space between board will allow a breeze through.

(post #166569, reply #2 of 6)

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Ralph, I think it is important to remember how dimensional lumber shrinks. The rate of shrinkage is greatest in the width of the board eg. a 10" wide cut board might shrink to 9" . The length and thickness shrinkage is more minimal 1/8". The rate also depends on tree species and time when the tree was cut. If you take these factors into account when building, you can work with the shrinkage not against it.

(post #166569, reply #3 of 6)

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jim your thoughts are true and good but adress mostly issues connected to sheathing type lumber. As I understand the proposal, Ralph wants to use green lumber only for the base framing. There should be no problem with this as long as he uses screws instead of nails. The tree will allow some movement so screws should be used no matter what lumber is used. Ken, wood will not ever shrink lenghthwise.

Ralph, The biggest concern I would have here is the engineering. wet, green oak is going to be tremendously heavy and PT is not much lighter. (BTW, all PT is wet because the chemical treatment is forced into the wood under pressure, thus the name. PT is not a good idea for kids to be crawling around on. I'm not a fanatical environmentalist but it's just not a good idea for them to be soaking up arsenic into their jeans.) Will the limbs you are fastenning to be able to stand up to it? And how will you hold it up there while working on it? How wil you presereve the tree so that it lasts for your 80 year life expectancy? Since this is up in the air, as long as you keep the water out you needn't worry about rot so lightweight, strong material should be what you are looking for. Cost seems to be no problem for you because I've never seen cheap oak.

(post #166569, reply #4 of 6)

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By the time the lumber dries out, your kids will be in high school. By the time the tree house is out of square, your kids will be college. By the time the out of square condition becomes serious, you will be in the nursing home.

I think it is like worrying about the 40 year warranty on calk.

(post #166569, reply #5 of 6)

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Piffan,
Green white oak currently sells for about $.60 bd.ft. at the mill. Depending on grade. For something like atree house you don't need or want FAS # 2's should be fine Drprnding on yout mill you could get it as low as $.30 bd. ft.
You can figure that it will take about one year per inch to reach a state where drying is no longer a factor. Most Mills have a pile or two of wood lying around which someone ordered but failed to come and get Not only will the price be better, but it may have been around for quite a while. Ask.
Building with green wood is done all of the time, most timberframes are built with green wood. As are barns and many structures. There is a book in my library tittled, Building With Green Wood.
Unless he's building something really huge white oak should be just fine. Just remember not to use steel or Iron when fastening it. Brass, stainless steel, or heavily galvinized fasteners. (oak has an acid which attacks steel or iron causing the metal to rust and the oak to rot)
Working with green white oak isn't as hard as you'd think. It cuts reasonably and with a decent nail gun ( Bostich N88) you can evan drive nails into it. Once it's dried it's a whole 'nuther story. You'll bend the nail trying to drive it and then the wood will split! (predrill all connections)
The great thing about white oak is that there are 500 year old timberframes over in Europe built with white oak heck they are evan older than that! His tree house may well outlast the tree it's built in.
When putting this in a tree remember to allow the tree to grow. make most connections clamp rather than fixed so the treehouse doesn't kill the tree! Installed improperly you'll simply girdle the tree and kill it or you'll fix it between to points which grow apart and tear the tree house apart.

(post #166569, reply #6 of 6)

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I am in the process of building a tree house for my sons and have access to three local sawmills that are now cutting white oak. I would like to use white oak for the foundation and support structure because of its strength and durability. The only problem is the sawmills only have green white oak.

I have gone to Lowes and Home Depot for pressure treated pine, and since it's stored outdoors, it's also wet.

In my opinion, both the white oak and PT pine are going to shrink once I secure them to the trees. Yet I fear either may pull out of square or level in the tree, making playing in it dangerous.

I am familiar with an early structure Frank Lloyd Wright built out of green lumber in the early 1920's, using it right on top of the dirt foundation. Of course, the structure is now in need of serious structural repair. However, for my purposes at present I'm thinking that if a green-wood built house can last this long, then surely a green-wood built tree house foundation would meet my needs.

Any input you can provide would be appreciated.

Thank you,
Ralph Beaty