# Tree house lumber



## Randy131 (Jan 12, 2017)

Hello,
I am about to start a 2 story tree house in Michigan and I want this to last for many years. Cedar siding and deck boards. My question is what do I use for the main beams and floor joists ? There are two beams, one on each side of a pair of trees that are approx. 28" in diameter and 13 feet apart. The floor joists will be 8' long.
Should I treat this wood (with what ?) before assembly to add to it's longevity ?
Thank you,
Randy


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## kelvancra (May 4, 2010)

I, certainly, am not an engineer or otherwise and expert, but I'd just go with the same materials you'd build the walls and floors of a house from.

You shouldn't need much, if any treated wood because you aren't dealing with ground contact. However, it might be good to use it at points where the house will tie to the tree and could be in contact with wet wood from rain or snow. Of course, flashing and otherwise sealing those points would be critical too.

I'd oil the heck out of beams exposed wood to address drying, which will cause the wood to shrink and split or crack, as well as become more brittle over time. The oil will inhibit moisture gain and, if enough it applied over the years, keep the wood more tolerant of flexing.

The nice thing about non-hardening oil finishes is, they get along with cedar fine, unlike hardening finishes, which break free from the ever flexing surface over time, and they can be applied with brush, roller, rag or sprayer (be mindful of the oily rag combustion problem).


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## JCamp (Nov 22, 2016)

I've never built a tree house but I've built about a dozen or so tree stands in trees. I've always used treated lumber. With that being said mine never had a roof over them or walls to help keep the water/ice/snow/wet leaves out. I'd personally still go with treated though just because wood boring bees r bad in my area an they do some wicked stuff to non treated lumber. I'd also seal it some way. Old timers always just but old motor oil on everything. I still use it on fence posts but I'm in the Boone docks. If u don't wanna oil it I'd put some good stain on it. After a few years u can replace a roof or siding but u really don't wanna b replacing the joists or beams that hold it up there


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## JCamp (Nov 22, 2016)

One more thing….. mak the holes in ur beams a little bigger than ur bolts (assuming ur bolting it to the tree) so that when the tree grows it can have a little room to move without having to damage the bolts or lumber


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## wormil (Nov 19, 2011)

I would treat it just like build a deck and use pressure treated or any other wood that is commonly used on decks. Oil is better than no oil but not by much. Oiling wood is about the same as oiling your skin. How well does suntan lotion hold up in the water, not very. If you're going to treat it, I'd use deck stain which blocks UV and gives some water resistance but needs to be renewed annually, maybe less often if it's out of direct weather. You mentioned a pair of trees, the structure won't be attached to both will it?


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## kelvancra (May 4, 2010)

Rick, you are, at least partially, mistaken on the effect oil has on protecting wood. If all you do is toss some oil on and wipe it off, for example, it isn't going to do much. On the other hand, if you keep applying it as long as it soaks it in, you work toward saturating the wood with oil. Keep doing that and, over time, you'll have well protected wood.

Key to making non-hardening oils work well as a protectant is, don't take the approach you would with hardening oils (put it on, then wipe the excess off) or use recommendations for commercial products like poly and such, which provide only a surface coat.

Thinned oil penetrates the wood and wicks cell to cell. An initial coat can seem to disappear in the course of a hot summer when, in fact, it has not evaporated and has only spread out into the wood.

I treated my solid wood garage door with oil. The first coat seemed gone in short order. The second coat fared only a bit better. The third application, however, was still evident a year later. What was happening was, each following coat built on the previous one.

I've treated cedar fences with aggressive non-hardening oil applications that soaked through the 3/4" thick boards. Because the oil swelled the wood, as it replaced lost moisture content, no cracks appeared in the boards, even years later. The neighboring fences looked like typical, dried and UV beaten boards with the expected cracks and splits.

On decks, the oil can swell the wood and close cracks and splits, just like the winter rains do. Of course, you may have to remove excess to use the deck.

I thin my oil (e.g., used motor oil) about fifteen percent and can put it on with a pump up garden sprayer (wear a mask, since it mists).

Just keep in mind, the oil will flow through knots quickly, so the oil will make it to the other side and be obvious, As such, the ideal is to hit both sides.

To qualify this, paint is said to be the ultimate protectant. However, to hold that title, it must be maintained properly. Otherwise, it can become your enemy. For example, if allowed to crack, water can get to the wood under it and swell the wood, breaking the less flexible finish loose. Of course, it doesn't leave as easy as it goes in.

The ideal, with regard to paint, is treat all six sides, install it, then maintain the finish.

On painting, if you have a southern sun exposure and are using the same color, you may have to paint the west side every three years, the south side every four, the east side every six and the north [or underside of the tree house] every ten or so. Of course, adjust for your location and for the quality of paint you are using.

_
Generally, you never treat cedar roofing with stains and things that seal the wood. You end up with a disaster when the wood continues to lose and gain moisture. If it has boiled linseed oil in its formula, avoid it for that use.

You might use stains on cedar siding, but at that point are just headed down the paint path, so might as well go with the cheapest siding you can and get the paint on.

You could take the non-hardening oil route, then once you are satisfied with penetration, say after a few years and when the surface will accept other finishes, apply your seal coat. That way, even if the seal coat fails, you have protection under it, and you have minimized the tendency of the wood to shrink and split.


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## wormil (Nov 19, 2011)

This is not new or controversial, you've just been taught an old myth. Honestly after decades of people trying to eradicate it I don't know how it keeps coming back. Also spraying used motor oil is bad and you shouldn't do it. I know, my dad and grandpa used to do things like that too but now we know better. Take it to an oil change place and they will dispose of it for free.


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## kelvancra (May 4, 2010)

Yep. You're probably right. All that has been debunked by experts. Meanwhile, a quick hi-jack of the link to talk about old wood butcher blocks.

Just a hint for those of you contemplating buying a used butcher block, which has separations, cracks or splits resulting from neglect. I restored a cutting block by slathering on non-hardening oil and leaving it to soak it, then slathering on more, as that disappeared.

The first bottle disappeared by quickly. As soon as I got to one end, I'd go back to where I started. Once the absorption slowed, I just slathered more on and found something else to do. Then, when that soaked in, I repeated the slathering process.

When the absorption process appeared at a stand still, I slathered more on and just ignored the butcher block for two or three weeks. When I came back, ALL the cracks, splits and separations were no longer visible. This is because the non-hardening oil swelled the wood, as it saturated it.

When you poured water on the wood, it just beaded off, because the wood was already saturated by oil.

Of course, some might call these things myths, but I recommend you try them yourself, before dismissing them.

It was only a couple decades ago I got into a heated discussion with one of the nationally known authorities claiming you cannot make wood harder. We, now, know that is not true. In the extreme, they have stabilization processes that use vacuum and air pressure. Other methods involve merely hardening the surface area of wood by filling the cells with polymers, then, sometimes, covering that with the same finish.


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## JCamp (Nov 22, 2016)

Randy take all this with a grain of salt. There's other places on the net to research these topics.

That being said years ago BEFORE TREATED LUMBER (hard to believe there was such a time right) farms all around use to cut trees An soak them in motor oil prior (sometimes for months) using them. This done at least two things. It made them water resistant because they had already absorbed the oil. And two it helped keep bugs from eating them. There's fence posts in front of my house on my neighbors farm that hav been there for a minimum for 50 years an still in there terry dang good shape. It is important to note that liberals An the EPA don't lik this method but it DOES WORK. Then again the groups I just mentioned also don't lik treated lumber. 
What Kelly said about the paint is correct tho. U can paint it but if it's exposed to the weather An not kept up an gets cracks in it then rain will get in an expand the wood creating more cracks an just continue to deteriorate until it's unsafe. 
If I was u I'd use treated lumber and a good quality out door stain. Also lik Kelly said go over it with more than one coat. 
Looking forward to seeing ur progress.


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## wormil (Nov 19, 2011)

If oil provided the protection you believe it does, we would paint our houses and decks in oil because it's a lot easier than everything else. We would use oil instead of varnish. And you are never going to saturate a deck with oil, or stick a tree house into a vacuum chamber so even if you are right, the practical thing to do is use something designed for the purpose that is going to do a better job than oil. Unlike a lot of people I believe oil is beneficial in the same way that moisturizer is beneficial to our skin but if I go out in the rain I'm still putting on a jacket.


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## JCamp (Nov 22, 2016)

Also if a little oil really hurt the ground then the farmers that use it on their post An along their fence would never hav weeds growing along their fence right? Well they still hav grass An weeds growing back. 
I wouldn't dump 50 gallons out in one spot but a little ever now an then won't hurt anything


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## wormil (Nov 19, 2011)

> It is important to note that liberals An the EPA don t lik this method but it DOES WORK.
> - JCamp


edit; rephrased

Could you have confused motor oil and creosote? I grew up on a farm and we reused everything possible including motor oil, we used it for lots of things we shouldn't, but we didn't use it on fence posts and growing up I never heard of anyone soaking fence posts in motor oil, that would be a lot of motor oil for us and we only had a few hundred acres. One of our neighbors did have a huge tank of creosote left by the railroad and they used for soaking fence posts.

And if liberals and EPA don't like it, there's probably a good reason (and there is).


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## wormil (Nov 19, 2011)

> Also if a little oil really hurt the ground then the farmers that use it on their post An along their fence would never hav weeds growing along their fence right?
> - JCamp


Motor oil is actually a very effective weed and grass killer, that was one of the primary uses we had for it, but over time the rain washes it away and it seeps into the ground water for your wife and babies to drink; not very good for the fish either.


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## JCamp (Nov 22, 2016)

Ground acts as a filter. Once again don't use 50 gallons n a spot but a little don't hurt. Also if anyone is stupid enough to pour it directly in or right around their well then they kind of hav it coming. 
Ppl used oil on everything (barns, wagons, fence out houses, homes and so on) for years an years. Oil an tar we're around long before stains Even Noah pitched the ark back on the OT. 
That's my last post on the subject. 
Hope to see pictures of the tree house


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## kelvancra (May 4, 2010)

Rick, read my post again. This time, note the applications I talked about and what I said about paint and non-hardening oils. This time, don't read things into it to support your claim.

I DID say paint is said to be the ultimate protection, but also pointed out details that are ignored. Manufacturers' recommendations are seldom adhered to whether the individual is applying and maintaining paint, oil, stain or whatever. Too, those directions are general and can be improved on. However, people would not buy products if they had to put the effort I described into a project. That is why guys like me made a living doing these very things - right up until retirement.

There is no silver bullet when it comes to exterior or even interior wood products. Everything requires maintenance. It is just a matter of determining how easy you want that maintenance to be. As well, one product may be good for one material, but poor for another.

If you want to paint your cedar roof or end grain butcher block with latex, be my guest, however, the ONLY thing you should put on either remains non-hardening oil and people might question your sanity, or worse.

As much as you may not like it, both hardening and non-hardening oil yet have their places. For one example, many of us have glazed a lot of windows over the years. Using your approach (refusing to consider using oils) would guarantee the job degraded quickly. The dry wood would leach the oils from the glazing and dry it prematurely. To avoid this, we applied a coat of boiled linseed oil to the wood and, before it hardened, placed the glazing.

A second example is, as I described, treating cedar shakes and shingles, or siding, which IS very common (ever heard of Chevron Shingle Oil?). A third example would be treated and untreated wood to address drying wood that, otherwise and including wood that is merely painted, would split. A fourth example is all the surfaces that do not get hit with rain and snow, such as visible floor joists and such. Finally, there is the butcher block [and bread board treatment, which, I note, you ignored].

Nowhere did I say to abandon paint. Had I taken more time for the post, I might have dissed using polys for exterior use, long oil finishes aside. Nowhere did I say oil was maintenance free. As I indicated, they can supplement and, if aggressively applied, can do more than paint in the circumstances described.

Oh, and you can saturate a deck. It just occurs over time, as the wood dries and you add more oil to replace lost moisture. Of course, the wood is not going to take the oil in straight out of the mill, at twenty percent moisture content. Too, most people aren't interested in anything but a quick [though similarly temporary] fix. Often, that one will require the laborious task of removing the old finish first, or settling for the rough appearance of chips and such.


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## DirtyMike (Dec 6, 2015)

Sorry about your thread Op.


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## wormil (Nov 19, 2011)

Oil is a poor moisture barrier. 50 walls of text won't change that.


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## wormil (Nov 19, 2011)

> Sorry about your thread Op.
> 
> - DirtyMike


Why, he got his answer.


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## kelvancra (May 4, 2010)

Therefore everything else it does is invalid? Good grief.



> Oil is a poor moisture barrier. 50 walls of text won t change that.
> 
> - Rick M


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## kelvancra (May 4, 2010)

Regardless of what others think, old technology can ace new in many instances. Look to the pine tar, turpentine and linseed oil mixes they used on military rifles. They held up to mud, rain and everything under the sun, and touch ups are a breeze. The only thing that really beat that finish out was - plastic.

I picked up some pine tar from a tack shop for a test run on some yard furniture and it has done better than paint or poly ever did. Of course, it's not maintenance free either.



> Ground acts as a filter. Once again don t use 50 gallons n a spot but a little don t hurt. Also if anyone is stupid enough to pour it directly in or right around their well then they kind of hav it coming.
> Ppl used oil on everything (barns, wagons, fence out houses, homes and so on) for years an years. Oil an tar we re around long before stains Even Noah pitched the ark back on the OT.
> That s my last post on the subject.
> Hope to see pictures of the tree house
> ...


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## Randy131 (Jan 12, 2017)

Excellent discussion so far but your ideas generate more questions. The concensus so far seems to be toward using treated lumber. This would probably be in the form of 3 ea. 2×10's bolted together with stainless bolts as laminated is much stronger than equally sized solid lumber. I would also glue them together if possible but never had much luck gluing wet lumber which brings me to the questions.

1) I am all for oiling the wood. I have used boiled linseed oil on treated wood before but I was/am not sure this is the best product. Some are recommending thinned motor oil. Is this better than linseed oil ? and what is used as the thinner ?
2) I have never purchased treated lumber that was not practically water logged. The top of my table saw rusts quickly after cutting it. So, with so much water content how will the wood soak up much of this oil treatment ?

I am thinking I need to purchase the wood immediately and get it inside to start drying to be able to oil it in any appreciable manner to still be able to build this tree house by late spring. My problem with this is that treated lumber tends to warp dramatically while drying if not fastened down 

I will post photo's when completed but that will not be until early summer.

Thank you for all your advice to this point and for what is to follow


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## Ted78 (Dec 3, 2012)

Wow, What a thread. Ok my two cents. Use treated lumber. Clean up well, don't breath the sawdust or burn the scrap it is a bit toxic. Don't use used motor oil, does it work? sure, but not as well at treated lumber and polluting your yard with nasty carcinogens is stupid, recycle it, they will turn it back into clean motor oil. Don't use Boiled linseed oil, it can actually promote rot. Treat it regularly with some sort of deck sealant. Raw linseed oil is good for things like shovel handles that are prone to cracking, but not to rotting, but I'd stick with treated lumber and deck sealant on something like a treehouse. Also I think you are right tryin to oil fresh treated lumber seems futile. It's not going to mix with the water. People used motor oil over linseed oil for two reasons. A) availability, they had it, and B) it doesn't promote rot, like natural oils will, but don't use it. It's nasty stuff. It's not good in a fence post in the middle of a filed but in a tree house it's just plain stupid.


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## JCamp (Nov 22, 2016)

Randy will the tree house be close to your house or will it b out in the woods? 
If it will b close to ur home then I would go to lowes/Menards/HD or someplace lik that an get a couple gallons of stain in a color that would match the color theme of ur home. 
If it's going to b in the woods then probably the cheapest way to do it would b to use old motor oil (as long as u are comfortable with using it an no one will report u) on it. I personally don't thin motor oil and I would think that linseed oil would b a very costly option 
I'm with you on the treated lumber being wet. If u want to wait a while before starting the project then u could buy it now an let it dry before use but it will likely still b a good bit wetter than normal lumber. I've built a lot of decks and the most common method to build it an let it set for a few months to dry out (I'm thinking in the summer heat) then stain it. Once again do several coats of stain to make sure it absorbs as much as it wants. If I want a really good long lasting protective finished I would recommend at least three coats of stain (mayb over a three day period) an then do it at least once a year after that.

Treated lumber will last for a good bit without any sealant so building it an then taking ur time to determine the best finish shouldn't b a problem. I hav seen treated lumber rot but that's when it hadn't been maintained for many many years


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## gargey (Apr 11, 2016)

Build the whole thing out of plastic


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## tomsteve (Jan 23, 2015)

"So, with so much water content how will the wood soak up much of this oil treatment "

it wont

if youre using treated lumber youre not going to want to put any type of finish/oil on it for some time. here in Michigan, If I frame a deck in spring, early summer, I suggest giving it at least 3 months if the deck is in the sun, and even then verticle lumber will dry at a diferent rate than horizontal. some say stain/finish can be applied when water doesn't bead on it.

as for your triple beams, if ya bolt them together every 16 or so inches, you wont have to worry about glueing them.

personally, id suggest getting the lumber when your ready to build- frame it up wet. if ya get it all now and let it dry, you very well could be pitchin a fit tryin to frame with it.
then give it a year before putting any oil/stain on it.

look at it this way_ youre building a deck in a tree. start lookin around at decks in your area. find out how many had the floor joists have extra protection added and how old they are.
1st deck I built 30 years ago is still standing in northern Michigan. some deck boards have been replaced, but the framing is still good to go.


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## Randy131 (Jan 12, 2017)

Guess I am about decided on a course of action. Treated 2×10's bolted together and slathered with a good quality deck stain at the end of the summer over the course of 3-4 days so the wood will soak up all it can and repeat this procedure at the end each summer for a few years. I will do the same with the floor joists. The deck boards themselves will be 'plastic' as much as I dislike 'plastic' on a house 
In my contractor life I specialized in kitchen make-overs and decks so I am familiar with the wait-to-dry-before-stain procedure. This tree house is in the woods approx. 50 yds. from the house and 10' above ground level so it won't be the handiest thing to stain after building but - if it was easy everybody would be doing it 
As I mentioned before, photo's will be posted when the project is completed and thank you all so very much for the educational conversation. In fact it was so good I can't wait to ask another question


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## JADobson (Aug 14, 2012)

> This would probably be in the form of 3 ea. 2×10 s bolted together with stainless bolts as laminated is much stronger than equally sized solid lumber.
> 
> - Randy131


Probably don't want to use stainless bolts as the high copper content in treated lumber will corrode them. Look for hot-dipped galvanized fasteners instead. See: http://www.finehomebuilding.com/2012/09/06/whats-the-difference-fasteners-for-pressure-treated-lumber


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## tomsteve (Jan 23, 2015)

when it comes staining time, one of them 2 gallon garden pump sprayers might help make the job a little easier.

end grain is where ya want the most protection. that's where most moiture enters and exits lumber and where most rot starts.


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