"Knowledge is wonderful but imagination is even better."
— Albert Einstein
— Albert Einstein
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| A home in the trees for 4 young brothers |
Nearly
every rough carpenter I know built a tree fort when they were kids.
It's just in the blood. I remember well the one my brother Joel and
I built when we were 11 and 12 yrs. old. Even at that young age we
already had a fair amount of carpentry experience. It fell upon us
“men” of the family to upkeep the small farm where we grew up.
Between the two of us we built horse corrals, sheds,
chicken/rabbit/pheasant coops, and any other structure that may have
been required. We also made time to invent secret places. One such
place was our tree fort that was totally invisible to the outside
world. From there we could defend our ranch with great
effectiveness against the raiding marauders of Lomita CA just down
the hill (or escape from our sisters). Other than just farm boy
ingenuity, I have no idea how we came up with the tree fort design.
50 yrs ago there was no Internet of course so our “go to”
resource was the infamous Encyclopedia Britannica. It was heavily
relied on for homework assignments so it could well have been that we
copped an idea from there or maybe our incentive came from a Tom
Sawyer novel. In any case, without building department approval (not
even sure if that gov. welfare job had been invented yet) and under
the cover of darkness we constructed our masterpiece. We could not
risk drawing enemy attention to our project. Not only was this long
before the Internet but thankfully this was also long before spy
satellites. Otherwise, we would have had to coordinate our building
efforts for when these devices were over the horizon and blind. As
it was, in those days we only had to worry about a stray U2 that may
have confused Los Angeles with Moscow. That was an acceptable risk
knowing the U2 was based out of England and would run out of fuel a
long ways before reaching Southern CA. (Photo 1)
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| Photo 1 - U2 |
In our personal Sherlock forest we
found two straight trees that were situated about 12 feet apart
having a trunk size of about 8”-10” diameter. I can’t remember
the tree species but they were green. At 8’ above the ground and
spanning from tree to tree we attached a 2x8 to each side of the
trunk using lag bolts. In effect we had sandwiched the two trees. The two 2x8s were
run level from side-to-side and from end-to-end. On top of these we framed a 4’x 12’ floor using 2x4
joists at +/-24” OC and sheathed it with scrap pieces of plywood.
At each end of the floor section we ran a pair of knee braces down to
the tree trunk at 45 degrees to keep the deck from rocking. (Fig.
1) We didn’t fret much about a handrail as we shaped and wove
the tree branches to create a perimeter. To get up to the fort you
either scaled one of the support trees or climbed a rope that was
hung appropriately. We didn’t want to make it too easy for the
enemy to invade.
Fast-forward
some 50 yrs to the year 2009, and we once again catch up with one of
those 2 young brothers. He now limps around a bit, being an old,
well abused rough framer who is many decades past his prime. But for
some strange reason this brother never outgrew dreams of building
tree houses. On the highest shelf of his sparse little “office”
there are half a dozen dusty books on the subject that get pulled
down now and then to be looked over on a rainy day. If you haven't
already figured it out - that poor soul is I.
Times
certainly have changed since those early days. There is now a myriad
of spy satellites in the sky so advanced that they can read the words
off a newspaper just about anywhere in the populated world. Be hard
to build a tree house undiscovered nowadays. Even
your communications are at risk since the feds have drones that fly around and suck data off your cell
phone. Yep cell phones - you heard me right. No more land lines -
and that wonderful sounding ching-ching-ching of the rotary dial
telephone. Hard to believe what has happened in that young man's
lifetime. Man has been to the moon and he even keeps an “outer
space house” where he can escape from the wife for a break if
needed. That is why it is up there isn’t it? (Photo 2)
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| Photo 2 - space station |
I
have been blessed to be a part of many extravagant building projects
during my career but I can never seem to dash the longing to design
and build a Swiss Family Robinson style tree house. I have so many
cool ideas to try out (they are secrets). I
hope I get the opportunity before I hit the grave. I have
seen many articles/videos/etc on tree houses (ie: Treehouse Masters,
etc) but I would have to say that many do not meet my definition of a
real “tree house”, which states “that the structure must be
totally supported by the tree itself - no posts or braces to the
ground”. (Photo 3) To use the ground as support is
definitely cheating and bad ju -ju. Only a set of stairs to access
the tree house is allowed to touch the ground. And that is only as
a concession for old disabled folks like me who can no longer shimmy
up a climbing rope or rope ladder. Building a house on stilts in amongst the
trees so their branches appear as porch plants does not constitute a tree
house.
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| Photo 3 - a REAL tree house |
Needless
to say, I was utterly delighted when the wife of a dear friend called
to ask if I would build a tree house for their 4 young boys. Having
seen my design work and construction on various other specialty
projects she gave me free range to do as I pleased within a set
budget. So without another word, I jumped in my old truck and went
snooping around their property to find a tree that I could use.
Unfortunately, I discovered that all the available trees were
relatively young Eucalyptus (10” diameter). These certainly
couldn't support a tree house of any real size so I came up with the
idea to build two smaller tree mounted structures and connect them
using a cable car. Something fun for the boys to do. One structure would
be an enclosed tree house (ETH) with 4 beds for overnight stays while
the other would be an open viewing platform with bench seats (VP).
Both would have incredible views of the nearby volcano. A stairway
would provide access to the ETH while the VP could either be accessed
by the cable car or a climbing rope. After getting approval for this
plan from the owner, I began formulating a strategy of how best to
accomplish the construction. Since it was a small job and I would be
inventing on the fly, I decided to build the project solo.
Tree
house construction has no real standard methodology. One must invent
a special support system to fit each tree’s unique form in light of
the local weather conditions. The home site where I would build
these two tree structures faces 6 months of monsoon rains followed by
3 months of strong winds each year so I would need to use very
durable materials and keep the tree house’s wind profile small. A
tree house may seem innocent enough but in strong winds it acts like
a giant sail that can easily overload the root system’s ability to
resist the flexing load and down goes the tree. Give it a few years
and the tree should upgrade its root system somewhat to help
counterbalance the new added load. The structural design in this
case would also need to allow for plenty of tree trunk movement otherwise
the constant wind generated movement would just jiggle everything
apart in no time.
I
chose to put the ETH into a Eucalyptus tree that divided into 2
separate trucks about 5 feet above the ground while the VP would be
installed in a fairly straight Eucalyptus tree about 100’ away. I
determined to set the ETH floor about 12’ above the ground. This
was as high as I could place the structure so that its roof was just
below where the trunks flowered out into a myriad of fingers. The
VP’s height would match the ETH at a position exactly horizontally
level. This would facilitate travel by cable car between the 2 tree
structures.
One
consideration a tree house builder must have when building a tree
house is to make effort to protect the tree’s health. The fewer
penetrations into the trunk the less likely it is to hurt the tree.
The last thing you want is for the tree to die and all your hard work
be for neigh. After some brainstorming, I devised a method where I
would attach the ETH to the tree itself using only 3
“through-the-tree” fasteners while the viewing platform I would
attach to the tree with (4)- 4” long lag bolts at two different
levels. Every penetration into the trunk would be well sealed using
spray car undercoating. This would go a long way to protect the tree
from bug and disease infiltration.
My
first problem was to devise a good way to work up high in the tree
with ease. My experience as a roof stacker had prepared me well for
this challenge since I was always inventing ways to get up high and
frame various parts of complicated roofs. I detest working from
ladders therefore I quickly devised a simple platform type scaffold
built around the tree itself. Upon it I would assemble the complete
floor joist system and connect it to the tree. This scaffold method
would work well for both tree structures even though they had
different systems of support. (Fig. 2) To start, I framed
two moment frame units laid flat on the ground using (2) 2x4 verticals and
a 2x6 horizontal for each of the two trees where the tree structures
were to be built. I set the height of the horizontal member so the top
surface of the scaffold planks when in place would match the bottom
of the platform's floor joists (FJ). I also adjusted the leg lengths
to conform to the unevenness of the terrain so that when the moment
frames were stood they would create a level working plane. The
moment frames were X-braced while laid flat and then stood on
opposing sides of the tree. Foot long flat 2x6 blocks were placed
under each leg to keep them from sinking into the ground when it
rained. After these moment frames were braced plumb using some
temporary angle braces to the ground, I connected the two units at
the scaffold level on each end using a pair of 2x4 horizontal cross
ties that spanned between the vertical legs and then X-braced the
assembly on these two connecting sides. I also drove a stake into
the ground at each leg and connected it to the 2x4 vertical leg. I
next fastened 2x4 horizontal corner ties at the scaffold level on two
opposing corners for extra rigidity (Roof Cutter's Secrets
pg. 37). Finally, I tossed up some long 2x12s planks that spanned
between the two cross ties and on top of them I tossed up 2 more
planks that went the opposite direction. The scaffold platform
looked somewhat like the number (#) symbol when viewed from above. I
made the moment frame support structure wide enough so that I could
easily slide the planks out to use outside the building structure
when it came time to install the exterior siding. I feel confident
that one could easily use this system of construction up to a height
of 20'-22’ above ground level. Above that I have another trick
idea that I will save to share some other day.
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| Fig. 2 |
With
the scaffolds up I began work on the floor structures. Up on the ETH
scaffold I mocked up a trial floor system using some 2x4s to see what
kind of joist layout would work around the two tree trunks. Since
the ETH was to be a 7’x12’ structure (that including a 3.5’
front porch facing a spectacular mountain view), I positioned (2) 2x4s -
12’ (laid flat) on top of the scaffolding simulating
the building’s long sides. Perpendicular to and on top of these
long boards, I set various 8’ long 2x4s to simulate FJs and moved
them around until I achieved a decent layout that would work
considering the two tree trunks. I had already determined that the
vertical rear tree trunk would pass centered through the enclosed
tree house space while the angled front tree truck would pass through
the front wall and out the porch. I decided to use two of the joists
as “king” members from which the whole tree house structure would
get its support. One of these “king joists” (KJ) would be
solidly attached to the vertical trunk using a single piece of ¾”
all-thread while the other KJ would hang from a the front trunk using
two equal length pieces
of 3/8” wire cable (imagine using two nylon
slings to set a ridge beam
with a crane). Since both trunks would move independently, this
system allowed that to happen
without torquing the structure. I would use Guayacan for all the
wood components in the building process except the siding, which
would be Spanish cedar. Guayacan is so strong and dense that it
actually sinks in water. It
is impervious to bugs and weather of any type. I am told you can
bury a piece of this wood in the ground and come back some 50 yrs later and find
it in the same untouched condition. (link
to http://en.wikipedia.org/wiki/Lignum_vitae).
The two KJs along with the outside rims on the ETH would be 2x8s
with all intermediate joists 2x4s (full dimensional sized lumber).
The decking would be 1x4s.
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| Photo 4 |
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| Photo 5 |
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| Photo 6 |
For
both structures and throughout the building process I prebuilt as much as I could in sections on the ground near the tree. Sections that
were too big to move up in one piece were partially disassembled and
reassembled on top of the scaffold. For example: to construct the
ETH floor, I bolted all the joists together using ½”machine bolts and brackets fabricated
from angle iron (Photo 4 - no Home Depots around here),
numbered everything, disassembled it, threw the pieces up on the
scaffold, and reassembled it in place. I could have set a winch
block up high in the tree and incorporated my trucks winch to lift
things but that wasn't necessary.
With the floor structure set solidly
on the scaffold, I only had to attach it to the tree trunk. As
described previously I through-bolted one of the KJs to the vertical
trunk using 3/4” all -thread. About 5' down and directly
below this KJ connection I installed a 1.25” diameter 4130 steel
pin through the rear trunk to use as the anchor point for the lower
ends of two separate diagonal braces made of angle iron. (Photo 5)
They reached upward like a “V” and bolted to the KJ, stabilizing
it from side-to-side in the level position.
Up on the front trunk I
installed a second steel pin of the same size through the trunk about
5' above the KJ. I hung the front KJ from the outside end of this
pin while planning to use the inside end of the pin as my anchor
for the cable car’s support cable. (Photo 6) To help
dampen any side-to-side swinging movement of the front KJ, I ran a
wire cable down and back from one end of the front KJ to the lower
steel pin at the rear tree trunk. In combination with the staircase
coming up from the ground on the opposite end of the KJ it did a good
job of stabilizing the hung end of the tree house. (Photos
7, 18)
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| Photo 7 |
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| Photo 8 |
I
prepared the decking on the ground by aligning them flat,
side-by-side on stickers. Then I gang-cut them to length, routered a
¼ round on the top edges and predrilled/countersunk for all the
decking screws. Once I had the decking laid out on top of the
joists, I worked from one end to
the other screwing them in place. Since Guayacan is so hard I had to predrill the joists
for the screws as well. Using one electric hand drill set up with a
drill bit and a second electric hand drill set up with a screw driver
bit I finished the floor deck installation in short order. I used
3/16” x 2.5” Tapcon concrete screws (with a little wax rubbed on
the threads) to secure the decking to the joists. I left a 2”
spacing between the decking and the tree trunk to allow for movement and
future growth. (Photo 8)
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| Fig. 3 |
The
VP floor system incorporated four major support 2x4s (full
dimensional lumber) horizontal arms (HA) each having a 45-degree 2x4
knee brace set below that kicked back into the trunk from about 2/3 the
distance out. (Fig. 3) These arms were positioned at 0, 90,
180, and 270 degrees around the tree trunk. The HA length was
calculated using trigonometry to find the diagonals of the 8' square
viewing platform less the diameter of the tree trunk at their attach
level and then the result was divided in half. I used the tree's
circumference at the HA attach level to come up with the tree's
diameter. Next I took a piece of flat cardboard and cut a hole a
taste larger than the tree's diameter to form a pattern. I placed
it around the tree at the HA level to confirm if indeed the trunk was
uniformly round or if I would need to adjust the HA's lengths to
compensate for fluctuations. This cardboard pattern also served as a
guide to position the interior ends of the HAs at each 90 deg.
cardinal position. (Fig. 4)
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| Fig. 4 |
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| Fig. 5 |
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| Photo 9 |
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| Photo 10 |
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| Photo 11 |
The
knee brace (KB) lengths were calculated individually taking into
account variations in the width or tilt of the tree trunk at their
lower end attach point in relation to the HA attach point above.
These variations were found by plumbing down to the KB attach level
from the cardinal positions of the HAs on cardboard pattern and
noting the actual isosceles triangle's leg length for each KB. (Fig.
5) With that measurement, the KB lengths and hanger positions
could be calculated using trigonometry. Obviously, a KB having a
longer length would have its hanger positioned lower to accommodate
the increased length while a KB having a shorter length would have
its hanger positioned higher.. The KBs were notched into the
underside of the HAs and the two were connected with plate straps
installed along the sides. (Photo 9)
These
4 units had to be killer strong as they were the foundation for the
entire VP. Both the horizontal arm and knee brace sat in specially
fabricated 1/4” thick hangers that attached to the tree using a
single 5/8”x 4” galvanized lag bolt. Short ½” through-bolts
kept the interior ends securely fixed in the hanger pockets. (Photo
10) Since there would be an outward pulling tension force
at the interior end of the HAs as a result of weight on the
cantilevered part of the joists, I ran a piece of 3/8” wire cable
around the trunk through each of the 4 support joists about 8” away
from their ends. This made it impossible for the support arms to
pull away from the tree. (Photo 11)
Since
the bottom ends of the knee braces would have a compression force
against the tree trunk as a result of the VP's weight, separation
would not be a problem so I only blocked this end to add rigidity.
(Photo 12)
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| Photo 12 |
Next
I installed some a ring of temporary 2x4s connecting the outer ends
of the support arms to lock them into their correct 90 deg. positions
while I installed 2x4 girders around the perimeter of the viewing
platform. These girders were hung below the four support arms using
carriage bolts and would carry the loose end of the intermediate
finger joists. (Photo 13)
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| Photo 13 |
The
floor decking for the VP was cut on the ground and installed in the
same fashion as was done with the ETH but while the floor for the ETH
was a simple straight run having all the decking boards cut to the same
length, the floor for the VP was a constantly decreasing four sided
square where each ring of boards was 8” shorter than the
previous ring. It was more work but sure looked nice.
(Photo 12)
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| Photo 14 |
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| Fig. 6 |
I
decided to frame the living structure situated on the ETH floor
platform using an unconventional method. Not only is it impossible
to use nails in Guayacan without predrilling but my gut told
me that with the strong winds and tree movement, the standard wall to
roof framing connection methods would eventually loosen. Therefore,
I chose to inseparably connect the vertical framing members of the
wall (studs) directly to the horizontal members of the roof (shed
roof rafters) to create a solitaire “n” shaped truss unit
similar to the rib of a boat hull. This connection between the stud
and rafter was made with a single ½”x 8” machine-bolt sent down
from top edge of the rafter straight into the vertical shank of the
stud directly below. I used the “perpendicular intersecting hole”
technique (Roof
Cutter's Secrets pg. 260)
to position a nut and fabricated square washer inside the
stud to catch the bolt from above. I also applied some wood epoxy
on the two fitted surfaces. (Photo 14) I assembled
five of these “n” shaped wall/roof truss units to be spaced at
24” OC starting from the back of the 7'x12' platform going forward. One side of the “n” shaped units had a stud length of
6' above the floor surface while the opposing wall had a stud length
of 7' above the floor surface. The height difference between the two
walls created a 12” shed roof drop across the 7' wide floor. Once
these units were stood in place, the lower end of each stud was
attached to the outside face of the two long rim joists using two
½”x 6” carriage bolts. A 1”x 8” notch was made at the very
bottom inside edge of each stud to facilitate placement while
providing a solid bearing surface that supplemented the shear value
of the two ½” bolts. (Fig. 6) After the skeleton of the ETH
structure was in place and plumbed, I stick framed the front and back end walls, together with the window and door openings using the same
“intersecting hole” machine-bolt installation technique. |
| Photo 15 |
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| Photo 16 |
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| Photo 17 |
On
top of, and perpendicular to the shed roof rafters, I installed flat
1x6s at 24”OC to carry the metal sheet roofing (actually it was a
fiberglass version of the same). These 1x6s ran long on the front
and back of the building to create a 12” overhang where a 2x4 barge
fascia board was installed from below to finish off the eave detail.
(Photo 15)
The roofing was installed, the building was
sided (Honduran pine ship-lap), the windows and doors were installed,
and everything was trimmed out. On top of the roofing I screwed down
pieces of ½” PVC pipe around the perimeter to keep the wind from
grabbing the outside edges of the roofing sheets and ripping them up.
(Photo 16) Where the tree passed through the roofing
material I installed strips of 4” wide aluminum coated roof seal
tape to close off the opening. This tape would need to be redone
yearly if one wanted to keep rain from entering around the trunk. I
had the idea to install an aircraft tire inner tube around the tree
trunk at the roofing level to close the gap and make it water tight
but never got a hold of one of these tubes so it goes untested. One
would need to cut the tube open so it could fit around the trunk then
glue it back together. Once inflated I believe it would provide a
good water seal while accommodating the tree's movement
I finished
off the interior with the installation a few shelves and 4
trick “hide away” beds that folded into the wall framing when not in
use. (Photo 17)
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| Photo 18 |
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| Photo 19 |
The
stairway to the ETH was fabricated using 4” galvanized steel
“carriolas” (thin gauge metal C-joists). I chose to use a 11”
rise and 6” run for the stairway pitch (+/-60 deg.). This pitch,
although steep for standard stairs in a normal house, seemed to
have the correct feel for a real tree house. Because the tread was
open and there was a good handrail it was no sweat even for an old
guy like me to motor up/down. (Photos 18, 19)
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| Photo 20 |
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| Photo 21 |
Since
kids would be undoubtedly be leaning over and hanging on the
handrails some 15' up in the air, I wanted the handrails for both the
ETH and VP to be bullet proof strong so I decided to use the same
“intersecting hole” machine-bolt connection to attach the
handrail to the balusters. (Photo 20) The lower end of
the balusters themselves where attached to the 2x8 rim joists on the
ETH using two ½” carriage bolts in shear (Photo 6) , while on the VP (which
was built using smaller sized 2x4 joists), angled metal straps
installed at the intermediate balusters provided the required
rigidity. (Photo 13)
To avoid hand rail separation at the VP's 90 deg. outside
corners, small 1/8” steel plates spanning from bolt-to-bolt just
under the wood hand rail were installed. (Photo 21)
One would need a tractor to take these tree houses down.
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| Photo 22 |
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| Photo 23 |
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| Photo 24 |
The
last project was the cable car. I strung a 100' long strand of 3/8”
wire cable from the eucalyptus tree located on the far edge of the VP
to the ETH's porch situated trunk and tensioned it into place using a
come-along style hand winch. I placed drilled 2x4 spacer
blocks around the trunks to keep the cable from strangling the tree.
On the VP end of the cable, I circled the trunk twice and tied it
back to itself. (Photo 22)
On the ETH end of the
cable, I circled the trunk twice and tied it off at the inside end of
the KJ's supporting 1.25” steel pin. (Photo 23)
I
originally fabricated a 2 person cable car (passengers facing each
other) but found it was too heavy for the situation so I chopped it
in half to create a single seat version. (Photo 24)
With an overhead pulley assembly one could easily whisk back and fort
between the two platforms. (Photo 23) Lots of fun even
for older kids like me.
Check
out this video which gives a tour of the completed ETH and VP
including using the cable car to travel back and forth.
NOTE:
Unfortunately, not being a great computer person I lost the digital
file containing the photos which documented the construction process.
I returned to the job site in 2014 (5 yrs later) and took all the
photos that are included in this article except Photos 6 and 12.
Notice how the years of tropical weather has greyed out the beautiful
natural Guayacan color. Its brilliance could have been maintained easily with an occasional coat of varnish. Now it will take a little sanding to bring that color back out.
