The Making of a Platform House

From a dream to reality...

In the summer of 1998, I decided to build my son a tree house.  Actually, since we have no real trees our our property, it was to be a platform house - built on stilts.   Chris was 9 years old.  Two years ago, we had donated his old play set to his school.  At the time, his terms were that we replace the playset with something else; something like a tree house.  I let one summer go by without holding up my end of the bargain, so this year I felt compelled to actually do something.

While I was building this project, I talked to a number of other people that said that their fathers had built them a tree house at about the time they were Chris's age.   It seems to me that making a play house like this, fills some inner need on the part of the parent.  We know that our child is soon going to be becoming more independent.  Yet we want to keep them close.  And we know that they are still at an age where they would actually "play" in a playhouse.  We want to create for our child his own private world - yet one into which we can still play a part.

I've been accused of being a big child myself - so of course building this house was something I was very interested in all on my own; Chris has given me many convenient excuses over the years for indulging my child-like impulses.

Planning the Project

I had never built a livable structure before; the closest I've come is watching shows about deck building.  So, I figured a platform house could not be much more complicated that constructing a deck, putting it up on very tall supports, and then framing a little shed-like structure on top.

I started buying books about tree houses and deck building.  The two best books on tree houses I've found have been by Peter Nelson.  Peter also lives in Seattle.   At many points I was sorely tempted just to call Peter and see if he would build our tree house for us.

The first of his books, Treehouses, is an incredible collection of photographs of inspiring tree houses.  The center of the book shows a detailed sequence of photographs of Peter building a 200 square foot octagonal jewel perched 30 feet up an old growth fir in British Columbia.  This book contains some history of tree house building and some detailed drawing and sequence for his BC project.  But mostly, this book provides inspiration.  The houses and photography in the book are gorgeous (if you like tree houses!).  See Peter's company web site, TreeHouse Workshop, for more information.

His second book, Home Tree Home, while not as beautiful as the first, provides much more in the way of practical advice on tree house construction.  It describes how to put up walls, windows, and doors.   How to actually suspend and support a house in a tree.  Unfortunately, there is nothing in this book about building up in the air with artificial support.   Lacking a tree, we needed to make our own supports and had to make them both strong enough and rigid enough to provide a comfortable platform for our construction.

For real practical building information, I relied on two books from Sunset books.  The first, Complete Deck Book, had great information on how to build the basic platform.  Since many decks are a bit raised off the ground (though usually attached to a house on at least one side), it also had some good info on supporting our platform.  I got my computations on structural loading from this book (deciding how big the joists and beams needed to be to support the platform, house, and occupants).

Finally, since I had not had any real building experience, I use Sunset's Basic Carpentry as a source of information from everything about nail selection to framing a wall, and installing a roof.  This is the book I used most at the job site to help me make the day to day decisions about the materials I'd need and how to accomplish the basic building tasks.

Chris and I started out the project with a blank sheet of paper in May of 1998.  What would it look like?  We decided to build a platform that was 8 feet by 10 feet.   I figured it would be easy to do the flooring with 4' x 8' sheeting of some sort if we kept one dimension to 8 feet.  But we also wanted to have a little balcony on the end of the building so you  would be able to be outside when you were up in the air, and not feel you were trapped in a little box.  We figured we could build the house about 8 feet in the air - I figured I could get posts of that length easily.

I started sketching a little 8' x 8' cabin with a 2' balcony, a roof, and a beam that would extend off the balcony to support a hoist/pulley system for pulling stuff up into the house.  We also planned that the main entrance would be through a trap door in the floor, and that we would build some sort of rope ladder to climb into the house.   Being up so high, we knew that the legs would need some sort of bracing to keep the platform rigid.  It turns out that we needed quite a bit more bracing than we originally planned, but we started out our plan with a standard "Y"-bracing to add some stiffness to the support structure.

We also decided to build out some interior furniture.  Chris would want some built-in bunk beds.  And his dream was to be able to be up in the tree house and play video games up there with his friends.  So we planned on wiring it for electricity, building in bunk beds and some desk surfaces for video game machine and television.   We drew three possible floor plans which we needed to choose between in order to plan the placement of the door to the balcony.  Chris chose "Plan 3".

Next came the detailed drawings and construction.  This was very much a learn-as-you-go project.  I'd decide to build something, figure out from the books what kind of lumber was needed, draw some sketches to make sure I understood how things would fit together, and then build it.  Home Depot was my hang-out for the next couple of months.  I got to know Amy, one the the checkers there quite well over the summer and she would ask me each weekend how the tree house was coming along.

Construction

The first project phase was to build the platform itself.  I assembled all the lumber for the platform framing on the ground.  I could attach all the joist hangers to the main support beams on the ground instead of trying to do this once the beams were raised up into the air.  This went relatively quickly and the basic platform shape and trapdoor took shape.  Now it was time to venture to Home Depot again for the "legs" of our platform house.

I went expecting to buy 8' long 4"x4" pressure treated posts.  But, to my surprise, they also stocked much longer pieces.  They had 10' and 12' long posts.   Perhaps some even 14' long.  Cool!  The more height, the more fun.   After weighing the added difficulty of building higher, I compromised on the 10' posts.  High enough to really feel that you are "up in the air" but not so high as to make reaching the structure with a normal step ladder impossible.

After attaching posts to beams, raising the legs required the help of some neighbors.   The Albertson's were kind enough to come over and lend a hand.  This felt like a traditional barn raising to me.  While the neighbors held the legs in place, I scurried up a ladder to nail in two joists to make the basic box suspended in the air.

I was not satisfied with how secure the joists were resting in their hangers when we were done - there was a gap of about 1/4" between the end of each joist and the beam.  To fix this, I came out the next morning and rigged up a "squeezer".   By wrapping a rope around the structure and twisting with dowel, I was able to pull the two beams up snug against the joists and then reset the nails holding them in.  I was now able to complete the "Y" bracing, making a more rigid structure.

We dug holes where the legs should go, and I poured four concrete footings with embedded post ties.  Again the neighbors came back and helped lift the legs up unto the posts and we bolted them in place.  After hauling all the remaining joists up and nailing into place the basic platform frame was completed.  The next trial was getting the floor decking installed.  I had not realized how scary it would be to be over 10 feet in the air working on a very open framed structure.  It also swayed a bit.  Ten foot posts are not as stiff as I though they would be and the whole structure would oscillate quite easily as you moved around it or bumped against it.

Each sheet of 4' x 8' flooring weighed about 80 lbs. (or so it felt).  Deb helped hold the ladder as I climbed up with each sheet and threw it on top of the platform.   Chris and I both then nailed the flooring into place.  We now had a completed "deck", 10 feet in the air.  But it was quite wiggly and very scary to be standing up there.

Now was time to actually plan the framing of the building itself.  This took quite some time to figure out how to make the frame, learn how to frame a window, and be sure that I could build the roof/rafters on top.  After purchasing the 2"x4"s, I built all the walls in the driveway.

Framing proceeds rather quickly, and I was able to assemble the frame for the tree house on the ground, with all the sections tied together with string.  It was quite fun to walk around inside the frame and get a feeling for the size of the room-to-be.

Again, we had to haul these quite heavy walls up onto the platform.  Again both Debbie and rope came in handy.  About this time, Gerry Albertson again came to the rescue.  Being in the construction business, Gerry owns portable scaffolding.  He let me borrow it for much of the summer.  Now I could wheel a portable 16 foot high platform around to any side of the tree house to help install siding, place the window, and install the roof.  I don't know how I could have completed this project without it.

One of the most difficult things to figure out was how to attach the rafters.  I had at first thought I would notch out each piece with a triangular cut called a "bird's mouth".  The problem is, determining exactly where to make this cut, and at what angle so that the rafter rests squarely on the top of one wall while it attaches to the ridge beam.  This was much harder (for me) than it sounds.  I finally gave up and bought special metal ties that eliminate the need to notch the rafters at all.

With rafters in place, I nailed 4'x8' sheets of siding up into place and nailed all the walls together.  Having the building framing in place added a bit more stiffness to the structure but it was still quite wiggly.  I considered pouring some more concrete footings and attaching buttress-like supports to each of the legs.  Eventually, and more simply, I was able to add additional cross-bracing from mid-span to the base of each leg.  This was able to add the stiffness that was needed and it now feels quite solid.  We brought up an old window from our house and nailed it into place in the west-wall opening.

The roofing was something I really knew nothing about.  I decided to install cedar shingles across the roof, with no underlayment - I figured it would be pretty waterproof, although may not be perfect.  It was now August, and we were starting to get some really hot weather in Seattle.  There's nothing like sitting out in the sun on a hot roof in the summer.  I was glad we at least did not live in Texas, who in 1998 had temperatures over 110 degrees.

I calculated that I installed 500 shingles and drove 1000 nails.  I did all this without the aid of a nail gun.  That was a mistake.  Due to my, I'm sure, poor technique, the knuckles in my right hand still ache from the jarring they received doing all that hammering.

With the roof installed, I then built and hung the door, and built the balcony railing (copying the style of the railings used on the deck of our house).  With the exterior complete, we built two bunk beds, a desk, and four shelves inside.  Finally, in September/October I was able to complete wiring for lights and electrical outlets.   Debbie purchased foam and covered them to make cushions for the bunk beds.

Everything complete, Chris and I impatiently decided to sleep out in the tree house that night.  It was November, and about 25 degrees outside.  Man, was it cold.   Chris was able to sleep through most of the night, but I was tossing and turning.   The total cost of materials was about $2000 (about $25/square foot - not counting labor).  I spent another $400 on tools, books, and videos during the project.

Now, we've bought some property and are planning on building a house for ourselves.   We're going to have to figure out how to move a platform house in a couple of years!