How to Build A Tree Fort

This summer my sons and I built a pretty awesome tree fort (technically it's just a fort near a tree, as we didn't want to injure the tree). Before building, I read through the tree fort guide in the Black and Decker Complete Guide to Outdoor Building. I love Black and Decker's guide books, especially their Home Wiring guide.

Supports

Figure 1: Posts and Rim Joists, Side View from the South

Figure 2: Posts and Rim Joists, Side View from the East

I opted to use concrete "feet" rather than proper footings, as the latter is far more permanent. I used Home Depot's cedar-tone treated lumber for all of the supports. I notched the posts to support the rim joists, as shown in Figure 1.

I wanted the fort to feel "up high" to my kids, so we put the deck about four feet off the ground.

Deck

Platform in progress. The temporary diagonals between the joists keep it square.

The deck is a six foot square platform built with a 2x8" rim joist and 2x4" joists. The joists are supported by a perpendicular 2x4" screwed to the rim joist, as shown in Figure 3. I opted to use this method instead of more expensive joist hangers as the span is short and the load is relatively small.

Figure 3: Joist Support, Side View from the South

Figure 4: Platform, Top View, North Up

Enclosure

I stick-built the enclosure from un-treated 2x4" lumber. The enclosure is a four by six foot structure, four feet tall on one side and six feet tall on the other. 

Figure 5: Enclosure Side View (From the South)

Figure 6: Enclosure Side View (From the East)

After erecting the  frame of the enclosure we sheathed it with plywood. For most of the structure I used 15/32 plywood, though for the rock climbing wall I opted for 29/32.

Enclosure with plywood sheathing

Roof

I ran 2x4" rafters from the west (lower) side to the east (higher) side, covered that with plywood, and then used tin roofing. 

Siding

My parents gave us some extra cedar shingles, enough to cover about half of the enclosure. The only place I could find additional cedar shingles was Fleet Farm. We stained them and stapled them. 

Porch

I used cedar boards for decking on the porch and treated cedar tone 2x2" boards for the railing.

Windows

I used 1" pine boards to build box windows, then I use a table saw to cut grooves in them for insect screen attachment.

Window with grooves cut for rubber screen attachment

Nuts and Bolts

For most structural connections I used GRK 2.5" star drive self-piloting construction screws. These are more expensive than most other screws, but the cost is absolutely worth it. Note that as the rim joists sit directly on the posts, I did not need to use lag bolts. 

The best screws in the universe