The hemlock this one wraps around is close to 140 years old, and the family who owns the land had watched three generations of kids build rope ladders into it. They wanted something that would outlast the ladders without pretending the tree wasn't there.
We split the interior into two rooms around the trunk itself, which runs straight through the middle of the structure and out through a collared opening in the roof. A steel collar three inches wider than the bark gives the tree room to grow for the next twenty years before anyone needs to touch the framing again.
There's a woodstove no bigger than a bread box, vented through a triple-wall pipe, and a window seat that gets full sun until about two in the afternoon. In February, the family reported it was the first place condensation didn't form on the glass — the stove does more work than its size suggests.