How to build a treehouse on a stump

May 15, 2017 10:19 AM

Hurricane Matthew left us with a stump in our backyard, and I'd like to put a treehouse on top of it for my daughters. How should I do it?

Saltwater intrusion finally killed off our enormous, sickly camphor tree, and I asked the tree removal guys to leave the stump intact so that I could build my daughters a bitchin' treehouse. Here's the stump in question; it's nearly 4 feet across and somewhat level but far from perfectly level. I think I'll be able to get away with about a 5'5" by 5'5" square building. I want to get going on this project but I have very little construction experience and have no idea where to even begin. Well scratch that, I do know where to begin, I need to build a platform first. So how do I begin that? Specifically:

- Can I anchor the bottom of the fort to the stump itself, or am I going to have to sink posts on the corners to support it? I'd definitely prefer the former if possible.
- What should I build the platform out of? Assume that I'll eventually frame four walls and build a simple gabled roof for the building.
- What form should the platform/floor actually take?
- Anything else I should be thinking of?

I have access to power tools, I'm relatively handy although (obviously) have very little carpentry experience, I'm willing to spend some money (but not a ton) on materials and plenty of time on this, and we're in Florida so rain and humidity will be a big factor.

Also, if you've got general suggestions or ideas for how to make a small treehouse really amazing for an extremely imaginative and not particularly athletically adventurous five-year-old I'm all ears. I'm sure I'll be back here asking about subsequent phases of this project but I'm happy to hear y'all's thoughts on roofs and stuff now.

posted by saladin to Home & Garden (11 answers total)

One thing you should do is seal the top of the stump to delay rot.

Plastic lumber won't issue splinters. Go with a light color that won't heat up in the sun.
posted by Mr. Yuck at 10:45 AM on May 15, 2017

the stump will rot, so don't rely on it for anything structural.

For the pilings you'll probably need, make sure it's ground-contact rated pressure-treated wood (vs the more generic decking type of pressure treated wood).

Do you want the stump to be like a table in the middle of the tree house ? The house to "sit" on the top of the stump ? (It doesn't look tall enough to attach the tree house to the side of the stump.. )
posted by k5.user at 10:58 AM on May 15, 2017

It's true the stump will rot, eventually, but if you seal the top and then construct the tree house in such a way that the stump stays as dry as possible, it will hold up for quite a few years. Long enough for the kids to outgrow it. So I would go ahead, and just check it once a year for structural soundness. For insurance, you probably should install some diagonal wood braces, like 4x4s, from the corners of the treehouse platform to the base of the stump. Eventually, if it gets wobbly, you'll have to install vertical posts in the corners, down to footings in the ground.
posted by beagle at 11:26 AM on May 15, 2017 [2 favorites]

Also, check with the municipal building department. From the photo it looks like a place with rigorous building codes, and sometimes they frown on treehouses and such.
posted by beagle at 11:28 AM on May 15, 2017

Yeah, I was just going to say, how nebby and complainy are your neighbors? Because I don't know about where you live but here that would require a permit (I was just talking to a neighbor yesterday who had to pull a permit to build a pergola in his garden.)
posted by soren_lorensen at 11:43 AM on May 15, 2017

Seal yes, rot inevitable long term, but unless you're going full Shane or dynamite that trunk will be there a long time. Treehouse site worth browsing. Seems like a great project!
posted by sammyo at 12:09 PM on May 15, 2017

Best answer: Yes, I think you can build on the stump. Normal rules for cantilevering is that your floor beams can cantilever out 50% of their supported length; you can do this on both sides, so if it's 4', you could cantilever out up to 2' on each side. I'd use 2x8s for the floor beams and install a center beam that runs perpendicular to the rest (if you really want to go crazy, make a grid), with them all notched out so that they can interlock and rest on the same level. Box in the exposed butt ends of the beams.

Shave the top of the stump as level as you can, then lay the substructure on top of that, shim it out to make it really level, and then attach it to the stump using angle irons, bolts through the floor beams, and lag bolts into the stump.

Once you've built that substructure, you can lay whatever kind of flooring you like on it, and then build walls on top of the floor, and a roof on top of that; probably the simplest thing would be a single-pitch roof with the rafters tied into the wall studs with joist hangers.
posted by adamrice at 12:26 PM on May 15, 2017

Best answer: Yes, the stump will eventually rot. However, your daughters will grow up before the stump is gone. It looks solid and intact, so it could give it years of service.

I think that you can anchor your little house to the stump. You can spike the base to the stump with long nails. Use treated wood 2 x 6's, and consider shimming them to make them level. Cross the 2 x 6's with 2 x 4's, and put planks or plywood over it. Get the girls' input on trim and paint colors.
posted by Midnight Skulker at 12:32 PM on May 15, 2017

Involve your daughters in the making of the treehouse!

Also you can get some mini tiles and let the kids do some decorative tiling on the stump-top.
posted by aniola at 12:59 PM on May 15, 2017

Response by poster: Hell yeah, thanks folks. No permit required for this thing, according to the city. I think I'll try to build an interlocked box as adamrice suggested. Then it's on to figuring out the walls, and the roof...

Followup question: what tool would I even use to try to level the surface of the stump?
posted by saladin at 7:31 AM on May 16, 2017

Leveling the stump will be tough. My first guess would be to drive 6 or so stakes around the trunk, at least as tall as it. Then tie string around all of them, and level the string equal with the lowest spot on the trunk top (go all the way around at least a couple of times; I've done this before—it's slow work). Then transfer the string's height to the trunk using small nails (or something). This will involve a lot of eyeballing and will be approximate. Then shave around the top with a chainsaw down to the markings. That will at least get the outer perimeter (most chainsaw blades aren't long enough to reach to the center). That will leave you with a "plug" in the middle that you could probably take off with an undercut saw, a hand-pulled chainsaw, or judicious use of a powered chainsaw.

At this point, it should be reasonably level, and you'll be too tired to try to make it any more level.
posted by adamrice at 10:12 AM on May 16, 2017