How Would You Roof This Treehouse? (Rafter Layout)

My buddy is trying to determine the best way to roof the treehouse he is building. He is ready to start cutting the rafters, but he is not sure how to deal with the trunks. You'll notice the issue immediately.
We have some ideas, but I don't want to influence anyone, so I'll keep them to myself for now.
This question is mainly about rafter layout, not about sealing the roof from rain, although suggestions/experience related to that are also welcome.
Ground Level View
https://i.imgur.com/AS3HhDw.jpg
Crotch Level View (leave it alone!) The board is there just to show the height of the crotch
https://i.imgur.com/xuP7NfY.jpg
Bird's Eye View (simulated)
https://i.imgur.com/VI41CBE.jpg
The smaller branches are not an issue, they will be cut. It's the 2 main trunks that need to be dealt with. Based on the location of the trunks, neither 16" OC or 24" OC will clear them.
Have fun!
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On 7/25/18 10:03 PM, DerbyDad03 wrote:

First thing that jumps out to me is a four sided hip roof and pyramid hip roof. All the rafters would terminate near the two trunks and you could get creative with how it all joins together at the peak.
--

-MIKE-

"Playing is not something I do at night, it's my function in life"
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On Wednesday, July 25, 2018 at 10:51:27 PM UTC-5, -MIKE- wrote:

Hmmm.... I would certainly hope that the carpenters had that skill set. I am thinking of trying to header off the common rafters someway, then creati ng a stable frame to hold up the hip rafters, then fitting in each jack raf ter (cheek cuts on one end, bird's mouth on the other)in an unsquare and un stable roof structure. A lot of work for a tree house.
I looked at the pics and the last drawing said that there was a "preferred" direction of the rafters. Personally, I would change that. Then you coul d make a simple offset gable roof that used all common rafters and simply b lock out around the trunks. In fact, you could cut the roof closely enough around the tree trunks that you could flash the base of the penetration, t hen attach a counter flashing (like a storm collar) around both trees and s olve the water proofing as well. By counter flashing the penetrations (tre es) in that fashion they would not be compromised in a windy environment.
Robert
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On Thursday, July 26, 2018 at 3:41:35 AM UTC-4, snipped-for-privacy@aol.com wrote:

I am thinking of trying to header off the common rafters someway, then crea ting a stable frame to hold up the hip rafters, then fitting in each jack r after (cheek cuts on one end, bird's mouth on the other)in an unsquare and unstable roof structure. A lot of work for a tree house.

d" direction of the rafters. Personally, I would change that. Then you co uld make a simple offset gable roof that used all common rafters and simply block out around the trunks. In fact, you could cut the roof closely enou gh around the tree trunks that you could flash the base of the penetration, then attach a counter flashing (like a storm collar) around both trees and solve the water proofing as well. By counter flashing the penetrations (t rees) in that fashion they would not be compromised in a windy environment.

That was one the ideas we had.
The reason for the "preferred direction" and center ridge is because of the view. He is hoping to have the gable face the house instead of a bunch of shingles.
After a few more responses, I'll ask a question about an idea we had to ret ain the preferred direction.
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On 7/26/18 2:41 AM, snipped-for-privacy@aol.com wrote:

What's been done so far looks pretty legit, so I assumed the builder had a decent skillset to begin with.
However, even with the preferred rafter direction, he could sandwich the tree trunks and have a rafter going between the two. Then just block in around them.
--

-MIKE-

"Playing is not something I do at night, it's my function in life"
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On Thursday, July 26, 2018 at 10:25:35 AM UTC-4, -MIKE- wrote:

Well his skill set is growing along with the tree house. I've done decks and walls, etc. so I've been coaching him a bit in that regard. He picked up a lot of "treehouse" support structure skills from the company that he bought the treehouse hardware from. He's a pretty smart guy in general.

That's basically where we were heading. Just looking for some other options from the real experts.
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On Wednesday, July 25, 2018 at 11:51:27 PM UTC-4, -MIKE- wrote:

That's probably not happening unless he hires it out. That's not happening.
His kids, his build. ;-)
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On Wednesday, July 25, 2018 at 10:03:57 PM UTC-5, DerbyDad03 wrote:

building.
The house seems to be only about 10' X 10'. That's not so large that a st andard type layout is sufficient, especially if he uses 2X6 ceiling & roof joists, rather than using 2X4s. Beyond a standard layout, he should be abl e to improvise, reasonably so, the necessary structure around the tree trun ks.
Also, and besides, what's wrong with adding a few extra rafters, if & where need be, where standard alignment won't align/fit, i.e., rather than all r afters/joists being 16" OC, some could be 24", 10" or 8" apart... whichever fits. The 2X6s would be more than strong enough to accommodate any offse t rafter/joist alignment, for that small size room. Also, a diagonal rafte r running between the trunks AND between two normally running (~~ adjacent) rafters, should be no problem for sufficient support & stability.
Overkill? Use some Simpson strong ties to further the joinings.
Sonny
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On Thursday, July 26, 2018 at 9:35:46 AM UTC-4, Sonny wrote:

s building.

standard type layout is sufficient, especially if he uses 2X6 ceiling & roo f joists, rather than using 2X4s. Beyond a standard layout, he should be a ble to improvise, reasonably so, the necessary structure around the tree tr unks.

re need be, where standard alignment won't align/fit, i.e., rather than all rafters/joists being 16" OC, some could be 24", 10" or 8" apart... whichev er fits. The 2X6s would be more than strong enough to accommodate any off set rafter/joist alignment, for that small size room. Also, a diagonal raf ter running between the trunks AND between two normally running (~~ adjacen t) rafters, should be no problem for sufficient support & stability.
That is very close to what we had in mind, other than the "diagonal" rafter between the trunks. Considered it, not sure it's needed.
The main idea was to "box" in each trunk with 2x6's and run a rafter from t he wall to the both corners of each box, if that makes sense. Something like t his, although I realize that there are all sorts of angle and rafter heights to deal with.
https://i.imgur.com/JTUQ4RN.jpg

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On Thursday, July 26, 2018 at 10:46:05 AM UTC-5, DerbyDad03 wrote:

er

Along the line of over kill(?), your "not sure it's needed" comment: The t runks to be boxed in, with the boxing members at 90°. A diagonal brac ing, in the corners or in some fashion, would further prevent racking, if t he boxed joints area are the weakest, in the structure's whole system.
I don't know tree house construction. Maybe my idea of a more rigid frami ng system is not correct. Maybe the structure needs to be a little flexib le, for when the trees move in the wind, etc. But I would think one needs to guard against too much racking, potential racking.
Sonny
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On Wed, 25 Jul 2018 20:03:54 -0700 (PDT), DerbyDad03

Just thinking outside-the-box - if it doesn't need to be weather-tight or insect-tight perhaps a couple or three colourful tarps could be used .. ? John T.
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On Thursday, July 26, 2018 at 2:17:14 PM UTC-4, snipped-for-privacy@ccanoemail.ca wrote:

As I mentioned to my buddy last night: A couple of tarps would be pretty easy to install. And easy to install again. And easy to install again. And easy to install again. And easy to install again.
;-)
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On Thu, 26 Jul 2018 12:06:46 -0700 (PDT), DerbyDad03

I used one on my stand-alone play structure - bright blue 6 x 8 - it would last about 4 years - so I replaced it 2 or 3 times in the life of the structure - easy & cheap.. John T.
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On Thursday, July 26, 2018 at 3:37:06 PM UTC-4, snipped-for-privacy@ccanoemail.ca wrote:

I'll wager that the tarp on your play structure looked more like this...
http://qaria.co/wp-content/uploads/2018/03/playset-tarp-heavy-swing-walmart.jpg
...than this:
https://i.imgur.com/UhTlqtO.jpg?1
My point is that there is not going to be any way to neatly - and tautly - put a tarp over a 10' x 10' square structure that has a double trunk tree coming up through the middle of it
Wind, rain, snow and gravity are sworn enemies of sloppy tarps.
I know you said "if it doesn't need to be weather-tight" but other than building a large box around the tree and running the tarps in 4 directions, leaving a huge hole in the middle, I don't see a way to use a tarp and have it last. And if there is a hole the size of the 2 trunks in the roof, I don't think it would be proper to call it a tree *house* anymore. ;-)
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