2024 PTJ project - round wood pavillion build

Hey there, my PTJ projects got shuffled and now I'll be leading a big build.  Making a roundwood timber frame pavilion/pergola in the space between the Fisher Price House (main house) and the Library.

Due to risks and uncertainties, we'll break the project into a number of stages.  Getting Stage 1 complete is reasonable.  If we are chugging along well, we can consider taking on Stage 2.  Stage 1 involves 4 posts, two horizontal beams and two sloping rafter-like beams with a lot of angle braces.

The posts would normally be sunk 4' deep but this spot has crumbly bedrock within a foot or two of the surface.  So we'll be setting the posts on that and experimenting with ways to pin them down.  This means that angle bracing the structure will be more important than usual.

The current thought is to build two "cants" and tilt them up into place.  Each cant will include two posts, their beam and angle braces.  Once they're up (and temporarily held in place), we'll put the rafter beams up.  

We'll likely get to build a gin pole to lift stuff up in the air.  We'll likely get to debate the merits of different kinds of joinery.  I suspect we'll be encouraged to not have any metal in the build (except for the joint with bedrock).

Stage 1 will enable mounting a shade sail and hanging lounge chairs in the space.  Stage 2 (I believe) would be to put a roof on the structure to keep the patio mostly dry.  Stage 3 (I believe) would be to add two more posts and make the structure extend farther to the East.  

Challenges:
- The logs are currently attached to the ground and have needles growing from them.  We'll have to harvest, peel and transport them to the site.  The tractor would be very helpful, as would the log arch
- There is a big picnic table that may be in the way.  But working on the patio (instead of up in the air) might be nice
- Developing joinery that won't collect water and rot is important.  This isn't holding up an eathen roof so we may have a few options
- Paul loves huge logs so we'll have to balance the size vs what's really needed
- I'm struggling to think of ways to connect the logs and brace them without fasteners.  In a way that won't uplift or disassemble in a strong wind....

Ok, I've done more thinking about this and am curious about everyone's opinion.  Especially if you have some experience with this sort of stuff.

I got some great info from Kris Harbour Woodworking's youtube channel.  

Here's one showing a draw bore mortise with roundwood and how to lay it out.  Please note how long it takes to do this sort of joint and he has a chainsaw mortiser:


And here he is doing an angle brace.  He said for his first one (with his level of experience) it took him 3-4 days to do two angle braces.  I'm thinking this is more advanced than what we can accomplish.


My current thinking is to add two beams to the crude drawings in the first post. So each cant (two posts, the beam and two angle braces) will stand up and then a pair of horizontal beams will connect them with tenons.  This seems to be how timber frame buildings are designed.  Then the rafters can just sit on the assembly and they're no longer holding the structure together.

The first drawing shows the cant details.  The posts would have a square end with a tenon sticking up from them.  The beam would have some shallow flat spots carved in them to rest on the posts.  I've read that getting the heartwood of the beam sitting on the posts is a good idea.  Offset peg holes would be drilled through the beams and tenons so when a peg is driven in, it would suck the tenon into the mortise a smidge.  Kris aims for 4mm of offset.  I'm thinking these pegs should be 1.5" diameter?

The angle braces will sit on flat spots with a lower shelf on the posts.  To keep them in place, two pegs will be toenailed at different angles through them into the post.  These will probably be 1" pegs.

The second drawing shows the new beams that tie the two cants together.  I think drawbore tenons would be a good way to pull the structure together.  One issue is that one of the cants would have to move towards the other to seat the tenons in the mortises.  Not impossible...  These beams would be pretty high, likely above the person door into the library.  

We'll probably need to build some beefy sawhorses to hold the cants and logs as we work on them...

It is coming together. Here is an animation of the main beam being lifted into place, from Clay McGowen's post.