Yestermorrow Practicum Project - Post 20

Grinding out the roof structure. I'm getting faster but it is going to take three or four days to complete the whole roof. After building the model I should be cured of any desire to build a real world version.

Also added a couple of windows since the previous post. All in all I'm making good progress toward getting this thing done on time.

Yestermorrow Practicum Project - Post 19

Working on the final model for my project. Making progress but it's slow tedious work. Glad this is nearing an end so I can switch to more viable designs. There must be an easier way to do organically curved roofs but I'm not seeing it yet. Probably something involving molds and lots of technology. 

The two images below show the framework for the roof overhangs.

Yestermorrow Practicum Project - Post 18

I made much progress over the past week or so. Following is a sequential photo essay that captures the "big moments".

Two inch diameter dowel pieces attached to the top of each post with Timberlock screws.


Previously created frame deconstructed for parts. It would be really nice to have the hub joist hangers available as a custom part like this.



Assembled hubs placed over the 2" dowel pieces. Turns out that tightening the bolts that hold the joist hangers in place is a bit of a challenge with the dowel in the center of the tube segment. This can be solved by temporarily removing the dowel pieces, one at a time, after putting together the triangular frame.


First beam/joists hung between the post hubs. I'm using 3/4" plywood with a depth of 12".


First triangle completed. The beams are 12" deep at the posts, 8" at the eaves. I jury rigged a jig to help do the length and angle measurements. It worked but I'd build something better and easier for an actual production.


The three triangles of the prototype completed. When I ran out of plywood I started raiding my scrap wood pile.


Fascia details. This, for a change, was actually easy to do as measurements can be taken off the existing framework. The cuts to match the adjacent fascia boards would be a bit of a challenge.

A sample cross-brace to reduce the span for the covering plywood triangles. Worked well but took more time than I would like.


An experiment using 2x4 pieces to "float" the roofing triangles above the framing. This would be fairly easy to do and could be used to increase the roof thickness for a higher R value.


Finally, a device I created to "measure" the irregular triangular shapes of the the roofing framework so as to be able to cut matching triangles from plywood sheets. I was originally planning on filling in between the joists with hempcrete, but now believe that there is likely to be too much movement for this approach to be viable. It is possible to "box" in parts of the eave triangles by cutting a triangle that will rest on top of the hempcrete wall on the in side. This "box" could be filled with dense pack cellulose. It was in trying to figure out how to easily measure the shape of the bottom of this "box" that I came up with the idea for the triangle shape reproducer.


Again, lots accomplished. The prototype is essentially finished but serves as a great test bed for further experiments. 

Yestermorrow Practicum Project - Post 17

Lots of progress. Just needed some cooler weather to make working bearable. I learned a great deal about how to build better forms. The approach I used here is too complicated, and has other issues, but I now see how to easily make simple good formwork. I'll elaborate more in a future post.

I'm quite pleased with the look of the wall. Love the curves.

Some shots of the formwork I used for this prototype. The first three pictures show how I set the window boxes on a few inches of hempcrete, before putting up the wall forms.

Next a couple of shots of the formwork filled with hempcrete.

Finally a few pictures of the wall prototype with the formwork removed.

Yestermorrow Practicum Project - Post 16

Very hot today so I only worked for a few hours, but they were productive. I added the insulation between the 2x4s of the sill plate. Foam board for the straight runs and expanding poured foam around the posts. Then I built a couple of plywood boxes for the window openings. (Ohh, for a good table saw.)

I really don't know what the tricks are for doing things like this so I just work along slowly and try to learn as much as possible as I go. Tomorrow I should be able to start mixing and adding the hempcrete.

I'm starting to wonder what I'm going to do with this thing when I'm done. Probably keep it around for a while and then deconstruct it. It's all a learning exercise.

A few pictures of today's work.

Yestermorrow Practicum Project - Post 15

It was a day of two steps forward, one step back. Lots of rethinking caused by the reality of working with real materials at full scale. In general though, it was a productive day in which I discovered I could avoid some complicated steps that turned out not to be needed. For instance, there is no need to cut the tops of the posts into circular shapes to match the pipes that will sit on them. I'd thought I needed to do this so that the rafter bottoms wouldn't hit the posts, but realized that I could just trim back the rafter bottoms as needed to clear the posts.

Another thing I was reminded of today is the importance of making jigs for any repetitive process. It probably helped that Bruce Beeken, the furniture maker who gave Yestermorrow's summer lecture number two, stressed the importance of jigs in his work.

Here is a picture of a simple jig I made to help build the formwork jig to hold the hardboard wall forms in place.

Then here is the wall form holding jig, made with the help of the first jig.

Finally, the form holding jig moved up the post to near where it will be attached.

Yestermorrow Practicum Project - Post 14

Did some work on the wall prototype today. I completed the wooden parts of the sill plate. The hempcrete will go on top of this. The work went pretty well. I first made a jig to help figure out the curves.

Then using the jig, and a 12" by 26" piece of hardboard representing a straight wall segment, I layed out a wall section with three posts on a piece of 3/4" plywood. Made a few mistakes but nothing major; the usual sort of thing when building a prototype. Tomorrow I'll add the truncated posts and the sill insulation, then build the form for the hempcrete, which will include a window opening. It's fun to be building at full scale, even it's only a prototype.

Yestermorrow Practicum Project - Post 13

The mache-covered wood shed has been drying out in the sun for the past few days. Yesterday I noticed some shrinkage on a couple of the sides. As the mache dried it pulled back from the edge an eighth to a quarter of an inch. This may actually be an opportunity as I've been wondering how to handle the edge condition. I used some Liquid Nails adhesive to bridge the space between the mache edge and the plywood edge. After I've painted the roof, and its had a chance to weather, it will be interesting to see how the adhesive edges hold up compared to the mache edges. In either case the solution is not ideal and I'm still looking for a better approach.

Here are a few images of the roof and the shrinkage.

Yestermorrow Practicum Project - Post 12

I've been working on a truss system to replace the ceiling rafters. The advantages to using a truss instead of a solid beam are that less wood is needed (in theory) and there is less thermal bridging. In order to get an R-60 dense-pack cellulose roof a thickness of around 18" is needed. For R-80 24" is needed. For those kinds of roof thicknesses a truss especially makes sense. Here are a few images of my latest truss designs.

Yestermorrow Practicum Project - Post 11

A sample of Stuc-o-Flex "Waterway" rainscreen drainage mat arrived in the mail yesterday. It is the material I hope to use between the triangular plywood roof sheathing and the smoothing mache layer. 

I mixed up a small batch of mache and applied it to the top of the mat. The mache will take a few days to dry but after working with "Waterway" a bit I think it will work quite well. I love this mixture of very high tech and very simple technology.