OK, that was quick. The advantage of being on vacation and having some time to play.
I mixed up a batch of smooth mache using the ammonium sulfate cellulose; about a gallon in quantity. Then I used a plastering trowel to smooth the material instead of my hands. What a difference. This was a enjoyable process that produced a beautiful result. Very encouraging!
I added a second layer of mache to the test roof yesterday. This was a smooth mache mix which -after it dries in a week or so- will be touched up with joint compound and then painted. Although the layer turned out well enough it was frustrating to build. Partly this was because I was mixing mache in small quantities (about a gallon at a time) and partly because I didn't start with a good technique for spreading the mache, especially around the edges. I used my hands again to push and mold the material, a process that is both very time consuming and leaves behind marks of the hand working. To use this material at a larger scale it will be necessary to involve hand tools (like trowels) to spread and mold the mache. My next experiment will be in this area.
I'm still working out how to handle edges. In this case I will sand/shave off the uneven mache along the edges once the material has dried. Definitely looking for a better solution.
A couple of images of the roof with the second layer.
A double-shell roof. Latest ideas and a request for help.
Coming up with a method for venting an organically-curved roof was a challenge, but thanks to the help of John Unger Murphy and Bill Hulstrunk I believe I have a solution. In essence the roof consists of a double shell. The inner shell is composed of plywood triangles, which are attached to the framing, and covered on the outside with a vapor permeable "paintable" membrane like Tremco ExoAir 220. The outer shell is composed of hard paper mache covered with a paintable waterproof membrane such as roof mastic. In between the two layers would be a drainage mat -perhaps the Stuc-o-Flex WaterWay Rainscreen 9120 - which would allow moist air to flow up to the dome peaks to vent via small cupola like structures. The rainscreen would also allow the mache to "float" free of the plywood, helping to prevent cracks. That's the theory anyway. If you see problems with this approach please share your concerns!
Here are a couple of sketches that may help you visualize the double-shell approach.
There are two components for which I could use some help. These are the waterproof roof membrane and something that could be added to the mache to help it dry faster (the mix I'm using now takes about a week to dry). Bill Hulstrunk suggested I try duct mastic for the mache mix and I'll give that whirl in the next few weeks. Any other suggestions are much appreciated!
Worked on my first large-scale use of hard-mache to smooth a roofing surface composed of irregular triangles. Used about 5 gallons of mache to put a first coat on the small structure that covers my firewood.
It went well, and the new surface is definitely more rounded and smooth. A second less-rough coat of "finish" mache will go on in a few days; after this coat has a chance to dry.
The following two photos of a test piece provide some sense of how the finish coat will go over the rough coat, and then on top of everything will be a layer of waterproof mastic.
Wall framing on a structure with an organically curved roof is going to be a little different. I've played around with lots of ideas. This post reflects my latest thinking. Rather than attempt to explain in writing I've created a short video which is embedded below.
Insulating the foundation of a building is important in order to prevent the concrete from acting as a thermal bridge. Othen this is done by applying foam board to the outside of the foundation's concrete walls. With a curved foundation wall I was curious how this might work. Yesterday I did a little test. I scored one side of a piece of 2" foam board and was then able to bend it without a problem. This should work very well with my foundation wall, which consists of short curves and longer straight runs.
I'm considering using Hemcrete® for the walls of the organically-curved structure I'm designing for my Yestermorrow practicum project. I learned about Hemcrete from Thomas Simon (of Hempfully Green) during Robert Riversong's Hygro-Thermal Engineering course at Yestermorrow last March. Thomas brought some samples of Hemcrete and shared them with the other students in the course during breaks. Recently he very kindly provided me with some materials so I could mix up and experiment with my own batch.
I built a simple curved form yesterday using some scrap wood. The curved sides were formed with brown fiber board, which can easily handle the gentle curves of my design.
I'm thinking of using PVC tubing for posts so I placed a piece of tube at the position where posts will be located.
The mixture is three parts hemp shiv (the woody core of Industrial Hemp) to one part water and one part a lime based binder called Tradical® HB.
The three parts mix up easily into a material that has the consistency of a dryish concrete.
Wearing gloves (the lime can do a job on skin) I hand placed and gently tamped the mixture into the form.
I'd seen Tom remove a form only a few minutes after loading and tamping in a mix of Hemcrete so I knew it should be OK to remove the formwork. Still, it was with a bit of trepidation that I gently started releasing the form. There was nothing to fear, the mix held its shape beautifully.
I'm very pleased with the experiment. The material is easy to work with, environmentally friendly, and handles curves with aplomb!
Yestermorrow is a wonderfully creative and quirky design/build school I've been attending since last September. I'm in their Sustainable Building and Design certificate program and have just one weekend class left to complete my coursework. I've spent over six weeks in residence at the school since starting in September and have a pretty good sense of Yestermorrow's culture. My background is in education so while I've been absorbing all kinds of great information about design and building I've also been observing and thinking about the pedagogy used to convey that information. If I have any design strength it is in the use (and teaching of) SketchUp. Some of my SketchUp work can be found here and here.
In my three week sustainable design core class I was the only student who made significant use of SketchUp. I wrote about this experience in a previous blog post. There was an interesting discussion about SketchUp at the end of the my project's crit session. During this discussion it became clear that the Yestermorrow teaching community is struggling with whether to continue teaching traditional drafting techniques or bite the bullet and move to SketchUp. John Connell, Yestermorrow's founder, participated in that discussion and mentioned that he was going to teach a sustainable prefab design course in April in which SketchUp use would be required. I attended that course last week (see previous post) and want to share some thoughts about how SketchUp was taught/used.
Most students in the class arrived with very little SketchUp experience. There was an optional Sunday evening session for students who wanted help getting a handle on the program. The intuitive nature of SketchUp's interface, especially the Push/Pull tool, allows students to start using the program quickly, but without a solid understanding of good SketchUp practices a quick start can often lead to signifcant modeling problems down the road. That dynamic very much characterized the use of SketchUp for many in the class. There was much more frustration than there needed to be, and the students' house designs could have developed much further than they did.
So the question is, how to quickly develop good SketchUp use practices?
Here are some suggestions.
1. Require students read SketchUp for Dummies by Aiden Chopra before the class. Aiden is an architect and SketchUp employee. His book is by far the best introduction and reference to SketchUp that I've found.
2. Have a scanner in the classroom so that floor plan drafts done on paper can be scanned and imported into SketchUp.
3. Teach students how to use groups and components as early as possible. All significant elements of models should be grouped as soon as they are created.
4. Show students how to grab site information from Google Earth as soon as possible.
5. Have students set up and memorize (or learn the default) keyboard shortcuts for at least the Move, Orbit, Push/Pull, Line and Hand tools.
6. Require all students to have a mouse.
7. Teach students to pay attention to the hints that SketchUp is constantly providing.
8. Teach students how to effectively use the Dimensions box.
9. Provide a SketchUp house model made with best practices. This model could include basic elements which students could copy into their models.
In the following video I build a simple house model making use of some of the practices listed above. If students master the techniques I present in the video they would tend to have a much more positive experience with SketchUp, and teachers could focus more on design concepts and less on SketchUp. (Note: This video was made in one take and a number of the illustrated techniques could be better explained in shorter better prepared presentations.)
I had the distinct pleasure of attending a course on sustainable prefab housing last week at Yestermorrow. The course was taught by architects John Connell (who founded Yestermorrow) and Giocondo Susini. One couldn't ask for a more thoughtful, kind, knowledgeable and entertaining pair of teachers. John Connell is massively connected into the architectural and building community in the Mad River Valley and surrounding environs. These connections benefited the class via the field trips and speakers John was able to arrange.
My classmates were a delightful mix of folks hailing from as far away as Austin, Texas and having a wide range of design/build experience. Everyone was in good spirits and we all shared many ideas through the week as our projects developed.
I worked on a possible retirement house design based on modules offered by Huntington Homes, a family-owned company whose factory we visited early in the week. Below are a couple of renderingsof the ranch-style home model I developed that would use four HH modules for the main structure. The garage and screened porch would most likely be stick built on site. Larry Roux, a HH homes sales manager, was kind enough to provide a preliminary quote for the building, which I'm pleased to say was within our price range.
HH is producing a very well constructed module with a 12" thick double 2x4 wall using dense-pack cellulose for insulation. This wall assembly struck me as a good compromise solution to a super-insulated wall, reaching an R-value of around 40.
We also had a great visit to the Connor Homes factory. Connor produces all the components for its higher-end houses and ships them out to the building site as contractors are ready for them. They produce really beautiful versions of the region's tradtional vernacular architecture.
In addition to the field trips we had guest lectures from representatives of structural insulated panel (SIP) maker Vantem and the famous (at least to fans of This Old House) Benson Wood timberframe/prefab company. Both lectures were extremely informative.
The class used SketchUp right from the start for all our design work. Students were required to bring a computer to the class capable of running SketchUp. I applaud Yestermorrow for taking this step, and hope that they apply it to the core class for the Sustainable Design and Building certificate program. There are still some rough edges in the approach Yestermorrow is taking to using SketchUp (more on that in my next post) but it is definitely the right way to go in a world with increasingly powerful digital tools.
If you are considering building a home you could do yourself a big favor by attending a future meeting of this course.
How to smooth a surface composed of irregular triangular faces like this?
It's a problem that I hope to solve using hard paper mache. If I can find a mache that hardens to the right consistency then I should be able to work up a smoothly curving surface by covering the triangles with a varying thickness parge of mache. This surface would need to be covered in turn with a waterproof layer of some kind; shingles or a monolithic membrane are both possibilities.
I've been using cellulose insulation for the paper ingredient of the mache experiments. I started with cellulose that uses ammonium sulfate as a fire retardent, and it produces a very strong and hard mache. There are some potential issues with ammonium sulfate however, so I'm also experimenting with cellulose that uses borate as a retardent. My first experiments with the borate cellulose were disappointing. The mache did not dry to the same hard consistency I've been obtaining with the ammonium sulfate cellulose. I'm continuing to experiment but suspect there may be something about the borate which interferes with the mix hardening and cohering. I recently mixed up identical batches of mache with the excepttion that each has only one of the cellulose varieties. The mixtures take about a week to dry fully so I should have a better sense by the end of April whether the borate cellulose will work.
I use 32 oz. plastic yogurt containers as my measuring unit. In the following ingredient list "cup" refers to one of these containers. The mix below seems to consistently produce a strong hard mache when using the ammonium sulfate cellulose.
1 cup industrial hemp fiber cut to 1" to 2" lengths (loose) * 1 cup cellulose (packed) 1 cup water 1/2 cup joint compound 1/2 cup saw dust 1" (in the cup) of wood glue
*I've also used cut up Phragmites tufts. which seem to work just fine.
Here's a picture of my laboratory. Very high tech.
To give you a sense of the strength of the mache I took this picture of a piece of mache bridging between 2x4s and supporting my full 200+ lbs.
In the next picture you can see the thickness of the mache piece in the image above.
A hard stable strong mache has many possible uses in building construction. I think of it as being almost like moldable wood. Definitely an interesting material with potential. If you are doing any experiments with hard mache, or would like more information about my experiments, please get in touch!