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LoreNo. 75Online ArticlesPlasterPrefabricated PanelsWinter 2024

Building with and Plastering the Future of Straw Construction

By J HendersonMarch 4, 2024April 17th, 2024No Comments
A Zen Buddhist temple under construction in Albany NY using straw panels

A Builder’s Perspective

 

Over the years of my career in natural building and contract plastering, I have seen, plastered, and framed up many different types of homes, wall systems, and straw bale assemblies in Australia and the northwest U.S. When building a straw bale house in Australia or the U.S., a wooden frame of some sort is normally erected, then a roof is installed before the bales arrive. Some contractors do load bearing (Nebraska-Style) straw bale construction, but on most legally permitted builds, the straw goes in after the roof is on. This method has the advantage of protecting the straw and other building elements from rain damage. It also creates an interesting and often complex dance between engineering, wood framing, straw stacking, and architectural design.

 

Many people over the last 30 years have developed extremely complex systems to navigate this dance that are difficult to execute in the field. Others have created fairly straightforward systems. Often, chainsaws are used to cut notches into the straw bales so that they can fit around the wood framing. The noise, dust, and danger of chainsaw use disrupts the idyllic barn style bale raising party that many people dream about when deciding to build with straw. It is possible to minimize or even eliminate the use of chainsaws in baling a house, but this is not often the case. Even without the use of chainsaws, a lot of waste straw accumulates everywhere during a bale raising. This straw needs to be constantly cleaned up to mitigate fire and rodent risk. This is one of those super dusty, not-so-fun jobs that only appeal to a select few people.

 

As much as I have enjoyed the challenge of stacking straw bales into varied wooden framing systems over the years, I now have my sights set on prefabricated straw wall panels. The speed and ease with which prefabricated panels can be erected and joined together on site is astonishing. The walls end up straight and the jobsite remains relatively clean. Taking the difficult dance of straw and wood framing off site and into a factory makes so much sense. Now we can build straw wall assemblies under cover at any time of year, and the risk of moisture damage is massively reduced. As a contractor I find the whole concept of prefabricated panels to be very appealing. The possibility to accurately predict when the straw will be delivered on site and how long that straw needs to be exposed before plastering is a game changer.

 

This spring I was fortunate enough to be asked to run a plaster training on a straw panel project in Albany, NY. I jumped at the opportunity to see and plaster straw panels from EcoCocon, a leading European prefab manufacturer, first hand. Peter Jensen, CEO of Build With Nature and Ecococon’s U.S. representative, was contracting a new temple for a Zen Buddhist organization. The community wanted to plaster the temple and I was asked by Peter to come and train them. Unfortunately I did not arrive in Albany until just after the walls were erected. Still, the sight of EcoCocon panels up close is as impressive as they look in photos. The straw is almost perfectly flat. I can’t imagine how they get it into the panels. There are different sized and shaped panels for different areas in the building and they all fit together easily with an impact driver and large structural screws. A crane or Telehandler is used to place the panels into position. Only a small amount of temporary bracing is needed during assembly. Once the walls are done, the crane or Telehandler can put the roof framing or trusses on top before leaving the site. Doubling up functions of big machinery in construction has huge cost benefits. Once the roof is watertight the plastering starts. As Ecococon’s panels are not plastered on either side when they arrive, it is very beneficial that the speed of erection minimizes the amount of time that raw straw is exposed on a job site. The plaster systems used on the panels differ for internal and external applications. Externally, EcoCocon specifies a wood-fiberboard sheathing before an exterior plaster system or siding is installed. This complicates things if the building is to be plastered, as sticking a lime based plaster to a wood-fiberboard in an area with serious freeze thaw cycles ain’t easy. The two choices for external plaster on wood fiber are a mechanical key, like FibaLath or PermaLath, or an adhesive key coat. Both of these stucco lathing systems add time, material, and environmental costs to what should be a fairly straight forward job. EcoCocon has a European exterior plaster system they recommend. The system relies on three different products from a company called Baumit. As Baumit is a large company with trade secrets, I can only guess at what is in their products. They claim that the system is vapor open. The first product is a priming paint that has sand or grit in it. The second product is an adhesive base coat that has some lightweight aggregate in it. This product is troweled or sprayed on and a fiberglass mesh embedded into it. The final top coat is a sodium silicate based lime plaster that also has lightweight aggregate. I would hope and assume that the aggregate is natural. The Albany project is using the Baumit system. I have used a version of this system that used thinset tile adhesive onto the wood fiber board, then a hydraulic lime plaster. This was on an experimental Econest cabin at Robert Laporte’s home in Ashland, Oregon. Four years later the plaster is still in great shape, how it holds up over the next 50 years remains to be seen.
 

“Taking the difficult dance of straw and wood framing off site and into a factory makes so much sense.”

A joint between three straw panels
The alternative to adhesive plaster is a mechanical key using a stucco type lath.

 

The small amount of wood framing at the edges of the Ecococon panels would not create enough places to firmly attach the lath. This would require stitching the lath through the wall, as in structural shear wall plaster systems. Needless to say, both these systems are complex, expensive and should be specified by an expert. Unfortunately the addition of wood fiber board seems to make an elegantly simple wall system complex and expensive. On the inside the raw straw makes a beautiful key – just like what straw bale builders are used to. The flatness of the panels requires far less plaster than hand stacked straw bales. First a lime wash or clay slip is sprayed on with a sheetrock texture gun or plaster pump. Then two to three coats of plaster can be done quickly and easily.

 

The big wins for straw panel construction are, 1: speed of on- site assembly 2: less plaster, thus faster application. These two advantages would really help to speed up the construction timeline on our straw bale jobs. A 1500SF straw bale house takes Northwest Natural Homes LLC about four to five weeks to frame up the floor, walls, and roof. Installing the straw bales takes one to two weeks, depending on the complexity of the design. Using prefabricated straw panels this could be halved. Plastering the same 1500SF house inside and out takes us about four weeks at the moment. This could be reduced by at least a week. By using prefabricated straw panels we could potentially reduce the time to frame, bale and plaster a 1500SF house from 10 weeks to six weeks. The savings in labor costs would be great.

 

The cons are, 1: Engineering in higher seismic zones is problematic. The few engineers that I have spoken to about this issue have told me that for west coast installations of prefabricated straw panels, the panels will most likely be seen as non-structural infill. The sheer element will have to be dealt with separately with a post and beam frame, Simpson Strong Walls, or another solution. 2: Exterior wood- fiberboard systems are complex and expensive.

 

Neither of the two cons are deal breakers, just things to work around. If the cost savings gained through a faster construction schedule can offset the engineering and exterior plastering costs, I would say we will see a big future in prefabricated straw panel construction. As a contractor who builds with straw, I hope to see prefabricated straw panel systems become widely used. They could pave the way for conventional builders to start using them, as the strange and difficult straw stuff is done in the factory. I have met many conventional builders over the years who would love to branch out into ecological building, but do not have the desire to learn a whole new craft. Prefabricated straw panels are a plug and play building system that any seasoned contractor could easily learn to use. Personally, I can not wait to start building with them.
 
James Henderson has worked with straw bales and other natural materials for the last 20 years. He is co-owner of NW Natural Homes LLC, a design / build company, and the co-owner of Goldhill Clay Plaster LLC, producers of clay plaster. He lives in Joyce, WA in a straw bale house that he built on a permaculture property.

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