Tiny Tuesday: What is Straw-Cell Construction?

The strawbale is a terrific source of insulation. Its R-value is comparable to dense-packed cellulose – after all, straw is basically cellulose. It’s easy to build with, coming in a Lego-like package that’s easy to handle and stack. Surprisingly, it’s more fire-resistant than fiberglass batts – the material is packed so densely that no oxygen can flow. And best of all, it’s a naturally occurring byproduct with a low embodied energy and no toxins to mess with air quality.

One can build strawbale walls strong enough to support a roof, and to date the majority of strawbale construction has taken this form, as seen previously on Tiny Tuesday. There’s an appealing economy of material when the insulation is also the structural system, but it requires specially trained builders to build strawbale walls with the proper reinforcing, and few building codes recognize it. A different system holds more promise to bring strawbales into the mainstream.

Straw cell hybrid construction combines the insulation properties of the straw with the familiarity and constructability of stick frame. Dimensional lumber, either 2×4 or 2×6, is used to frame exterior walls and support roofs. Then, directly inside of the studs, stacked strawbales (typically 18 inches wide) form a nonstructural insulation layer. Finally, the lumber cavity is filled with dense-packed cellulose. The total thickness of insulation is 22 to 24 inches, for an R-value of 45 to 50.

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Cellulose packing on the exterior of a straw-cell building.

Strawbales provide a flexible interior surface: builders can carve out niches and round off corners, finishing the walls with plaster. Meanwhile, the exterior wall is dimensional lumber spaced 16 or 24 inches on center, enabling the use of plywood or OSB sheathing and wood or vinyl siding. The assembly requires about half the lumber needed for double-wall construction.

Determining the return on investment for straw-cell construction – or for any non-traditional building method – is difficult. One must evaluate the cost of materials and labor, the land value (24-inch-thick walls steal a lot of potential floor space), and personal values such as embodied energy and occupant health. Consider this a work in progress!

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Tiny Tuesday: Introducing the Minim

I met Brian Levy almost three years ago at the Yestermorrow Tiny House Fair, where he debuted his masterpiece of a tiny house on wheels. At that time, Brian had just finished building a prototype at Boneyard Studios, an outdoor showcase in Washington, DC that hosts numerous tiny houses as a demonstration of urban infill. Brian calls his house the Minim.

I’ve never seen so many brilliant design decisions packed into a single home. The Minim is wider than most houses on wheels, measuring 11 feet out-to-out. You need a state highway permit to tow anything wider than 8 feet 6 inches, but Brian reasons the permits are not that expensive and the house won’t get moved much, so it’s worth it for the extra space. The exterior is built using structural insulated panels (SIPs), which erect quickly and provide better insulation than most stud walls of the same thickness.

It’s hard to pick a favorite aspect of this house. I love the lack of interior walls, the multitude of windows, the full-width kitchen, the storage sofa/banquette, and especially the raised office that conceals a roll-out bed. On the other hand, I’m not wild about the exterior aesthetic, and with no roof overhangs I’m concerned about leak potential. Recently Brian has been working on a production line to build Minims for retail; the first one should be complete next month. Read all about the house and how to buy one here.

Tiny Tuesday: Homes for the Homeless

Hailey Fort (aptly named!) is a student in Washington state with a heart for the homeless. Over the past three years, Hailey has donated hundreds of pounds of produce from a homegrown garden to local charities, as well as hundreds of articles of clothing from friends and neighbors. Taking the efforts in a new direction, the philanthropist recently designed and built a 32-square-foot shelter on wheels for one homeless man, and plans to make a dozen more in the next year.

One more thing: she’s 9 years old.

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Hailey cuts insulation made from recycled blue jeans for a house she’s building. (picture from Hailey’s Harvest Facebook page)

You can read about Hailey’s construction skills, her parents’ involvement (less than you would think), and her fundraising efforts in this Popular Science article. You can also like her nonprofit, Hailey’s Harvest, on Facebook. I love this story most of all because it defies our expectations. What sort of person builds a house independently for the purpose of giving it away? I’ll bet you didn’t picture a little girl – it doesn’t fit our preconceptions. Hailey shows us how useless those preconceptions are. Not only is she outstandingly generous, she’s also a pretty awesome carpenter.

We tend to write scripts about people based on their age, sex, race, place of origin, etc. The news is full of sad stories in which someone innocent dies because someone else basically followed the scripts. It’s refreshing to challenge the same assumptions with something so cool and so happy.

Thanks to Robin Jaeger.