From outside, the house appears to be a Craftsman. Clapboard siding. Decorative kneebraces under the eaves. A big porch.
But inside, the walls of this newly constructed Southeast Portland home once swayed in a Beaverton wheat field. They're made of straw – specifically, the big rectangular bales of straw found on any farm.
When done, the bales will be plastered over and unseen from even the inside.
But they'll be known to the happy occupant who, owing to straw's insulating capacities, will burn less fuel for heating or cooling. And hear less noise because of sound-deadening walls more than a foot thick. And breathe air free of the chemicals that can emanate from new and synthetic building materials.
Straw bale homes are not a new technology. They were constructed in tree-scarce Nebraska more than 100 years ago. Now they're not uncommon in the arid American Southwest.
But this is Multnomah County's first permitted straw bale home. And extra precaution will be taken to ensure water stays out – that the home perform as well in drenched Portland as it does in sunny climes, where straw bale structures withstand earthquake, fire, insect infestation.
Just 800 square feet of living space – the size of a comfortable one-bedroom apartment – it is designed for the eco-conscious dweller and the work of Lydia Doleman, a building contractor who has erected straw-bale structures in Clark County and southern Oregon, as well as a straw bale addition in Portland.
Straw bales: low tech, high potential benefit
Energy efficiency
A straw bale wall is thick, gobbling up valuable space; and heavy, requiring a sturdy foundation. But some experts estimate a bale wall to be up to three times as energy efficient as conventional framing. Over time, the savings add up.
Fire risk
Loose straw is really bad – a form of tinder. Tightly compacted straw, however, behaves like a phone book – not enough air to easily burn. Stacked bales are further compressed before plastering.
Sound insulation
The straw bale wall is its own fortress – typically more than a foot thick – and a sound-killer. In some settings, it's deal for separation between common wall homes, such as townhomes or rowhouses.
Design challenges
Bales take up more floor space than regular stud walls. But they invite easy invention, in the form of window seats and flush-mount cabinetry within the walls themselves. Careful installation and climate figure in: Any water infiltration can destroy the capacity of the wall to take structural loads.
Fighting the rot
Oxygen and water are required for decomposition. Keeping moisture out through careful construction assures long life. Straw has been used as an insulating material for centuries – it's even been found in good condition in Egyptian tombs thousands of years old.
Source: The builder Andrew Morrison's Web site.
Now Doleman wants to bring the straw bale single family residence to the city. And she has done so adjacent to her own home, on the same double lot, just steps away.
"I want people to see this as a viable option and that they're not compromising aesthetics," she said.
The inside smelled like a cozy barn last week as Doleman and her friends stacked bales against the stud wood frame. The walls are not load-bearing, a precaution against accidental failure from moisture. But Doleman designed things to stay dry: 2 feet of eaves extend over the side of the house, sheathed in water-shedding Tyvek beneath the clapboard exterior.
Straw, a plentiful and inexpensive agricultural waste product, is not to be confused with hay, a food source for animals. Tubular in shape, it is tightly bound into a 30-to 40-pound bale measuring 18-by-16-by-44 inches. In this state it is a bad conductor of heat or cold and contains so little airspace that it resists fire.
Each bale is a large "brick" to build with, and Doleman will stack roughly 160 of them in this house. The she will run straps around them and use a machine to compress them against each other and the framed wall. The result is a continuous insulated wall whose studs, if they were in a conventional drywall, would insulate less by conducting heat and cold. The final walls will be more than a foot-and-a-half thick.
The straw is trimmed flat with a chainsaw-like cutter and then finished with cob plaster, which sticks to rough surfaces. Atop that will be a fine layer of lime plaster.
The City of Portland energy code requires walls to have a minimum insulation rating of R21. Doleman estimates her walls will be R30 or better – a significant measure beyond.
That sounds about right to David Cohan, market research & evaluation project manager for the
. He said straw bales have a long and wonderful history but that design and execution - as with anything - is key.
"If they don't get installed properly and sealed properly they will perform like garbage," he said. Insufficient compression will cause heat loss. And the intrusion of moisture will cause rot and mold.
But Doleman, who says her construction costs at $150 per square foot compare that of a stick-built new house, is confident her straw bale house will hold up. She teaches a course on alternative building design at Portland Community College. At the Rock Creek campus she built a one-room straw bale structure that will be used for the school's weather station.
She first learned how to build straw bale homes in Colorado at age 20. She moved to Portland seven years ago specifically do to natural building in an urban setting.
Energy efficiency drove her design of this house.
It faces south with plenty of windows for passive solar heat. The ceiling will be insulated with formaldehyde-free fiber glass. Water heated by rooftop solar panels will circulate through pipes in the floor to heat the house – avoiding the dust problems associated with forced hot air. And other photovoltaic cells will supplement the house electrical system.
Doleman thinks in the distant future.
"If you're looking at energy efficiency, you should think about it in 500-year chunks," she said. "How long could it last? It's our cultural responsibility."
Doleman, whose business goes by the name
, said she will sell this house to a friend who is helping to build it – Matt Phillips. When he becomes her next-door neighbor, however, he will join others on Doleman's property, which features two occupied Craftsman homes as well as this new one – along with a shared garden and chickens.
"It's more about quality of life than quantity of space," said Phillips of the 800-square-foot structure.
Photo gallery
To view photos of the straw-bale house, go
.
Straw bale construction strikes a warm spot with city officials.
Valerie Garrett, the green building specialist with the city of
, said she likes that straw bales area a renewable resource. She said it's exactly the kind of house she wants to put in the annual Build it Green! Homes Tour, which happened last week – an outcome that would surely delight Doleman.
Garrett said she loves that it's conventional on the outside and radical on the inside.
"If something . . . feels really really different, it's harder for someone to embrace it," she said. "It's very smart for her to do that."