TAMARACK STRAWBALE PROJECT
is now a resource library fall 2002
2323 SE TAMARACK, PORTLAND, OREGON 97214
architect: Candace Gossen of solar7.83 and project partner: John Thomas
built by: workshop students of Portland Community College
Jay Almarode . Irv Bloom . Lyle Gayman . Tony Hauser . Debra Jarcho . Charles Lauck . Ben Martinsen . Cylene Nathan . Per Slotfeldt . Leonard Zack . Margo Gardiner
with special assistance from: Barry Boring,Banks Construction; and Jean-Paul Peyralans, Professional Applications
Much Gratitude for expert advice and terrific customer service Alan Moore, Carlson Systems (strapping co.)
This research project is a 10' x 12' load-bearing structure, now a resource library. Originally began in September of 1997, rained out, and completed May of 1998. This project incorporates the ideas of recycled building materials as well as various techniques for sustainability in the Northwest Region of North America.
Data recording and testing PHOTOS
12 moisture sensors were placed in the walls on June 12 for continual observation and metering of the water transpiration in the straw walls as well as the stucco and plaster materials. For more information about the moistures sensors and how to make them for yourself see the summer 1998 issue of The Last Straw.
Moisture testing after 5 years of data show that the straw has remained dry and below 20% critical moisture levels where molds and mildews and where straw begins to decompose. The range of moisture testing: < 6% up to 11% depending on the location of the sensor, the depth in the wall, and season.
The main objective of the project is to further the study of using straw, a waste by-product of agriculture, as a building material and its viability in a wet, temperate environment. This structure will also benefit the local building community in its search for understanding building codes and the alternative building permit, as well as further researching embodied energy and its environmental implications relative to the building construction industry.
Building Components: PHOTOS
Foundation - A rubble trench design using an 18" deep by 2' wide stem wall around the perimeter of the foundation was built using 12" of recycled concrete from a dump site and filling the rest of the trench to grade with 1-1/2" river rock. 18 recycled tires, two levels high, for a total of 36 were laid on top of the river rock to provide a 14" minimum plinth wall for waterproofing and better seismic control. A 3' vertical 1/2" rebar was placed in the center of each tire for direct connection with the foundation and lateral stability as well as for the first level of bales. At the bottom of each tire a 2" concrete cap was poured. The tires were rammed using a traditional southwest rammed earth mix:
20% aggregate of 5/8" minus, 32% silt, 15% clay, 30% sand (coarse & fine), and 3% cement to stabilize the mix, <10% moisture was added
All tires were rammed using manual labor and homemade tools of sledge hammers that worked the best. 8-12 pounds of weight worked great. Mud and straw stucco was used for infill between the tires .
Trex-a recycled wood/plastic product was used to level and cap off the tops of the tires for a thermal and moisture break. A water-based rubber sealant was place on top of the concrete caps and on all of the rebar to deter condensation on the metal when placed in the straw. 30# felt paper was laid on top of the trex as an underlayment and moisture break before the bales were placed.
- When this project started Portland had an early rain and we had not stockpiled the bales thinking that September would be a dry month. Most to all of the straw crops waiting to be baled were wet and we did not want to take a chance on wet straw. We bought 60 straw bales via a local feed store, Foster Feed and they purchased from a farmer in Idaho and it was trucked in. The disadvantage was the amount of fossil fuel and transportation costs for embodied energy! The consolation was that the straw was beautiful. It had less than 10% moisture and was bright yellow and smelled great! Each bale weighed approximately 90 pounds. The bales were all 3 string polypropylene bound. The bales survived storage in our garage for 9 months until the rains stopped and we could build in May. The moisture content actually reduced to about 5%. Proper storage is always key. Never put the bales on the ground, rest them off the ground so that air can circulate beneath, especially if there is concrete below. Tarp off all leaks around doors, windows, etc.
The original design called for 60 bales, 7 levels high. Upon further assessment we only used 42.
- The workshop was held as a class at Portland Community College with 4 weeks of lecture discussing strawbale history, building construction techniques, and codes and regulations in various forms of media.
The building weekend began mid-day Saturday May 30 (due to rain), but it turned out to be a sunny day and we started with the building of the trusses, box beam and door and window bucks. Soon thereafter we placed the first bale. The first level were placed on the vertical rebar, and upon placing the 4th level of bales we began pinning with bamboo pins 4-5' long that had been retrieved from a burn pile at a bamboo farm. On the 5th level we did another pinning for the final stages before placing the box beam on top.
- We decided to minimize the amount of metals and steel used in this structure and purchased polypropylene strapping from Carlson Systems, Clackamas, Oregon. The 5/8" strapping is rated at 1200 lbs. tensile strength. When completing the foundation we placed the stapping beneath the tires for a direct connection to the foundation. Strapping was used every two feet for every tire and ran over the top of the box beam and was crimped on the inside of the structure. Horizontal strapping was also used on every other level of the bales on all 4 corners as well as at the tops of the structure in all 4 directions. (We learned that the building guides are really important. We set two up and opted not to use them on the opposing corners. We definitely had a 2-4" bow out because we did not have the guides properly secured.)
Box Bond Beam
- A box beam constructed of 2x6's and scrap pieces between for support was placed on top of the 5 level of bales. The box beam was built before the bale walls were raised and was put up in 4 sections. 5/8" CDX plywood finished off the bottom and tops of the box that was filled with straw flakes. The box beam was strapped and compressed after being squared with the walls and foundation. The trusses were next.
- 7 trusses were made and placed 2' on center. 2 x 6's were used for a 2'-6" rise over a 5' span in which the roof will be used for water catchment. Building to code we placed 5/8" CDX on the roof for sheathing with a minimum of 2'-4" overhang on the south side, 2' overhang on the East and West and because of property lines an 18" overhang on the north.
When the stuccoeing is complete, we will apply the permanent roof system, a recycled aluminum shingle by "Rustic Shingle". It is a 100% recyclable product using 100% post-consumer aluminum. The color will be sierra brown.
Prepping and Stuccoes
- Because this structure is experimental and for research we will be using 3 different recipes for earth and cement stuccoes using natural and local additives. We will also be using coconut fibre used in soil erosion control for a replacement of wire lath on two of the walls. 30# felt paper will be used around the windows on the east and west as well as the door buck on the south. A 12" strip of asphalt paper was placed around the bottom for splash waterproofing at the base of the bales, as well as covering the box beam at the top.
17 & 18th of July 1998 - The scratch coat used a variety of additives. The batch was made of 20 shovel fulls of clean, screened soil and clay soil. 1 bag of portland cement (94lb bag), 1/2 bag of clean med. to fine sand (80lb bag), 8 oz. (1% by volume) linseed oil for hardener, 24 oz (skim milk, for casein) up to 5% per volume for resistance to humidity, and 4 handfulls of chopped straw to 1/2" long. Mixed with water this made a very durable mix.
8th August 1998- The second and "brown coat" was applied to the earthen plaster. Straightening the walls or leaving them curved was a big question and debate. The problems occurred when too much stucco was applied, "too thick" and it cracked several hours later. The corners that had been squared cracked right off. The day after, the cracked portions were removed and refilled with thinner applications.
We applied a mix of: 1 bag of type s lime (50 lbs), 1/2 bag of cement, up to 1-1/2 bags of med. clean sand, 1 gal of skim milk, 8 oz. of linseed oil, 8 oz. of borax powder, and 3-5 gals of water.
The weather was hot, but we had to take advantage of the sunshine here in Portland, and stucco in the sun. Perhaps the heat, the amount of water, the amount of cement were all factors in the cracking.
almost ready, waiting for final stucco
The final coat was completed in October 1999. A thin cement stucco dyed a ochre color in the mix.
- The interior floor is comprised of a sand bag foundation on top of 3" of river rock. The sand bags were originally nylon rock bags. After placing the sand blocks in the floor another layer of 3-4" of loose sand was laid on top of the sand bags. Then the final layer of recycled demo bricks taken from a demolition site in downtown portland was dry laid to create a 4" thermal mass floor. No mortars used.
Further details as they progress.
APPEAL - OCTOBER 13 - TUESDAY @ 9AM
CONFERENCE ROOM C, 2ND FLOOR, PORTLAND BUILDING, 1120 SW FIFTH AVE, PORTLAND OREGON
The Appeal was granted in our favor, the Strawbale structure will be completed by summer 1999, and after the survey we gained a new property line in our favor.
Thanks for all the support, letters and for those special people that appeared at the appeal.