Strawbale vs Cob - GreenHome Institute · 2016-01-01 · Strawbale vs Cob: Choosing the best...
Transcript of Strawbale vs Cob - GreenHome Institute · 2016-01-01 · Strawbale vs Cob: Choosing the best...
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Strawbale vs Cob:Choosing the best natural building materials
to build durably in cold and wet climates
Down to Earth Designnatural building designhands-on workshops www.buildnaturally.com
Presented by: Sigi Koko
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Down to Earth design
“Meet the present needs without compromising the ability of future generations to meet their own needs”
--UN definitionof “sustainable”
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Down to Earth design
WHAT are natural building materials?
• locally available
• rapidly renewable
• non-toxic
• use technologyappropriately
• provide multiplebenefits
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Down to Earth design
Inexpensive Materials
Labor Intensive
Simple Construction Techniques
Recipe for Community
“Barn-Raising”
+
+=
Down to Earth design
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Down to Earth design
Understand Material
Properties:
insulation vs. thermal mass
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Down to Earth design
INSULATION…
…slows down how fast heat flows
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Down to Earth design
USE INSULATION
WHEN…
…you have long periods of time
where your desired temperature inside differs significantly
from the temperature outside
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Down to Earth design
INSULATING MATERIALS INCLUDE:
strawhemp
clay-slip strawpumicecottonwoolair
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Down to Earth design
INSULATION VALUES TO SHOOT FOR:Below a slab = R-10
If slab is heated = R-15Crawl space floor = R-24
Walls = R-30Roof envelope = R-48
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Down to Earth design
Don’t forget the detailing!
Seal air spaces to avoid leakage.
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Down to Earth design
THERMAL MASS IS…
…a battery that stores heat energy
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Down to Earth design
THERMAL MASS can be
used to store heat
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Down to Earth design
THERMAL MASS can be used to store
coolness
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Down to Earth design
USE THERMAL MASS WHEN…
…you want to moderate rapid
temperature swingsOR
to absorb & store heat or cool energy
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Down to Earth design
cobadobe
clay plaster lime plaster
rammed earthearthen floors
stonewatersoil
THERMAL MASS MATERIALS INCLUDE:
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Down to Earth design
BEST BET IN OUR MIXED
CLIMATE:
Use insulation & thermal mass TOGETHER
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Down to Earth design
Effective use of thermal mass & insulation are
essential to effective passive
solar design
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Down to Earth design
A quick note about thermal
bridging…
...the performance of
clay + straw mixed together depends on the amount of clay
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Down to Earth design
Understand Water:
moisture vs. vapor
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Down to Earth design
IF YOU CAN BUILD WITH WOOD YOU CAN BUILD
WITH STRAW
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Down to Earth design
MOISTURE IS…
…liquid water
VAPOR IS…
…water that is suspended in the air
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Down to Earth design
FIRST MANTRA:
KEEP LIQUID
WATER OUT
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Down to Earth design
RULE #1:
Protect the base of the wall
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Down to Earth design
RULE #2:
Make sure all water sheds
well at door & window
openings
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Down to Earth design
RULE #3:
Provide deep roof overhangs
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Down to Earth design
SECOND MANTRA:
DON’T TRAP VAPOR
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Down to Earth design
RULE #4:
Avoid condensation points inside
walls
NO METAL
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Down to Earth design
RULE #5:
Use breathable finishes (paints, plasters, sealers)
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Down to Earth design
1. absorb heat (from heat source in Winter; from air in Summer)
2. moderate humidity
3. create a breathable finish
USE CLAY TO:
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Down to Earth design
1. insulate
2. insulate!
3. insulate!!!
USE STRAW TO:
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Down to Earth design
“Be the change you wish to see in the world…”
--M. Gandhi