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Moisture Content in Straw Bale Walls A Study of
the Effect of Precipitation, Relative Humidity
and Temperature Erin Cathers, Institute for
Environmental Studies, Shepherd College Thanks to
Al Thomas, Bradley Sanders and Patrick Drohan,
Methods
Why This Study Is Important
Ø  The site is an installed straw bale addition
adjoining a barn in Shepherdstown, West
Virginia. The straw bale walls have not yet been
stuccoed. Ø   14 points along the exterior and
interior of the two walls were chosen as
locations for moisture sensors (see diagram
below). These sensors were checked with a Timber
Check moisture meter five times a
week. Ø   Relative humidity and temperature data
were taken every two hours inside and outside
the structure. Ø   Wind speed, wind direction and
precipitation data were recorded five times a
week.
Ø   Straw bale walls are a sustainable
alternative to conventional building and
insulating materials because they are non-toxic,
recyclable and energy efficient. Ø    Plastered
straw bale walls outperform wood-frame walls in
fire tests and have a higher r-value (thermal
resistance). Ø   Straw is generally considered a
waste product on farms and is burned, which
causes large C02 emissions every year. Using the
straw not only helps reduce C02 emissions, but
also reduces the need to use less sustainable
resources such as timber.       Ø   Straw begins
to rot at 20 percent moisture content. Can straw
bale insulation be efficiently used in the humid
climate of West Virginia?
Results
Conclusions
Ø     Highest recorded MC level was 12 Ø    
Position D Low Out had the highest average
MC Ø     Position C Low In had the lowest average
MC Ø     Lower wall had higher average MC values
than the lower wall, the only
exception being on the coldest
days Ø     The northern wall had higher average
MC values than the western wall Ø     The general
trend was that the outer wall had higher average
MC values than inner wall Ø     Spearman tests
showed that the greatest factor in determining MC
appeared to be the outer temperature, with a
positive correlation of 0.383 Ø     Wind speed
had the next strongest correlation at
0.365 Ø     The third strongest correlation was
inside RH with a positive correlation of
0.347Ø       Ø     Surprisingly, precipitation
did not appear to be a very large factor in
determining the MC of the straw, although they
did follow the same general trend