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Compressed Earth Block & Strawbale Home: Monitoring and Assessment of a Hybrid Wall Assembly

Greg Leskien1,a, Jordan Hoogendam1,b and Henry Wiersma2,c

1Zon Engineering Inc., Kitchener, Ontario, Canada

2970233 Ontario o/a Earth Block Construction, Cobourg, Ontario, Canada

[email protected], [email protected], [email protected]

with contributions from Colin MacDougall, Queen’s University and John Straube, University

of Waterloo

This project was partially funded by Canada Mortgage and Housing Corporation (CMHC)

under the terms of the External Research Program, but the views expressed are the

personal views of the authors and do not represent the official views of the CMHC.

Keywords: Compressed, Earth, Block, Straw Bale

Abstract The primary objective of this study is to measure, analyze and comment on the moisture and

thermal characteristics (and ultimately the durability) of the wall assembly in question: a

compressed earth block (CEB) and straw-bale hybrid assembly. In support of this, the following

tasks will be discussed:

• Long term monitoring of moisture and heat conditions and flows within the wall enclosure

assembly

• Air infiltration testing of the demonstration home

• Measurement of the energy performance and identification of heat loss/gain characteristics of

the test home

In the end, the intent is that the observations and conclusions made in this report will be used in

conjunction with the findings presented in the structural study titled “Compression Testing of

Weathered Compression Earth Block (CEB) Prisms” as published by Queens University to help

answer the following question:

"Can compressed earth blocks (CEB) and straw bales be used in conjunction with one another to

produce a wall enclosure assembly that is environmentally friendly, energy efficient, and durable?"

Introduction

Project Description. The demonstration home is two storey structure constructed by and on the

client's property north of Cobourg, Ontario. The building has a usable floor area (measured to the

inside of the walls) of roughly 84.5 m2 (910 ft2) and an interior volume of approximately 217 m3

(7,660 ft3).

Fig. 1: Southwest Facade of the Demonstration Building

Of particular interest are the above-grade wall assemblies, which are a hybrid construction of

compressed earth blocks (CEBs) and straw-bales. The 4" high by 10" wide by 14" long CEBs were

manufactured onsite using ground-source clay excavated on the property. They play a dual role in the

wall assembly, creating the support structure for the second floor and roof framing above, as well as,

serving as the interior finish for both the ground and second floor levels. The interior face of the CEBs

have been left unfinished and exposed, while the exterior face was parged with a surface coat of clay

slurry (1/8" to 1/4" thick) to protect the blocks from the weather during construction. Straw-bales, 18"

in thickness, have been placed on the exterior side of the CEBs and serve as the insulation layer in

the wall assembly. The exterior face of the straw-bales were first dipped in a 2" deep clay slip mixture

(a "soupy" mix of clay and water) which served as the first coat of plaster, and eliminated the need

for wire or plastic mesh. After the bales were in place, they were finished with earthen plaster (3/4"

to 1" thick). A section of the wall assembly is provided in Fig. 2.

Fig. 2: Typical Above-Grade Wall Section

Windows are comprised of vinyl frames (with wood cladding inside) with 7/8" thick insulated

glazing units complete with 2 panes of 3mm clear glass, with a Cardinal CG LowE-272 low-

emissivity coating on surface #2 and an XL Edge spacers separating the glass. Doors are handcrafted

out of solid wood and are 2 1/4" thick.

The structure of the roof assembly is provided by 3x6 reclaimed hemlock joists spaced at 24"

on centre. 2x8 lumber at 4'-0" centres and 2x4 lumber at 2'-0" centres were placed on top of the

hemlock as strapping. Three 2" layers of reclaimed black rigid foam (waste from the manufacturing

process of foam board) was installed between the 2x8 roof joists. Samples sent for testing in a guarded

hot plate revealed an average R-value of 3.1 (h°F ft²)/Btu. A 6 mil polyethylene sheet was placed on

the interior side of the insulation and finished with 3/4" pine boards treated with hemp oil. On the

exterior, a layer of 1/2" spruce plywood was attached to the 2x4 lumber strapping and covered with

shingles.

Fig. 3: Second Floor - Southeast and Southwest Dormers

Foundation walls are constructed with two (2) rows of 8" expanded polystyrene ICF blocks,

16" in height. In addition, 3 1/2" of concrete was cast-in-place directly against the interior surface of

the innermost ICF blocks in order to make the foundations wide enough to bear the walls above. This

concrete was not reinforced or tied to the ICF wall in anyway. Supporting the foundation walls are 8"

deep and 39" wide concrete footings that run around the perimeter of the demonstration home. Four

(4) feet of 2" thick extruded polystyrene insulation was also installed, and extended out from the

foundation, horizontally away from the building.

Fig. 4: Radiant Floor Heating Installed for Ground Floor

The ground floor consists of 4" thick CEBs placed on 1" of sand over 1 1/2" of extruded

polystryene board insulation. Inside the sand are radiant heating tubes attached to a layer of 6x6 wire

mesh.

Fig. 5: Interior - Ground Floor

Heating was provided during the study period by radiant floor heating (ground floor only)

supplied with hot water from a 40 gallon storage type electric water heater mounted inside the building

on the ground floor. No cooling or ventilation were provided to the building.

Long Term Monitoring

Methods. Long term monitoring of the of the demonstration building was carried out for a period of

one year (August 2011 through August 2012). During this time, temperature and relative humidity

readings were collected at fifteen (15) minute intervals at ten (10) locations around the building. Each

location consisted of five (5) temperature sensors (thermocouples) and three (3) relative humidity

sensors located at various points on and within the wall assembly. For the purposes of this report, 4

locations distributed around the building have been selected for analysis and are shown in Fig. 6 and

summarized in Table 1.

Fig. 6: Sensor Locations

Table 1: Wall Sensor Summary

Type1 Mounting Description

A T and RH Near ground, exterior face of CEB

T and RH 42" up, exterior face of CEB

T and RH Bale embed, 42" up, 14" from exterior face of CEB

T only 78" up, exterior face of concrete at this location

T only 78" up, exterior face of CEB

B T and RH Near ground, exterior face of CEB



T only 42" up, embedded in CEB

C T and RH Near ground, exterior face of CEB



T only 42" up, embedded in CEB


D T and RH Near ground, exterior face of CEB



T only Under window, exterior face of CEB


Humidity readings at the wall locations were acquired using Honeywell HIH-4021-003

humidity sensors mounted within a vented rigid plastic tube as depicted in Fig. 7. Also mounted inside

the tube is a type T thermocouple. Type T thermocouples mounted in separate plastic tubes were are

also used for the remaining two (2) temperature only sensor points at each location.

Fig. 7: Integrated Humidity and Temperature Sensor

Temperature readings from the Type T thermocouples were measured by two (2) Campbell

Scientific AM25T solid-state multiplexers. Humidity sensors were measured by one (1) Campbell

Scientific AM16/32B relay multiplexer. All measured temperature and humidity readings were then

acquired and stored by a single Campbell Scientific CR1000 measurement and control system. Fig. 8

shows the multiplexers and measurement and control system mounted to the interior walls in the north

corner of the building.

Fig. 8: Data Acquisition System for Wall Temperature and Humidity Sensors

Interior temperature and relative humidity was also recorded at fifteen (15) minute intervals

over the monitoring period. These readings were collected by an Onset HOBO Pro v2 data logger

located on the ground floor, at the center of the building, and mounted at a height of 2.0 metres. Fig.

9 shows a photo of this data logger. Its location is shown on Fig. 6.

Fig. 9: Interior Temperature and Humidity Data Logger

Similarly, exterior temperature and relative humidity was collected at fifteen (15) minute

intervals over the monitoring period by an Onset HOBO Pro v2 data logger mounted to the fascia

board on the northeast facade of the building. The external temperature/humidity sensor of this data

logger sensor was mounted in a solar radiation shield to acquire ambient temperature readings. Fig.

10 shows a photo of this data logger. Its location is shown on Fig. 6.

Fig. 10: Exterior Temperature and Humidity Data Logger

During the one-year monitoring period there were instances where readings from the interior

and exterior monitoring stations were unavailable. For these occurrences, interior temperature

readings were replaced with those recorded using the onboard thermocouples present in the

acquisition equipment used for wall readings. In instances where data collection was interrupted,

exterior readings were obtained from the "Cobourg (Aut)" weather station via the Environment

Canada website. Since weather station readings are only available at one (1) hour intervals, the same

readings were used at the fifteen (15) minute intervals to augment missing data.

Results and Observations. Fig. 11 through 14 present the relative humidity readings collected at

Locations A, B, C and D over the course of one year. Each location includes readings taken at the

following positions:

• Exterior face of CEB - approximately 6" above the top of the foundation wall

• Exterior face of CEB - approximately 42" above the top of the foundation wall

• Exterior face of the straw bales at a height of 42" above the top of the foundation wall -

approximately 14" from the exterior face of the CEB

The values collected at these locations were plotted along with interior relative humidity values,

as well as, interior and exterior temperatures. [Note that interior relative humidity values for the period

of mid November 2011 through April 2012 are unavailable, and have been discontinued during this

time on the graphs below].

Fig. 11: Relative Humidity at Location A from August 2011 through 2012

Fig. 12: Relative Humidity at Location B from August 2011 through 2012

Fig. 13: Relative Humidity at Location C from August 2011 through 2012

Fig. 14: Relative Humidity at Location D from August 2011 through 2012

It is important to consider three pertinent details when reviewing the data presented above.

First, the building remained incomplete for much of the test period. From the period of August 2011

through March 22, 2012, the building was protected by a series of plastic tarps to allow the final coat

of earthen plaster to be applied to the exterior face of the straw bales. Fig. 15 shows the demonstration

home in this state.

Fig. 15: Demonstration Home Protected by Tarps During Finishing

With the tarps in place, the lower half of the building was never fully exposed to the elements.

This had two side effects. Firstly, it protected the wall assembly from rain and snow, minimizing the

moisture that would have potentially been added to the wall had it been exposed to these sources.

Second, it sheltered the building from the drying potential it might have experienced had it been

exposed to wind and an environment with lower relative humidity values. Although not fully air tight,

it is thought that that tarps functioned as a vapour retarder to some degree, slowing evaporation and

vapour transport by diffusion to the exterior environment.

Second, the permanent in-floor heating system was not operated until March 28, 2012.

Without a constant source of heat, the interior temperature of the building drifted with exterior

temperature and solar gain. As a result, the drying potential of the building was drastically reduced,

limiting the ability of materials to dry to the outdoors by vapour diffusion. From time to time an open

flame portable propane heater (i.e. salamander) was used inside the building to keep workers warm

as they finished interior details. Although this would have increased the drying potential during these

times, it is important to note that it would also add moisture to the inside air as propane fuel was

burned.

Third, the types of materials and construction used to build the wall assemblies of this home

inherently result in high amounts of "built-in" moisture. The CEBs, CEB grout, CEB exterior parging,

straw-bales, and exterior earthen plaster finish all contain high moisture contents when installed. It is

important to deal with these high amounts of moisture soon after the building is complete in order to

avoid potential durability issues (e.g. mould and rot). This is done by maximizing the drying potential;

mainly diffusive drying to the outdoors (during heating periods) and evaporation from the exterior

surface of the straw-bales.

When considering Fig. 11 through 14, it is clear that the relative humidity readings at all three

positions in the wall at locations A, B, and C are high; greater than 60% for much of the year, and

more typically around 80%. This is also true of location D, except for the measurements taken within

the straw bale. [Note: The measurements taken within the straw bale at location D fell consistently

between 40 and 50% throughout the year. The reason(s) for the comparatively "low" readings within

the bale are not known at this time. Plans have been made to acquire and insert a portable straw bale

moisture probe next to the sensor to check that the embedded sensor is operating properly.]

The high, and relatively constant, relative humidity readings observed within the walls are

thought to be a combined result of the high built-in moisture and a low drying potential. This is in

some part reinforced when studying the data acquired after the tarps were removed (March 22, 2012)

and the in-floor heating system was operational (March 28, 2012). During the entire month of April

and the early part of May, the building was being actively heated (except during thermal mass

observations). When looking at this time period for all four locations (A, B, C and D), the relative

humidity readings at all three sensors in the walls drop considerably (20% in most cases). This would

make sense as the outward vapour pressure has been increased (increasing drying by vapour diffusion

to the outdoors), as well as, the evaporation from the straw bale surface (which is now exposed directly

to wind and sun). Fig. 16 and 17 present the relative humidity and corresponding temperature values

recorded during this time period at location B.

Also evident in Fig. 11 through 14 are the large increases in relative humidity readings

throughout the walls at all four locations during the month of March 2012. This is thought to be a

direct result of the procedures that were used to install a plaster drip edge to the bottom of the straw

bales around the perimeter of the building. During this time an open flame portable propane heater

was used (between the temporary tarps that enclosed the building and the exterior walls) to heat the

air and surface of the walls to allow for the application of the plaster. The heated air was continuously

circulated around the building by two large fans, ensuring that heat was evenly distributed within the

tarps. The builder also noted that the ground inside the tarps had started to thaw as a result of the

added heat, creating a wet and muddy walking surface. Given these details, it is evident that a

significant amount of moisture was introduced into the space between the tarps and the exterior wall;

moisture from burning fuel, moisture from the thawing ground and moisture for the plaster drip edge.

Since the air surrounding the exterior walls was warmer than the inside of the building, and because

the walls of the building are more vapour permeable than the tarps enclosing it, any moisture present

between the tarps and exterior walls would likely have been driven into the building at this time. This

is supported by the graphs, which show very similar increases humidity at all location during this time

period.

Also worth noting are the occurrences of 100% relative humidity readings measured at

locations C and D for sensors positioned on the exterior face of CEBs, approximately 42" above the

top of the foundation wall. At location C, these high readings are observed as "spikes", and with the

exception of the occurrence in mid-October, appear to coincide with drastic reductions in exterior

temperatures (i.e. 10°C), and the because the building was not permanently heated, drastic reductions

in interior temperatures as well (refer to Fig. 18). Reduction in temperature will increase the relative

humidity, but not to the extent observed. Although the building was enclosed at this time, this location

was on the most exposed side of the building and nearest to the temporary door in the tarped structure.

This location may have been exposed to "free" water at these times, but may have had the ability to

dry out relatively quickly. This location will continue to be monitored to see if these occurrences

continue as the building is heated and occupied.

As can be observed on Fig. 14, the 100% relative humidity readings at location D are much

more consistent, occurring from January through March 2012. This suggests that moisture in liquid

form may have entered the wall at the sensor location and was unable to sufficiently dry out until

building tarps were removed in late March and the building heat turned on at the beginning of April.

It is unclear why the sensor located in the same plane, but mounted 6" above the foundation wall had

much lower readings during this period. This location will continue to be monitored for periods of

high relative humidity, and if required, a test hole will be drilled, and a portable straw bale moisture

probe will be inserted into the wall to verify proper sensor operation.

Fig. 16: Relative Humidity at Location #B for April 2012

Fig. 17: Temperatures at Location #B for April 2012

Fig. 18: Relative Humidity at Location #C for from August to November 2011

Concluding Remarks. It is important to consider the relative humidity and moisture content

thresholds related to the durability of straw bales and CEBs. For straw bales, mould growth is typically

thought to occur at relative humidity values 80% (or 20% moisture content) and higher, over sustained

periods of time [1]. Further to this, rot is known to occur in wood when exposed to extended periods

of warm temperatures and humidity values higher than 95%. Straw is thought to have the potential to

rot in slightly lower relative humidity conditions because of its higher surface area per unit volume.

When reviewing the straw bale readings shown in Fig. 11 through 14, it is evident that relative

humidity values at locations A, B and C were in the 80% range for up to five consecutive months

(August 2011 through January 2012). This suggests that the potential for mould growth may have

existed for these locations. After January 2012, the relative humidity readings for these locations

steadily declined and remained below 80% until June 2012, when values started to increase toward

this threshold again. The readings at location D never approached 80%, consistently remaining

between 40% and 50% relative humidity. The highest relative humidity reading recorded was 90%

and occurred at location A (March 2012). This value is below the 95% threshold, and was not

sustained over a significant period of time, suggesting that risk of rot is remote.

For CEBs, the primary durability concern relating to moisture content is spalling resulting from

freezing of moisture present within the blocks. For this to occur the blocks would need to be near

saturated (100% relative humidity) and temperatures below freezing. During the one year monitoring

period presented in this report, the only sub-zero temperature recorded on the exterior face of the

CEBs was -0.4°C at a relative humidity of 81.7%. This suggests that the risk of freeze/thaw damage

did not occur at any of the locations during the monitoring period.

One aspect of the wall assembly that will continue to be monitored into the future (especially when

the home becomes habited by occupants) is its ability to control vapour diffusion. In a more typically

straw bale home, a vapour control layer is provided on the interior of the wall system by applying a

low vapour permeable paint (≤ 300 metric perms) to the interior facing of stucco [1]. This is done to

throttle the amount of vapour that moves from the building interior into the wall assembly, to a point

where it can condense within the straw. In the demonstration home, this control layer don't appear to

exist, as only the CEBs (and an exterior parge coat) are present on the interior side of the straw bales.

Durability may be compromised if the CEBs and exterior parging coat are unable to provide sufficient

vapour diffusion resistance. This is more prevalent in air tight buildings such as this one (refer to “Air

Tightness Testing” section) when vapour diffusion contributes more significantly to the amount

moisture that is present within the enclosure assembly. If it is determined that the CEB does not offer

suitable vapour resistance, one solution may be to seal the interior face with a product that serves as

a suitable vapour retarder.

Looking to the future, it would be beneficial to continue to monitor the demonstration home for

changes in relative humidity values for at least the next year. In particular, the following points should

be considered when reviewing the data:

• Reduction in "Built-in" Moisture: Based on the high relative humidity readings observed over

the monitoring period, it is thought that "built-in" moisture from the materials is still present

in the building. Over the next year, values are expected to decrease and stabilize (to some

extent) with exposure to exterior environment (i.e. wind and sun) and a constant source of

interior heating during the winter months.

• Changes in relative humidity with building use: While it is expected that relative humidity

values will drop over the next year as "built-in" moisture is reduced, it is also anticipated that

the building will be occupied at some point during this time. When this happens, occupants

and their activities (e.g. cooking) will contribute to moisture within the building.

• Sustained relative humidity values of 80% or higher: The first three months of data collected

during the monitoring period showed sustained RH values near 80%. It will be important to

ensure that this trend does not continue and lead to problems such as mould growth.

• Relative humidity values nearing 100%: Values of 100% mean the air has reached saturation,

suggesting that moisture in liquid form is present inside the wall. In addition to posing the risk

of rot for straw, this condition is risky for the CEBs if the temperature at the same location is

below freezing.

Air Tightness Testing

Methods. Air tightness testing was carried out on the demonstration building for two (2) reasons. The

first was to demonstrate the low-infiltration potential for this type of construction; the second reason

was to obtain data to educate the heat/loss gain testing that is explained in “Whole Home Heat

Loss/Gain Testing” section.

Testing was carried out on July 30, 2012 starting at 1:00pm. The weather during the test was

clear, the wind relatively calm (11 km/h from the SSW from Environment Canada), the exterior

temperature approximately 27°C and the interior temperature 25°C. Tests were carried out using a

Minneapolis Model 3 blower door fitted with a "D" ring (suitable for a flow range of 115 cfm down

to 30 cfm) and equipped with the DG700 pressure and flow gauge to record measurements.

Before any measurements were made, the building was depressurized to -50 Pa and a general

inspection of the building was carried out to identify locations of air leakage. This was done by

observing movements in the smoke produced by sticks of burning incense held closely to suspected

leakage points. Locations with noticeable air flow were noted. After leakage locations were identified,

the blower door fan was turned off, allowing the building to reach pressure equilibrium with the

outdoors.

Immediately following the general inspection, two multi-point tests were carried out (1:30 pm

and 1:45 pm) to quantify the air tightness characteristics of the building. For both tests a pre-test

baseline pressure measurement was made and "zeroed out" using the DG700 gauge, allowing the

actual change in building pressure made by the blower door fan to be displayed and recorded. Testing

started by depressurizing the building to ±60 Pa and slowly reducing the pressure across the enclosure

to ±15 Pa. A total of eight (8) building pressure (Pa) and eight (8) corresponding blower door fan flow

(cfm) measurements were made during each test across the depressurization range. This data was then

used to calculate air leakage characteristics for the building.

Fig. 19: Blower Door Used During Air Tightness Testing

Results. The air leakage characteristics measured with the blower door are presented in the Table 2.

Based on the test results, the demonstration home is extremely air tight, and is a testament to the care

and attention to detail with which this house was constructed. With an air change per hour (ACH) of

approximately 0.7 at 50 Pa, this house far exceeds the R-2000 requirement (1.5 ACH50) and falls just

short of the stringent Passivhaus target (0.6 ACH50).

Table 2 - Demonstration Home Air Leakage Characteristics

Test #1 Test #2

Airflow Characteristics

Air Flow at 50 Pa 40 L/s

(85 cfm)

42 L/s

(88 cfm)

Air Changes per Hour (ACH) at 50 Pa 0.66 0.69

Air Flow at 50 Pa per unit of floor area 0.47 L/s/m2

(0.0931 cfm/ft2)

0.47 L/s/m2

(0.0970 cfm/ft2)

Air Flow at 50 Pa per unit of surface area 0.092 L/s/m2

(0.0181 cfm/ft2)

0.096 L/s/m2

(0.0188 cfm/ft2)

Leakage Areas

Equivalent Leakage Area (EqLA) at 10

Pa

40.0 cm2

(6.2 in2)

47.1 cm2

(7.3 in2)

Effective Leakage Area (ELA) at 4 Pa 17.4 cm2

(2.7 in2)

21.9 cm2

(3.4 in2)

Building Leakage Curve

Flow Coefficient (C) 2.9 4.1

Exponent (n) 0.82 0.79

Correlation Coefficient 0.99437 0.99432

The air leakage locations, although minor, are identified on Fig. 20 and in Table 3. The flow

exponent (n) values measured in the two tests were both above 0.7, which indicates that smaller holes

tend to dominate the leakage area. This is consistent with the observations that were made during the

general inspection prior to the testing.

Of the locations presented in Table 3, air leakage through the underground conduits supplying

data and power to the building were by far the worst, but could be addressed by injecting spray foam

into the top few inches of the opening. The remaining locations could easily be remedied with

caulking and by replacing weather-stripping at the base of the entry doors. Note that no detectable air

leakage locations were observed on the second floor within 8 feet of the floor.

Fig. 20: Air Leakage Locations

Table 3 - Air Leakage Locations

Location Description Leakage

Appraisal1

Potential

Solution

Southeast Door

Leakage occurred between

the door shims adjacent to

the upper hinge.

Low

Caulking

or spray

foam

Light Switch

Electrical Box (West

of Southeast Entrance

Door)

Leakage was observed

where wires pierce the

body of the electrical box

Low Caulking

Underground Data

Conduit

Leakage was noted at the

end conduit High

Fill end of

conduit

with spray

foam

Underground Power

Conduit

Leakage was noted at the

end conduit High

Fill end of

conduit

with spray

foam

Northwest Door

A section of the door

sweep was deformed allow

air to pass underneath.

Low New door

sweep

Note 1: Leakage appraisal is qualitative, with leakage locations being compared against one another.

Whole Home Heat Loss/Gain Testing

Methods. When this project was initially conceived, the approach to assessing the heat loss/gain

characteristics of the demonstration home was to carry out using a Short-Term Energy Monitoring

(STEM) test. This test protocol was developed in the 1990s by the National Renewable Energy

Laboratory (NREL) based in Golden, Colorado, to provide a fast and cost-effective means of verifying

energy performance and to afford a quantitative assessment of heat losses and gains, including

conduction losses, air infiltration, and solar heat gain. However, after contacting NREL, acquiring

procedures and past test reports, and reviewing the software package, it was evident that the

procedures and equipment required to carry out this type of analysis were far beyond the scope of this

project. The main limiting factors were the need for a complex data acquisition system and the

computer programming required to process and convert the data collected by it into a format that can

be used by the STEMWIN Version 2.02 software. It should also be noted that NREL no longer uses

the STEM test in part due to criticism the procedures have received over the years. In the end, a

decision was made to take a different approach to commenting on the heat loss/gain characteristics of

the demonstration home.

Borrowing from the STEM test procedures, a multi-day analysis was carried out and involved

"co-heating" and "cool-down" periods. During the "co-heating" period, the building was heated for a

two-day period by a storage-type electric water heater (located in the building) in conjunction with

the in-floor heating system (pump and tubing). A Dwyer Series TS Digital Temperature Switch was

used to turn on and off the electric water heater (and pump circuit) as required to maintain a constant

interior temperature of 22ºC (as measured at a height of 6'-6" on the northwest wall). During this

period all electrical energy being consumed in the building (i.e. water heater, pump, and temperature

controller) was measured by an EKM Metering EKM-25IDS-N v.2 single-phase energy meter.

Interior and exterior temperatures were recorded at 15 minute intervals by the same Onset HOBO Pro

v2 data loggers as were described in the “Long Term Monitoring” section.

Data collected during the "co-heating" period was used to comment on the building's effective

thermal resistance and its response to external factors such as temperature change and solar gain.

During the night time, conduction and air infiltration were expected to be the primary sources of heat

loss. During the day, the interior temperature was allowed to drift upwards (above the 22ºC set point)

as the building responded to solar energy absorbed through transparent and opaque surfaces. The

measurements made during these times were graphed to provide a visual illustration of the

demonstration home's response patterns.

Fig. 21: Temperature Controller and Energy Meter

Immediately following the "co-heating" period, the set-point of the temperature controller

was set down to 15°C, causing the water heater (and pump) to turn off, and allowing the building to

drift with the exterior temperature and effects of solar insolation. This "cool-down" period lasted a

total of six days. The purpose was to observe the heat capacity (thermal mass) characteristics of the

building and monitor how the building responded to changes in the exterior air temperature. It was

also used to study the effects of solar heat gain on the unheated building.

Results. The interior and exterior temperatures collected at 15 minute intervals over the 2 day "co-

heating" period and 6 day "cool-down" period are shown in Fig. 22. Also shown on the graph are the

period for which energy consumption was recorded as the building was being heated, and the heating

temperature set point during both the "co-heat" and "cool-down" periods.

Fig. 22: Heat Loss/Gain Characteristics

During the co-heating period, a total of 42.2 kWh of energy was consumed over the time that

the heating system operated. This value is the total energy delivered to the interior of the building to

overcome heat losses to the exterior by modes of conduction, convection and radiation. One of the

limitations of the energy meter that was used in this study is that it did not have the capability to

record energy consumption at intervals. However, if we make a general assumption that the energy

consumption varies linearly with the difference between interior and exterior temperature (and ignore

the effects of solar heat gain; a reasonable assumption giving the trends in Fig. 23) it is possible to

roughly approximate the total amount of energy consumed over each 15 minute period. If steady state

heat flow is assumed over each 15 minute interval, the constant heat flow (W) that is required to

produce the approximated energy consumption for that interval can be calculated. By using the

constant heat flow (W) value and temperature change (ºC) assumed for each interval, the in-situ

overall building heat loss coefficient (W/ºC) can be estimated. For the demonstration home, this value

is approximately as 64 W/ºC.

It is important to note that the total surface area of the demonstration home is dominated by a

few assemblies. As can be seen in Table 4, the roof and walls make up 65.6% and 19.3% respectively

(85% in total), of the total surface area of the building. This fact is highlighted to suggest that the

building heat loss coefficient, and the home's thermal performance in general, is heavily impacted by

these surface areas. This should come as no surprise, however, the effective thermal resistance value

of the roof is thought to be much less than that of the CEB-straw-bale walls, meaning that the energy

measured during this test is more of a comment on overall building performance (which is dominated

by roof performance) than wall performance.

Table 4: Breakdown of Building Surface Areas

Surface Area (m2) % of Total Area

Ground Floor 42.3 9.7%

Above-Grade Walls 84.0 19.3%

Roof 286.3 65.6%

Dormers 13.7 3.1%

Windows 6.7 1.5%

Doors 3.4 0.8%

Total 436.3 100%

A portion of the in-situ overall building heat loss coefficient is also attributed to the air leakage

heat loss coefficient (Uair) where,

Uair = 0.3 x n x V [2]

where,

n = number of natural air changes per hour (ACH) = 0.021

V = total air volume of the building (m3) = 217 m3

and,

Uair = 0.3 x 0.02 x 217 = 1.3 W/°C

[Note 1: The ACH value is the average annual natural infiltration rate estimated by the TECTITE

blower door software using the calculation procedure contained in ASHRAE Standard 136. It is based

on the average values calculated from the data collected during blower tests #1 and #2, and presented

in Table 2.]

The air leakage heat loss coefficient makes up 2% of the overall building heat loss coefficient.

The remaining 98% is attributed to heat loss through the enclosure surfaces; walls, floor, roof,

windows and doors.

As was mentioned previously, the heating system set-point was set to 22°C. This meant that

during the day, it was possible for the interior temperature of the demonstration home to rise above

that value in response to solar gains. Fig. 23 shows a detailed view of the temperatures measured

during the "co-heating" period. The interior temperatures during the daylight hours on April 5th and

6th vary little, and with no distinguishable pattern the would be attributed to solar gain through a

window. This suggests that solar heat gain is negligible in the demonstration home. This is supported

by the fact that both days were clear and had good solar insolation values being recorded consistently

at the nearby Burnley weather station (refer to Fig. 24 and 25).

Fig. 23: "Co-heat" Period

Fig. 24: Measured Solar Insolation on April 5, 2012

(acquired from www. wunderground.com for Burnley, Ontario weather station)



However, when studying the graph of the "cool-down" period (refer to Fig. 26) a slightly

different trend is apparent as the interior temperature begins to decrease. As can be seen in Fig. 27

and 28, 4.8, April 7th and April 8th were clear days that resulted in good solar insolation values

(very similar to April 5th and 6th). A small increase in interior temperature (approximately 0.5°C)

was recorded on both days just before noon. Conversely, if we look at the insolation plots for April

9th, 10th and 11th (Fig. 29, 30, 31), it is evident that these days were overcast, resulting in poor and

varied insulation values. On these days, no increase in interior temperature was observed. These

observations suggest that the demonstration home, does have a response to solar heat, albeit small.

This is thought to be a result of the relatively few number of window openings and their small

apertures.

Fig. 26: "Cool-Down" Period











Also evident from the "cool-down" period illustrated in Fig. 26 is the difference in the rate

of temperature decrease inside the building when compared to that of exterior temperature as it tries

to reach equilibrium with the outdoor environment. The slope of the interior temperature changes

are much more shallow than that of the exterior temperature changes. The difference results in very

different changes of temperature recorded over the same periods of time. For example, the exterior

temperature dropped from 15°C on April 8th to 2°C on the morning of April 9th; a temperature

change of 13°C over a period of 15 hours. If we look at the interior temperature trend over the same

time period, a change of only 1°C was recorded. These observations are in part attributable to the

volume of air in the building that needs to be cooled down. However, the high thermal mass of the

building is also suspected to be at play, effectively dampening the magnitude of interior temperature

swings from the changes taking place in the outdoor environment. This dampening effect, was also

evident during the "co-heating" period, allowing the heating system to easily react to changes in

exterior temperature, and never letting the building drop by more than 0.5°C below the 22°C set-

point during the coldest evening (-2°C).

Another trend visible from Fig. 26, is the time delay between the lowest exterior and interior

temperatures recorded for each day. On April 7th the lowest exterior temperature recorded was -1°C

which occurred at 6 am. On the same day, the lowest interior temperature was 20°C and occurred at

9 am, 3 hours after the exterior temperature. This "thermal delay" is also suspected to be a result of

both thermal mass and high volume of air needing to be cooled.

Concluding Remarks and Future Research Opportunities

The demonstration home is a prototype building that showcases construction techniques not

typical in the Canadian building industry, but that will likely be considered more frequently as

concerns about the condition of our environment escalate. It not only emphasizes the importance

and viability of using only local materials to construct our buildings, but also demonstrates that

concrete earth block structures can be combined with reclaimed materials and other natural

materials to produce an attractive, well insulated and extremely air-tight home. As energy security

and environmental issues continue to threaten our planet, it will be important to continue to develop

non-traditional forms of construction such as CEB and straw-bale in the years to come. Studying

and documenting the thermal performance, effects of moisture on, and the durability of these

buildings will be essential. Not only will this aid in the development and constant improvement of

the techniques used, but it will also inform those individuals resistant to the need for a change in our

approach to the built environment, making them aware of the potential of these construction styles.

Based on the observations presented in study, there are a number of recommendations that

should be considered. For the demonstration home in particular, it would be extremely beneficial to

continue to monitor it for changes in relative humidity values over the next year (at the very least).

In particular, the following points should be considered when reviewing the data:

• Reduction in "Built-in" Moisture: Based on the high relative humidity readings observed over the

monitoring period, it is thought that "built-in" moisture from the materials is still present in the

building. Over the next year, values are expected to decrease and stabilize (to some extent) with

exposure to exterior environment (i.e. wind and sun) and a constant source of interior heating

during the winter months.

• Changes in relative humidity with building use: While it is expected that relative humidity values

will drop over the next year as "built-in" moisture is reduced, it is also anticipated that the building

will be occupied at some point during this time. When this happens, occupants and their activities

(e.g. cooking) will contribute to moisture within the building.

• Sustained relative humidity values of 80% or higher: The first three months of data collected

during the monitoring period showed sustained RH values near 80%. It will be important to ensure

that this trend does not continue and lead to problems such as mould growth.

• Relative humidity values nearing 100%: Values of 100% mean the air has reached saturation,

suggesting that moisture in liquid form is present inside the wall. In addition to posing the risk of

rot for straw, this condition is risky for the CEBs if the temperature at the same location is below

freezing.

For future CEB-straw-bale buildings that will be studied, the following recommendations are made:

• Finishing the Building: As is evident from the “Long Term Monitoring” section, high humidity

readings measured consistently for a number of months is a concern. Due to the nature of the

materials used in this type of construction, we know these buildings have the potential to start

out with high amounts of "built-in" moisture. To avoid potential problems (i.e. mould growth

and rot) it is be important to allow the structure to release the moisture to the outdoors as

quickly and as easily as possible. This means removing tarps (if used) and heating the building

sooner; steps that should not be a problem taking if the building is occupied soon after

construction.

• Add People: In order to truly comment on the durability of this type of wall construction the

building must be used for its intended purposed. Monitoring moisture and temperature in an

occupied home will provide crucial insight into how the walls respond to varying moisture loads

associated with indoor activities such as cooking and bathing. The data collected would help

determine the type of vapour control that is required to avoid/minimize the presence of vapour

in the wall assemblies.

• Energy Consumption: Energy consumption should be monitored over the course of at least one

year to provide a better indication of how the building performs during peak heating and cooling

conditions. If the effective thermal resistance value of the CEB-straw-bale wall assembly is

desired, it should be done in a guarded hot-box or similar controlled environment to eliminate

the effects of other building components such as complex and area-dominating roofs. Finally, a

energy monitoring device with interval logging capabilities is highly recommended for

commenting on trends observed in tests such as the "co-heating" and "cool-down" periods.

References [1] J. Straube, Building Science for Strawbale Buildings (Building Science Digest 112), Building

Science Press. 2009-01-30.

[2] E.Burnett, J. Straube, Building Science for Building Enclosures, first ed., Building Science Press,

2005, pp 205.

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