**5.1. Thermal performance of mini-roof structures**

### *5.1.1. Mini-roofs*

C

F) [30]. Green roofs

**•** Green roofs have excellent noise attenuation, especially for low frequency sounds. An extensive green roof can reduce sound from outside by 40 decibels, while an intensive one

**•** Green roofs can sustain a variety of plants and invertebrates, and provide a habitat for

Historically, studies on green roofs have explored their energy performance compared with traditional roofs. Thermal performance indicated a significant reduction (~40%) of a building cooling load during the summer period [26]. Similar results were achieved for a nursery school, with reductions ranging from 6% to 49%, and reduction ranging from 12% to 87% on the last floor of the nursery school [27]. Wong *et al*. [28] note that green roofs tend to experience lower surface temperatures than the original exposed roof, especially in areas well covered by vegetation. When green roofs are well covered by vegetation, the resulting substrate moisture will tend to keep substrate temperature lower than the original exposed bare roof. These studies determined that over 60% of the heat gain was mitigated by vegetated roof systems. Summertime data have indicated significant lower peak roof surface temperature and higher nighttime surface temperature for green roofs as compared to conventional roofs [29]. The maximum average daily temperature seen for the conventional roof surface was 54.4o

F) in his study, while the maximum average day green roof surface temperature was

help minimize environmental burdens, conserve energy, and extend the life span of the roofing system in overall sustainability [31]. Up to 30% of total rooftop cooling is due to plant tran‐ spiration [32]. Bell and Spolek [33] compared different types of plants for use in increasing the thermal resistance (*R*-value) of green roofs, and found that ryegrass delivered the highest effective *R*-value compared with bare soil, *Vinca major, Trifolium repens,* and *Sedum hispani‐ cum.* Also, though increasing the depth of bare soil from 5 to 14 cm (2.0 to 5.5 inches) increased the *R*-value, no difference was found for different depths of planted soil. This implies that the bulk of benefit toward *R*-value is from evapotranspiration and leaf shading, rather than the

There are several detailed building simulation programs (BSPs) that take into consideration the complete interaction between all thermal-based elements. The most popular BSPs are A Simplified Energy Analysis Method (ASEAM), Building Design Advisor (BDA), Building Load Analysis and Systems Thermodynamics (BLAST), Builder Guide, Bus++, Dynamic Energy Response of Buildings (DEROB), DOE-2, Energy-10, Energy Plus, ENERPASS, ENER-Win,

UAB has utilized Visual DOE in the past with great success in the analysis of innovative structures designed for energy efficiency. VisualDOE uses the DOE 2 calculating core and provides output in both numerical and graphical forms. This software is a preferred calculation method due to its cost, previous verification/validation success, ease of use, database support and reasonable input/output requirements. We envision that this computer simulation tool will be able to effective capture the differences in roof types being explored in the purposed

ESP, FEDs, Home Energy Saver, Hot 2000, TRNSYS, and VisualDOE ([34]; [35]; [36]).

kWh/day) to maintain an average room air temperature of 25.7o

C lower than the conventional roof). Green roofs offer cooling potential (~3.02

C (78.3o

can reduce sound by 46-50 decibels.

various bird species.

26 New Developments in Renewable Energy

(129.9o

C (~21.7o

moist soil [33].

research.

32.8o

During this study, 15 mini-roof combinations were observed for trends in internal tempera‐ tures. The various 15 mini-roof combinations are summarized in Table 1. Several of the miniroof structures are depicted in Figure 1. This photo shows the layout of the 15 mini-roofs, and a vegetated roof from which surface temperatures of the mini-roofs were measured periodi‐ cally using an infrared thermometer (see Figure 1).

**Figure 1.** a) Layout of the 15 mini-roods; (b) vegetated mini-roof (surface temperatures were measured using an IR thermometer.

The roofing materials used are all standard commercial flat roof materials. Flat roof materials were only looked at during the study, since the primary application for the roofing combina‐ tions will be on a commercial flat roof top, and not a slanted roof structure. Each mini-roof is 2.4-m (8.0-ft) long x 1.2-m (4.0-ft) wide x 1.2-m (4.0-ft) deep (see Figure 1). A number of different roofing systems are being examined for their energy performance. All roofs are insulated with 5.1 cm (2.0-in) of extruded polystyrene. Then the particular roofing combination being investigated is applied over the insulation and sealed. The roofs also include a proper drainage spout, to ensure correct water evacuation, such as on a real roof.

The roofing systems being studied using the 15 mini-roofs are listed in Table 1.


**Figure 2.** Depiction of a Typical Mini-Roof System.

**Figure 3.** Mini-roof system showing temperature sensor installed inside a mini-roof.

Energy Savings Resulting from Installation of an Extensive Vegetated Roof System on a Campus Building in the…

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Notation – TPO: thermoplastic polyolefin; SBS: styrene-butadiene-styrene; PVC: polyvinyl chloride; EPDM: ethylene propylene diene monomer; IRMA: inverted roof membrane assembly.

**Table 1.** Mini-roof descriptions.

To investigate the thermal properties of the roofing structures an ambient temperature probe was placed inside of each roof (see Figures 2 and 3) recording temperature data every 10 minutes of each day, for more than 3 years. This data was then automatically sent to a data logger and placed into an Excel file for review later. The temperature probe reports the temperature to the nearest hundredth of a degree Centigrade.

Energy Savings Resulting from Installation of an Extensive Vegetated Roof System on a Campus Building in the… http://dx.doi.org/10.5772/55997 29

**Figure 2.** Depiction of a Typical Mini-Roof System.

**Mini-Roof No. Mini-Roof Description**

28 New Developments in Renewable Energy

1 (Sensor B) White TPO/PVC/ Elvaloy fully adhered, FiberTite Membrane.

3 (Sensor D) Black 60-mil EPDM fully adhered, Mule Hide Membrane.

4 (Sensor E) Beige TPO/PVC/Elvaloy fully adhered, FiberTite Membrane.

5 (Sensor F) White granular modified, Firestone SBS Modified Membrane.

6 (Sensor G) Black granular modified, Firestone SBS Modified Membrane.

8 (Sensor I) Bituthene IRMA with lightweight "T Clear" pavers.

9 (Sensor J) Bituthene IRMA with river rock ballast.

7 (Sensor H) Black granular modified coated/white urethane, Firestone SBS Modified Membrane.

10 (Sensor K) Bituthene IRMA with vegetative green roof, ½-in. drain mat, 350-lbs dry soil.

11 (Sensor L) Bituthene IRMA with vegetative green roof, 1-in. drain mat, 350-lbs dry soil.

12 (Sensor M) Black 60-mil EPDM loose, ballasted with river rock, Mule Hide Membrane.

13 (Sensor N) Black 60-mil EPDM loose, ballasted with #300 marble chips, Mule Hide Membrane.

14 (Sensor O) White TPO/PVC/Elvaroy loose laid, ballasted with river rock, FiberTite Membrane.

15 (Sensor P) Bituthene IRMA with vegetative green roof, ½-in. drain mat, 350-lbs dry soil.

Sensor T Sensor under the white TPO/PVC/Elvaloy loose laid, ballasted with river rock.

Notation – TPO: thermoplastic polyolefin; SBS: styrene-butadiene-styrene; PVC: polyvinyl chloride; EPDM: ethylene

To investigate the thermal properties of the roofing structures an ambient temperature probe was placed inside of each roof (see Figures 2 and 3) recording temperature data every 10 minutes of each day, for more than 3 years. This data was then automatically sent to a data logger and placed into an Excel file for review later. The temperature probe reports the

Sensor S Sensor inside mini-roof No.10 (inside the soil of the green roof).

propylene diene monomer; IRMA: inverted roof membrane assembly.

temperature to the nearest hundredth of a degree Centigrade.

**Table 1.** Mini-roof descriptions.

2 (Sensor C) Black 60-mil EPDM fully adhered/coated/white urethane, Mule Hide Membrane.

**Figure 3.** Mini-roof system showing temperature sensor installed inside a mini-roof.

Figure 4 presents some typical temperature profiles on several different days.

**•** Over time, the reflective (white) roofs become dirty, losing some of their reflectivity,

Energy Savings Resulting from Installation of an Extensive Vegetated Roof System on a Campus Building in the…

**•** White marble chips behaved slightly worse than green roofing materials, but considerably

**•** While it is too early to come to a definitive conclusion, preliminary evaluations indicate that the "white" and "green" roofs both significantly reduce the roofs surface temperature and

Surface temperature measurements during the months of June and July on the various roofing materials used with our mini-roof systems were collected. During this time period, roofing

temperature values occurred on the roofing combinations primarily made of a coating or

large counterpart, the pilot roof on top of the University of Alabama at Birmingham (UAB)

the specific roofs contained in each subset of Table 1, it was observed that generally, the lighter colorization of the roof resulted in cooler temperatures. For example, the white Firestone SBS is cooler than the black Firestone SBS on any given day. This thermal property is observed due to the reflectivity of the roof. The darker colored roofs absorb more incoming light radiation than the light colored roofs causing the dark roofs to become hotter. (Since the roofs temper‐ atures observed are taken during the late spring and early summer, it can be inferred that

Photographs of several of these mini-roofs are presented in Figures 5 through 9. Figure 10 presents a typical temperature profile of the 15 mini-roofs during the course of a typical summer week. Series 1 through 5 denoted in the figure refer to the fifteen mini-roofs listed in Table 1. This figure shows a cyclical nature of the temperature readings over each day, generally showing a sinusoidal behavior of temperature; the temperature is cool in the morning, warms up, and is at its hottest during mid-afternoon, and then cools down during

Trends seen in statistical comparisons of internal temperatures of similar roofs (using the null

**•** Between the two river rock roofs, Roof 9 will most likely always be hotter or equal to roof 12.

**•** Between the 3 vegetative roofs, all the roofs are statistically equal to each other in thermal

**•** Both SBS Firestone roofs are statistically the same, but roof 6 is usually hotter.

C were observed. The lower surface temper‐

C to 61.1o

C to 82.2o

C to 52.2o

C. The vegeta‐

C, while their

C. When looking at

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31

C, are found in a loose rock or stone roof combination. The higher

F to 82.2o

resulting in the roof being less energy efficient.

surface temperatures ranging from 20.6o

C to 48.3o

ature values, 20.6o

evening hours.

properties.

better than black roofing and granular roofing materials.

therefore, the air temperatures above and around the roof.

membrane; these roofs exhibited temperatures roughly between 25.6o

tive mini-roofs exhibited surface temperatures ranging between 21.7o

Hulsey Center, exhibited higher temperatures ranging from 31.7o

overall roof temperature will increase during late summer).

hypotheses: μ1 ≥ μ2) are summarized below [38]:

**•** The TPO/PVC/Elvaloy Roofs are statistically the same.

**•** The 60-mil EPDM roofs are also statistically the same.

**Figure 4.** a. Temperature profile inside the various mini-roofs on May 26, 2008. b. Temperature profile inside the vari‐ ous mini-roofs on May 27, 2008 [37]. c. Temperature profile inside the various mini-roofs on June 5, 2008.

The results from these mini-roof structures have shown the following trends [37]:


**•** Over time, the reflective (white) roofs become dirty, losing some of their reflectivity, resulting in the roof being less energy efficient.

Figure 4 presents some typical temperature profiles on several different days.

**Figure 4.** a. Temperature profile inside the various mini-roofs on May 26, 2008. b. Temperature profile inside the vari‐

**•** Clean white roofs resulted in consistently lower temperatures inside the mini roof than the

however, they will dampen the drainage of rainfall during a rain storm through the retention

C (2-3o

F) higher than the white roofs;

ous mini-roofs on May 27, 2008 [37]. c. Temperature profile inside the various mini-roofs on June 5, 2008.

The results from these mini-roof structures have shown the following trends [37]:

**•** Bituthane (river rock) performs only slightly better than black roofing materials. **•** White granular roofing behaved similarly to black granular roofing materials.

**•** Black roofs resulted in the highest temperature readings. **•** Green roofs resulted in temperatures typically ~1.1-1.7o

other roofing materials.

30 New Developments in Renewable Energy

of water onto the soil.


Surface temperature measurements during the months of June and July on the various roofing materials used with our mini-roof systems were collected. During this time period, roofing surface temperatures ranging from 20.6o F to 82.2o C were observed. The lower surface temper‐ ature values, 20.6o C to 48.3o C, are found in a loose rock or stone roof combination. The higher temperature values occurred on the roofing combinations primarily made of a coating or membrane; these roofs exhibited temperatures roughly between 25.6o C to 82.2o C. The vegeta‐ tive mini-roofs exhibited surface temperatures ranging between 21.7o C to 52.2o C, while their large counterpart, the pilot roof on top of the University of Alabama at Birmingham (UAB) Hulsey Center, exhibited higher temperatures ranging from 31.7o C to 61.1o C. When looking at the specific roofs contained in each subset of Table 1, it was observed that generally, the lighter colorization of the roof resulted in cooler temperatures. For example, the white Firestone SBS is cooler than the black Firestone SBS on any given day. This thermal property is observed due to the reflectivity of the roof. The darker colored roofs absorb more incoming light radiation than the light colored roofs causing the dark roofs to become hotter. (Since the roofs temper‐ atures observed are taken during the late spring and early summer, it can be inferred that overall roof temperature will increase during late summer).

Photographs of several of these mini-roofs are presented in Figures 5 through 9. Figure 10 presents a typical temperature profile of the 15 mini-roofs during the course of a typical summer week. Series 1 through 5 denoted in the figure refer to the fifteen mini-roofs listed in Table 1. This figure shows a cyclical nature of the temperature readings over each day, generally showing a sinusoidal behavior of temperature; the temperature is cool in the morning, warms up, and is at its hottest during mid-afternoon, and then cools down during evening hours.

Trends seen in statistical comparisons of internal temperatures of similar roofs (using the null hypotheses: μ1 ≥ μ2) are summarized below [38]:


**Figure 7.** Mini-roof equipped with river rocks.

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**Figure 8.** Mini-roof equipped with crushed marble chips.

**Figure 5.** Black mini-roof.

**Figure 6.** White (reflective) mini-roof.

Energy Savings Resulting from Installation of an Extensive Vegetated Roof System on a Campus Building in the… http://dx.doi.org/10.5772/55997 33

**Figure 7.** Mini-roof equipped with river rocks.

**Figure 5.** Black mini-roof.

32 New Developments in Renewable Energy

**Figure 6.** White (reflective) mini-roof.

**Figure 8.** Mini-roof equipped with crushed marble chips.

After acquiring the necessary raw data from the mini-roof sensors, Microsoft Excel (version 2010) was used to plot the data to discover trends in the temperature readings. Subsequent to discovering the trend, a mathematical model was fit to the data. It was noticed that the temperatures cycled in a sinusoidal fashion on yearly and daily time frames, and therefore a general form sine function was utilized as a potential model. Fourier transforms were utilized in order to determine the oscillation frequency of the temperature (ω 0 from the general form *x* = *A* sin (ω <sup>0</sup> *t* + ϕ) + *C*) by transforming the time domain of the collected raw data into a frequency domain. Two major peaks were discovered from the spectrum: one representing the yearly frequency and the other representing the daily oscillations. After calculating the frequencies, the phase angle (ϕ) and the amplitude (*A*) of the general form were determined

Energy Savings Resulting from Installation of an Extensive Vegetated Roof System on a Campus Building in the…

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35

The modeling procedure was applied for all 15 mini-roofs in the study. The developed sinewave functions indicated that most roofs were statistically different from one another from an amplitude aspect but the phase angles were statistically the same. It was also discovered that almost all roofs had significantly different average mean roof temperatures, but the signifi‐ cance was mostly prevalent in the summer months. During other times of the year, the roofs behaved in a similar fashion (see Tables 2 and 3 for statistics and means of roofs). The fitted

**Statistics of Phase Angles**

4.0303 0.00343 4.0276 4.0242 0.01329 0.000177 12.0174 3.3228 0.05512 4.0211 4.0762 60.4541 15

sine wave functionalities for the 15 mini-roofs are listed in Table 4.

through a regression analysis.

Mean Standard Error Median Mode Standard Deviation Sample Variance Kurtosis Skewness Range Minimum Maximum Sum Number (count)

**Table 2.** Summary of statistics for the phase angles from curve fitting.

**Figure 9.** Vegetative mini-roof equipped with sedum plants.

**Figure 10.** Typical internal mini-roof temperatures during the course of a week.

After acquiring the necessary raw data from the mini-roof sensors, Microsoft Excel (version 2010) was used to plot the data to discover trends in the temperature readings. Subsequent to discovering the trend, a mathematical model was fit to the data. It was noticed that the temperatures cycled in a sinusoidal fashion on yearly and daily time frames, and therefore a general form sine function was utilized as a potential model. Fourier transforms were utilized in order to determine the oscillation frequency of the temperature (ω 0 from the general form *x* = *A* sin (ω <sup>0</sup> *t* + ϕ) + *C*) by transforming the time domain of the collected raw data into a frequency domain. Two major peaks were discovered from the spectrum: one representing the yearly frequency and the other representing the daily oscillations. After calculating the frequencies, the phase angle (ϕ) and the amplitude (*A*) of the general form were determined through a regression analysis.

The modeling procedure was applied for all 15 mini-roofs in the study. The developed sinewave functions indicated that most roofs were statistically different from one another from an amplitude aspect but the phase angles were statistically the same. It was also discovered that almost all roofs had significantly different average mean roof temperatures, but the signifi‐ cance was mostly prevalent in the summer months. During other times of the year, the roofs behaved in a similar fashion (see Tables 2 and 3 for statistics and means of roofs). The fitted sine wave functionalities for the 15 mini-roofs are listed in Table 4.


**Table 2.** Summary of statistics for the phase angles from curve fitting.

**Figure 9.** Vegetative mini-roof equipped with sedum plants.

34 New Developments in Renewable Energy

**Figure 10.** Typical internal mini-roof temperatures during the course of a week.


These results of this study were in agreement with research conducted by Watson [39] addressing the urban heat island effect for the City of Birmingham, Alabama. By studying the effect from different building facades, building materials and seasonal traits. The data indicates amplitudes (*A*) ranging from 19.5 to 20.7 degrees and phases angles roughly 4.2 to 4.3 radians.

Energy Savings Resulting from Installation of an Extensive Vegetated Roof System on a Campus Building in the…

Based on the information collected on these mini-roof systems, the UAB Facilities Management Department decided to install an extensive vegetated roof on top of Hulsey Center as a roofing retrofit. UAB wants to obtain more fundamental information and knowledge for establishing green roofs in the southeastern U.S. In the Birmingham, Alabama area, fairly high rainfalls [approximately 132.1 cm/year (52 inches/year) on average] are obtained. However, during the summer months, it is common to have periods of drought with minimal rainfall and very hot

require plants that can withstand both significant rainfall events and drought conditions.

Photographs of the construction of the pilot green roof system on Hulsey Center are shown in Figures 12 to 14. Photographs of the system taken in June 2009 are shown in Figures 15 to 17.

F range]. Such climatic conditions

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37

 values ranged from 0.69 to 0.71showing the data modeling was applicable to under‐ standing the trends. The best model developed was for roof 3 (see Figure 11), having the highest

The *r* <sup>2</sup>

correlation coefficient of all 15 mini-roofs.

**Figure 11.** Fitted sine wave regression for a mini-roof system.

and humid days [with temperatures in the 32.2+oC (90+o

**Table 3.** Summary of statistics for the means from curve fitting.


**Table 4.** Fitted sine-wave functionalities describing the internal temperatures in the mini-roofs.

These results of this study were in agreement with research conducted by Watson [39] addressing the urban heat island effect for the City of Birmingham, Alabama. By studying the effect from different building facades, building materials and seasonal traits. The data indicates amplitudes (*A*) ranging from 19.5 to 20.7 degrees and phases angles roughly 4.2 to 4.3 radians. The *r* <sup>2</sup> values ranged from 0.69 to 0.71showing the data modeling was applicable to under‐ standing the trends. The best model developed was for roof 3 (see Figure 11), having the highest correlation coefficient of all 15 mini-roofs.

**Figure 11.** Fitted sine wave regression for a mini-roof system.

**Statistics of Means**

 T = 20.5499\*sin ((2\*π\*3.18 e−8 x t) +4.02272)+66.63564 20.550 4.023 0.701 66.636 T = 20.392\*sin ((2\*π\*3.18 e−8 x t) +4.07624)+66.47947 20.392 4.076 0.712 66.479 T = 20.482\*sin ((2\*π\*3.18 e−8 x t) +4.021125)+66.35505 20.482 4.021 0.698 66.355 T = 20.4891\*sin ((2\*π\*3.18 e−8 x t) +4.03214)+67.54093 20.349 4.032 0.701 67.541 T = 20.7812\*sin ((2\*π\*3.18 e−8 x t) +4.03142)+68.46883 20.781 4.031 0.699 68.469 T = 20.2886\*sin ((2\*π\*3.18 e−8 x t) +4.02415)+67.08382 20.289 4.024 0.701 67.084 T = 20.7812\*sin ((2\*π\*3.18 e−8 x t) +4.02415)+66.18969 20.781 4.024 0.695 66.190

10 T = 19.8608\*sin ((2\*π\*3.18 e−8 x t) +4.02758)+66.6981 19.861 4.028 0.697 66.698

13 T = 19.9914\*sin ((2\*π\*3.18 e−8 x t) +4.0325)+66.47272 19.991 4.033 0.696 66.473

66.67 0.18 66.62 N/A 0.68 0.46 3.11 1.11 3.06 65.42 68.47 1000.12 15

**Amplitude from sinefind.exe**

**Phase**

20.163 4.022 0.696 66.683

20.329 4.025 0.701 66.919

20.013 4.026 0.697 66.623

20.048 4.028 0.694 66.274

20.066 4.032 0.689 65.423

19.463 4.029 0.692 66.272

**Angle** *r 2* **Mean**

Mean Standard Error Median Mode Standard Deviation Sample Variance Kurtosis Skewness Range Minimum Maximum Sum Number (count)

36 New Developments in Renewable Energy

**Table 3.** Summary of statistics for the means from curve fitting.

<sup>1</sup> T = 20.1632\*sin ((2\*π\*3.17894 e −8 x t)

<sup>9</sup> T = 20.3285\*sin ((2\*π\*3.18 e−8 x t)

<sup>11</sup> T = 20.0128\*sin ((2\*π\*3.18 e−8 x t)

<sup>12</sup> T = 20.0479\*sin ((2\*π\*3.18 e−8 x t)

<sup>14</sup> T = 20.0661\*sin ((2\*π\*3.18 e−8 x t)

<sup>15</sup> T = 19.4628\*sin ((2\*π\*3.18 e−8 x t)

+4.021975)+66.68283

+4.024975)+66.91944

+4.026215)+66.62328

+4.027853)+66.27383

+4.032494)+65.42343

+4.028672)+66.27177

**Table 4.** Fitted sine-wave functionalities describing the internal temperatures in the mini-roofs.

**Roof Final Equation**

Based on the information collected on these mini-roof systems, the UAB Facilities Management Department decided to install an extensive vegetated roof on top of Hulsey Center as a roofing retrofit. UAB wants to obtain more fundamental information and knowledge for establishing green roofs in the southeastern U.S. In the Birmingham, Alabama area, fairly high rainfalls [approximately 132.1 cm/year (52 inches/year) on average] are obtained. However, during the summer months, it is common to have periods of drought with minimal rainfall and very hot and humid days [with temperatures in the 32.2+oC (90+o F range]. Such climatic conditions require plants that can withstand both significant rainfall events and drought conditions.

Photographs of the construction of the pilot green roof system on Hulsey Center are shown in Figures 12 to 14. Photographs of the system taken in June 2009 are shown in Figures 15 to 17.

**Figure 14.** Initial vegetative roof immediately after installation on top of Hulsey Center.

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39

**Figure 15.** Vegetative roof on top of Hulsey Center (June 2009).

**Figure 12.** Construction phase for installing a pilot vegetative roof on top of Hulsey Center.

**Figure 13.** Construction phase for installing a pilot vegetative roof on top of Hulsey Center.

Energy Savings Resulting from Installation of an Extensive Vegetated Roof System on a Campus Building in the… http://dx.doi.org/10.5772/55997 39

**Figure 14.** Initial vegetative roof immediately after installation on top of Hulsey Center.

**Figure 12.** Construction phase for installing a pilot vegetative roof on top of Hulsey Center.

38 New Developments in Renewable Energy

**Figure 13.** Construction phase for installing a pilot vegetative roof on top of Hulsey Center.

**Figure 15.** Vegetative roof on top of Hulsey Center (June 2009).

Of the roofing area of 1709.4 m <sup>2</sup> (18,400 ft <sup>2</sup>

green roof on top of Hulsey Center was ~\$150,000 (USD).

top of Hulsey Center.

building energy reductions of 20% to 25%.

) for Hulsey Center, an extensive pilot green

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41

roof has been installed on ~1388.0 m 2 (14,940 ft 2), i.e., occupying ~81.2% of the roofing area, or approximately 1375.9 m 2 (0.34 acres). [Prior to installing the pilot green roof, the UAB civil engineering senior design class investigated the loading of a wet vegeta‐ tive roof on top of Hulsey Center, and found that the current building infrastructure could withstand the loading associated with the vegetative roof. Hulsey Center was originally designed to have two additional floors in the building]. This pilot green roof contains more than 20,000 sedum plants (*Sedum hispanicum*). In the construction of this vegetated roof, the existing roof was removed down to the structural concrete deck. A waterproof roofing membrane was installed directly to the concrete deck. A layer of 7.6 cm (3-inches) of extruded polystyrene roofing insulation was then applied, to which a 226.8-gm (8-oz) non-woven geo-textile scrim sheet was applied. Then, 0.6-m (2-ft) x 0.6 m (2-ft) x 5.1-cm (2-in) prestressed pavers or brick pavers were installed for design, decoration, and access to the vegetative roof. Then, 8.9-cm (3.5-inches) of light weight engineered soil were applied. Sedum plants were planted at the rate of 1615 plants per 100 m 2 (150 plants per 100-ft 2). The cost of retrofitting the roof and installing a pilot

Energy Savings Resulting from Installation of an Extensive Vegetated Roof System on a Campus Building in the…

The current pilot green roof on top of Hulsey Center was installed in July 2008. Research conducted at Penn State University shows that green roofs planted with sedum plants reduce the building energy costs [40]. UAB's Facilities Management Department maintains records of the utilities bills (e.g., natural gas, water, and electricity) for each building on campus. The costs of utilities prior to and after implementation of the pilot green roof are shown in Figures 18 through 20 for natural gas, water, and electricity. Since 2006, the costs of natural gas, water, and electricity have increased by 47%, 28%, and 145%, respectively. Due to the increasing rates of these utilities, a more accurate determination is shown with the usage of these utilities, shown in Figures 21 through 23. In the graph symbols, those indicated with a red interior color depict the cost or usage after installation and implementation of the vegetative roof system. The other symbol colors depict the cost or usage prior to installation and implementation of the vegetative roof system. Generally, the usage of natural gas, water, and electricity are lower than that compared to the utility usage prior to installation of the green roof on

The current pilot green roof on top of Hulsey Center was installed in July 2008. Research previously conducted at Penn State University indicated that green roofs planted with sedum plants reduce the building energy costs [41]. The Facilities Management Depart‐ ment at UAB maintains records of the utilities bills (e.g., natural gas, water, and electricity) for each building on campus. The quantities and costs of utilities prior to (5 years) and after implementation (~3 years) of the pilot green roof have resulted in

**Figure 16.** Vegetative roof on top of Hulsey Center (June 2009).

**Figure 17.** Close-up of vegetative roof on top of Hulsey Center (June 2009).

Of the roofing area of 1709.4 m <sup>2</sup> (18,400 ft <sup>2</sup> ) for Hulsey Center, an extensive pilot green roof has been installed on ~1388.0 m 2 (14,940 ft 2), i.e., occupying ~81.2% of the roofing area, or approximately 1375.9 m 2 (0.34 acres). [Prior to installing the pilot green roof, the UAB civil engineering senior design class investigated the loading of a wet vegeta‐ tive roof on top of Hulsey Center, and found that the current building infrastructure could withstand the loading associated with the vegetative roof. Hulsey Center was originally designed to have two additional floors in the building]. This pilot green roof contains more than 20,000 sedum plants (*Sedum hispanicum*). In the construction of this vegetated roof, the existing roof was removed down to the structural concrete deck. A waterproof roofing membrane was installed directly to the concrete deck. A layer of 7.6 cm (3-inches) of extruded polystyrene roofing insulation was then applied, to which a 226.8-gm (8-oz) non-woven geo-textile scrim sheet was applied. Then, 0.6-m (2-ft) x 0.6 m (2-ft) x 5.1-cm (2-in) prestressed pavers or brick pavers were installed for design, decoration, and access to the vegetative roof. Then, 8.9-cm (3.5-inches) of light weight engineered soil were applied. Sedum plants were planted at the rate of 1615 plants per 100 m 2 (150 plants per 100-ft 2). The cost of retrofitting the roof and installing a pilot green roof on top of Hulsey Center was ~\$150,000 (USD).

The current pilot green roof on top of Hulsey Center was installed in July 2008. Research conducted at Penn State University shows that green roofs planted with sedum plants reduce the building energy costs [40]. UAB's Facilities Management Department maintains records of the utilities bills (e.g., natural gas, water, and electricity) for each building on campus. The costs of utilities prior to and after implementation of the pilot green roof are shown in Figures 18 through 20 for natural gas, water, and electricity. Since 2006, the costs of natural gas, water, and electricity have increased by 47%, 28%, and 145%, respectively. Due to the increasing rates of these utilities, a more accurate determination is shown with the usage of these utilities, shown in Figures 21 through 23. In the graph symbols, those indicated with a red interior color depict the cost or usage after installation and implementation of the vegetative roof system. The other symbol colors depict the cost or usage prior to installation and implementation of the vegetative roof system. Generally, the usage of natural gas, water, and electricity are lower than that compared to the utility usage prior to installation of the green roof on top of Hulsey Center.

**Figure 16.** Vegetative roof on top of Hulsey Center (June 2009).

40 New Developments in Renewable Energy

**Figure 17.** Close-up of vegetative roof on top of Hulsey Center (June 2009).

The current pilot green roof on top of Hulsey Center was installed in July 2008. Research previously conducted at Penn State University indicated that green roofs planted with sedum plants reduce the building energy costs [41]. The Facilities Management Depart‐ ment at UAB maintains records of the utilities bills (e.g., natural gas, water, and electricity) for each building on campus. The quantities and costs of utilities prior to (5 years) and after implementation (~3 years) of the pilot green roof have resulted in building energy reductions of 20% to 25%.

**Electricity Costs for Hulsey Center, 2005 - 2009**

Energy Savings Resulting from Installation of an Extensive Vegetated Roof System on a Campus Building in the…

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43

0 2 4 6 8 10 12 **Month**

**Natural Gas Usage in Hulsey Center, 2005 - 2009**

0 2 4 6 8 10 12 **Month**

0

0

**Figure 21.** Natural gas usage for operation of Hulsey Center, 2005 – 2009.

1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

**Natural Gas Usage, (ccf)**

**Figure 20.** Cost of electricity for operation of Hulsey Center, 2005 – 2009.

2,000

4,000

6,000

**Cost, (\$)**

8,000

10,000

12,000

**Figure 18.** Cost of natural gas for operation of Hulsey Center, 2005 – 2009.

**Figure 19.** Cost of water/wastewater for operation of Hulsey Center, 2006 – 2009.

Energy Savings Resulting from Installation of an Extensive Vegetated Roof System on a Campus Building in the… http://dx.doi.org/10.5772/55997 43

**Figure 20.** Cost of electricity for operation of Hulsey Center, 2005 – 2009.

**Natural Gas Cost for Hulsey Center, 2005 - 2009**

0 2 4 6 8 10 12 **Month**

**Water and Wastewater Costs for Hulsey Center, 2006 - 2009**

0 2 4 6 8 10 12 14 **Month**

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

**Figure 19.** Cost of water/wastewater for operation of Hulsey Center, 2006 – 2009.

**Cost, (\$)**

**Figure 18.** Cost of natural gas for operation of Hulsey Center, 2005 – 2009.

**Cost, (\$)**

42 New Developments in Renewable Energy

**Figure 21.** Natural gas usage for operation of Hulsey Center, 2005 – 2009.

**6. Summary and conclusions**

C (2-3o

typically ~1.1-1.7o

behaved in a similar fashion.

vegetated roof system).

fit. The vegetated roof is ~1388.0 m <sup>2</sup> (14,940 ft <sup>2</sup>

The behavior of different roofing materials affects the heating loads placed upon the buildings and their heating, ventilation, and air conditioning (HVAC) systems. Black roofs resulted in the highest temperature readings. Black roofing materials and bituthane (river rock) perform the poorest of the roofing materials tested, resulting in the highest heating load being placed on the building infrastructure. White granular roofing behaved similar‐ ly to black granular roofing materials. Clean white roofs resulted in consistently lower temperatures inside the mini-roof than the other roofing materials; however, over time, the reflective (white) roofs become dirty, losing some of their reflectivity, resulting in the roof being less energy efficient. Green (vegetated) roofs are fairly efficient in terms of energy performance due to evapotranspiration effects. Green roofs resulted in temperatures

Energy Savings Resulting from Installation of an Extensive Vegetated Roof System on a Campus Building in the…

drainage of rainfall during a rain storm through the retention of water onto the soil, and thereby lessen the discharge into stormdrains. Green roofs can significantly reduce stormwater runoff, reduce peak flow quantities, and lengthen the time of concentration from roofing structure [23]. "White" and "green" roofs both significantly reduce the roofs surface temperature and therefore, the air temperatures above and around the roof.

Hypothesis testing indicated that, between the 3 vegetative mini-roofs, all the min-roofs are statistically equal to each other in thermal properties. Both SBS Firestone mini-roofs are statistically the same, but mini-roof 6 is usually hotter. The TPO/PVC/Elvaloy mini-roofs are

The temperature varies in a sinusoidal fashion both during the course of the day and on an annual basis. For the various mini-roof structures, the phase angle (ϕ) and the amplitude (*A*) of the general form were determined through a regression analysis. The developed sine-wave functions indicated that most roofs were statistically different from one another from an amplitude aspect but the phase angles were statistically the same. It was also observed that almost all roofs had significantly different average mean roof temperatures, but the signifi‐ cance was mostly prevalent in the summer months. During other times of the year, the roofs

Based on the information collected on these mini-roof systems, the UAB Facilities Manage‐ ment Department installed a vegetated roof on top of Hulsey Center as a roofing retro‐

sedum plants. Utility bill information both prior to and after implementation of the green roof were gathered for electricity, natural gas, and chilled water were collected. The costs of utilities prior to and after implementation of the pilot green roof indicated utility bill (energy) savings of ~20% to 25% (compared to the case prior to implementation of the

) in area, and contains approximately 20,000

statistically the same. The 60-mil EPDM mini-roofs are also statistically the same.

F) higher than the white roofs; however, they will dampen the

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**Figure 22.** Water/wastewater usage for operation of Hulsey Center, 2006 – 2009.

**Figure 23.** Electricity usage for operation of Hulsey Center, 2005 – 2009.
