15th International Brick and Block

Masonry Conference

Florianópolis – Brazil – 2012

THEORETICAL ANALYSIS OF THERMAL PERFORMANCE OF

CLAY AND CONCRETE MASONRY STRUCTURAL UNDER VARIOUS

CONDITIONS

Grabarz, Regina Candeloro1; Souza, Léa Cristina Lucas

2; Parsekian, Guilherme Aris

3

1 MSc Candidate, Federal University of São Carlos, Civil Construction Graduated Program,

regina.cg@hotmail.com

2 PhD, Professor, Federal University of São Carlos, Civil Engineering Department, leacrist@ufscar.br

3 PhD, Professor, Federal University of São Carlos, Civil Engineering Department, parsekian@ufscar.br

Currently, masonry construction system has been widely used in Brazilian housing

construction as it offers significant advantages in relation to building execution time

consumption and costs. Considering the wide use of this system, it is important to assess

whether the commonly wall thickness, material and rendering meets the levels of minimum

thermal comfort required by the Brazilian performance codes. Analyzing the thermal

performance of concrete and clay structural masonry walls, the thermal properties of these

systems were calculated and its adequacy for different bioclimatic zones in Brazil has been

verified. The results indicate that the structural clay masonry has better performance than the

concrete masonry when compared to uncoated internal and external walls. As a conclusion, it

is pointed out the regions in which clay and concrete masonry walls built in accordance to the

common construction standards are thermically adequated.

Keywords: Low-Income Housing, Structural Masonry, Thermal Performance

INTRODUCTION

Among serious social problems faced by Brazilians, accessibility to housing is placed in

focus. The Brazilian housing deficit in 2007 was 6.273 million households (BRASIL, 2009).

Achieving a high demand for Social Housing - SH is not an impossible challenge. The

adoption of industrialized building systems is a response to the promotion of this type of

building. Mainly because the actual demand requires optimization of time and costs of

execution. On this point, the structural masonry construction system becomes a very

advantageous solution. It can be applied to projects of SH, because it reduces the total project

costs and it is easy to implement. It is conceived through rational calculation, having as its

main characteristic, the multi-functional masonry, functioning both as a seal and as a building

structure. In order to attend the current needs, in July 2001 the Associação Brasileira de

Cimento Portland (ABCP) launched a project called CASA 1.0. The main objective of this

was to assist in reducing the housing deficit in Brazil.CASA 1.0 was developed with focus on

the evolution of processes towards industrialization, seeking the optimization of project.. This

optimization is based on several premisses, among which we highlight here the environmental

projects aimed at user comfort, well ventilated and lit (ABCP, 2002).

15th International Brick and Block

Masonry Conference

Florianópolis – Brazil – 2012

Despite the need for user comfort, many builders, architects and engineers indiscriminately

adopt the building system with structural masonry, without any regard to the thermal

performance of the building envelope.

Studies conducted by various Brazilian researchers show that the achievement of users'

thermal comfort in low-income housing is rare. The main reason of this is the adoption of

projects without consideration to the climate region where they are constructed.

Based on the above, this article seeks to theoretically study the adequacy of the application of

clay building block and concrete - the most applied in Brazil - and their structural masonry for

different climatic regions in Brazil. In order to do so, we take into account the bioclimatic

zones of Brazil established by NBR 15220-3:2005 and the minimum performance conditions

determined by it.

The theoretical approach initially establishes the key concepts involved in the thermal

performance of residential buildings, then presents the methodological steps and finally points

out the results, analysis, discussions and conclusions.

FUNDAMENTS, CHARACTERISTICS, DEFINITIONS AND DELIMITATIONS

The thermal performance of residential buildings depends on climatic conditions of the site

and on construction features they present. While the climate and weather conditions are

responsible for the amount of thermal energy available in the environment, the design

characteristics influence the passage of heat through the building envelope (façades and

roofs). The properties of building materials determine their behavior on admission, transfer,

storage and heat emission. The main characteristics involved in this process are defined by the

NBR 15220-1:2005, some of which are highlighted in Table 1.

Table 1: Relevant Characteristics to the thermal performance of buildings (NBR 15220-

1:2005) Characteristics Definition Symbol Unit

Thermal Conductivity

Physical property of a homogeneous and isotropic material, in which there is a constant

heat flow, with a density of 1 W/m2, when

subjected to a uniform temperature gradient of

one Kelvin per meter.

W/(m.K)

Apparent mass density Ratio of mass to apparent volume of a body. kg/m³

Specific Heat or

Specific Heat Capacity Ratio of heat capacity by mass. c J/(kg.K)

Transmitance W/(m².K) Level of heat transfer corresponding to the

layers of an element or component. U W/(m².K)

Thermal lag (hours/s)

Elapsed time between a thermal variation in a

medium and its manifestation on the surface

opposite to a constructive component

subjected to a periodic regime of heat transfer.

h

Solar heat gain

coefficient of opaque

elements

Ratio of the rate of solar radiation transmitted

through an opaque component on the rate of

total solar radiation incident on the outer

surface of the same.

FSo -

15th International Brick and Block

Masonry Conference

Florianópolis – Brazil – 2012

The NBR 15220-3:2005 provides recommendations and guidelines for climate adaptation of

social interest houses. With regard to the masonry, the standard classifies three types of walls

(external seal): light, reflecting light and heavy. To each of these classes is assigned a

minimum value required for the walls (Table 2), whose parameters are given through the

thermal transmittance, thermal lag and the solar heat gain coefficient. In order to calculate the

transmittance and the thermal lag, one should consider if the wall is composed of

homogeneous layers (containing thermal resistances in series) or non-homogeneous and

homogeneous layers (with thermal resistances in parallel).

Table 2: Parameters of thermal transmittance, thermal lag and solar heat gain

coefficient for eligible walls (NBR 15220-3:2005)

External Building Envelope

Thermal

transmittance - U

W/m².K

Thermal lag - Hours

Solar Factor- FSo

Walls

Light U ≤ 3,0 ≤ 4,3 FSo ≤ 5,0

Light reflective U ≤ 3,6 ≤ 4,3 FSo ≤ 4,0

Heavy U ≤ 2,2 ≥ 6,5 FSo ≤ 3,5

For each of the 8 (eight) bioclimatic zones (Figure 1) established by the NBR 15220-3:2005,

it is recommended a type of building envelope, as is summarized in Table 3.

Figure 1: Brazilian bioclimatic zones (NBR 15220-3:2005)

Table 3: Recommending building envelope wall for each of the eight Brazilian

bioclimatic zones (NBR 15220-3:2005) Recommendation wall for each of the eight bioclimatic Brazilian zones

WALLS ZONES

Light 01 – 02

Light and Reflector 03 – 05 – 08

Heavy 04 – 06 – 07

15th International Brick and Block

Masonry Conference

Florianópolis – Brazil – 2012

METHODOLOGY

The methodology was divided in two stages: consisted on a planning phase and then the

processing and analysis. The planning stage allowed to raise the dimensional characteristics of

the masonry units, define the case study layout in structural masonry, choose the software to

be used and the sources of information. The stage of processing and analysis allowed the

establishment of the performance of masonry units studied for the selected project and

verification of the adequacy of the building system to the Brazilian bioclimatic zones.

An overview of the work steps is shown in Figure 2.

Figure 2: General steps of the methodology

CHARACTERISTICS OF MASONRY UNITS STUDIED AND DATA SOURCES

Two types of units were studied: clay and concrete hollow blocks. The units studied were

selected depending on the availability of the product in the Brazilian market, the degree of

implementation and the cost. The criterion for choosing the size of the masonry unit was

taken from the publication of the file available electronically by the ABCP, (2001) entitled

CASA 1.0. This project layout was developed specific for the use of concret structural

masonry. Among the available dimensions in the market, the 14 cm x 19 cm x 39 cm (width x

height x length) block was selected.

For a more comprehensive study, apart from the concrete block, suggested by the ABCP, the

clay block of the same dimension was also investigated. Currently, both are the most widely

used structural masonry units in Brazil and are shown in Figure 3.

15th International Brick and Block

Masonry Conference

Florianópolis – Brazil – 2012

(a) (b)

Figure 3: Illustration of structural masonry units, (a) concrete and (b) clay

The source of information used as a database to calculate the characteristics of the masonry

units was the Manual Técnico de Alvenaria, (CHICHIERCHIO, 1990) which provides data of

specific density (ρ) and thermal conductivity coefficient (λ). For information on specific heat

(c), the reference was NBR 15220-2:2005, Table B.3. Thus, the characteristics of each

masonry unit type studied here are presented in Table 4 and Table 5.

Table 4: Characteristics of concrete blocks, specific density (ρ), thermal conductivity

coefficient (λ) and specific heat (c) BLOCK A BLOCK B BLOCK C

Specific density (kg/m³) 2.300 2.100 2.200

Thermal conductivity

coefficient (W/mºC) 1.81 1.80 1.70

Specific heat (kJ/kg.K) 1.00 1.00 1.00

Table 5: Characteristics of clay blocks: specific density (ρ), thermal conductivity

coefficient (λ) and specific heat (c) BLOCK A BLOCK B BLOCK C

Specific density (kg/m³) 1.800 1.800 1.800

Thermal conductivity

coefficient (W/mºC) 1.00 1.00 1.00

Specific heat (kJ/kg.K) 0.92 0.92 0.92

MASONRY STRUCTURAL CHARACTERISTICS AND DATA SOURCES

The ABCP model CASA 1.0 is a model of Social Housing applied throughout Brazil. This

study considered the elements described in CASA 1.0 report as the reference for calculations

of the masonry around the unit (block). The report describes that external walls have acrylic

paint applied directly on the blocks, and the inner walls (dry areas) are covered with

industrialized plaster mortar, 0.5-cm thick.

A brief survey of colors indicated that yellow (or variations of this color) is one of the most

common color applied in external walls of Brazilian social houses and also that few houses

are painted white. Therefore, this was considered in calculating the solar heat gain coefficient.

SOFTWARE USED IN CALCULATION OF THERMAL PROPERTIES

Transmitância 1.0, developed by the Laboratório de Eficiência Energética em Edificações –

LabEEE, Universidade Federal de Santa Catarina – UFSC, were the software used to apply

the method for calculating the thermal performance of ISO 15220. The input data of this

software are: heat flux, external surface, data of section (height x length x thickness), thermal

conductivity coefficient (λ), specific density (ρ) and specific heat (c). The outputs of the

15th International Brick and Block

Masonry Conference

Florianópolis – Brazil – 2012

software are: thermal transmittance (W/m².K); thermal resistance (m².K/W); heat capacity

(kJ/m².K); solar heat gain coefficient and thermal lag (hours).

Thus, the input data of the program are related to the element or component data and sections

and layers data. The elements or components data area related to flow direction, external and

internal superficial resistance, characteristics of external surface, absortance and emissivity.

The section data referring to the layers finishing are the height and length, while the data

corresponding to the layer itself are the thermal conductivity, the density, the specific heat and

the thickness.

The flows were considered horizontal, as they were walls, and the sections used for

calculation are described in Table 6 and Figure 4.

Table 6: Sections used for calculation of thermal properties Concrete block 14 cm x 19 cm x 39 cm

(width x height x length) Clay block

Mortar 1 cm in thickness between blocks

Plaster 0.5 cm thick (inner wall)

(a) (b)

Figure 4: (a) single element and (b) wall element

According to the standards, the thermal resistance of external surfaces is 0,04 (m2.K)/W,

while the resistance of internal surfaces is 0.13 (m2.K)/W, The absortances and emissivities

were made available by the software. Their values are 0.30 for yellow paint absortance and

0.90 for yellow paint emissivity. For the concrete blocks and clay blocks these values were in

both cases 0.65 e 0.85.

SUITABILITY FOR BIOCLIMATIC REGIONS

In order to analyze the performance of structural clay masonry and concrete, the

recommendations described in NBR 15220-3:2005 were adopted. The suitability of them for

each of the eight bioclimatic Brazilian zones was verified.

The calculated values were compared with the parameters of Tables 2 and 3. Then it was

possible to point out the climate regions where the building systems studied have adequate

thermal performance.

15th International Brick and Block

Masonry Conference

Florianópolis – Brazil – 2012

RESULTS AND ANALYSIS

The results obtained for the concrete blocks and clay are shown in Table 7 and Table 8. For

consideration of the possible variations according to different manufacturers, the mean values

were also calculated and compared with each other and are presented in Table 9.

Table 7: Characteristics of concrete blocks: Transmittance W/(m².K), Thermal lag

(hour/s) and Solar Factor BLOCK A BLOCK B BLOCK C AVERAGE

Transmittance W/(m².K) 4.04 4.04 3.96 4.01

Thermal lag (hour/s) 3.1 3.0 3.2 3.10

Solar Factor 10.5 10.5 10.3 10.4

Table 8: Characteristics of clay blocks: Transmittance W/(m².K), Thermal lag (hour/s)

and Solar Factor BLOCK A BLOCK B BLOCK C AVERAGE

Transmittance W/(m².K) 3.23 3.23 3.23 3.23

Thermal lag (hour/s) 3.6 3.6 3.6 3.60

Solar Factor 8.4 8.4 8.4 8.40

Table 9: Thermal characteristics of concrete blocks and clay: Transmittance W/(m².K),

Thermal lag (hour/s) and Solar Factor CONCRETE CLAY

Transmittance W/(m².K) 4.01 3.23

Thermal lag (hour/s) 3.10 3.60

Solar Factor 10.4 8.40

ANALYSIS OF THE RESULTS OF THERMAL PROPERTIES

Regarding the thermal analysis of the masonry unit, the survey found that the clay block has

better thermal performance than concrete blocks. While clay blocks have a thermal

transmittance of 3.23 W / (m². K), the concrete blocks have to 4.01 W/(m².K). The clay

thermal lag is 3.6 (hour/s), whilst the concrete one is 3.10 (hour/s). Solar heat gain coefficient

for clay block is 8.40 and for concrete block is 10.4.

With the data obtained it is possible to compare the thermal performance of both masonry as

shown in Table 10. The structural clay masonry under the same conditions of structural

concrete masonry, presented the best thermal performance among the systems, because it

transmits 0.71 W/(m².K) less than the other, it has a thermal lag with a gain of 0.3 hours/s and

solar heat gain coefficient of 0.9 less than concrete.

Table 10: Thermal performance of the blocks, masonry and their difference:

Transmittance W/(m².K), Thermal lag (hour/s) and Solar Heat Gain Factor CONCRETE CLAY

Block Masonry Relative

Difference Block Masonry

Relative

Difference

Transmittance

W/(m².K) 4.01 3.91 2.5% 3.23 3.2 0.93%

Thermal lag

(hour/s) 3.1 3.3 6.5% 3.6 3.6 -

Solar Factor 10.4 4.7 54.8% 8.4 3.8 54.8%

15th International Brick and Block

Masonry Conference

Florianópolis – Brazil – 2012

By adding elements of painting, plaster and mortar, there was a significant difference in the

thermal performance of the construction elements (blocks) and components (masonry),

especially with regard to the Solar Factor, which dropped 54.8% masonry to block, in both

cases.

The clay block is more stable to the new elements that made up the masonry than concrete

block.

CLIMATE ANALYSIS OF SUITABILITY IN BRAZIL

Initially, considering the bioclimatic zones for which the light walls are recommended by

NBR 15220-3:2005, Table 11 highlights the values of some parameters disposing of the study

zones 01 and 02 compared with the concrete and clay masonry, according to the memorial of

the ABCP CASA 1.0 (outside wall with yellow paint on the masonry and the inside wall with

0.5 cm of plaster), which were highlighted (bold and underlined) values according. It can be

seen that both walls have an adequate response as to the thermal lag and solar factor, but with

regard to the thermal transmittance, none of them reached the recommended amount, so none

of the masonry should be assigned to these regions.

Table 11: Study of Bioclimatic Zones 01 and 02

WALLS Transmittance - U

W/ (m².K) Thermal lag - (hour/s) Solar Factor - FSo

Light U 3.00 4.3 FSo 5.0

Structural CONCRETE

masonry 3.91 3.3 4.7

Structural CLAY

masonry 3.20 3.6 3.8

For light reflective walls, Table 12 allows the study of bioclimatic zones 03, 05 and 08 (on the

same conditions as the previous study). Leading the recommended values for the building

envelope, light and reflective wall, it is clear that the structural concrete masonry has adapted

itself only in relation to the thermal lag. Thus it fits the minimum recommended by the

standard.The structural clay masonry falls in all the values recommended by the standard and

may be indicated for zones 03, 05 and 08 as light and reflective wall type. It is noteworthy

that this statement meets the requirements of the study - building block of 14 cm x 19 cm x 39

cm (width x height x length), outer paint directly onto the surface of the masonry and plaster

cover of 0.5 cm.

Table 12: Study of Bioclimatic Zones 03, 05 and 08

WALLS Transmittance - U

W/ (m².K) Thermal lag - (hour/s) Solar Factor - FSo

Light and Reflector U 3.60 4.3 FSo 4.0

Structural CONCRETE

masonry 3.91 3.3 4.7

Structural CLAY

masonry 3.20 3.6 3.8

15th International Brick and Block

Masonry Conference

Florianópolis – Brazil – 2012

For the bioclimatic zones 04, 06 and 07 (on the same terms as the previous study), the

recommendations correspond to heavy walls. None of the walls studied fulfilled the minimum

established by standards. This statement can be verified on the values shown in Table 13.

Table 13: Study of Bioclimatic Zones 04, 06 and 07

WALLS Transmittance - U

W/ (m².K) Thermal lag - (hour/s) Solar Factor - FSo

Heavy U 2.20 6.5 FSo 3.5

Structural CONCRETE

masonry 3.91 3.3 4.7

Structural CLAY

masonry 3.20 3.6 3.8

DISCUSSION AND CONCLUSIONS

The structural clay block as an isolated element has presented a better thermal performance

than the structural concrete block.

Covering the study within the masonry, it was possible to verify that the addition of elements

such as painting and internal plastering within the standards specified in the survey, structural

clay masonry still stands out with a better thermal performance than concrete structural

masonry.

Analyzing the structural masonry as a function of adaptation to Brazilian bioclimatic zones,

and according to recommendations of NBR 15220-3:2005, it was established that both,

concrete and clay, are not suitable for two types of building envelopes, light and especially the

heavy. Therefore they are not suitable for zones 01, 02, 04, 06 and 07. With regard to the

zones 03, 05 and 08, only the structural clay masonry fits the minimum values indicated for

building envelopes, because they can be considered light and reflective.

These results indicate the need for specific analysis of the various masonrys units and

structural systems before its indiscriminate application. They cause thermal performance

below the minimum required. Considering that many buildings are already being developed

with these solutions, there is a urgency of taking effective measurements for the achievement

of a better quality of life for users.

REFERENCES

ASSOCIAÇÃO BRASILEIRA DE CIMENTO PORTLAND (ABCP). Manual Técnico para

Implementação – Habitação 1.0 ® Bairro Saudável. População Saudável. São Paulo, 2002.

88 p.

ASSOCIAÇÃO BRASILEIRA DE CIMENTO PORTLAND (ABCP). Casa Modulada em

Blocos de Concreto: Sugestão de Projeto. 2001. Available at:

<http://www.abcp.org.br/conteudo/wp-

content/uploads/2010/01/AE_Planta_Kit_sugestao.pdf>. Accessed: 01 set. 2010.

ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS (ABNT). NBR 15220-1:

Desempenho térmico de edificações Parte 1: Definições, símbolos e unidades. Rio de Janeiro,

2005.

15th International Brick and Block

Masonry Conference

Florianópolis – Brazil – 2012

ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS (ABNT). NBR 15220-2:

Desempenho térmico de edificações Parte 2: Métodos de cálculo da transmitância térmica, da

capacidade térmica, do atraso térmico e do fator solar de elementos e componentes de

edificações. Rio de Janeiro, 2005.

ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS (ABNT). NBR 15220-3:

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construtivas para habitações unifamiliares de interesse social. Rio de Janeiro, 2005.

CHICHIERCHIO, L. C. Conforto Ambiental: Desempenho térmico e acústico e proteção

contra fogo. In: ASSOCIAÇÃO BRASILEIRA DA CONSTRUÇÃO INDUSTRIALIZASA.

Manual técnico de Alvenaria. São Paulo: ABCI/PROJETO, 1990. p 119-141.

Laboratório de Eficiência Energética em Edificações (LabEEE). Universidade Federal de

Santa Catarina (UFSC). Transmitância versão 1.0 (beta). [20--?]. Available at:

<http://www.labeee.ufsc.br/software/transmitancia.html>. Accessed: 24 nov. 2010.

MINISTÉRIO DAS CIDADES, SECRETARIA NACIONAL DE HABITAÇÃO. Déficit

Habitacional no Brasil 2007. Belo Horizonte, 2009. 128 p.