Construction Time of Three Wall Types Made of Locally Sourced Materials: A Comparative Study

Similarly to any other industry, the construction sector puts emphasis on innovativeness, unconventional thinking, and alternative ideas. At present, when sustainable development, ecology, and awareness of people’s impact on the environment grow in importance, low impact buildings can become an innovative alternative construction technology for the highly industrialized construction sector. ,e paper presents a comparative study of three walls made of available materials used locally, which can be classified as biosourced materials, in terms of construction time. ,e comparison of times necessary to make 1m of the wall allows us to decide which building technology is more advantageous in terms of the construction duration. A shorter construction time means lower labour costs and lower expenses for construction machines. In order to obtain answers to the questions posed, the authors made extensive searches of source data on the time-consuming building works which used locally sourced materials. Reference is made to “Temporary principles of erecting clay buildings” issued by the Institute of Housing Construction inWarsaw (Poland). ,ree types of walls made of locally sourced materials were studied: a wall made of clay blocks insulated with mineral wool boards, a wall made of clay compacted in formwork, and one insulated with mineral wool boards and wooden frame structure filled with straw bales and cladded with fibreboards. ,e layers have been chosen in such a manner that heat transfer coefficient values for the studied variants are as equal as possible (0.2W/mK), thus allowing a reliable comparative study.


Introduction
Modern material and technological solutions-concrete, steel, glass, and intelligent systems-have become the synonyms of modernity and luxury [1].Buildings made of locally sourced materials are on the other extreme of modern construction.ese solutions are based primarily on tradition and local, low-cost raw materials that do not require special treatment, which are readily available, such as soil, clay, straw, and sand.Human hands are the main building force, while the use of complicated techniques or expensive expertise is limited.Low impact buildings avoid complex technical solutions and support generally accessible raw materials.e construction market, dominated by giant construction companies, does not support the development of such solutions since they are not profitable.is makes it difficult to popularize such a building method on a large scale.Despite this, buildings made of locally sourced materials are becoming more common and perfectly fit into the idea of sustainable development.
e most important features of a building characterized by sustainable development can be described using four Rs: reduce, reuse, recycle, and recover [2].Less material and energy are used to build such a building compared to conventional construction e materials used should be recycled and should allow for reuse after the end of the life of the building.Low impact buildings derive the materials from the surrounding environment.is supports local development and cultural independence of the region.Production of materials does not require high energy and high temperature processed and does not produce CO 2 , so it consumes less energy needed to construct the building than conventional building construction.Transport of materials is only done locally [3].And the structure itself is completely biodegradable, and after the end of its life, it does not leave harmful waste, hard to break down by the environment.Building made of locally sourced materials allows for carrying out a lot of the work on one's own.It is available to all and creates local jobs [4].
Research in the eld of natural building technologies is not numerous.Among them in paper [5] a comparison of the mechanical performance of structural elements built in three basic techniques, Earth block (adobe) masonry, rammed Earth, and cob, is presented.Up to present, few studies are available concerning the mechanical behaviour of straw bales in buildings.Such study is presented in [6] and aims at investigating the behaviour of straw bales and leads to recommendations for required bale densities.In [7], the viability of straw-bale construction has recently been investigated, in particular, its resistance to moisture.Similarly in [8], two options for the use of straw to ll envelop walls were investigated in the Andean Patagonian region: the direct use of straw bales, whether in whole or in halves, and the manufacturing of straw-clay blocks.All straw options analysed result in signi cantly better thermal performance than current choices of red bricks or concrete blocks, which are commonly used in the region.In turn, in [9] was evaluated a straw-bale house located in Bavaria, Germany.e experimental work included compression tests, moisture content, thermal stability of bales, and pH.Reference [10] examines the use and accuracy of a moisture probe used in the walls of a straw-bale building.e measurements from a number of moisture probes placed in the walls of a case study strawbale building over a 2-year period are presented.Similarly [11] concludes results from a study on moisture monitoring in straw-bale construction and includes the development of an empirical equation which relates the straw moisture content to surrounding microclimate relative humidity and temperature.Reference [12] presents results from a study on the thermal conductivity of some plaster materials that could be used for straw-bale buildings.Walls constructed in the straw-bale technology can boast excellent health qualities, which are di cult to obtain in traditional technologies [13].
Up until today, few studies are available concerning the time of construction of walls made of locally sourced materials.In this paper, the construction time of 1 m 2 of three types of walls built in these technologies was studied.
e layers of the walls were chosen in such a manner that the heat transfer coe cient values for the studied variants are as equal as possible (0.2 W/m 2 K), thus allowing a reliable comparative study: (i) A wall made of clay blocks insulated with mineral wool boards (ii) A wall made of clay compacted in formwork, insulated with mineral wool boards (iii) A wooden frame structure lled with straw bales and cladded with breboards Construction time allows us to tell which technology is more advantageous.In order to obtain answers to the questions posed, the authors made extensive searches of source data concerning the timing of building works using locally sourced materials.Literature does not actually present any time standards.e exception is "Temporary principles of erecting clay buildings" issued by the Institute of Housing Construction in Warsaw (Poland), which were used in the comparison.

Wall Made of Clay Blocks Insulated with Mineral Wool
Boards.e rst studied structure was a wall made of 10 × 25 × 38 cm clay blocks insulated with mineral wool boards.
e structural layer of the wall is 38 cm thick (Figure 1).On the outside, the wall will be insulated with 16 cm thick mineral wool boards and covered with lime plaster.On the inside, the wall will be covered with a two-layer clay plaster.Woodbreboards have also been considered as insulation as more environmentally friendly, but this solution is presently too expensive to be compared with a ordable EPS (expanded polystyrene).

Wall Made of Clay Compacted in Formwork, Insulated with Mineral Wool Boards.
e other studied solution was the wall made of clay compacted in the formwork whose structural thickness was 30 cm (Figure 2).e formwork was demountable panels.
e remaining wall layers were the same as in the clay block wall.

Wooden Frame Structure Filled with Straw Bales and Cladded with Fibreboards.
e third variant was the wall made of small 31 × 41 ×70 cm straw bales placed in wooden frame structure (Figure 3).e frame structure will be erected in the timber-frame house technology where posts are made as frames, so-called ladders.e wooden frame skeleton will be cladded on both sides with 12-millimetre breboards for      Advances in Materials Science and Engineering good adhesion and improved thermal insulation.e wall will have a lime plaster on the outside and two-layer clay plaster on the inside.

Thermal Conductivity λ and Heat Transfer Coefficient U
ermal conductivity λ (W/m K) is a measure of how well a material insulates the flow of heat.Porous, low-density materials have low thermal conductivity and hence are better insulators in comparison with denser materials.
While it is quite easy to obtain information on physical properties of typical construction materials, obtaining such information on locally sourced materials may prove a challenge.
e thermal conductivity of a straw bale and any other material depends on its compaction and moisture content.
e values for straw bales in Table 1 are based on the studies conducted in November 2015 by the Building Research Institute in Warsaw (Poland) [15].e study comprised evaluation of a 600 × 600 × 200 mm straw bale, with density of about 100 kg/m 3 .
e thermal conductivity of compacted clay, clay blocks, and clay plaster depends on the clay composition and used admixtures.Table 1 gives values for highly compacted (compacted clay and clay blocks) and medium-compacted clay (clay plaster).
e heat transfer coefficient "U" is a measure of how well a building enclosure transfers heat.e "U value" is expressed in W/(m 2 K) and denotes how many watts of thermal energy pass through 1 m 2 of enclosure when the temperature difference between the inside and the outside is equal to 1 K.
e lower the heat transfer coefficient is, the better the insulation properties a particular enclosure has.
e heat transfer coefficient is expressed by [3] U where R T is the total thermal resistance of a building partition, and total thermal resistance R T for homogeneous partitions is described by the formula: where R si is the heat transfer resistance on the inner surface, is the design thermal resistance of each layer, and R se is the heat transfer resistance on the outer surface.ermal resistance of a homogeneous layer with thickness d is obtained from the following equation: where d is the thickness of the material and λ is the design thermal conductivity of the material.Tables 2-4 present the calculations of a heat transfer coefficient for the studied walls.e layers have been chosen in such a manner that the "U" values for the studied variants are as equal as possible, thus allowing a reliable comparative study.

Seasonality of Construction Works and Dependence on Weather Conditions
In temperate climate, the construction works and their effectiveness depend on the season and weather.Clay and straw are particularly sensitive to weather conditions and must be protected from water and subfreezing temperatures.After being put into the structure, the straw will be protected by the plaster, and clay must be protected from water at all times.e construction works with locally sourced materials must be performed during a warm and relatively dry period, generally from late spring to early autumn.e works with conventional materials can be performed all year long if suitable precautions are taken, with exception of really low subfreezing temperatures.e exceptions among the locally sourced materials are dried clay blocks which also can be installed all year long if suitable precautions are taken.
In that area, conventional materials have a clear advantage over the alternative materials, although conventional materials must be protected from a long-term exposure to water and subfreezing temperatures.Such protection is however much simpler that in case of locally sourced materials.
Straw must not be wet when installed as it takes a long time to dry.Styrofoam, on the other hand, does not absorb water and is easy and quick to dry.Clay must be protected from precipitation at all times during the construction works by special roo ng and by eaves when the building is in use.Dependence of studied technologies on seasons and weather conditions is given in Table 5.

Clay Block Wall.
e study of time required to perform works in case of clay block walls refers to the "Temporary Principles of Erecting Clay Buildings" by the Institute of Housing Construction [16].e standard times are expressed in m-h/m 3 -man-hours per cubic metre of the clay block wall.
Standard times for making the clay blocks (Table 6) include maintenance of the storage yard for nished blocks, maintenance of machinery, tools, and xtures, and squaring of the blocks and putting them in trestles.
ey do not, however, include storage yard levelling, construction of protective roo ng, and excavation of drainage ditches.
Clay block walls are erected in the same manner as brick walls (Tables 7 and 8).e standard times include erecting walls using clay mortar, transport of blocks and mortar for a distance up to 20 m, and additional mortar mixing.e clay block walls are measured in m 3 , and the openings in excess of 1 m 2 are subtracted from the wall volume.
Clay mortar should have the same composition as clay blocks (Table 9).e standard time for making clay mortar includes handling auxiliary materials at the distance of 10 m, mixing mortar with water, and operation and maintenance of machinery.e standard time does not include making a box for the mortar preparation and placement and relocation of machines used to make the mortar.e penultimate column of the Table 5 includes the time for making the mortar needed to erect 1 m 3 of the nal clay block wall.e last column includes the time for preparing the mortar needed to make 1 m 2 of 1 cm thick plaster.
e clay plastering standard times include additional works: substrate wetting using a hose, surface scratching with a rake, application of plaster strips and skim coat and trowelling, and others (preparation and substrate cleaning) (Table 10).e clay plaster is made in layers, each 1 cm thick.
e time of making 1 m 2 thermal insulation using mineral wool boards has been taken from the Contractors Estimator KNR 33/2/4.e standard time for application of outside paster has been taken from the Contractors Estimator KNR 202/906/2.e time to make 1 m 2 of the clay block wall (Table 11 and Figure 4) has been averaged due to various units of measure for intermediate operations (e.g., prefab lintels are expressed in m-h/m).

Compacted Clay Walls.
e study of time required to make compacted clay walls also refers to the "Temporary Principles of Erecting Clay Buildings" by the Institute of Housing Construction [16].
e standard times are expressed in m-h/m 3 -man-hours per cubic metre of the compacted clay wall.
Time to prepare the clay (Table 12) for compaction includes its mixing with cracking prevention admixtures and pouring into moulds after mixing.It does not include cutting of fibrous materials and protecting the materials from precipitation.
e amount of prepared clay compound is measured in cubic metres. 1 m 3 of the compacted wall is an equivalent of about 1.55 m 3 of loose mixture.
Standard times for making compacted clay walls (Table 13) include transport of the mixture to the hoist at the distance of maximum 20 m, transport on the scaffolding at the distance of maximum 20 m, pouring into formwork, levelling of the poured layer, compaction, placement of window and door templates, and making of lime battens or placement of ceramic inserts.
e standard times, however, do not include protecting the walls from weather conditions, making the insulation, handling of window and door templates, and making of the levelling layer as a cover for lintels (Table 14).
e unit of measure for walls in excess of 24 cm in thickness is m 3 , and up to 24 cm in thickness is m 2 .Openings larger than 1 m 2 should be subtracted from the wall volume.
e times of making the clay (Table 15 and Figure 5) mortar for inside plasters, mineral wall insulation, and outside plasters are identical as in case of the clay block wall.
e time to make 1 m 2 of the compacted clay wall has been averaged due to various units of measure for intermediate operations (e.g., prefab lintels are expressed in m-h/m).

Straw-Bale Walls.
e standard times for erecting walls in the straw-bale technology (Table 16 and Figure 6) have    e time to make 1 m 2 of the compacted clay wall has been averaged due to various units of measure for intermediate operations.

Conclusions
e comparison of times necessary to make 1 m 2 of the wall allows us to decide which construction technology is more advantageous in terms of construction duration.e small surfaces in the wall or surfaces with numerous windows and doors, as well as the drying time between Earth wall making and rendering operation, are calculated by additional time; therefore, they were not taken into account in this paper.e shorter construction time means lower labour costs and lesser expenses for construction machines.
In the case of investors, the construction time is an important measure of project success, as the shorter payback periods mean a quicker opportunity to reinvest or reuse nancial resources.e construction time is equally important for people building a home for themselves.It is a huge advantage for them to be able to perform the works in a favourable weather and to move in and use the house earlier.
e studies and Figure 7 allow us to draw the following conclusions: (i) Compacted clay walls have the shortest wall erection time from among the studied natural building technologies.(ii) Time to make 1 m 2 of the clay block wall is signicantly longer as a result of a very time-consuming clay block preparation process.In the paper, it was assumed that blocks are made in-house, using mainly materials available free at the construction site.(iii) e straw-bale technology had the worst results in the comparison.e factor which determines the long time needed to make 1 m 2 of the straw-bale wall is the necessity to erect the wooden framework structure.(iv) Two-layer clay plaster can be an alternative to other contemporary inside wall nishing solutions.

Figure 4 :
Figure 4: e percentage of the share of individual operations in making of 1 m 2 of the clay block wall.

2 )Figure 7 :Figure 6 :
Figure 7: Time to make 1 m 2 of the wall in individual technologies.

Figure 5 :
Figure 5: e percentage of the share of individual operations in making of 1 m 2 of the compacted clay wall.

Table 1 :
Figure 3: Cross section of the wall made in the straw-bale technology.Density and thermal conductivity of used materials.

Table 2 :
ermal properties of a clay block wall.

Table 3 :
ermal properties of a compacted clay wall.
Source: own study.

Table 4 :
ermal properties of a straw-bale wall.
Source: own study.

Table 5 :
Dependence of studied technologies on seasons and weather conditions.
Source: own study.

Table 7 :
Time necessary to build the clay block wall (wall thickness 38 cm).
Source: own study.

Table 9 :
Time to make clay mortar for masonry works and plastering.

Table 10 :
Time necessary to make inside clay plasters (1 layer).
Source: own study.

Table 11 :
Time necessary to make 1 m 2 of the clay block wall.

Table 12 :
Time necessary to prepare the clay for compaction.

Table 15 :
Time needed to build 1 m 2 of the compacted clay wall.
Source: own study.

Table 13 :
Time necessary to make compacted clay walls.

Table 16 :
Time needed to build 1 m 2 of the straw-bale clay wall.
Source: own study.