Because of its availability and suitability to hot, arid climates, earth has been used in construction since ancient times, particularly in desert regions. (Alex, 2018; Fernandes et al., 2019). Earthen houses are those that use unfired earth as a primary component. (Marsh and Kulshreshtha, 2021). They have lower environmental impact, low embodied energy, and improve air quality and thermal comfort (Uzoegbo, 2016; Yang and Wang, 2019; Kasinikota and Tripura, 2021). They require less energy to extract, manufacture, and transport materials, have high load-bearing capacity (UN-Habitat, 2009; Burroughs, 2010; UN-Habitat, 2012; Kulshreshtha et al., 2020), and are fire and insect resistant (Egenti and Khatib, 2016; Yang and Wang, 2019). Despite the advantages of earthen masonry constructions, they were abandoned due to their link with poverty, reduced durability, reduced shear and tensile strengths, and consequent shift to reinforced concrete buildings with fired and cement bricks. In recent decades however, earth techniques have regained popularity due to concerns about the environment and affordability (Burroughs, 2010; Fernandes et al., 2019; Di Gregorio et al., 2020; Kulshreshtha et al., 2020; Marsh and Kulshreshtha, 2021).

The UN-Habitat (UN-Habitat, 2009; UN-Habitat, 2012) and Marsh and Kulshreshtha (2021) have listed several types of earthen masonry depending on the context:

• Compressed stabilized earth bricks or blocks (CEB or CSEB), often known as an enhanced version of adobe bricks, are created by a machine pressing a mixture of soil and a stabilizer.

In March 2016, Egypt adopted its first code, “Building with stabilized earth—Part One: Building with compressed stabilized earth units,” highlighting CSEB as a potential alternative to adobe and fired brick masonry units (EG-SE2016). Hanafi (2021)’s investigation on the possibilities of employing CSEB in Upper Egypt’s rural areas discovered that CSEB as a modern version of adobe bricks was the most environmentally, economically, and socially appropriate; also confirmed in other contexts (UN-Habitat, 2009; Di Gregorio et al., 2020; Kasinikota and Tripura, 2021).

CSEB are made by manually or hydraulically compressing soil, water, and a stabilizer. The quality of bricks depends greatly on the soil type, compaction force, type and percentage of stabilizer, production and curing procedures, and weather (Wells, 1993). Cement is the most prevalent stabilizer associated with sandy soil CSEB, and the brick is still considered green with up to 10% by weight because cement contributes to its strength and durability (UN-Habitat, 2009; UN-Habitat, 2012; Bogas et al., 2019; Edris et al., 2021; Kasinikota and Tripura, 2021). Although recent researches has experimented with natural materials, as well as agricultural and industrial waste to minimize or replace cement (fly ash, polymers, geopolymer binders, sugarcane fibers) (Omar Sore et al., 2018; Idriss et al., 2022; Tchouateu Kamwa et al., 2022; Nadia et al., 2023), cement was selected in the production of EH bricks. This is because it is the most tested and utilized stabilizer associated with CSEB production, its commercial availability and lower price in Egypt, higher strength results, and most importantly its suitability to sandy soil and mass-production (UN-Habitat, 2009; UN-Habitat, 2012; Bogas et al., 2019; Edris et al., 2021; Kasinikota and Tripura, 2021).

When interlocking (ICSEB or ISSB), CSEB gains additional benefits because this feature reduces the need for conventional mortar thickness and cement quantity (UN-Habitat, 2009, 2012), provides greater in-plane and out-of-plane shear resistance, reduces skilled labor requirement, enables self-construction, and cuts construction time (Al-Jabri et al., 2005; Uzoegbo, 2016; Ma et al., 2019; Di Gregorio et al., 2020; Wang et al., 2021). When left unfinished, ICSEB walls should be coated with water-based resin or acrylic varnish to withstand moisture and boost durability (Di Gregorio et al., 2020). When reinforced, masonry walls in general gain more resistance to lateral forces. CSEB manufactured with holes allows wall reinforcement by installing rebars and filling them with concrete, giving the structure resilience and reduces its cost (UN-Habitat, 2009; UN-Habitat, 2012; Di Gregorio et al., 2020; Saari et al., 2021). Moreover, they become lighter, allow internal electrical conduits (Di Gregorio et al., 2020), and have improved thermal performance (Uzoegbo, 2016).

In the Ecofordable House, compressed stabilized earth brick walls with interlocking and reinforcing characteristics (hollow ICSEB) and finished with water-based acrylic varnish were used because of these benefits and aspects.

Curved roofs under compression, such as vaults, domes, catenaries, and doubly curved roofs (funicular shells), have traditionally been utilized in many buildings, including houses, temples, mausoleums, palaces, churches, and mosques. They were found in the Middle East at a very early date, and were typically made of sun-dried bricks, fired bricks, or stones, depending on the available local materials (Cowan, 1977; Cowan, 1981; Öztürk et al., 2020; Duarte et al., 2021).

According to the UN-HABITAT report on traditional and industrialized building materials, masonry vaults and domes were traditionally common across Egyptian countryside (Sims and Fattah, 2016). Although they have aesthetic, economic, and environmental benefits, they also have certain potential weaknesses such as brittleness, poor tensile strength, and cracking (Bradley et al., 2018). Solutions that might improve their performance include the integration of beams capable of withstanding the lateral force generated by the structure. Hybrid roofs that combine the structural advantage of beams and aesthetic and economic advantages of masonry are found in funicular shell domes and jack-arch vaults (Sivakumar et al., 2015).

“Funicular” means “having the form of or associated with a cord usually under tension” (Merriam-Webster, 2023a). If it is formed like a catenary, the shell is under total tension as a rope, and when turned upside down, it forms a single curve under compression. Funicular shells are doubly-curved (catenary in both axes). These have higher ultimate strength because the dead load is evenly distributed. Funicular shells can cover large areas as a single shell or as waffle slabs. They span square, rectangular, triangular, and non-orthogonal spaces (Cowan, 1977; Jain, 2000; ICAEN, 2004; Kumar and Maheswari, 2019). The largest masonry catenary structure is in the Great Hall of the Palace of Taq Kisra, built around 550A. D. This vault inspired the modern catenary thin concrete shell (Cowan, 1977; Cowan, 1981; Duarte et al., 2021), possibly foreseen by Robert Hooke in 1,675 and influential throughout the 20th century (Cowan, 1981; Jannasch, 2017). A funicular roofing system can be made with concrete shells, bricks, or waste stone/ceramic pieces supported by RC beams. This type provides an improved alternative solution that blends traditional and modern technology, allowing the adoption of natural resources, optimizing the use of steel and cement, adding upper stories, improving aesthetics, and ensuring stability (Keswani, 1997; Jain, 2000; ICAEN, 2004; Kumar and Maheswari, 2019). EH utilized funicular shells made of bricks and waste stone/ceramic, a solution that could significantly contribute to the issue of waste in Egyptian, as well as other countries’, building sector (Daoud et al., 2021). This roof was adopted by several building centers in India (mainly Anangpur Building Center) (Keswani, 1997). A single shell spans 0.8–3.0 m with a rise to span ratio of 1/6, allowing for a second floor (Keswani, 1997; ICAEN, 2004; CSIR and BMTPC, 2021).

A “jack arch” is defined as “a flat arch (as a lintel with a keystone)" (Merriam-Webster, 2023b). The term “Jack” refers to “something that supports or holds in position” as well as “to move or lift” (Merriam-Webster, 2023c). The jack arch roof is a composite roof (Venkatarama Reddy, 2009; Venkatarama Reddy et al., 2014) (also known as a floor) that is an improved version of traditional vaults (ICAEN, 2004). It is made up of brick or concrete vaults that are held up by RC beams or rolling steel joists (I-beams). Single brick arches are placed on edge to make a masonry jack arch using reusable sliding formwork. Beams are typically 1–1.5 m wide and can be prefabricated or cast in place. The rise-to-span ratios of the arches range from 1/8 to 1/12, resulting in a relatively flat roof for intermediate floors. Because the horizontal thrust from the arches cancels each other out, the beams are only intended for vertical loads. However, steel tie rods are transversally installed in the outer bays as arches lack balancing horizontal thrust (Adam and Agib, 2002; BDC 13, 1981; ICAEN, 2004; Khan et al., 2013). Historically, jack arch roofs were made of brick vaults supported by timber joists, which were later replaced by iron as new industrial materials became available. In more recent years, RC beams have been introduced using the same technology (Diodato et al., 2015; Garcia-Castillo et al., 2021). The jack arch originated in Europe, expanded to the Americas, and by the mid-twentieth century was used in East Europe, the Middle East (Maheri et al., 2012; Khan et al., 2013) as seen in Iran (Eslami et al., 2012; Zahrai, 2015; Shabdin et al., 2020), Iraq (Kharrufa, 2007), Turkey (Ozdemir et al., 2017), and Sudan (Mukhtar, 1980; Adam and Agib, 2002), Nepal (Motra et al., 2021), and the Indian subcontinent (Maheri and Rahmani, 2003; Maheri et al., 2012; Khan et al., 2013). It provided span flexibility, upper levels, structural safety, ease of building due to labor and material availability, and good thermal performance (Maheri and Rahmani, 2003; Khan et al., 2013; Leo Samuel et al., 2017). Steel I-beams were one reason the jack arch became socially unpopular and associated with poverty, according to Kharrufa (2007). It caused cracks along the plaster of joists and sometimes at their wall intersections, giving the finish a poor, crackly look. EH incorporated RC joists and lateral beams to address these challenges.

For over 5,000 years, the Date Palm has been planted throughout the Middle East and North Africa (El-Mously, 2018; Midani et al., 2020). Its Latin name “phoenix dactylifera” comes from “phoenix daktulos,” where “phoenix” refers to the color purple or red in Greek and “daktulos” means finger, pointing to the fruit’s color and form (Zaid and de Wet, 2002; Ghnimi et al., 2017). The Middle East and North Africa alone produce 90% of the world’s date, with Egypt topping the list with 18% in 2020 (FAO, 2020b). The date palm has long been an essential element of the region’s economic and social lives (Agoudjila et al., 2011); it may live for more than 100 years, leaving an average of 13 leaves (per palm) as a huge agricultural waste due to the yearly pruning (Midani et al., 2020). Pruning entails eliminating products that have already served their natural purposes and have become unnecessary to the palm, such as midribs and leaflets (El-Sharbasy, 2018; El-Mously, 2020). The midribs have been traditionally used as a wooden alternative in rural areas for making roofs, fences, furnishings, and boxes, whilst leaflets have been used to create utensils as baskets, mats, hats, brooms (Zaid and de Wet, 2002; El-Mously, 2018). However, the introduction of plastic and a shift in Egyptian consumption patterns caused a drop in date palm-related items since the 1950s (El-Mously, 2018). At the same time, Egypt, like most Arab countries, is dry with little tree cover, making its market fully reliant on imported raw wood. In 2020 for instance, 4.3 million m³ of sawnwood and industrial roundwood were imported to meet the local demand (FAO, 2020a).

Since 1991, researchers at Ain Shams University have experimented with DPLM to evaluate it as a wood substitute. Being able to withstand hot desert storms and millions of loading cycles without breaking due to its unique flexible tissue (Agoudjila et al., 2011; El-Mously, 2018; Midani et al., 2020), the midrib has equivalent physical and mechanical qualities to commercial woods such as beech and spruce (El-Mously, 2018, 2020). Several attempts have created blockboard, particleboard, and blocks with DPLM, but their uses were limited to small scale crafts and industries due to expensive machinery and time-intensive processing (El-Mously, 2018; El-Mously, 2020; El-Mously and Darwish, 2020). The EH have unconventionally reintroduced the DPLM craftsmanship in the manufacture of doors, shutters and pergolas to combine durability while reviving the functions and patterns of wooden mashrabiyyas, a latticework found on the windows of historic Cairo that traditionally ensured privacy and improved indoor thermal comfort (Abdel Gelil, 2006).

Direct costs of CSEB construction depend on the availability of suitable soil for brick production, current material prices (especially stabilizer), transportation, equipment, wage rates, labor productivity, and construction techniques (Pacheco-Torgal and Jalali, 2012; Uzoegbo, 2016). In the Indian context, a finished solid CSEB masonry is between 15% and 20% less expensive than fired bricks (Singh et al., 2022). A proposed model for alternative multi-story low-cost housing in India suggests that the price of an apartment with masonry CSEB is 13% lower than with reinforced concrete and fired brick walls (Unni and Anjali, 2022). They explained that this reduction is inconsistent with other research studies that suggested savings of up to 40% and that this was justified by the fact that all components, except the CSEB walls, were similar to conventional housing. Using a digital proposal for an Ugandan house, Nuwagaba (2020) found that, while hollow concrete blocks had less embodied energy than fired bricks, they were 36% more expensive per m² wall, confirming UN-Habitat (2009)’s calculations. CSEB walls were 18% cheaper and had less embodied energy than fired-brick walls (Nuwagaba, 2020). In Sudan, Adam and Agib (2001) revealed that using CSEB blocks in “Al-Haj Yousif experimental prototype school” cut wall costs by 70% when done ‘self-help.’ With Kenaf sand cement corrugated sheets roofing, savings were 40% per m². In Kenya, CSEB walls cost 20%–70% less than concrete block walls, depending on production.

A feasibility study in Sri Lanka by Davis and Maïni (2017) discovered that CSEB technologies are labor-intensive, with labor costing 60% and materials 40%. According to the report, a 14 cm manually pressed CSEB wall costs 2,007 LKR/m², a motorized press CSEB wall costs 1,850 LKR/m², and a 19 cm fired brick wall costs 2,803 LKR/m². As a result, the first is 28.4% less expensive, while the second is 34% less expensive than fired bricks. When including press, infrastructure, and other costs, CSEB is 26.2% cheaper for manual blocks and 29.9% cheaper for motorized blocks.

Another feasibility study (Kumar et al., 2018) looked into the economic benefits of reinforced interlocking CSEB in the Gulf Coast region of the United States. ICSEB walls, which cost 38,891 $, and CSEB walls, which cost 57,890 $, were 42% and 13.5% less expensive than fired-brick walls, which cost 66,997 $, respectively. A house would cost 104,000 $ if built with reinforced ICSEB, 123,000 $ with CSEB, and 132,107 $ with fired bricks, with the first and second methods being 27% and 18.3% cheaper than fired bricks, respectively.

In South Africa, cement stabilized ICSEB is about half the cost of comparable concrete masonry (Uzoegbo, 2016). In Brazil, the estimated costs of a reinforced ICSEB masonry system is 14% less expensive than traditional fired bricks with RC components, using purchased ICSEB. Making bricks on-site saves 23%, while community engagement in building could save up to 50% of the house’s cost (Di Gregorio et al., 2020).

Several factors make the funicular shell domes economical. First, the amount of steel required for the supporting beams is reduced by 75% (Keswani, 1997). Another study found a 60% save in steel (CSIR and BMTPC, 2021). Second, cement is used only for beams and exterior plastering, saving an average of 35% (CSIR and BMTPC, 2021). Third, free waste materials are used. Fourth, inexperienced workers can build it without centering, unlike masonry domes and vaults (Keswani, 1997; CSIR and BMTPC, 2021). Fifth, in large-scale production, shuttering timber can be replaced with reusable fiberglass molds. Rao and Raina (2005) found that a brick funicular shell roof saves 30% compared to a conventional RC roof. No cost breakdown was found in the literature.

The jack-arch vault, on the other hand, may last for more than 30 years with little or no maintenance with suitable design and finishing (Adam and Agib, 2002). Additionally, it is a less expensive alternative, saving up to 15% of the cost of a typical RC roof, according to Rao and Raina (2005). Again, no analysis was found in the literature to support these figures.

In the literature, there was no cost information on DPLM products and very little structured research on raw material costs was found. The raw material was discovered to be 25%–90% less expensive than other natural fiber sources (Al-Oqla et al., 2015; Elseify et al., 2019). A 2015–2017 economic survey on DPLM in Damietta Governorate (Metwally and Hamza, 2017) found that the profitability for investing 1000 DPLM was 35%, depending on the application, which ranged from crates to chairs. 1000 DPLM cost 557 E£; the total is 1453 E£ when adding all expenses, with labor accounting for more than half (52.2%).

External and internal walls are 25 cm and 12.5 cm thick (as per ECP 204–2005) and reinforced based on the structural design (Figures 2A, B). They are made of 25 × 12.5 × 7.5 cm hollow CSEB. The bricks were manufactured from sandy soil available at the MSA University’s campus (70%–75% sand, 25%–30% fine particles, including 10% clay), and field tests determined their suitability based on EG-SE2016. Standard bricks were made of 90% soil and 10% cement stabilizer by weight (Supplementary Table S3); water was added gradually during mixing, with manual tests to determine the optimal amount. The mixture was then pressed in a semi-hydraulic machine. High strength bricks (HS) for the first three courses and two brick beam courses were made with a 15% cement mixture, with some variations if coloring oxide is added. The bricks were then cured in a humid environment for 28 days. Standard bricks have an average compressive strength of 5.1 N/mm² and water absorption of 13.6%, while high strength bricks have more than double the strength, 11.4 N/mm², and lower water absorption, 10.7%. A clear water-based acrylic varnish significantly reduced the standard brick’s water absorption to 6.2%.

The following are brief explanations of the construction steps (see Figure 3).

• 80 × 40 cm plain concrete foundations were casted.

Figure 4A shows the completed jack arch and funicular shell roofs, while Figure 4B depicts their construction steps.

• At roof level, reinforced concrete beams were partially cast halfway up. The design determined their cross section and rebar count (Ø 12). The funicular shells were supported by 25 cm × 32 cm beams with shear reinforcement at the edges. Jack arches’ joists were 16 cm × 32 cm (WxH), and their edge beams were identical to funicular shells but without shear reinforcement because the tie rods compensated.

Palm midribs replaced wood in internal doors, window shutters, and pergolas (Figures 5A, B). The architect communicated the designs to the craftsman, who manufactured them using traditional furniture and crates making techniques (Figure 5A) and hand tools. The midrib is divided into slats, which are then inserted together to create latticework patterns. To protect the midrib from potential mites, a pesticide (Clorzane) was sprayed. Because the DPLM was bent, wooden strips were attached to the vertical edges of the door to secure and straighten the midribs. Furthermore, polycarbonate sheets were installed and secured behind the DPLM patterns of the doors (Figure 5B).

To produce 800 bricks, four non-skilled laborers (trained for 2 days) and one engineer were needed daily (Supplementary Table S4). Labor costed 850 E£, while materials costed 290 E£ (540 E£ for high-strength bricks, hereafter HS) with 74.6% accounting for the labor and 25.4% for the soil and cement, including their transportation (Figure 7). After considering maintenance, water, electricity, tools, and other expenses, the total standard bricks costed 1390 E£ per day. The self-help production (i.e., without manpower, hereafter SHP) costed 540 E£ per day, representing thus a 61% saving. In general, a standard brick costs 1,74 while SHP costs 0.68 E£ based on Eq. 3. C o s t   o f   o n e   b r i c k = d a i l y   l a b o r   w a g e s + d a i l y   m a t e r i a l s   c o s t + o t h e r   e x p e n s e s n u m b e r   o f   b r i c k s   p r o d u c e d   p e r   d a y (2)

CSEB mortar is also made from soil (for detailed expenses see Supplementary Table S5). A 10 m² half-brick (12.5 cm) wall required 70 L of dry soil-cement, which included 60 L soil, 9 L cement (12.5 kg), and 0.5 L of white glue for adhesive. A more expensive option is pure white glue. Water is added to form a soft paste. 1 m² costed 2.9 E£ (7 L), compared to 38 E£ for conventional mortar (25 L), representing a 92.4% saving. The former required 1.25 kg of cement per m² while the latter required 7.5 kg, saving 83% by weight. The unit rate of 1 L soil-cement mortar is 0.41 E£ based on Eq. 3. C o s t   o f   1 L   d r y   m o r t a r = c o s t   o f   s o i l + c e m e n t + w h i t e   g l u e   p e r   s q . m . 7 (3) where 1 m² wall requires 7 L dry mortar.

1 m² wall needed 54 bricks and 7 L (dry) of soil-cement mortar (Table 1); a mason and helper built 10 m² per day. 12.5 cm wall without finishing costed 137 E£ and 79.6 E£ (SHP) per m²; 25 cm wall costed double these values. Acrylic coating per 1 m² increased the cost of a 1 m² wall to be 166 E£ and 108.6 E£ (SHP) for a 12.5 cm wall and 303 E£ and 188.2 E£ (SHP) for a 25 cm wall. Without reinforcement, materials and labor accounted for 70% and 30% of the total cost, respectively (Figure 7). In the case of SHP brick walls, the breakdown is 54% and 46%. These percentages are comparable to those in Sri Lanka’s feasibility study (Davis and Maïni, 2017). When using SHP CSEB instead of labor produced, a saving of 34.5% (12.5 cm wall) and 37.9% (25 cm wall) was found, compared to 70% saving in Sudan back in 2001 (Adam and Agib, 2001). C o s t   o f   1 s q . m .   C S E B   m a s o n r y = C o s t   o f   C S E B   b r i c k s + s o i l   c e m e n t   m o r t a r + a c r y l i c   c o a t i n g + l a b o r   w a g e s   p e r   s q . m . (4)

141 holes were reinforced according to the design. Rebar, stirrups, plain concrete 1:2:1 (cement: sand: gravel), and epoxy mortar (to secure the rebars in the foundation) were used (Table 1). The holes needed 1 m³ of plain concrete. Three workers anchored the rebar into the foundation, 7 workers cut and fixed rebars and stirrups, and 6 workers and 6 helpers poured the concrete. After adding the overall labor cost (4,600 E£), the microcolumns costed 12,486 E£ (without the bricks, which are considered in the masonry). The cost per microcolumn was 88.55 E£, with materials accounting for 63.2% and labor for 36.8% (Figure 7). The brick beam course was filled with 0.4 m³ concrete (1:2:1) costing 136.5 E£, and 47.5 kg stirrups costing 711 E£ (Table 1). One worker per beam was needed to cut, shape, and fix the stirrups, while 2 workers and 2 helpers poured the plain concrete, costing 1,050 E£. The beam costed 1,897.5 E£ (without bricks), with materials accounting for 55.3%, labor 44.7% (Figure 7) and a rate of 13.18 E£ per m long. C o s t   o f   r e i n f o r c e d   c o m p o n e n t s   h o l e s   &   b r i c k   b e a m s = C o s t   o f   m a t e r i a l s   r e b a r s + s t i r r u p s + p l a i n   c o n c r e t e + C o s t   o f   l a b o r   f i x i n g + a n c h o r i n g + c a s t i n g (5)

EH has a masonry area of 167 m², including 92 m² external, 52 m² internal, 14.5 m² external HS and 8.5 m² internal HS (first 3 courses and 2 beam courses). When masonry, microcolumns, brick beams, finishing, and first course cement mortar expenses were added (Table 2), the overall cost was 59,201.4 E£ and 43,630 E£ (SHP), or 354 and 261 (SHP) per m² wall. The SHP-brick saved 26.3% in walls. T o t a l   c o s t   o f   C S E B   r e i n f o r c e d   s y s t e m = C o s t   o f   f i n i s h e d   C S E B   m a s o n r y + C o s t   o f   r e i n f o r c e d   c o m p o n e n t s (6)

350 fired bricks were needed to build a 1 m × 4 m² jack arch, as well as 166 L of dry cement mortar (1:4) for the mortar and plastering the vault from the outside, as shown in Table 3. The materials per m² costed 124.25 E£ and the labor, which included two masons and two helpers, costed 200 E£ per m². When the average tie rod expense and the average formwork wood expense were considered, the material costs were 139.85 E£ per m², representing 41%, while the labor costed 201.56 E£, representing 59%. The 15 jack arches (42.73 m²) costed 14,588 E£, i.e., 341.4 E£ per m². A 2 m × 2 m fired-brick funicular shell required 470 bricks and 100 L of dry rich cement slurry mortar (1:2), as well as 66 L of cement mortar (1:4) for outside plastering. When the shell was built using fired-bricks, broken marble and granite or broken ceramic tiles, or limestone tiles, the materials per m² costed 166.5 E£, 134.25 E£, and 184.25 E£, respectively, where the second and third types had the same material cost. The labor, which included two masons and two helpers per shell, costed 200 E£ per m² without the formwork labor cost. The formwork was completed for each funicular shell in the manner described in the construction process; two workers were required per funicular shell, at a cost of 300 E£ (75 E£/m²). When the average formwork wood cost per 1 m² was considered, the total material costs became 171.2 E£, 138.95 E£, 188.95 E£, representing 38.4%, 33.6%, and 40.7%, respectively, while total labor costed 275 E£, representing 61.6%, 66.4%, and 59.3% for fired-bricks, broken marble and granite or broken ceramic tiles, and limestone tile shells, respectively.

The volume of the RC beams is 6.3 m³, accounting for 25.3 m² of the roof. Their 66 m² sides needed plastering and painting (Table 3). The cost of alternative roofing system ranged between 53,806–55,147 E£, including beams. Despite the beam cost (18,610 E£) being higher than the masonry work (14,576 E£) of the jack arch, this system was the cheapest, 558.32 E£/m², with the beam representing 56% of its cost (Figure 8). It was followed by broken marble, granite and ceramic shells, 582.6 E£ (beam 46%) then fired bricks, 607.1 E£ (beam 44%), and finally limestone, 620.6 E£ (beam 43%). The difference between the jack arch system and the limestone shell system is 10%. A removable PVC formwork would have reduced the cost of the funicular shell (more cost-effective for mass construction). The jack arch was 23.6% cheaper than the fired brick shell without beams (341.4 E£ vs. 446.25 E£, but just 8% cheaper when they are included.