“Re-evaluating the health performance of historical buildings using WELLV1 rating system”

The Southeast Tunisian cave dwellings of Matmata are a well-known historical model which amazingly adapt with cultural, environmental and climatic features of its surrounding. Many studies have discussed the sustainability of these dwellings but none has thoroughly discussed its performance on light of health and wellbeing of its dwellers. The WELLV1 rating system, established in 2016, is a first of a kind certification system that solely focus on the health performance of the built environment. It gives credit to designs that enhance and promote physical and psychological health of the users. The study examines the health performance of Matmata cave dwellings in the light of WELLV1 recommendations and features. The study revealed that these subterranean historical dwellings have proven good performance in relation to daylight saturation, indoor thermal relief, solar glare control, physical activity enhancement, exterior noise reduction, biophilic design and cultural enrichment. On the other hand, they lack sufficient performance in relation to air purification, social interaction, clean water supply, and altruism encouragement. Considering the scientific background, materials and technologies available for those who designed and built these dwellings, the health-related performance of their work seems unique and impressive.


Introduction
An increasing literature is linking our modern lifestyle with the prevalence of certain diseases which our ancestors had rarely suffer.For example, many cardiovascular diseases, such as strokes, high blood pressure, heart attacks, and atherosclerosis are strongly linked with various modern lifestyle factors such as tobacco use, unhealthy diet, chronic noise exposure and lack of physical activity (Mathers and Loncar 2006).Diabetes, on the other hand, is a metabolic disorder that is often associated with obesity and physical inactivity (Boles et al 2017).Chronic respiratory diseases such as asthma and chronic obstructive pulmonary disease are also linked to lifestyle factors such as smoking and air pollution (Steyn et al 1992).Obesity, as a modern lifestyle disease, is linked with physical inactivity, disruption of sleep/wake cycle, depression and air pollution (Lechat et al 2021).Modern lifestyle diseases have a significant impact on our health and well-being, and can lead to disability, reduced quality of life, and premature death (Balwan and Kour 2021).The prevailing incidence of diseases linked to the built environment's design has raised questions about contemporary architecture and how historical buildings were healthier and more ecofriendly.Vernacular architecture has been commonly thought to be more health promoting, though no direct scientific evidence has proved this concept.However, many studies have discussed the sustainability and environmental benefits of vernacular architecture, which could indirectly contribute to the health of its users.For example, Pardo 2023 has discusses how traditional buildings are usually considered a model of sustainability in the use of available resources, with a minimal negative environmental impact, minimization of costs, and a reduction of energy demand (Pardo 2023).Morover, Biradar, et.al, (2017) have stated that vernacular buildings had evolved gradually to meet environmental, socioeconomic, and sociocultural characters of the society to meet the changed lifestyle over a period of time (Biradar and Mama2017).The Mediterranean vernacular architecture, for specific, was stated by Tawayha, et al 2019 to be respecting environmental and climatic factors, construction materials, and morphology and harmonizing between buildings and its local cultural, environmental and traditional context (Tawayha et al 2019).This paper discusses the health aspect of vernacular architecture and how it affected the health and wellbeing of our ancestors.The main research question is: Did vernacular architecture promote the health and wellbeing of its dwellers?In what manner, and how to measure this promotion? .The methodology used as a measure tool is the WELLV1 Building Standard, which is the first evaluation tool that focuses entirely on health performance of built environment (The International WELL Building Institute (IWBI ™ ) 2017).The reason of choosing WELL V1 as an evaluation tool, that it is the only rating system that gives credits solely to health and wellbeing of building users.Green rating systems such as LEED, BREEAM, DGNB et cetera, are mainly addressing the health of the planet and the environmental performance of the building, while WELLV1 addresses mainly the health, comfort, welfare and relief of the building users, regardless any other economic or environmental factors (The International WELL Building Institute (IWBI ™ ) 2017).The vernacular site of Matmata, located in southern Tunisia, was chosen as a case study to examine the health performance of vernacular architecture using WELL V1 measurement tool.

WELL Rating system
The WELL V1 Building Standard, established in 2016 is designed by the International WELL Building Institute ™ (IWBI ™ ), in coordination with the Green Business Certification Inc. (GBCI), which is the organization responsible for LEED certification system.The built environment that WELL V1 certifies can assist its occupants achieve better nutrition, fitness, mood, sleep, comfort, and performance (The International WELL Building Institute (IWBI ™ ) 2017).These improvements are accomplished by applying certain policies, plans, and methods that promote active, healthy lifestyles and reduce tenant exposure to harmful chemicals and pollutants.
WELL V1 is categorized into 100 features, subdivided into "Preconditions", that must all be met, and "Optimizations", which are supplementary to achieve WELL's goals.The main seven categories are shown in Table 1.

Matmata
Matmata is considered one of the few remaining Berber villages in southern Tunisia.Best known for its underground houses carved into the stone, Matmata's unique architectural structure and treasured Berber heritage make it a popular spot. it is thought to be named after a tribe that sought refuge in the mountains during the Islamic conquest.The village used to be called Athwab in Amazigh, which means 'the land of happiness and wellbeing (Mamdouh Mohamed Sakr 2001).
It is a well-known ecolodge destination which resembles a perfect integration between architecture and environmental design.The Matmata dwellings are a living example of historical sustainable vernacular construction, as they are economically efficient, environmentally friendly, and energy efficient as well.These man-made excavations are a source of inspiration for a number of fields such as architecture, economics and environmental studies and even eco-tourism; these dwellings can easily ensure the economic sustainability of the whole settlement (Gideon 1982).
Matmata's troglodytes (earth-sheltered dwellings) are considered to be one of the most unique examples of North African vernacular architecture.,A troglodyte is basically a vertical shaft that is cut and excavated through soft sandstone layers to create a circular courtyard as shown in Fig. 1.This courtyard is usually the center of a following subsidiary excavations designed as auxillary rooms that are directly attached to the main courtyard.(Bruun 1898).
The troglodytes of Matmata are appropriate building types that met the inhabitants' needs in terms of both function and aesthetics.These earthen structures are amazing examples of how people have effectively adapted to a frequently hostile environment with minimal cost and primitive technology.This accomplishment was made possible through ongoing exploration and knowledge that was passed down from one generation to the next.
Most of Matmata dwellings consist of a main courtyard surrounded by several rooms (caves) dug into the soil as shown in Fig. 2. The main entry of 12 m long delivers into an external courtyard serving for ventilation of surrounding livestock rooms.After-which the pathway continues downwards till it delivers into a main court serving as a main living and ventilation area for living and sleeping spaces.The main court has slopes towards its center point for rainwater collection in a huge tank underground used as a water well around the year (Gideon 1982).

WELL V1 Compatible Criterions in Matmata
Among the 100 criterions of WELL V1 system, we list here the main eleven matching criterions applied in historical houses of Matmata:

Healthy Entrance
"Healthy Entrance" is the 8 th criterion in WELL V1 , stated as a "precondition" under the "Air" category of the rating system.As harmful contaminants are often dragged into indoors by occupants, with many  (Gideon 1982) including bacteria, heavy metals, landscape pesticides, and other toxic substances that unintendedly attach to occupants' garments, WELL V1 requires proper design for entrances to minimize this intrusion.Occupants can also drag contaminated air into building during the frequent entry/exit process.Unhealthy entrances may affect the following systems in the human body: Cardiovascular, Immune, and Respiratory systems (The International WELL Building Institute (IWBI ™ ) 2017) as shown in Fig 3.

Criterion Requirements
WELL V1 "Healthy Entrance" criterion requires certain design strategies to minimize the intrusion of outdoor contaminants as follows (The International WELL Building Institute (IWBI ™ ) 2017): For the building's regularly used entrances: • Installing long cleanable grilles or grates in the main direction of travel, with ability to clean underneath whenever needed/ or.. • Installing an entryway walk-off system with dimensions not less than 3 m long and width not less than the width of the entrance door./or..
• Designing an entry vestibule before the main building entry, with 2 normally-closed doorways.• Installing a revolving entry doors for all outdoor entrances/ and.. • Installing at least 3 normally-shut doors to separate occupied indoors from outdoors' contaminants.

Matmata's compatibility with this criterion
Matmata houses use long narrow entrance passage which starts from earth surface and downwards to the main court as shown in Fig. 4. The passage's exterior entry point has a tilted walkway for seclusion and defense against other tribes' attacks and sandstorms as well.This design assures protection against contaminants and harsh weather year-around (A.AAl -Temeemi et al 2004).
On the other hand, the exposed courtyard allows possible contamination with contaminants especially during sand storms and windy seasons.This was reduced by deep digging to make the house safe from harsh storms, and by excessive tree planting to achieve soil stabilization and air purification.

Direct Source Ventilation
"Direct Source Ventilation" is the 17 th criterion in WELL V1 , stated as an "optimization" under the "Air" category of the rating system.There are many potential sources of indoor air pollution that generate inside the building due to indoor regular activities.Such sources include: cleaning products, humid environments, chemical storage with possible harmful vapors, paints and finishings that may emit VOCs, aerosols like pesticides and herbicides used for pest control and indoor planting, etc., (The International WELL Building Institute (IWBI ™ ) 2017).These contaminants can trigger asthma and allergies in susceptible individuals, while VOCs are linked to cancer and central nervous system damage.
Poor access to outdoor ventilation may spread air-borne diseases which affect both respiratory and immune systems in the human body (The International WELL Building Institute (IWBI ™ ) 2017).

Criterion Requirements
WELL V1 features encourage the use of direct outdoor ventilation and that air gets exhausted and expelled rather than recirculated inside the building.

Matmata's compatibility with this criterion
Matmata homes are entirely dependent on passive ventilation and natural air all year round.All rooms have direct access to the central court from which they get

Circadian Lighting Design
"Circadian Lighting Design" is the 54 th criterion in WELL V1 , stated as a "precondition" under the "Light" category of the rating system.Light has 3 main impacts over our human body: visual impact, which controls our ability to see our surroundings, emotional impact, which controls our feelings and emotions, and biological impact, which controls our ability to perform our daily tasks, especially intellectual ones.The biological impact of light is regulated by the "intrinsically Potosensitive Retinal Ganglion Cells (ipRGCs), also called the melanopsin-containing Retinal Ganglion Cells (mRGCs).which are non-image-forming photoreceptor neurons located in the retina of the human eye (The International WELL Building Institute (IWBI ™ ) 2017) as shown in Fig. 6.The (ipRGCs) controls the circadian system, which regulates the hormonal secretion via pineal body to adjust our sleep-wake cycle in compliance with light levels around us.If indoor light is designed to have a high intensity and high frequency, circadian system responds by increasing awakeness and alertness, and if the room is dim or dark, our circadian system responds by reducing energy expenditure and preparing us for sleep and rest.The circadian Lighting Design affects Muscular, Nervous and Skeletal system in the human body as shown in Fig. 6.

Criterion Requirements
WELL V1 requires that circadian rhythm be controlled by proper indoor lighting design to match the required functions along day-night hours.

Matmata's compatibility with this criterion
Matmata's dwelling depends basically on the natural daylight cycle by utilizing sun light as the main source for illumination of interiors.The biological cycle of the dwellers is synchronized with sunlight cycle by the interaction of daylight and light receptors in the brain of the dwellers.This assures good sleep times and high alertness during morning hours with minimal ache and fatigue.

Solar Glare Control
"Solar Glare Control" is the 56 th criterion in WELL V1 , stated as a "precondition" under the "Light" category of the rating system.Good and sufficient exposure to daylight during morning hours is a good design feature that WELL V1 encourages.But on the other hand, as excessive exposure may cause glare, WELL V1 requires good control of solar glare levels as a distinct feature among the same Light category (The International WELL Building Institute (IWBI ™ ) 2017).
Glare is defined as strong or dazzling light caused by uneven levels of brightness in the visual field.When light scatters within the eye (intraocular scattering), it creates a "veil" of luminance that diminishes the luminance contrast as received by the retina.Glare can negatively affect human health by causing visual fatigue and discomfort.Solar glare can be caused indoor by unshielded or poorly shielded light, or sunlight directly hitting the eye or reflective surfaces.Solar glare affects Muscular, Nervous and Skeletal system in the human body (The International WELL Building Institute (IWBI ™ ), 2017) as shown in Fig 7.

Criterion Requirements
WELL V1 features encourage the avoidance of glare caused by sunlight by applying modifications to block or reflect direct sunlight away from building users, using the following tools:

4.4.1.A View Window Shading
If glazing is less than 2.1 meters above floor level in regularly occupied spaces, Fig. 6 The main systems affected by indoor circadian lighting design in the human body (The International WELL Building Institute (IWBI ™ ) 2017) (right)-and the mechanism of melatonin suppression in the brain by the incoming light spectrum received by retinal ganglion cells (Erren et al.1972) (left) WELL V1 requires that at least one of the following 3 tools is applied (The International WELL Building Institute (IWBI ™ ) 2017): • Installing interior window shading or blinds that can be either manually controlled by building users, or automatically programmed to prevent glare whenever light sensors detect excessive brightness.

Matmata's compatibility with this criterion
As part of the Tunisian desert, Matmata receives about 5.8 kWh/m 2 of direst solar irradiation each day as shown in ((Fig.8), right).That's why solar glare has been an important issue in Matmata.Glare has been controlled by applying the troglodyte structure which depends on cave dwelling (underground dwelling) type.The sides of the main court are shaded alternatively due to high depth of excavation.Shaded sides don't suffer the "glare" problem while the unshaded sides are exposed to direct sun exposure (Omrani et al 2019) as seen in Fig. 8 up left.This problem was faced by applying small narrow doors and openings of the surrounding rooms to minimize the sunlight intrusion in side living and resting rooms.Shading coefficient as well as thick narrow mouths of the rooms both had minimized the incidence of glare, (Fig. 8, down left).A light analysis has been made by the researchers using "Design Builder" tool at both the main court and the surrounding rooms during the hottest season of the year.The analysis shows that the daylight factor in all rooms start with 10.8% at the entrance and ends with 0% at the bottom, (Fig. 8, down middle) (Alexis Aguilar Sánchez 2014).

Right to Light
"Right to Light" is the 61 st criterion in WELL V1 , stated as "optimization" under the "Light" category of the rating system.Good and sufficient exposure to daylight during morning hours is a good design feature that WELL V1 encourages.Exposing the building users to sufficient levels of direct and indirect sunlight during morning hours can enhance their mood, health, as well as promoting their visual, physical and psychological performance (The International WELL Building Institute (IWBI ™ ) 2017).most people should be able to make all their essential daily dose of vitamin D they need from exposure to sunlight, thus promote their skeletal health and proper bone density (The International WELL Building Institute (IWBI ™ ) 2017).The vicinity to windows, outdoor views and natural daylight inside indoor spaces, are some of the most desired design features.As such, buildings should utilize daylight as a primary source of lighting to the greatest extent possible.Exposure to day light affects the following systems in the human body: cardiovascular, digestive, endocrine, immune, muscular, nervous and Reproductive systems as shown in Fig. 9.

Criterion Requirements
WELL V1 requires that 75% of all regularly occupied spaces area is located within 7.5 m of exterior windows, or 95% of all of workstations are within 12.5 m of a court, an atrium, or a window with exterior views clearly visible to the indoor users (The International WELL Building Institute (IWBI ™ ) 2017).

Matmata's compatibility with this criterion
According to simulation done by Omrani et al., 2019 to Matmata houses, rooms don't have enough daylight all day long due to long depth of the rooms which may exceed 10 m long.The study showed that north-facing rooms have day light factor distribution ranging from 45% to about 0% measured at the reference line shown in fig (Tawayha et al 2019).This low level of light may be done on purpose to assure low level of light exposure at bedrooms and resting spaces.But on the other hand, Matmata dwelling unit occupants can easily enjoy the direct sunlight by getting out to the courtyard during early mornings and late afternoons, especially in hot bright summer days (Alexis Aguilar Sánchez 2014).

Interior Fitness Circulation
"Interior Fitness Circulation" is the 64 th criterion in WELL V1 , stated as "precondition" under the "Comfort" category of the rating system.The integration of interior indoor pathways and staircases into the built environment can promote and enhance the occupants' involvement into short and repetitive periods of physical activity during the day hours, thus combat sedentary habits and reduce inactive time periods.
Building design that encourage stair climbing offer a low-impact, moderate-to-vigorous intensity physical activity that promotes burning of calories and improves cardiorespiratory fitness and minimizes the risk of stroke (The International WELL Building Institute (IWBI ™ ) 2017).To encourage building users for greater use, pathways and stairs should be decorated with artistic aesthetics and vivid plantings, and be easily accessible from high-traffic routes.Interior Fitness circulation affects the following systems in the human body: Cardiovascular, Muscular, and Skeletal systems as shown in Fig. 10.

Criterion Requirements
WELL V1 features require intermittent bouts of indoor physical activity and reduction of sedentary behavior through accessible, safe, and visually appealing stairs, entryways, and corridors.This is done by applying the following required tools (The International WELL Building Institute (IWBI ™ ) 2017):

4.6.1.A Stair Accessibility
In projects of 2 to 4 floors, at least one common staircase meets the following requirements: • Stairs must be accessible to regular building users during all occupation hours.• Wayfinding signage and point-of-decision prompts are present to encourage stair use (at least one sign per elevator bank) in offices and non-residential indoors.

4.6.1.B Stair Promotion
In projects of 2 to 4 floors, at least one common staircase must fulfil the following requirements: • Stairs are located within 7.5 m of the entrance to the building or the edge of its lobby.• Stairs are clearly visible from the main entrance to the project, or located visually before any elevators.• Staircase must be present upon entering from the main entrance.• Stair width is no less than 1.4 m between handrails.

4.6.1.C Facilitative Aesthetics
In projects of 2 to 4 stories, both common stairs and heavily travelled routes exhibit aesthetic appeal by incorporating at least two of the following tools: a. Artwork, including decorative painting.b.Music.c. Daylighting using windows or skylights of at least 1 m 2 in size.d.View windows to the outdoors or building interior.e.Light levels of at least 215 lux should be present when the stairs are being used (The International WELL Building Institute (IWBI ™ ) 2017).

Matmata's compatibility with this criterion
Matmata houses promote physical activity by forcing the dwellers to climb more than 50 m long and 10 m high upstairs to reach street level.They also apply indoor stairs within the house to connect downstairs rooms to upstairs ones (Louis 1972).Some dwellings depend on wall holes rather than stairs which the dwellers climb using their hands and feet as shown in Fig. 11 to reach upper rooms.Furthermore, long walkway distances inside the court and surrounding spaces promote physical activity as well.Indoor stairs climbers enjoy full access to daylight, aesthetic plantings, and fresh air supply (Louis 1972).

Thermal Comfort
"Thermal Comfort" is the 76 th criterion in WELL V1 , stated as a "precondition" under the "Comfort" category of the rating system.Thermal comfort in human body is regulated by the "homeothermy" process.Homeothermy is responsible of balancing heat gains and losses inside the human body to keep the its core temperature within a specific range of 36-38 °C.The main regulating body of homeothermy is the hypothalamus.Thermal comfort can affect mood, performance and productivity of indoor users (The International WELL Building Institute (IWBI ™ ) 2017).Because temperature preferences may greatly vary from one person to another, it might be a challenge to balance the energy needs of large indoors in huge structures occupied by many users with diverse thermal preferences.
Thermal Comfort affects the following systems in the human body: Immune, Integumentary, Nervous and Respiratory systems as shown in Fig 12.

Matmata's compatibility with this criterion
The subterranean dwellings are generally considered capable of reducing the extremities of day/night temperatures around the year.Al- Temeemi & Harris, 2004 have stated that sunken courtyard can combat the harsh climate and decrease energy consumption by 25-35%, compared to their adjacent above-grade peers (A.AAl-Temeemi et al 2004).
For Matmata, a study conducted by Golany, 1982, has measured the thermal performance of the sunken courtyard of Matmata and its adjacent rooms around the year.The study concluded that the temperature of the rooms facing the sunken courtyard was nearly 17°C cooler in mid-summer and 9°C warmer in mid-winter than the maximum and minimum outside dry-bulb temperatures respectively (Gideon 1982) as shown in Fig 13.The thermal performance of Matmata dwellings was furtherly examined by many other researchers.Krarti (1998) has measured the indoor temperature in both main court and surrounding rooms in six different houses during the hottest season of July.He stated that the temperature was nearly constant all-day hours at 29 C inside the rooms, while it varied from 25 to 46 outdoor the dwelling as shown in Table 2.The relative humidity was 30% at all sites while it was 15% (desert dry weather) outdoor in July (Krarti 1998).Comparing this performance with ASHRAE standards 55-2013 Section 5.4, these measures are within the comfort zone of naturally ventilated spaces.

Olfactory Comfort
"Olfactory Comfort" is the 77 th criterion in WELL V1 , stated as "optimization" under the "Comfort" category of the rating system.Strong or distinct odors may cause disruption in physical or psychological functions of the human body system.Main possible symptoms include nausea, headache, vomiting, and irritation of eye, nose or throat.Prolonged exposure to such odors may cause chronic bronchial asthma and other respiratory ailments.WELL V1 identifies this design criteria as "Olfactory Comfort" requirement, listed among the "Air" design category.Olfactory comfort can significantly improve occupant comfort and well-being.It affects the digestive, endocrine, immune, integumentary, nervous and respiratory systems of the human body (The International WELL Building Institute (IWBI ™ ) 2017) as shown in Fig 14 .WELL V1 strategies aim to: 1-limit any possible release of aggressive odors inside the built environment.2-Minimize any possible transmission of strong or distinct odors within the building.

Matmata's compatibility with this criterion
In Matmata's dwellings, the odor-generating spaces like cattle sheds and hey reserves are separated from the main dwelling by a narrow path with a shutting door and a vestibule as shown previously in Fig 2 (Gideon 1982), which minimizes the odor intrusion to occupants.Furthermore, all rooms are separated from the main court with narrow openings (necks) to assure minimal intrusion of heat, glare, noise, and odor into living and resting spaces (Nahla Adel Elwefati 2007).

Exterior Noise Intrusion
"Exterior Noise Intrusion" is the 74 th criterion in WELL V1 , stated as "precondition" under the "Comfort" category of the rating system.Loud, intense and recurrent exterior noises are capable of causing certain health problems in exposed humans.Hypertension

Criterion Requirements
WELL V1 features encourage the reduction of acoustic disruptions by limiting external noise Intrusion, this is applied by assuring that : Average sound pressure level from outside noise intrusion should not exceed 50 dBA in each regularly occupied space as measured when the space and adjacent spaces are unoccupied, but within 1 hour of normal business hours (The International WELL Building Institute (IWBI ™ ) 2017).

Matmata's compatibility with this criterion
For Matmata, the subterranean nature of the dwellings work as a natural barrier against outdoor generated noise.The cellular form of Matmata's dwellings which are separated by thick layers of earthen material led to complete isolation from exterior disruption as shown in Fig 16 .In addition, room-to-room noise leak has been combated by thick soil barriers separating rooms from each other, thus ensuring a strong insulation and enhance the individual privacy of family members (Taleghani, (2012).For the central courtyard users (generally women), both visual and acoustic privacy was achieved by the depth disparity, the planting elements, and the sand and clay finishes, which all work as an absorber for both heat and noise coming from aboveground neighborhood.(Tafti et al., 2018).Many occupants of earth-sheltered buildings suffer from lacking access to external world and the feeling of isolation and extreme disconnection (Tafti et al., 2018).

Beauty and Design
"Beauty and Design" is located twice in WELL V1.The "Beauty and Design I" is the 87 th criterion stated as a "precondition", while "Beauty and Design II" is the 99 th criterion stated as an "optimization" credit, both located under the "Mind" category of the rating system.Enriching the interior design with indoor aesthetic elements that represent the cultures and morals of the users, is positive criteria required by WELL V1 .Such beatification with cultural arts can enhance the heritage and values of the users, as well as boosting their mood, wellbeing and morale, and positively affecting the nervous system in the human body (The International WELL Building Institute (IWBI ™ ) 2017).It also requires the following for optimization: a-Ceiling height must not be less than 2.7 m for rooms of 9 m width, with additional + 0.15 m of height for every additional 3 m of width over 9 m.b-Artwork must be integrated to add complexity to the visual field in entrances, lobbies, and all regularly occupied spaces greater than 28 m 2 (The International WELL Building Institute (IWBI ™ ) 2017).

Matmata's compatibility with these criteria
Matmata houses have the character of vernacular architecture where art work is present all over the indoor spaces as shown in Fig. 17.Pots, ceramics and earthen-wares decorated with beautiful local motifs are used for food storage and water gathering.The colorful woven mats, curtains and bed sheets are handmade by local women or by the house dwellers themselves for their own use (Bruun 1898).Storage boxes made of twined straw and date palm leaf, giving special character for the space and attracting tourists to enjoy the local heritage of this unique place.
Considering the optimization, the ceiling height of excavated rooms were measured as 2.5 to 2.85 in lower rooms, and 2.2 to 2.5 in upper rooms (Louis 1972).The purpose of these comparatively low heights is the desire to reduce the excavation costs and efforts, give space for upper rooms to exist, assure good soil consolidation, and achieve human scale intimacy as shown in Fig. 18.
On the other hand, the optimization of artwork integration is already achieved in all spaces, including entrances, lobbies, rooms and courtyards as well.

Biophilia
"Biophilia" is located twice in WELL V1.The "Qualitative Biophilia" is the 88 th criterion stated as a "precondition", while "Quantitative Biophilia" is the 100 th criterion Fig. 16 Deep excavation heights as well as the cellular type of Matmata's dwellings separated by thick layers of earthen material, both had led to isolation from exterior disruption (Tafti et al., 2018, Louis 1972) Fig. 17 Local motifs of Matmata dwellers: colorful woven mats, curtains and bed sheets(left), twined straw boxes (middle)and food storage ceramic pots (right) stated as an "optimization" credit, both criteria are located under the "Mind" category of the rating system.Biophilia is defined as the human tendency to engage with nature and various forms of life (The International WELL Building Institute (IWBI ™ ) 2017).Most humans have an affinity towards the natural world and prefer to exist around life and life-like processes.The engagement of humans with natural views and aesthetics can boost positive sentiments and absorbs depression, while interior environments that are cold, sterile and devoid of life might diminish our experience, mood, and happiness (The International WELL Building Institute (IWBI ™ ) 2017).Biophilic environments can reduce tension and stress in healthy individuals, and hasten the healing process and shorten recovery time in sick ones.WELL V1 requires certain biophilic requirements that involve conducting historical, cultural, ecological and climatic studies to inform biophilic elements and creating a biophilic framework that tracks biophilia during each stage of the project's design (The International WELL Building Institute (IWBI ™ ) 2017).The main system that is directly impacted with biophilia inside the human body is the Nervous system as seen in Fig. 18.

Criterion Requirements
WELL V1 features require that the project must incorporates nature through the following:

Matmata's compatibility with these criteria
Matmata's dwellings incorporate nature by planting palms, trees and native plants inside the main court to provide shade and food (i.e., olives and fruit) for the inhabitants.The dwelling also incorporates daylight, natural elements and environmental elements (Mamdouh Mohamed Sakr 2001, Tafti et al 2018) as shown in Fig. 19.

Conclusion and summary
The houses of Matmata have some design privileges that promote human health and welfare.Some of these privileges are related to high thermal comfort even during the hottest season of the year, interior physical circulation that promotes health and fitness of the dwellers, natural daylight supply which improves their visual and mental health, and regulates their circadian rhythm and improves their sleep-wake cycle, minimal noise intrusion that assures quiet environment and improves blood pressure and hormonal secretions, reasonable olfactory comfort that improves respiratory and digestive systems and prevent allergies and respiratory ailments.Matmata dwellings also have the privilege of direct natural ventilation, solar glare control which prevents headaches and visual impairments, as well as the beautiful applications of native planting, motifs, and artwork that all help enrich both visual and spiritual joy.On the other hand, many other WELL V1 criterions cannot be discussed upon Matmata due to its historical nature, but many other criterions can be easily added if modern technology is applied to the historical site with proper conservation.The main WELL v1 criteria of Matmata dwelling and its health impacts are summarized in Table 3.

Recommendations
Vernacular architecture has adapted to the specific needs of communities and played a significant role in promoting the health and well-being of people in ancient times.The close connection between vernacular architecture and the natural environment allowed for effective ventilation, optimal sunlight exposure, and the use of locally-sourced materials with inherent thermal properties.This harmonious relationship between humans and their surroundings fostered a healthier lifestyle, free from many of the diseases that afflict modern society.Many diseases caused by modern lifestyle can be avoided by following the vernicular concept of design and urbanization, but in modern technology methods.Ignoring health aspects of modern design has led to environments that may compromise physical and mental health.Poor ventilation, limited access to natural light, and the use of synthetic materials in contemporary buildings have contributed to an increased prevalence of health issues.The stark departure from vernacular principles underscores the importance of reevaluating our approach to architecture and design to restore a balance between human well-being and the built environment.However, further modifications are needed to improve the health performance of vernacular architecture of Matmata to assure clean air supply, safety against heavy rains and floods, good social contact with neighbors, clean water supply and affordable modern sewage system, as well as better energy performance and acoustic isolation for exposed courtyards.Further studies are recommended to examine other vernacular sites with health impacts to conclude the links between historical design and human health.

Fig. 4 Fig. 5
Fig. 4 Illustration of Matmata dwelling twisted entry: a floor plan of entry (up left), a view of being steep descending (up middle) and being twisted to avoid storm and pollutants (up right), and the entry hole from an exterior view (down) (Mamdouh Mohamed Sakr 2001, Gideon 1982, A. AAl-Temeemi et al 2004)

Fig. 7
Fig. 7 The main systems affected by solar glare incidence in the human body (The International WELL Building Institute (IWBI ™ ) 2017)

Fig. 8
Fig. 8 Solar Direct Normal Irradiation in Matmata (right), shading on side walls of the main court during day hours (up left), thich stone narrow openings of interior rooms (down left), and day light factor performance in similar structure done by the researchers (down middle) ( Omrani et al. 2019, Alexis Aguilar Sánchez 2014)

Fig. 9
Fig.9The main systems affected by light exposure in the human body (up-left) and light level in north-facing room in Matmata during summer noon (up-right) and Daylight factors distribution on the analysis grids of Matmata room,Omrani et al., 2019 (down) a sufficient level of indoor thermal comfort by applying what so called" Natural Thermal Adaptation" criterion.This criterion requires that all natural-ventilated spaces must meet the ASHRAE Standard 55-2013 Section 5.4, of adaptive comfort model (ANSI ASHRAE Standard ND).

Fig. 10
Fig. 10 The main systems affected by interior fitness circulation in the human body (The International WELL Building Institute (IWBI ™ ) 2017)

Fig. 11 Fig. 12
Fig. 11 (up) Wall holes installed in Matmata houses to reach upper rooms( left) and interior stairs inside the main court to reach: upstairs level (middle) and main door leading to the exit passage (right) -(down) step height of the indoor stairs in Matmata house (left) and cross section showing average climbing distance inside the main entrance passage (middle)

Fig. 14
Fig.14The main systems affected by olfactory disruption in the human body (WELL Guide book 2017) , diabetes, stroke and heart attack, all are possible outcomes for individuals who reside near repetitive noise source, especially traffic roads or aircraft facilities.Additional threats are psychological stress, depression, insomnia, and hearing loss.Dwellers of dense urban cores are the most susceptible individuals to such threats.The most affected systems by exterior noise intrusion in the human body are: the Cardiovascular, Endocrine, and Nervous systems (The International WELL Building Institute (IWBI ™ ) 2017) as shown in Fig 15.

Fig. 15
Fig.15The main systems affected by noise intrusion in the human body(WELL Guide book ,2017) a. Environmental elements.b.Lighting.c. Space layout.It also requires that the project incorporates the following for optimization: a Nature's patterns throughout the design the project provides sufficient opportunities for human-nature interactions: a. Within the building.b.Within the project boundary, external to the building (The International WELL Building Institute (IWBI ™ ) 2017).

Fig. 19
Fig. 19 Native plants and biophilic elements inside Matmata dwelling court (left and middle) and the nervous system of the human body affected by biophilia and human connection with nature (right)(The International WELL Building Institute (IWBI ™ ) 2017, Mamdouh Mohamed Sakr 2001, Tafti et al 2018)

Table 1
Main categories of WELL V1 Rating system (The International WELL Building Institute (IWBI ™ ) 2017) Matmata resembles one of the best examples of troglodyte architecture in the world

Table 3
Main WELLv 1 criteria of Matmata dwelling, fulfillments, and its health impacts (Designed by the Author) physical or psychological functions i.e., nausea, headache, vomiting, irritation of eye, nose or throat.Reduce incidence of chronic bronchial asthma and other respiratory ailments.Promote digestive, endocrine, immune, integumentary, nervous and respiratory systems Fulfilled 9 Exterior Noise Intrusion Reduce hypertension, diabetes, stroke and heart attacks.Prevent psychological stress, depression, insomnia, and hearing loss.Promotes Cardiovascular, Endocrine, and Nervous systems Fulfilled 10 Beauty and Design Boosting mood, wellbeing and morale, and positively affecting human nervous system Fulfilled 11 Biophilia Boosting mood and absorbs depression, reduce tension and stress, shorten recovery time in sick individuals and promotes human Nervous system Fulfilled