Architectural Heritage Conservation in Nigeria: The Need for Innovative Techniques

: Architectural heritage conservation in recent years has hinged on conventional methods and has failed to recognize innovative methods and emerging technologies. Consequently, in Nigeria, suboptimal conservation work results in the continual deterioration of architectural heritage, leading to the loss of heritage and its values and signiﬁcance. The study, therefore, sought to ex-amine challenges and prospects for implementing innovative techniques in the conservation of architectural heritage in Nigeria. The study examined three heritage conservation interventions in Nigeria, focusing on the applicability of innovative conservation methods for documentation, diagnosis, and treatment of deterioration of architectural heritage. Questionnaires were administered through purposive sampling to 40 heritage conservation professionals, with 31 (77.5%) completed and returned for analysis. A Cronbach’s alpha reliability test value of 0.76 established the validity of the research instrument. The ﬁndings afﬁrmed that heritage professionals have low familiarity (mean value of 2.19) with innovative techniques for conservation of architectural heritage. Of the respondents, 41.9% had gained a minimal level of technical knowledge of how to implement innovative techniques in conservation interventions. Improving the performance of conservation interventions also ranked highly as a potential strength of implementing innovative techniques. Conclusively, there is a need to improve advocacy and training in innovative conservation techniques based on their ability to characterize architectural heritage materials and investigate their chemical composition, microstructure, and morphological features.


Introduction
Architectural heritage of Nigeria encompasses buildings with cultural, historical, aesthetic, religious, or economic significance inherited from past generations. It consists of vernacular architecture, colonial architecture, Brazilian/Afro-Brazilian architecture, and post-colonial architecture. These buildings were constructed with a combination of artistry and craftsmanship in different parts of the country. Some of these buildings have been declared national monuments [1], while some are on the proposed list of national monuments. They are made of different materials, such as clay (including adobe), wood (timber), metal, brass, palm fronds, date palm, raffia, and stone [2]. The use of these materials in buildings stems from their availability in the locality where the buildings were constructed. Nigeria's architectural heritage is significant and valuable and, therefore, demands innovative conservation to preserve it for present and future generations.
The need to conserve Nigeria's architectural heritage arises not only from its significance but also because of its deteriorating state ( Figure 1). Generally, materials used in the construction of heritage buildings are prone to physical, chemical, and biological decay caused by changes in climatic conditions, wind, water, and anthropogenic activities [3,4]. Other causes of damage include salt, fire, microorganisms, and insects [5,6]. The effects of these agents of deterioration are manifested as cracks and bulges; patina, surface, and basal erosion; crust formation; and fragmentation.
Heritage 2021, 4 FOR PEER REVIEW 2 these agents of deterioration are manifested as cracks and bulges; patina, surface, and basal erosion; crust formation; and fragmentation. Conservation of architectural heritage in Nigeria is done jointly or individually by different stakeholders, which include government, individuals, and private organizations. These stakeholders apply the ICOMOS Charter [7] fully or partially during conservation, which entails gathering data about the history of the building, assessing decay, implementing the required treatment, and introducing control measures [8]. Despite this approach, the use of innovative methods is lacking in various conservation management plans for architectural heritage in Nigeria. Studies [9][10][11] have shown that the holistic use of innovative technologies as a complement to the traditional conventional methods boosts the efficacy of both methods for conservation purposes. The benefits of the proper application of traditional conventional methods lie in the principle of using materials that are of the same type as the deteriorated ones during conservation [12]. On the other hand, new technologies are useful for ascertaining the exact material structure and cause of decay and proffering ecologically friendly restoration techniques [13,14]. The need for the inclusion of innovative methods in the conservation management plan of architectural heritage in Nigeria is, therefore, vital. This paper examines the challenges and prospects for implementing innovative methods for surveying, recording, and presenting data and information about the deterioration of architectural heritage, diagnosis of the causes of deterioration, and determination of the restoration methods to employ.

Conservation of Architectural Heritage in Nigeria
A multidisciplinary approach is used whereby appropriate experts and different stakeholders are involved in the conservation process from the outset [7]. The stakeholders include local communities, government organizations, such as the National Commission for Museums and Monuments (NCMM), community leaders, such as traditional rulers, and non-government organizations [15]. These stakeholders, through their ideas, knowledge, and skills, are meant to ensure that the built heritage is not only conserved but also that its values are preserved during conservation [16,17]. The values of heritage buildings should be perceived in the cultural context in which the architectural heritage exists and should be retained accordingly during conservation ( Figure 2). Sabri and Olagoke [18] explain how the value-based approach helps experts and local communities where the built heritage exists to reach a consensus on the type of material to be used in conservation, but ICOMOS [7] has emphasized that conservation of architectural heritage Conservation of architectural heritage in Nigeria is done jointly or individually by different stakeholders, which include government, individuals, and private organizations. These stakeholders apply the ICOMOS Charter [7] fully or partially during conservation, which entails gathering data about the history of the building, assessing decay, implementing the required treatment, and introducing control measures [8]. Despite this approach, the use of innovative methods is lacking in various conservation management plans for architectural heritage in Nigeria. Studies [9][10][11] have shown that the holistic use of innovative technologies as a complement to the traditional conventional methods boosts the efficacy of both methods for conservation purposes. The benefits of the proper application of traditional conventional methods lie in the principle of using materials that are of the same type as the deteriorated ones during conservation [12]. On the other hand, new technologies are useful for ascertaining the exact material structure and cause of decay and proffering ecologically friendly restoration techniques [13,14]. The need for the inclusion of innovative methods in the conservation management plan of architectural heritage in Nigeria is, therefore, vital. This paper examines the challenges and prospects for implementing innovative methods for surveying, recording, and presenting data and information about the deterioration of architectural heritage, diagnosis of the causes of deterioration, and determination of the restoration methods to employ.

Conservation of Architectural Heritage in Nigeria
A multidisciplinary approach is used whereby appropriate experts and different stakeholders are involved in the conservation process from the outset [7]. The stakeholders include local communities, government organizations, such as the National Commission for Museums and Monuments (NCMM), community leaders, such as traditional rulers, and non-government organizations [15]. These stakeholders, through their ideas, knowledge, and skills, are meant to ensure that the built heritage is not only conserved but also that its values are preserved during conservation [16,17]. The values of heritage buildings should be perceived in the cultural context in which the architectural heritage exists and should be retained accordingly during conservation ( Figure 2). Sabri and Olagoke [18] explain how the value-based approach helps experts and local communities where the built heritage exists to reach a consensus on the type of material to be used in conservation, but ICOMOS [7] has emphasized that conservation of architectural heritage is the combination of values and authenticity of the heritage, which is beyond the physical heritage and cannot be fixed. On the other hand, Ewemade and Osasona [19] have argued that the 'spirit and meaning' of heritage are born in the historical interaction of people and community with the buildings. The cultural context of the architectural heritage is, therefore, considered a vital component in conservation. The community knows the value of the built heritage and explains this to conservators so that it will be retained during conservation.
Heritage 2021, 4 FOR PEER REVIEW 3 is the combination of values and authenticity of the heritage, which is beyond the physical heritage and cannot be fixed. On the other hand, Ewemade and Osasona [19] have argued that the 'spirit and meaning' of heritage are born in the historical interaction of people and community with the buildings. The cultural context of the architectural heritage is, therefore, considered a vital component in conservation. The community knows the value of the built heritage and explains this to conservators so that it will be retained during conservation. Conservation is necessitated by deterioration caused by leaking roofs, moisture, insect and microbial attacks, the dilapidation of drainage facilities, pollution, and inappropriate use [2,20]. Other factors are poor funding for proper maintenance, civilization and development, and neglect [21]. Decay arising from these causative agents is observed as crumbling plaster and paint, warping of doors, sagging of roofs, cracks, leakages, discoloration, exit holes, moist walls, and corrosion [18,22]. Apart from deterioration, conservation is also done to prevent occurrence of decay.
Omisore and Ikpo [21] examined the conservation work of different cultural properties in Ile-Ife, Nigeria. The researchers observed that repair/replacement of structural elements was the major treatment strategy applied. Ewemade and Osasona [19], in their study, also noted the potential benefits of rehabilitation as evidenced in intervention on Ile Olayinka in Ile-Ife. They suggested that such conservation processes should be done for all architectural heritage. In addition to rehabilitation, removal of biological growth and clearing of blocked drainages are also part of the conservation process [19]. The diagnosis of deterioration in the conservation processes examined by Omisore and Ikpo [21] and Ewemade and Osasona [19] were, however, conducted mainly by visual observation.
Despite the emphasis on innovative techniques by the ICOMOS Charter on the analysis, conservation, and structural restoration of architectural heritage, traditional methods of conservation are continually applied, which has resulted in various failures in conserving architectural heritage ( Figure 3). Feilden [23] noted that documentation, diagnostic, and treatment stages are vital components of conservation of architectural heritage. Perito and Cavalieri [24] and Fais and Casula [14] examined conservation in the 21st century and submit that emerging technologies and methodologies are contributing to the successes of various conservation interventions implemented in Europe. However, Gbadegesin and Osaghale [15] revealed that innovative techniques are not employed in the documentation, diagnostic, and treatment stages of conservation, which results in ineffective and poorly managed heritage conservation in Nigeria. Conservation is necessitated by deterioration caused by leaking roofs, moisture, insect and microbial attacks, the dilapidation of drainage facilities, pollution, and inappropriate use [2,20]. Other factors are poor funding for proper maintenance, civilization and development, and neglect [21]. Decay arising from these causative agents is observed as crumbling plaster and paint, warping of doors, sagging of roofs, cracks, leakages, discoloration, exit holes, moist walls, and corrosion [18,22]. Apart from deterioration, conservation is also done to prevent occurrence of decay.
Omisore and Ikpo [21] examined the conservation work of different cultural properties in Ile-Ife, Nigeria. The researchers observed that repair/replacement of structural elements was the major treatment strategy applied. Ewemade and Osasona [19], in their study, also noted the potential benefits of rehabilitation as evidenced in intervention on Ile Olayinka in Ile-Ife. They suggested that such conservation processes should be done for all architectural heritage. In addition to rehabilitation, removal of biological growth and clearing of blocked drainages are also part of the conservation process [19]. The diagnosis of deterioration in the conservation processes examined by Omisore and Ikpo [21] and Ewemade and Osasona [19] were, however, conducted mainly by visual observation.
Despite the emphasis on innovative techniques by the ICOMOS Charter on the analysis, conservation, and structural restoration of architectural heritage, traditional methods of conservation are continually applied, which has resulted in various failures in conserving architectural heritage ( Figure 3). Feilden [23] noted that documentation, diagnostic, and treatment stages are vital components of conservation of architectural heritage. Perito and Cavalieri [24] and Fais and Casula [14] examined conservation in the 21st century and submit that emerging technologies and methodologies are contributing to the successes of various conservation interventions implemented in Europe. However, Gbadegesin and Osaghale [15] revealed that innovative techniques are not employed in the documentation, diagnostic, and treatment stages of conservation, which results in ineffective and poorly managed heritage conservation in Nigeria. Heritage 2021, 4 FOR PEER REVIEW 4 Figure 3. Conservation works on cracks in the entrance stair of another architectural heritage, Ologbenla House, Ile-Ife, Nigeria [19].

Innovative Technologies in Architectural Heritage Conservation
Innovative technologies have been applied in the conservation of architectural heritage in developed countries with proven effectiveness [25,26]. Many of the techniques applied are non-destructive and are used for documentation, diagnostic, and treatment purposes. As explained by Fais and Casula [14], non-destructive conservation methods of architectural heritage help to obtain qualitative and quantitative parameters needed for the conservation process of the architectural heritage but they are time consuming and delicate. Sterflinger and Piñar [5] identified determining appropriate treatment methods as the main challenge in the conservation of architectural heritage.
ICE [27], Stylianidis and Remondino [28] and Zhao and Zhang [11] classified conservation processes into three methods. First, documentation methods involve a survey of the architectural heritage, recording the parameters needed for the conservation processes and visualization of the parameters recorded for communication with the conservation team. Second, diagnostic methods involve analysis of the recorded parameters and treatment of the decay. Third, treatment intervention methods involve different strategies for the restoration of the architectural heritage. Figure 4 reveals the details of the various innovative methods for conservation of architectural heritage.

Innovative Technologies in Architectural Heritage Conservation
Innovative technologies have been applied in the conservation of architectural heritage in developed countries with proven effectiveness [25,26]. Many of the techniques applied are non-destructive and are used for documentation, diagnostic, and treatment purposes. As explained by Fais and Casula [14], non-destructive conservation methods of architectural heritage help to obtain qualitative and quantitative parameters needed for the conservation process of the architectural heritage but they are time consuming and delicate. Sterflinger and Piñar [5] identified determining appropriate treatment methods as the main challenge in the conservation of architectural heritage.
ICE [27], Stylianidis and Remondino [28] and Zhao and Zhang [11] classified conservation processes into three methods. First, documentation methods involve a survey of the architectural heritage, recording the parameters needed for the conservation processes and visualization of the parameters recorded for communication with the conservation team. Second, diagnostic methods involve analysis of the recorded parameters and treatment of the decay. Third, treatment intervention methods involve different strategies for the restoration of the architectural heritage. Figure 4 reveals the details of the various innovative methods for conservation of architectural heritage.

Documentation Methods
Gulotta and Toniolo [29] assert that 'each historical object has its unique characteristics according to its physical condition and time'. Conservation processes of architectural heritage, therefore, involve the understanding of the histories, values, and significance inherent in the physical and emotional features of the heritage [7]. Therefore, in view to understanding the heritage, it is vital to gather data about the physical condition such as condition of the materials and investigate the chemical composition, microstructure, and morphological features of the heritage [30]. Mohd-Isa and Zainal-Abidin [17] described documentation of architectural heritage to include surveying, recording, and presentation of the data. Innovative methods for documentation of architectural heritage are, therefore, classified into image-based, non-image-based, and combinative methods, as revealed in Figure 5. the architectural heritage, recording the parameters needed for the conservation processes and visualization of the parameters recorded for communication with the conservation team. Second, diagnostic methods involve analysis of the recorded parameters and treatment of the decay. Third, treatment intervention methods involve different strategies for the restoration of the architectural heritage. Figure 4 reveals the details of the various innovative methods for conservation of architectural heritage.  Heritage 2021, 4 FOR PEER REVIEW 5

Documentation Methods
Gulotta and Toniolo [29] assert that 'each historical object has its unique characteristics according to its physical condition and time'. Conservation processes of architectural heritage, therefore, involve the understanding of the histories, values, and significance inherent in the physical and emotional features of the heritage [7]. Therefore, in view to understanding the heritage, it is vital to gather data about the physical condition such as condition of the materials and investigate the chemical composition, microstructure, and morphological features of the heritage [30]. Mohd-Isa and Zainal-Abidin [17] described documentation of architectural heritage to include surveying, recording, and presentation of the data. Innovative methods for documentation of architectural heritage are, therefore, classified into image-based, non-image-based, and combinative methods, as revealed in Figure 5. In addition, ICE [27] categorized documentation methods into recording and visualization techniques (Figure 4. Hassani [30] described image-based techniques as methods based on production and archiving photographic data, which are used for interpreting, measuring, and modelling the architectural heritage. Non-image-based techniques, as well, produce images through separate processes that are not based on the surveying processes, while combinative methods take the advantage of image-based and non-imagebased techniques.

Diagnostic Methods
Conservation of architectural heritage is preceded by proper assessment of its structural elements and material to determine the causes of decay and its degree as well as the appropriate conservation measure to be applied [10,29]. The preliminary assessment is done by visual observation, by which conservators and architects evaluate decay only with naked eyes without any instrument. Although this is the compulsory basic step, it In addition, ICE [27] categorized documentation methods into recording and visualization techniques (Figure 4. Hassani [30] described image-based techniques as methods based on production and archiving photographic data, which are used for interpreting, measuring, and modelling the architectural heritage. Non-image-based techniques, as well, produce images through separate processes that are not based on the surveying processes, while combinative methods take the advantage of image-based and non-image-based techniques.

Diagnostic Methods
Conservation of architectural heritage is preceded by proper assessment of its structural elements and material to determine the causes of decay and its degree as well as the appropriate conservation measure to be applied [10,29]. The preliminary assessment is done by visual observation, by which conservators and architects evaluate decay only with naked eyes without any instrument. Although this is the compulsory basic step, it does not give detailed information about past or ongoing deterioration, hence, the need for informative diagnostic tools.
Optical microscopy (OM) and scanning electron microscopy (SEM) has the potential to characterize heritage materials, detect potential biodeteriogens, and shows the spatial distribution of potential surface biodeteriogens [25,31]. Characterization of the material gives an insight into the type of stone used (for stone building), groin compartment, and pore size, all of which determines the susceptibility of architectural heritage to deterioration [14,32]. The work by Fais and Casula [14] and Adetunji and Essien [33] showed a multistep and integrated approach in the diagnosis of a decayed historical building. A 3D Terrestrial Laser Scanner was used to study the geomorphology of the stone used in the building, while ultrasonic measurement determined the thickness of the stone to ascertain its elastomechanical strength. Infrared Thermography was used to measure the temperature across the surface of the heritage. In the study, results of the OM and SEM revealed the type of stone, porosity, and presence of microorganisms.
The study by Urzì and De Leo [13] demonstrated the use of non-invasive and nondestructive techniques in carrying out the diagnosis. These techniques are advantageous because they do not destroy the underlying material [34,35]. Materials used in these techniques include adhesive tapes [35], nitrocellulose membranes [36], and sterile scalpel [37]. Environmental and biological parameters of the heritage, which favor the growth of biofilms, can also be obtained. Temperature and humidity are measured with a thermohygrometer [38], while a dust sensor is used to detect dust [39].
A Raman spectrometer is a vital and useful tool in the conservation of architectural heritage. It is used for in situ analysis to determine organic and inorganic substances on a stone substratum including conservation chemicals such as consolidants and water repellents. A Raman spectrometer is very useful when there is no documented report on previous conservation treatment [40,41], which is attributable to its ability to identify conservation treatments. Results obtained by Dominguez-Vidal and de la Torre-Lopez [42] on in situ characterization of plasterwork decorations of the Hall of the Kings in the Alhambra (Granada, Spain) with a Raman microspectrometer showed that they consist of different types of pigments. They were identified as cinnaban, minium, carbon black, synthetic ultramarine blue, and natural lapis lazuli. X-ray diffraction determined the nature of a crystalline compound and the structure of natural compounds, too [31]. However, this method is not advocated in all circumstances because of its destructive nature [11].
The 'omics', genomics and proteomics, are innovative molecular-based diagnostic techniques applied in cultural heritage conservation. Genomics gives knowledge of microbes inhabiting a deteriorated heritage and can be used to deduce the active biodeteriogens on the heritage [24,43,44]. The work of Li and Zhang [45] showed the use of this technique to show the array of microorganisms on stone monuments in the vicinity of the UNESCO World Heritage Site at the West Lake Cultural Landscape of Hangzhou. Bacteria, fungi, and cyanobacteria were the potential biodeteriogens discovered.
The use of proteomics before conservation is beneficial because it identifies organic binders used in paintings on a heritage material or in past conservation activities [46]. Even though proteomics has not been used on architectural heritage, it will be useful for the conservation of painted architectural heritage in Nigeria. Mass spectrometer (MS), Fourier Transform Infrared Spectrometer (FTIR), and Sodium Dodecyl Sulphate→Polyacrylamide Gel Electrophoresis (SDS→PAGE) are the tools used for this method. FTIR identifies organic materials and, in some cases, inorganic materials, while SDS→PAGE separates and identifies the particular protein present in the organic material.

Treatment Interventions
Recent developments in conservation of cultural heritage have resulted in effective, safe, and eco-friendly techniques. These techniques include biotechnology (bioconservation), nanotechnology, and laser technology among others (Figure 4). Clamor for the use of biotechnology in the restoration of cultural heritage started over a decade ago [47,48] and has been applied in developed countries [49,50] but not in Nigeria. The advantages of biorestoration over some traditional methods lies in its non-toxicity to conservators, nondestructive approach, specificity in action, ecofriendliness, and effectiveness [51]. Romano and Abbate [49] demonstrated the safety and effectiveness of using bacteria to remove nitrate salt efflorescence on stone samples. Nitrate and sulphate removal on Matera Cathedral, Italy, by microorganisms was also proved by Alfano and Lustrato [52]. The cloister entrance of San Jeronimo Monastery, Granada, Spain, was damaged by salt weathering and pitting due to environmental pollution. The architectural heritage was consolidated with a set of carbonatogenic bacterial communities [53].
Nanotechnology has been widely applied in heritage conservation as consolidants [54], cleaning agent [26,55], and biocide [56]. Van der Werf and Ditaranto [57] compounded a bioactive zinc (II) oxide (ZnO) nanocomposite for the conservation of the 12th-century church of San Leonardo di Soponto in Italy. The biocide was embedded in a water-repellent consolidant, tetraethyl oxysilane (TEOS), and/ or siloxanes-based material (SILO III and Estel 1100); TEOS, SILO III, and Estel 1100 are nanocomposite materials. SEM-EDS was used to ascertain the geomorphology of the stone monument. It was observed that the nanocomposites consolidated the weathered stone. Cioffi and Torsi [58] developed a copper polymer organo-composite that has antifungal and bacteriostatic properties that were tuned to be released gradually over time.

Materials and Methods
The study focused on the perceptions of heritage professionals in using innovative methods in conservation of architectural heritage in Nigeria. Forty heritage professionals participated in a questionnaire survey. Thirty-one (77.5%) questionnaires were dully completed and returned for analysis. The questionnaire was designed into five sections to examine the respondents' level of awareness of the methods (Table 1) Table 2 presents the spread of the respondents based on their level of education, profession, years of experience, and employment status. All the respondents have attained the minimum training of diploma in professions relevant to heritage management and conservation. Architecture (25.81%) and archaeology (19.35%) were the major professions of heritage experts in Nigeria, while 48.39% (n = 15) of the respondents were working in government organizations such as universities, polytechnics, and government ministries.

Awareness
The level of awareness about the innovative methods was measured based on three indicators (familiarity, technical know-how, and usage). As indicated in Table 3, familiarity with the innovative technologies was somewhat low (mean value of 2.19), which is a result of less than 30% of the respondents learning about any of the technologies during formal training and 41.9% gaining minimal level of technical know-how about the innovative technologies, attending 'on-the-job' workshops and training sessions. Familiarity is a subjective indicator but was defined in this study as having theoretical knowledge about innovative technologies. The low level of technical know-how (1.34) is also considered an impediment to usage of the innovative technologies in conservation intervention of architectural heritage in Nigeria. Of the respondents, 38.7% (n = 12) had participated in implementing the innovative technologies in conservation interventions. This could be due to low level of skilled heritage professionals who are capable of implementing the technologies. More than 80% of the respondents had implemented photography, GIS, 3D modelling, and photogrammetry for documentation, while 58.06% (n = 18) had implemented at least one of the innovative methods for treatment intervention.

SWOT Analysis
It is pertinent to understand the perception of respondents to the strengths of implementing innovative technologies for documentation, diagnosis, and treatment of deterioration in architectural heritage in Nigeria. The strengths focus on the positive impacts and attributes of the innovative technologies on the conservation of architectural heritage ( Table 4). The respondents strongly agreed that employing innovative technologies in conservation of architectural heritage will improve the performance of conservation intervention (mean value of 3.58), provide new knowledge to heritage professionals (3.62), and enhance the quality and quantity of data available on architectural heritage in Nigeria (3.79). On the other end, there was disagreement that implementing the technologies will engender inter-organization collaboration (1.84) due to the poor state of information sharing and collaboration that is experienced across the non-governmental and governmental organizations within the heritage management sector in Nigeria. The respondents also ranked enhancement of quality and quantity of data on architectural heritage as the most important strength of employing innovative conservation technologies while improvement of collaboration between organizations ranked least. The results shown in Table 5 reveal the potential weaknesses of employing innovative techniques in the conservation of architectural technologies in Nigeria. The cost of equipment and tools needed for the technologies, adequacy of trained professionals, and availability of funds constitute concerns to the respondents. The weaknesses need to be addressed to ensure realization of the benefits of the innovative technologies in protection of the values and significance of the architectural heritage in Nigeria. The increased cost of conservation intervention (ranked fourth) is also one of the weaknesses that need to be addressed because cost-benefit of implementing the innovative technologies is vital to determining how to conserve the architectural heritage. Tables 6 and 8 reveal the opportunities and threats to the implementation of innovative technologies in conservation and protection of architectural heritage in Nigeria, respectively. The results of mean and standard deviation in Table 6 reveal the main opportunity of the innovative technologies is 'protection of values and significance inherent in the architectural heritage' (3.84), while the potential of innovative heritage to encourage young people to study professions relevant to heritage conservation (1.45) is the least ranked opportunity of implementing the innovative technologies. The potential threats, as shown in Table 7, reveal that respondents considered the innovative technologies as threats to the local trades and practices used in conserving the architectural heritage. The respondents also agreed that the production of large amounts of data about the architectural heritage (2.79) could threaten the strengths and opportunities of implementing the innovative technologies in Nigeria.

Analysis of Conservation Intervention
Three conservation interventions were conducted by the National Commission for Museums and Monuments (NCMM) from 2018 to 2021 using different methods for documentation and treatment of different forms of deterioration and defects. Gidan Madaki, an example of earthen architecture built in 1860, was declared a national monument on 16 February 1956 and remains among the rare architectural heritage of the late Muhammed Durugu, a renowned master builder who designed various Emir palaces in Northern Nigeria. The palace of Deeji of Akure Kingdom, declared as a national monument on 15 February 1989, was built as a symbol of socio-political, economic, and spiritual development of Yorubas after the end of the trans-Atlantic slave trade. The walls, doors, and windows of the palace were embellished with artworks and motifs, while Zaria Friday Mosque was designed and built in 1830 by the master builder Babban Gwani Mikhaila to serve as space for Islamic religious activities. The mosque was declared a national monument in 1970 to serve as a source of knowledge about traditional architecture in Nigeria.
The three national monuments were built using mud bricks (tubali), stones, wood, sandcrete plaster, and local steel. The buildings, however, are threatened by termites, storms, floods, and other climate elements ( Figure 6). Therefore, NCMM implemented conservation interventions from 2018 to 2021 to address the extent and impacts of defects threatening the values and safe use of the monuments. Table 8 discusses the processes and methods implemented by NCMM to address the observed deteriorations on the three national monuments. The defects observed on the three monuments were documented using digital photography and physical observation but none of the defects was diagnosed to understand the causes and extents of the defects. The heritage professionals from NCMM addressed the defects through processes for removal, restoration, and reconstruction (see Table 8).
Heritage 2021, 4 FOR PEER REVIEW 11 storms, floods, and other climate elements ( Figure 6). Therefore, NCMM implemented conservation interventions from 2018 to 2021 to address the extent and impacts of defects threatening the values and safe use of the monuments. Table 8 discusses the processes and methods implemented by NCMM to address the observed deteriorations on the three national monuments. The defects observed on the three monuments were documented using digital photography and physical observation but none of the defects was diagnosed to understand the causes and extents of the defects. The heritage professionals from NCMM addressed the defects through processes for removal, restoration, and reconstruction (see Table 8).

Discussion
The findings of the study revealed that innovative technologies are most applied for documentation of architectural heritage to conduct activities related to surveying, recording, and presentation of data on architectural heritage. The results also show that many of the heritage professionals in Nigeria are government staff and have inadequate skill capacity to implement innovative tools. The findings corroborate Akinkunmi [2], who emphasized the need for improvement of skill capacity of heritage professionals in developing and implementing innovative methods for conservation of architectural heritage to address various forms of deterioration impacting the authenticity and values of the heritage.
Most of the heritage professionals, as well, are familiar with the innovative technologies, mainly through theoretical propositions without hands-on practice of the innovative methods for diagnosis of deterioration in architectural heritage. This is due to poor funding of government organizations with responsibilities of conserving and managing the architectural heritage in Nigeria, inadequate state-of-the-art equipment and facilities, and poor inter-organization collaboration and information sharing. Adetunji and Essien [33] also emphasized the need to review the curriculum in practice in tertiary institutions training heritage professionals to include 'hands-on' workshops and field work to expose the students to various technological innovations in heritage conservation.
In the study conducted by Osasona and Ewemade [60], the values of architectural heritage were embedded in the good and rare quality of craftwork and traditional knowledge that connects the building to histories of the people and positions the building in the identity of the community. This assertion is corroborated by the findings in the high ranking of the opportunity of the innovative technologies to protect the values and significance of the architectural heritage. Omisore and Ikpo [21] also confirm the significant relationship between the age of the building and the rate of conservation needed in architectural heritage in Nigeria.
The findings equally revealed that heritage professionals have concerns about the amount of data that will be produced if innovative technologies were implemented and the performance of conservation interventions. However, Hassani [30] regards the challenges in implementing innovative technologies for the documentation and diagnosis stages of conservation. It is, therefore, vital to develop appropriate policies and strategies for data management, especially for conservation intervention. Gbadegesin and Osaghale [15] emphasized the vital role of heritage management policies in improving the performance of conservation interventions and ensuring data collected during the interventions are used to improve research into various issues affecting heritage conservation in Nigeria.

Conclusions
Architectural heritage conservation in Nigeria is not effectively practiced compared to developed countries and it is still rooted in only traditional methods of conservation to the exclusion of innovative techniques. The application and benefits of innovative technologies in architectural heritage conservation cannot be overemphasized. The technologies are effective and could unravel the constituents of heritage materials, identify potential biodeteriogens, safely clean heritage surfaces, and consolidate materials and they are sustainable. Few studies have been conducted on innovative techniques in conservation of cultural heritage in Nigeria, but more studies are needed on the indicators of adopting innovative technologies and the perception of local communities to implementing the techniques in conservation of architectural heritage.
Conservation of values and significance of architectural heritage demands a combination of traditional and innovative methods to maintain the connection of local communities as well as to improve the success of conservation interventions through the implementation of evidence-based innovative techniques. The study, at first, advocates increased awareness through training of professionals involved in conservation on the usefulness of complementing the traditional methods with the innovative methods. Innovators should also communicate the need for these techniques in such a way as to connect innovation and practicality in the field. Second, the necessary equipment and materials needed to actualize the innovative methods to conservation of architectural heritage should be provided. Funding has been known to be a major challenge in conservation of architectural heritage in Nigeria. Stakeholders should, therefore, source funds to salvage Nigeria's architectural heritage. Based on the findings, employing innovative methods offers vast opportunities and benefits in improving the performance of conservation interventions. No doubt, the innovative methods will also assist heritage professionals to understand the values and significance of the vast architectural techniques and comply with internationally agreed standards for heritage conservation. Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.

Data Availability Statement:
The data presented in this study are part of ongoing doctoral research at University of Newcastle and are available in this article.