INSDAG: Creating Sustainable Rural Housing in Steel
In view of the need for Sustainable Rural Structures in India, INSDAG has developed different modules of rural buildings which are mainly steel intensive and have the benefits of being robust, functional, comfortable, low-maintenance and affordable.
Nibedita Dey, Senior Manager (Civil &Structural), Institute for Steel Development & Growth (INSDAG), Kolkata
Housing, Construction & Infrastructure industry consumes the maximum quantity of steel (approximately 60-65% of total steel consumption). Demand from building and construction segment, which accounts for 35-40% of steel demand, is expected to rise by 5-6% between FY 2021-22 and FY 2024-25, led by a pick-up in affordable housing, and ‘kutcha to pucca’ conversions in rural belts.
The per capita consumption of steel in urban areas has increased from 57.6 kgs to 81 kgs during the last five years. The government has an objective of increasing rural consumption of steel from the current 19.6 kg/per capita to 38 kg/per capita by 2030-31.
Government initiatives on the housing front through the Pradhan Mantri Awaas Yojana (PMAY) scheme for urban and rural areas will help drive steel demand growth. In rural areas, PMAY-G has a target to construct 29.5 million houses with all basic amenities by 2022. Despite good progress under the scheme, only 12.5 million units have been constructed, which leaves 17 million units yet to be constructed.
With the above targets in focus, INSDAG has initiated measures to enhance steel consumption and also to fast-track construction in rural areas, by working on steel-based models for rural buildings like Schools, Panchayat halls, Anganwadi centres, and individual houses.
Figure a
To achieve the goal of sustainable construction material and to promote steel as a sustainable construction material, INSDAG has developed building framing and cladding using structural steel and steel reinforcement for use in building foundations, and other elements.
Steel reinforcement is used in beams, columns and roof slabs of conventional RCC buildings with brick walls, but we can use structural steel sections like MB, Parallel flange, Square Hollow Section (SHS), Rectangular Hollow Section (RHS) etc. in place of RCC columns and beams. Steel angles and channels can be used in roof supporting trusses and thin steel sheets may be used in roofing. This can make construction faster and also affordable if properly designed using the right materials.
Steel Hollow Section has been selected as a member of the framing system for its strength and lightweight. Use of structural steel section and prefabricated elements in building framing, roofing and wall system will make it lighter weight and will ensure fast track construction. Precast Ferro-Cement panels of 15 mm thickness (which are thinner than brick) have been selected for cladding because of their capacity to withstand lateral loads due to wind, and also because of their durability despite the weathering actions of nature, termite attacks, etc. These panels are also lightweight hence an overall benefit in foundation design is possible due to the reduced self-weight of the materials.
For the foundation, isolated pad footings with pedestals and tie beams around the building tying the top of pedestals have been considered.
Additional cost due to protection of steel members against corrosion and fire can be considered minimum as it may be assumed that corrosion will be protected by intermittent standard enamel painting and maintenance, and in case of fire, the dwellers will get sufficient scope to go outside.
The aspects of heat insulation and ventilation have been given due consideration because they are directly related to the conservation of human energy. The thickness of Ferro-Cement Panels used in this design being only 15 mm, the insides of the buildings may not be thermally well protected when used in a single layer. Hence, a typical panel size of 1m x 1m for the cladding material has been chosen. Each panel is made of a 15 mm thick Cement-Sand mortar (1:1) skin with 1 layer of 0.265 mm diameter galvanized chicken mesh under a layer of 2.65 mm diameter reinforcement @ 25 mm c/c both ways as welded mesh placed centrally. The gaps (approx. 2 mm) between the panels and SHS sections will be sealed with waterproof grouting using SIKA / Accoproof or equivalent, to make the connections leak proof.
A double layer of Ferro-Cement panels can also be provided, one on each side of the Square Hollow Sections, thereby creating an air gap in between the two cladding panels for insulation. Thus, during summer, the inside of the building will remain comparatively cool with respect to the outside temperature, and during winter, the reverse situation will occur. The buildings have been planned and designed to create a healthy environment with proper ventilation and illumination. In the model house, the ferro-cement panel was fixed onto the steel members by cross members at the four corners. Thermocol was placed behind it and sand-cement (1:4) plaster laid on it from inside the house, with a square net placed on the thermocol.
The steel structural grid is earthed. The connections can be detailed in such a way that the steel sections remain concealed within the claddings. Further, insulated electrical wires can be routed through PVC conduits, hence, there is no chance of electrocution due to short circuit and the effect of thunder is minimised.
Typical Structural Arrangement with Hollow Steel Section with Ferro cement Panel
Left - Structural Frame & Ferro cement panels while Installation; Right - Connection of SHS with Ferro cement panel
Picture 1 & Picture 2: Prototype Buildings Installed by INSDAG
Structural Framework: The entire framework for the building has been conceptualized using Square Hollow Section with idealized panels approximately 1.0mx1.0 m. The members are connected with the SHS or RHS sections by insert plates.
Many more prototypes have been installed by INSDAG in places like Burdwarn, West Bengal (2013), Tripura, Talegaon, Maharashtra (2017) with FC Panels and with Bamboo Composite panels in Andhra Pradesh (2008).
Figure b: Model Rural House Installed at Rural Technology Park at the Campus of National Institute of Rural Development & Panchayat Raj, Hyderabad. (Installed in 2018 and in good condition in 2023)
Figure c & Figure d: Connection between Ferro-cement Panels flushing with SHS Section at Walls
Nibedita Dey, Senior Manager (Civil &Structural), Institute for Steel Development & Growth (INSDAG), Kolkata
Housing, Construction & Infrastructure industry consumes the maximum quantity of steel (approximately 60-65% of total steel consumption). Demand from building and construction segment, which accounts for 35-40% of steel demand, is expected to rise by 5-6% between FY 2021-22 and FY 2024-25, led by a pick-up in affordable housing, and ‘kutcha to pucca’ conversions in rural belts.
The per capita consumption of steel in urban areas has increased from 57.6 kgs to 81 kgs during the last five years. The government has an objective of increasing rural consumption of steel from the current 19.6 kg/per capita to 38 kg/per capita by 2030-31.
Government initiatives on the housing front through the Pradhan Mantri Awaas Yojana (PMAY) scheme for urban and rural areas will help drive steel demand growth. In rural areas, PMAY-G has a target to construct 29.5 million houses with all basic amenities by 2022. Despite good progress under the scheme, only 12.5 million units have been constructed, which leaves 17 million units yet to be constructed.
With the above targets in focus, INSDAG has initiated measures to enhance steel consumption and also to fast-track construction in rural areas, by working on steel-based models for rural buildings like Schools, Panchayat halls, Anganwadi centres, and individual houses.
Benefits of Steel Houses
A steel-based rural house is a modern and durable construction option for those seeking practicality, functionality, and aesthetic appeal. Steel, known for its strength and resilience, offers numerous advantages for rural homes:- Steel provides exceptional protection against extreme weather conditions like heavy rains, strong winds, and snow loads.
- Steel is resistant to pests offering homeowners peace of mind in rural areas where wildlife can be a concern.
- Steel houses can be engineered to withstand seismic activity in regions prone to earthquakes
- Steel’s versatility enables flexible floor plans, enabling homeowners to create spacious living areas, comfortable bedrooms, and customized layouts tailored to their specific needs.
- Steel construction allows for quick assembly, efficient construction, and timely completion.
- Steel is environmentally friendly as it can be recycled and has a lifespan that far exceeds traditional building materials.
INSDAG Initiatives
Figure aSteel reinforcement is used in beams, columns and roof slabs of conventional RCC buildings with brick walls, but we can use structural steel sections like MB, Parallel flange, Square Hollow Section (SHS), Rectangular Hollow Section (RHS) etc. in place of RCC columns and beams. Steel angles and channels can be used in roof supporting trusses and thin steel sheets may be used in roofing. This can make construction faster and also affordable if properly designed using the right materials.
Materials & Structural System
While selecting the materials and components required for constructing rural structures, due consideration has been given to the durability aspect like termite attack, strength to withstand the thrusts of wind, earthquake tremors, and comfort like temperature variations, proper ventilation, etc. The finished ground level of the housing units can be kept above the high flood level of a particular area at site. It has been observed from the data collected from villages that during an average monsoon the requirement of such elevation is 600 mm.Steel Hollow Section has been selected as a member of the framing system for its strength and lightweight. Use of structural steel section and prefabricated elements in building framing, roofing and wall system will make it lighter weight and will ensure fast track construction. Precast Ferro-Cement panels of 15 mm thickness (which are thinner than brick) have been selected for cladding because of their capacity to withstand lateral loads due to wind, and also because of their durability despite the weathering actions of nature, termite attacks, etc. These panels are also lightweight hence an overall benefit in foundation design is possible due to the reduced self-weight of the materials.
For the foundation, isolated pad footings with pedestals and tie beams around the building tying the top of pedestals have been considered.
Additional cost due to protection of steel members against corrosion and fire can be considered minimum as it may be assumed that corrosion will be protected by intermittent standard enamel painting and maintenance, and in case of fire, the dwellers will get sufficient scope to go outside.
The aspects of heat insulation and ventilation have been given due consideration because they are directly related to the conservation of human energy. The thickness of Ferro-Cement Panels used in this design being only 15 mm, the insides of the buildings may not be thermally well protected when used in a single layer. Hence, a typical panel size of 1m x 1m for the cladding material has been chosen. Each panel is made of a 15 mm thick Cement-Sand mortar (1:1) skin with 1 layer of 0.265 mm diameter galvanized chicken mesh under a layer of 2.65 mm diameter reinforcement @ 25 mm c/c both ways as welded mesh placed centrally. The gaps (approx. 2 mm) between the panels and SHS sections will be sealed with waterproof grouting using SIKA / Accoproof or equivalent, to make the connections leak proof.
A double layer of Ferro-Cement panels can also be provided, one on each side of the Square Hollow Sections, thereby creating an air gap in between the two cladding panels for insulation. Thus, during summer, the inside of the building will remain comparatively cool with respect to the outside temperature, and during winter, the reverse situation will occur. The buildings have been planned and designed to create a healthy environment with proper ventilation and illumination. In the model house, the ferro-cement panel was fixed onto the steel members by cross members at the four corners. Thermocol was placed behind it and sand-cement (1:4) plaster laid on it from inside the house, with a square net placed on the thermocol.
The steel structural grid is earthed. The connections can be detailed in such a way that the steel sections remain concealed within the claddings. Further, insulated electrical wires can be routed through PVC conduits, hence, there is no chance of electrocution due to short circuit and the effect of thunder is minimised.
Typical Structural Arrangement with Hollow Steel Section with Ferro cement PanelLeft - Structural Frame & Ferro cement panels while Installation; Right - Connection of SHS with Ferro cement panel
Steel Based Building Components in Rural Houses
Roofing: Roof sheeting is done with 0.5 mm thick Corrugated Galvanized/ Galvalume colour coated Steel Sheets spanning over purlins supported on steel portals or trusses made from Square Hollow Section/ Rectangular Hollow Section. A lighter weight Galvalume sheet and FC panel can also be used.Picture 1 & Picture 2: Prototype Buildings Installed by INSDAGStructural Framework: The entire framework for the building has been conceptualized using Square Hollow Section with idealized panels approximately 1.0mx1.0 m. The members are connected with the SHS or RHS sections by insert plates.
Many more prototypes have been installed by INSDAG in places like Burdwarn, West Bengal (2013), Tripura, Talegaon, Maharashtra (2017) with FC Panels and with Bamboo Composite panels in Andhra Pradesh (2008).
Figure b: Model Rural House Installed at Rural Technology Park at the Campus of National Institute of Rural Development & Panchayat Raj, Hyderabad. (Installed in 2018 and in good condition in 2023) Cost & Affordability
A building module by INSDAG would cost around Rs. 1450/- per sq. ft. (as estimated in August 2022 with CPWD schedule of rates), with steel usage of 55 kg steel per sq. ft. (structural steel & TMT bars) which is competitive and sometimes lower if constructed on a mass scale, compared to the construction cost of a common RCC frame house with a brick wall with steel usage (TMT only) of 35 kg per sq. ft. of construction area. This specific model will reduce construction time and give quicker use of the house to the owners.Figure c & Figure d: Connection between Ferro-cement Panels flushing with SHS Section at WallsConclusion
Steel intensive models in public buildings in the rural areas will not only increase steel consumption in the rural sector but will also generate employment in villages. Large scale application of these steel-based housing models will create more affordable housing schemes in rural areas. Use of more structural steel in rural structures will decrease the use of natural resources like water and sand in wet method construction and will help in supporting a more sustainable environment.References
- Report of Indian Steel Association (January 2021) on New Opportunities for Steel in Construction and Infrastructure prepared by CRISIL
- INSDAG Publications: INS/ PUB/ 052, INS/PUB 072, INS./PUB/13
ICCT, January- February 2024
