Conical Grain Bin
Floor & Roof Structure: MATERIALS ENCYcLOPEDIA
Applications for this system
Roof structure and sheathing for round buildings
Preformed steel panels
Bolts and brackets
Ratings Chart for conical grain bin roof
The ratings chart shows comparative performance in each criteria category. Click on the tabs below for detailed analysis of each criteria.
- HOW THE SYSTEM WORKS
- ENVIRONMENTAL IMPACTS
- EMBODIED CARBON
- ENERGY EFFICIENCY
- MATERIAL COSTS
- LABOUR INPUT
- SKILL LEVEL REQUIRED
- SOURCING & AVAILABILITY
- CODE COMPLIANCE
- INDOOR AIR QUALITY
- FUTURE DEVELOPMENT
Conical Grain bin roof System
Preformed, ribbed steel panels are bolted together with a compression ring at the top and connection ring at the base of the roof. The ring at the roof base is used to attach the roof to the top of the wall system. Depending on the size of the roof, additional rings may be required mid-span. A hatch or glazed skylight is installed at the peak of the roof.
The roof can be assembled in place on top of the walls, but they are often built on the ground and craned into place.
The roofs are available from manufacturers in a variety of diameters from 4–20 meters (12–60 feet).
The roofs are designed to sit atop round metal grain bins, and will require special adaption to fasten properly to the top of other wall systems and provide adequate overhang.
Environmental Impact Rating
Harvesting — High
The extraction of ore for steel production is a high-intensity process, with impacts including habitat destruction and air and water pollution. Recycled content can mitigate these impacts.
Manufacturing — High
Steel production is a high-intensity process, requiring several applications of high heat, with impacts that include fossil fuel use, air and water pollution. Recycled content incurs the same impacts. It can be difficult to trace the origins of the raw materials that are contained in a manufactured steel product like a conical grain bin roof.
Transportation — Moderate to High
Sample building uses 950 kg of steel and connectors for roof kit:
1.43 MJ per km by 15 ton truck
0.9 MJ per km by 35 ton truck
0.24 MJ per km by rail
Manufacturers exist in most regions. It is difficult to ascertain the transportation impacts of the material through the whole production cycle, as steel is a multinational industry.
Installation — Negligible
Prefabricated panels should result in no offcuts or waste.
Chart of Embodied energy & carbon
Conical roof systems are not designed to be insulated, so the energy efficiency of a home using a conical roof will depend entirely on the design and execution of an insulation strategy being married to the roof.
Two insulating strategies are possible with this type of roof. Additional framing can be built underneath the steel roof structure, with insulation blown or laid into the cavity between the steel and the framing beneath, or a spray-on insulation can be applied directly to the underside of the steel. In both scenarios, some type of finished ceiling will need to be installed to separate and protect the insulation. Performance will vary based on the quantity and thermal value of the chosen insulation. As there is no inherent framing depth in a conical roof, it can be straightforward to design an insulation strategy that is not limited by the depth of structural members, but rather suited to the insulation needs of the building.
Material costs: high
The cost of a conical roof kit is higher than any other “framing” system in this chapter, but the system is roof structure and roof sheathing in one assembly. To properly compare costs, a framing system and a sheathing system must be looked at together.
Labour Input: moderate
Conical roofs are designed to be quick to assemble and install. Most residential builders are likely to be unfamiliar with these systems, so extra time may be required to understand and follow the assembly instructions. As these roofs incorporate structure and sheathing in one assembly, they tend to require less labor time than systems that involve the construction of a frame, decking and then sheathing.
Much of the labor time will be involved in the construction of a system for containing insulation below the roof. The design of this system will have a large impact on labor time.
Skill level required for homeowners: easy to moderate
Conical roofs are straightforward to assemble, and beginners should have no problem following the instructions.
The framing of an insulation layer will potentially involve more skill than the roof assembly. A simple, flat ceiling design in which the conical space is empty attic and insulation is laid on the flat ceiling will be extremely fast and easy to install, though it will sacrifice the use of the conical space as a loft or second storey.
Sourcing & availability: moderate to Difficult
There are numerous manufacturers of conical roof systems in North America, and most regions will have available distribution from at least one. As the roofs are designed for agricultural use, they are not available from typical residential construction supply companies.
Conical steel roofs rely on the geometry of the steel panels and bolts to maintain their structural integrity, as there are no redundant structural members in the system. Galvanized steel is the most common material for both elements, and will have a long lifespan. Unlike other roofing systems where the structure is hidden beneath the sheathing and is therefore difficult to monitor, conical roofs can be structurally inspected from the exterior. Rusting will be the telltale sign of deterioration, and should be very visible. Most conical roofs do not show any signs of rust for at least twenty years, and structurally problematic rust may not occur for many decades afterward.
The round shape of the roof spreads loads evenly around the entire roof system and minimizes the effects of wind loads, which can help with durability through extreme weather cycles.
Residential building codes will not include conical steel roofs as an acceptable solution, as they are typically used in agricultural settings. Conical steel roofs are pre-engineered from the manufacturers, and should satisfy the requirements of objective codes. The point of connection between the roof and the wall system will likely be a custom-fabricated arrangement, and a structural engineer’s approval may be required to ensure the connection is code-compliant.
Indoor air quality
The conical steel roof will be entirely outside the building enclosure and will have no effect on indoor air quality.
Resources for further research
Conical steel roofs have been used for decades in agricultural settings, and the system has been well developed. Since circular designs for residential use are uncommon, it is unlikely that conical steel roof manufacturers will develop prefabricated fastening systems to attach the roofs to typical residential wall systems.
Tips for a successful conical grain bin roof
1. Conical metal roofs are proprietary products, and each manufacturer will have its own installation guidelines that should be followed closely.
2. Modifications to the roof connection system should be designed and approved by a structural engineer or the manufacturer of the roof system to ensure that loads are properly transferred to the walls and proper uplift resistance is achieved.
3. If a roof overhang is desired, the system must be modified to allow for a wall system of smaller diameter than the roof.
4. An insulation strategy must be designed for the roof system. As the steel roof is the structure, there are no framing members or depth to the system for resting or containing insulation. A secondary framing system is often employed beneath the metal roof to provide the required insulation depth.
5. The manufacturer or a structural engineer must approve modifications to the conical roof such as dormers or skylights.