Conical Grain Bin

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

Waste

Prefabricated panels should result in no offcuts or waste.

Chart of Embodied energy & carbon

Energy Efficiency

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.

Durability: High

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.

Code compliance

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

n/a

Future development

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.