A conoid is a special kind of warped ruled surface which, as a curved shell roof, can be used as an alternative to a barrel vault. The basic principle is that one edge of the shell is curved while the opposite edge is kept straight. In architecture, this is referred to as a ‘right conoid’.
Two basic geometrical forms are encountered:
- A straight line is moved along a curved line at one end and a straight line at the other end, the resultant shape being cut to the required length.
- A straight line is moved along a curved line at one end and a different curved line at the other end.
Spans of up to 12 m with chord lengths of up to 24 m are possible. The typical chord-to-span ratio is 2:1.
When conoids are made of reinforced concrete they require formwork on which to set the reinforcing steel and pour the concrete. The initial cost of making the formwork is usually high, but it can be reduced by pouring many shells on the same form.
There can be a solid infill or glazed end diaphragm. Glass panes set between adjacent conoids at the curved front of each conoid can allow for illumination. If the conoids face north they get the best natural light, which can be important for space such as factories.
 Related articles on Designing Buildings Wiki
- Barrel vault.
- Folded plate construction.
- Hyperbolic paraboloid.
- Long span roof.
- Pendentive dome.
- Portal frame.
- Shell roof.
- Suspended ceiling.
- Types of ceiling.
- Types of dome.
- The history of fabric structures.
 External references
- ‘Building Construction Handbook’ (6th ed.), CHUDLEY, R., GREENO, R., Butterworth-Heinemann (2007)
- ‘The story of a right wavelet conoid’ , J. Dolezal (2011)
Featured articles and news
Read about RSHP's British Museum extension which has been shortlisted for the 2017 Stirling Prize.
Read our introductory article to building a house extension.
More updates from DCMS about the large-scale testing of cladding systems and the number of buildings affected.
UandI secure resolution to grant planning consent for major new regeneration project.
IHBC article considers how heritage is dealt with when infrastructure schemes are authorised.
It was the tallest structure in the world for 3,800 years, but to this day the exact construction techniques are a mystery.
Shortlist for the industry's most coveted award announced.
Government responds to Mark Farmer's review of industry, rejecting the call for a levy on clients.
Peter Hansford to examine what wider lessons can be learned from the fire.
Every project is subject to uncertainty. How can construction better understand uncertainty for performance improvement?
MAD Architects reveal their designs for a futuristic campus for electric car manufacturer.
Homebuyers could borrow more with better forecasting of energy bills, according to industry consortium's new report.
Read our introductory article on carbon capture and storage.