The list of largest clear span structures needs a litte additional explanation:

Qualifying structures

In the context of this site, the size of a dome is taken to refer to the diameter of the largest horizontal circle that will completely fit inside the dome.

To qualify for the list:

  • Structures must be fully covered, or capable of being fully covered. A few Small holes in the roof are permitted - but large holes - or large numbers of holes that let in wind and rain - are not.

  • Structures must have a clear span of 100m or greater.

Air supported structures are permitted. Internal structures that reach up as far as the roof are permitted only if their structural element is very minor.

One example of a structure that does not qualify for this list, is the Commerzbank Arena. This can reach about 99% coverage when closed - but it appears that rain cannot currently be effectively eliminated from the interior.

Another structure that fails to qualify is the Arecibo Observatory. At 305m in diameter, this might be the largest clear-span structure in the world. However, currently the fabric of the roof is held down with numerous cables - and the fabric itself is porus - and lets in the rain - and so this structure doesn't currently appear on this list.


All figures are approximate - and may be subject to revision as more accurate information comes to light.

I've made an effort to calculate the clear span of The Millennium Dome at the point where the distance between the towers is the largest.

Corrections would be gratefully received. They may be submitted to the maintainer of this page here.

Alternative approaches

Instead of taking the size of a structure to represent a measure of the associated clear span, it is also possible to consider a measure of how much space is protected from the elements.

Such a list would look a little different:

The Muna bulk reservoir - at 340m in diameter - would be number one.
The Millennium dome at 320m in diameter - would be number two.
Structures such as the Haj Terminal might get into the list.

This approach was rejected on the grounds that the clear span was a more significant metric.

Tim Tyler | Contact |