Rabbit Arks/Apex Rabbit Runs
Apex or ark rabbit runs are triangular shaped runs. They are often cheap and most fold flat so they are popular with rabbit owners. However they do have some drawbacks that you should keep in mind before choosing one.
The major drawback with this style rabbit run is the sloping sides severely limiting the useable space. For example a 5'x2' apex run has an apparent floor area of ten square feet. However when you subtract the areas where the low sides make it impossible for your rabbit to sit up this is reduced by around 40% to only six square feet (3'x2' equivalent).
An average rabbit is around 25cm (10") tall when sitting. In a 2' wide apex run they will only be able to sit upright in the centre 14".
Improving an Apex Rabbit Run
If you already have an apex rabbit run and would like to increase the useable space, you can do this by building up the sides to increase the minimum height. This will allow your rabbit to sit upright and move about in the whole run area.
The easiest way to do this is to build a simple wooden frame, with four corner posts and boards between, and attach the run to the top.
Adding a frame around the sides approximately 8" tall will allow your rabbit to make full use of the run.
Remember, although this technique will maximise the run space, most apex runs are not large enough to provide all the exercise space a rabbit needs. They are best used as additional exercise space - perhaps to give access for grazing - rather than as the only exercise area. You could join multiple runs together to increase to space but this is only cost effective if you already own the runs, otherwise a standard run would be a better option.