Enclosure size
Enclosure size is always a contentious topic when it comes to housing snakes, my opinion is ‘bigger is almost always better.’ I prefer to ensure my snakes are kept in enclosures at least as long as they are, and if at all possible give them even more than that. While it may be possible to house snakes in smaller enclosures, my interest has always been in watching them enact their natural behaviours - moving, exploring, basking, climbing - and a larger enclosure allows more of this. It also gives greater scope to provide wider gradients in heat, and light which are so important to most reptiles. Diadem snakes are not inactive snakes and will move around a fair bit, so will appreciate as large an enclosure as you can give them.
Recently the Federation of British Herpetologists has produced a series of guideline minimum enclosure sizes for snakes mandating 0.9 (L) x 0.45 (D) x 0.3 (H) times the total length of the snake. Which for a snake of 48” length (the average size of an adult Clifford’s Diadem snake) would entail an enclosure at least 43” (L) x 21” (D) x 14” (H). A particularly large specimen of 55” length would require an enclosure at least 55” (L) x 24” (D) x 16.5” (H).
To my knowledge there is no enclosure on the market that fits either of those dimensions but for all but the largest Diadem snakes, an enclosure with dimensions of 48x18x18” is a fair minimum size, although I would personally prefer 48x24x24” as the ‘standard’ enclosure size for snakes in this size bracket. This gives them enough length to stretch out and enough height for them to indulge their propensity to climb. A particularly large individual would be best provided an enclosure 60x24x18” or more.
I first set up each of my new Diadem snakes individually in 48x18x18” wooden enclosures. As the years went by, I upgraded my animals into larger enclosures and even began keeping the adults in trios (one male with two females) in 72x24x24” enclosures. They have done well this way for years and cohabit well without fighting.