If I remember correctly the glass screens are an original feature. The grass is newer, originally the surface of the enclosure was yellowish sandy gravel.
IMHO the Ape House is far better than the Elephant & Reptile House. Although this orang section is not as good as the gorilla area, which has larger indoor areas, a grassy paddock and a thickly planted island. There is a discussion in the Chester threads about the possibility of Blackpool's orangs being boarded at Chester, if Blackpool can organise the upgrading of their accommodation.
I believe both the Orangutans and Elephants are due to have a revamp over the next few years. The Ape house is originally from the 1970's when they house all three Great Ape species (Chimpanzees, Orangutans and Gorillas). The Orangutan furthest away is 'Ramon/Raman' a hand raised male from Russia (St Petersburg).
But in the 1970's it was just a flat island with hardly any equipment on it. At that stage this outdoor area was shared(in rotation) by the young pairs of Gorillas, Orangs and Chimps. The little metal ladders in the back wall led to the small indoor cages of each species, which still comprise the indoor area for the Orangutans. There is an archival photo somewhere on here of how it was then with the young Gorillas outside.
Things improved with the building of the newer and far more spacious Gorilla wing and dispersal of Chimps. The Orang area has also been much improved with climbing equipment- I would rate it still one of the poorest in the UK but IMO better than Dudley or Twycross, climbing equipment-wise. A revamp is still badly needed though.