Building Regs On Rendering

My neighbour who is a protected tennant, has decided to put a rear ground floor extension and re-build his garage. He has done this all in breeze blocks, I thought he was going to render it but it turns out he doesnt plan to. The extension unrenderd looks really rough, someone mentioned there is a building reg that says it cant be left as breeze blocks is that correct ? I cant find anything

There are no regulations to dictate that walls must be rendered.

If it's a money issue, perhaps a lick of masonry paint will suffice.