Shower with a fan/outlet above it, but no window

[Sabatinitennis]

I have just moved into a brand new house in a terrace of six. All have different layouts inside. In the main bedroom on the first floor (located at the front) is an en-suite shower room.
Two of the houses in my terrace have windows in their en-suite shower rooms that face out onto the front, but my shower room does not have a window and relies on fans in the ceiling to allow the steam to escape via the attic where there is a sort of chute and then out into the sky via vents in the roof.
Would I be allowed to put a window in to the shower room to aid escape of the steam? If not, is it because it would change the original plans for the house, or alter the front facade of the house?
Are there building regs that dictate what I could do?
My solicitor pointed out that I was not allowed to make major additions to the property for five years, but a small window surely does not fit into this?

 

[^woody^]

There must be a reason why there is no window where other adjacent properties do have one.

If there is a condition on the sale that there are no alterations, that may include windows. Your legal advisor can give you the specific details

Building and planning regulations will apply.

 

[Sabatinitennis]

Thanks.