Around the non-playable area

Hi, I'm experiencing some trouble while mapping, to make my corridor believable.It does have to have doors and windows, but the question remains: what is the best way, optimization wise, to give the impression there are windows leading to another room?

I tried actually designing the rooms behind windows, but while it does take a huge amount of time, it impacts performances a lot, even with areaportals.. after that I tried to have frosted glass windows, and blinds to allow me not to have actual space behind them, but I didn't succeed selling it, so if anyone has a tip to design well these non playable areas I'd live to hear them

thanks in advance!

Well my issue is that my map takes place in modern offices, but there aren't shutters or things like that that usually work to mask the inside of the building. So when I did the facade, the wall itself was good but remained the fact that you could see through windows that there wasn't anything i tried todosomething like that: https://www.google.fr/search?q=frosted+glass+architecture&client=ms-android-samsung&source=android-browser&biw=360&bih=345&tbm=isch&tbo=u&source=univ&fir=TDz4tJEhDnMq2M%3A%2CVZ0hUBZM-DmbuM%2C_%3B-7xfNNsMhWr77M%3A%2CiA6Yva6sN6qItM%2C_&usg=__AAimOzFchXrNoNZ6PmDBsCYwdQI%3D&sa=X&ei=sZ90VejJJ8a4UcrIgLgF&ved=0CCQQ7Ak#imgrc=O_VUsPK9D0uTsM%3A%3BF-l-NOHp2N1R6M%3Bhttp%3A%2F%2Fcreatf.com%2Fwp-content%2Fuploads%2F2015%2F03%2Ffascinating-home-accessories-interior-design-modern-home-office-design-with-single-swing-frosted-glass-doors-designs-pleasant-frosted-glass-doors-designs-for-modern-house-Exclusive-Office-Doors-Design-Ideas.jpg%3Bhttp%3A%2F%2Fcreatf.com%2Fexclusive-office-doors-design-ideas%2Ffascinating-home-accessories-interior-design-modern-home-office-design-with-single-swing-frosted-glass-doors-designs-pleasant-frosted-glass-doors-designs-for-modern-house-exclusive-office-doors-design%2F%3B1166%3B768

but didn't succeeded this is why I posted here

I'll try and see in game then thanks for the ideas!