Firing LATW from within buildings largely depends on the state of the building. If its a well constructed building with intact doors and windows, the effect would be harsh on the firers and any other occupants in the room. But in a building with blasted out windows/doors/demolished-walls, etc, it is greatly lessened.
For first floor firers, it would also model the fact that they could duck outside quickly and fire. It does not have to model actually hanging out a window in other words.