A lot of investors ask what an egress window is and when one is needed. Technically, it's a window for a room below grade that a municipality has deemed large enough to be safe for exit in case of emergency. While there are some variations, the window needs to be large enough that a firefighter with an oxygen bottle on their back could get in, then carry out an injured person in a fire. Most often, it's associated with a basement bedroom window, making it a legal bedroom. Basement bedrooms without egress windows are illegal. Installing an egress window makes them legal.
The confusion is that different cities, counties and agencies have different size requirements and height-above-floor requirements for these windows. Therefore, before you start cutting into the concrete foundation you better make sure you've visited the local building department to get their requirements. In addition, HUD, distributing Section 8 vouchers, also has their own requirements for egress windows. So if you're going to rent to a Section 8 tenant make certain you know what their requirements are. If you don't, you won't get credit for that basement bedroom and get way less rent than you expected - believe me it happens every day.
To be honest, there are probably hundreds if not thousands of rentals in Metro Denver that have basement bedrooms without egress windows. In my opinion, this is not only illegal, it's immoral. And if that wasn't enough to discourage you from having one, ask yourself what happens if there is a catastrophic fire and someone dies in your illegal basement bedroom. Not good! For about $1,500 - $2,500 you can get a competent contractor to install an egress window (only one is required per basement bedroom) and sleep better at night.