You need a basement egress window when:
According to the 2006 IRC -- International Residential Code requirements, egress windows and wells are required under the following circumstances:
* If you add a bedroom a basement, an egress window must be installed in that bedroom.
* If you create a habitable space in your basement and you currently do not have an egress
window, one must be included with the installation of the habitable room.
EMERGENCY ESCAPE AND RESCUE OPENINGS
R310.1 Emergency escape and rescue required. Basements,
habitable attics and every sleeping room shall have at least one
operable emergency escape and rescue opening. Where basements
contain one or more sleeping rooms, emergency egress
and rescue openings shall be required in each sleeping room.
Where emergency escape and rescue openings are provided
they shall have a sill height of not more than 44 inches (1118
mm) above the floor. Where a door opening having a threshold
below the adjacent ground elevation serves as an emergency
escape and rescue opening and is provided with a bulkhead
enclosure, the bulkhead enclosure shall comply with Section
R310.3. The net clear opening dimensions required by this section
shall be obtained by the normal operation of the emergency
escape and rescue opening from the inside. Emergency
escape and rescue openings with a finished sill height below the
adjacent ground elevation shall be provided with a window
well in accordance with Section R310.2. Emergency escape
and rescue openings shall open directly into a public way, or to
a yard or court that opens to a public way.
Exception: Basements used only to house mechanical
equipment and not exceeding total floor area of 200 square
feet (18.58 m2).
R310.1.1 Minimum opening area. All emergency escape
and rescue openings shall have a minimum net clear opening
of 5.7 square feet (0.530 m2).
Exception: Grade floor openings shall have a minimum
net clear opening of 5 square feet (0.465 m2).
R310.1.2 Minimum opening height. The minimum net
clear opening height shall be 24 inches (610 mm).
R310.1.3 Minimum opening width. The minimum net
clear opening width shall be 20 inches (508 mm).
R310.1.4 Operational constraints. Emergency escape and
rescue openings shall be operational from the inside of the
room without the use of keys, tools or special knowledge.
R310.2 Window wells. The minimum horizontal area of the
window well shall be 9 square feet (0.9 m2), with a minimum
horizontal projection and width of 36 inches (914 mm). The
area of the window well shall allow the emergency escape and
rescue opening to be fully opened.
Exception: The ladder or steps required by Section R310.2.1
shall be permitted to encroach a maximum of 6 inches (152
mm) into the required dimensions of the window well.
R310.2.1 Ladder and steps. Window wells with a vertical
depth greater than 44 inches (1118 mm) shall be equipped
with a permanently affixed ladder or steps usable with the
window in the fully open position. Ladders or steps required
by this section shall not be required to comply with Sections
R311.7 and R311.8. Ladders or rungs shall have an inside
width of at least 12 inches (305 mm), shall project at least 3
inches (76 mm) from the wall and shall be spaced not more
than 18 inches (457 mm) on center vertically for the full
height of the window well.
R310.3 Bulkhead enclosures. Bulkhead enclosures shall provide
direct access to the basement. The bulkhead enclosure with
the door panels in the fully open position shall provide the minimum
net clear opening required by Section R310.1.1. Bulkhead
enclosures shall also comply with Section R3126.96.36.199.
R310.4 Bars, grilles, covers and screens. Bars, grilles, covers,
screens or similar devices are permitted to be placed over
emergency escape and rescue openings, bulkhead enclosures,
or window wells that serve such openings, provided the minimum
net clear opening size complies with Sections R31 0.1.1
to R31 0.1.3, and such devices shall be releasable or removable
from the inside without the use of a key, tool, special knowledge
or force greater than that which is required for normal
operation of the escape and rescue opening.
R310.5 Emergency escape windows under decks and porches.
Emergency escape windows are allowed to be installed under
decks and porches provided the location of the deck allows the
emergency escape window to be fully opened and provides a path
not less than 36 inches (914 mm) in h