Through the past few months we’ve been trying to take the building code and licensing regulations and put them in terms we all can understand for basement apartments. One question that continues to come up frequently is the windows glazing requirement. So let me try and do my best to clear this up.
The requirement is based on two different sections of the International Property Maintenance Code – 402 “Light” and 403 “Ventilation.”
Here is a quotation from the section:
2006 IMPC 402.1 – Every habitable space shall have at least one window of approved size facing directly to the outdoors or to a court. The minimum total glazed area for every habitable space shall be 8 percent of the floor area of such room….”
“Exception: Where natural light for rooms or spaces without exterior glazing is provided through an adjoining room, the unobstructed opening to the adjoining room shall be at least 8 percent of the floor area of the interior room or space, but not less than 25 square feet. The exterior glazing area shall be based on the total floor area being served.”
And the definition of habital space: HABITABLE SPACE – Space in a structure for living, sleeping, cooking and eating which does not contain, within such a unit, a toilet, lavatory and bathtub or shower.
There are accommodations made in the code to allow the substitution of artificial light for natural light in non-habitable rooms (IPMC 402.2 and 402.3).
And according to our code officials, 8 percent of the floor area is not that much.
In a 10’ x 15’ room = 12 sq. ft of glazing which is the equivalent of 1 window with 3’ x 4’ of glazed area or equivalent.
In a 15’ x 15’ room = 18 sq. ft of glazing which is equivalent of 1 window with 4.25’ x 4.25’ of glazed area.
For adjoining rooms, the minimum size of the opening between the interior room and the exterior room with the glazing needs to be 8% of the floor area (but not less than 25 sq. ft.) of the interior room. A standard door size opening (without the door) would generally suffice. However, the actual size of the glazed area must be at least 8% of the combined floor area.
Section 403 requires that, “every habitable space shall have at least one openable window.” There is an exception to this similar to that of section 402 in that “where rooms and spaces without openings to the outdoors are ventilated through an adjoining room, the unobstructed opening to the adjoining room shall be at least 8% of the floor area of the interior room or space, but not less than 25 square feet. The ventilation openings to the outdoors shall be based on a total floor area being ventilated.”
The code official also has the authority to consider alternative methods of complying with this provision. The applicant must provide sufficient information to demonstrate that they are complying with the intent of the code, but not necessarily with the letter of the code.
Hope this helps those who have asked. Please let us know if you have any questions in the comments.