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It is written -- let there be light, and a quantity of fresh air

September 23, 2007|James and Morris Carey | Associated Press

Did you know there are rules and regulations about how much natural light and natural ventilation must be present in each room of a home?

Before your building department approves a house, an addition or even a window change, certain light and ventilation rules must be met.

Closets, bathrooms, hallways and garages don't fall under these guidelines.

Here are the rules:

* Natural light -- A room must have a window or glass door sized to equal at least 10% of the floor area of the room. So, if a room is 10 feet by 12 feet, then the room area would be 120 square feet and the minimum size of the window in that room would have to be 12 square feet.

* Ventilation -- Natural ventilation must equal 5% of the floor area, or half the requirement for that of natural light. In the example above, the window also would qualify for minimum natural ventilation if half of it was operable.

Although handled as separate issues, natural light and natural ventilation have a very specific relationship to one another as far as calculation rules are concerned.

Why is it so important that the amount of light be double that of ventilation? Simple, natural light cuts down on the need for artificial illumination and, therefore, can save energy. In the winter, warming sunlight can reduce heating costs.

As for ventilation, Mother Nature's breath reduces mildew and mold. And unless you live in parts of Los Angeles, outside air is quite medicinal (lots of oxygen) and refreshing.

Of course, the rules get a little more complicated as you apply them throughout the house.

For example, adjacent rooms may be grouped together for light and ventilation calculation purposes. However, the size of their shared doorway must equal at least 50% of the area of the wall space that separates the rooms.

These guidelines just cover the minimums. There are also rules about maximums.

If you have a question, consult your local building department before you spend money doing something wrong.


For more home improvement tips and information, visit the Careys' website at, or call their hot line at (800) 737-2474, Ext. 59.

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