Light & Ventilation – Rules & Regulations

Large window with natural light

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

Before your building department approves a house or 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:

Oversized windows letting in natural light

For Natural Light

A given room must have a window or glass door that is sized to equal at least 10 percent of the floor area of the room.

So, if a room is 10 feet wide by 12 feet long, 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. A three-foot by four-foot window would provide 12 square feet of natural light to the room – again, the required minimum.

Pretty simple really. For every 10 feet of floor area, you need one foot of natural light area.

High air registers can create a tricky crown molding installation.

For Ventilation

Figuring ventilation is much easier. Natural ventilation must equal 5 percent of the floor area – or exactly half the requirement for that of natural light.

In our natural light example above the window also would qualify for minimum natural ventilation if half of it was operable.

Although handled as separate issues, you can see that natural light and natural ventilation actually have a very specific relationship to one another inasmuch as calculation rules are concerned. The required amount of light is literally double that of natural ventilation. Or stated another way, the amount of natural ventilation required is exactly half that of the natural light requirement. Have it your own way.

Why is this so important?

Simple, natural light cuts down on the need for artificial illumination and therefore can save energy. In the winter warming sunlight can cut on heating costs. As for ventilation, keep in mind that Mother Nature’s breath reduces mildew and mold. And unless you live in downtown LA – the outside air is usually quite medicinal (lots of oxygen) and refreshing.

Sliding glass door

Lighting Placement

The required window doesn’t need to be in the same exact room. For example: Let’s say we want a family room sliding glass door or window to provide the required light and ventilation for both the family room and the kitchen.

When a window or door in one room will provide light and ventilation to another room then the area of both rooms must be calculated together as one and the window or door must qualify for the entire area. But, there is just one tiny, little hitch.

There must be a big opening between the two rooms. And it can’t be just a doorway. The opening between the two rooms must equal at least 50 percent of the area of the wall space that separates the rooms.

In other words, if the separating wall is 8 feet high and 11 feet long (88 square feet), then the opening in the wall must be at least 44 square feet. Now you see why architects get so much money.

If you have a question simply bring the details to your local building department and ask what you can do – before you spend the money doing it wrong.

Living room with natural light

Natural Light Benefits

Light also has something to do with how a room feels. Giant windows bring the outside inside. They give a room a feeling of greatness – as big as the all outdoors. Inside colors are warmed up by outside light and make the room feel homier. Ever get locked in a closet when you were a kid? How would you like it if all of the rooms in your home were like that? If you are a sadist – don’t answer that question.

The texture of fabrics and wood in the home is enhanced by natural light – especially the wall texture. Natural light enhances the entire home – color and texture definitely are affected.

The bad side

When it comes to windows and glass doors providing light and ventilation, there are minimums. This is confused by the fact that when it comes to energy efficiency and glass there are maximums. That’s a whole other column.

Suffice to say that when it comes to light and ventilation there are the minimums we have related, but when it comes to windows there are equally as many rules about maximum amounts allowed. Again, always check with your building department when planning any construction.

Further Reading


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