Let It Breathe

 Let it BREATHE
 

Like people and wine, houses need to breathe too.  Older homes were built with relatively loose sealing doors and windows and have a much higher air infiltration rate than a new home. Modern construction methods are making our homes more and more air tight to conserve energy. As a result, we are learning to pay more attention to ventilation and exhaust air requirements.
Ventilation is key to a healthy and comfortable home. There are minimum standards of ventilation for any habitable living space.  Every room should have at least 5 % of the floor space in ventilation opening. That means a 12 foot by 14 foot room needs a minimum window dimension of 1200 square inches (like a 30 inch x 40 inch window opening). Obviously it doesn’t mean you have to keep the window open, but you should be able to get fresh outside air when you want it. Natural light (10%) is also required. 
Bedroom windows are special.  In the event of a fire, every room used for sleeping should have a means of secondary emergency egress. Unless there is a second door leading to the outside, the window is it.  Bedroom windows should measure at least twenty-four inches high by at least twenty inches wide, with a minimum opening of 5.7 square feet and an optimum sill height of forty-four inches. This facilitates an emergency exit by the occupant or an emergency egress for a fireperson wearing breathing apparatus. 
There are exceptions to the ventilation rule for rooms like kitchens and bathrooms where secondary emergency egress is not required.  For example, to meet the requirement, a bathroom may have an exhaust fan to move moist air to the exterior (not just to the attic). The exhaust fan is sized to move enough air to change the air in the room at the rate of 5 times per hour.  Exhaust fans are now also recommended in laundry rooms where there could be a build up of moisture laden air.  
That brings up the supply air issue.  If you have a gas fired clothes dryer, it needs air for complete combustion of the gas flame.  When you are using or removing air from a space, makeup air is provided by an opening through a wall or door. If you starve a gas flame, it can create excessive amounts of carbon monoxide, so we want to keep the flame well supplied with combustion air.
Every gas appliance needs adequate combustion air.  Although the air for combustion sometimes comes from living space, it preferably will come from outside.  Furnaces and water heaters often have outside air provided via the attic or crawlspace. 
Attics need to breathe to prevent a buildup of heat or moisture that can create unhealthy conditions. Vents for the attic can be in the eaves, the ridges or the gable ends or even dormer vents or in the roof.  Recently there is a new requirement that the rafter bays in a cathedral ceiling also be vented.   This is done with eave and ridge top vents.  Whatever the venting means, the openings should have screens to keep the pests and critters out of your attic. 
If your house is on a raised foundation, the crawlspace below the floor needs ventilation too.  Like the attic, it needs 1 square foot for every 150 square feet of area. Ideally the openings are within 3 feet of the corners to provide more efficient cross ventilation.  If the natural air flow is limited, it can be augmented with mechanical ventilation fans.  If you live in an area with high radon gas levels, you’re going to want a specialized ventilation system. 
Remember, for a healthy and comfortable home, breathe and let breathe.