Q&A / 

Ventilation Hints

Ventilation Hints

Many model building codes call for minimum ventilating areas for attic spaces. The requirements in many of these codes are based on net free ventilation area. This means that you must measure the space of the opening without any screening material which slows air flow. This is often overlooked by many builders. Pot vents with insect screening often have the net free ventilating area stamped on them.

1. The minimum net free ventilation area called for in many building codes is 960 square inches for each 1,000 square feet of ceiling area of the house. If you use a continuous ridge system combined with a continuous soffit system, you can reduce the net free area to 480 square inches.

2. NEVER vent exhaust air from clothes dryers, bathroom fans, or kitchen exhaust fans into attic spaces. These devices can exhaust massive quantities of moist, humid air into attic spaces. Kitchen fans can also exhaust grease laden air into attics which can create an extreme fire hazard.

3. Cathedral ceilings require special attention. Each joist space must be separately vented. Interruptions of framing members for skylights must be side vented to adjacent free flowing joist spaces.

4. During construction, be sure to caulk or seal around all pipes and wires that penetrate the top plates of walls. Air can readily leak into attic spaces around these openings.

I have found that it is often best to vent fans and dryers through the roof. I urge you to watch this video of mine to see how easy it is to install the correct vent-cap flashing on a roof. Have no fear - if done right you will have no leaks.

Column B47

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