Lower ambient temperatures and remove humidity. Keep out pests and control air quality.
Ventilation must be provided at the roof ridge or by roof ventilators. Baffles ( air chutes ) provide -1 an insulation spacer -2 air ventilation channel.
Attic must have no heat sources.
Cold air circulates from the soffit or eave under roof surface and exits at top or roof, keeping roof underside close to outside temperature.
Ideally attic ventilation would be just like a U.S. Army pup tent.
Green Attic Insulation installs baffles in every joist bay on every job possible. This ensures the entire soffit becomes an air chute not just were perforated soffits are present on the eaves.
Adequate ventilation is essential to the comfort and health of the people who live in a house and to the healthy of the building itself. By getting rid of excess heat trapped under the roof, ventilation lowers ambient temperatures and lowers energy costs for air conditioning. Roofing manufacturers support a cooler attic extends the life of the roofing as well.
Perhaps the best reason to vent the attic is to get rid of excess moisture.
Household occupants generate water vapor when cooking and showering. Exhaust fans can help reduce interior moisture. Because warm air rises, a large portion of that water vapor will collect near the ceiling, where is will migrate into the attic through leaks in the recessed ceiling can lights, seams between drywall and framing ( bypass ), and uninsulated shafts and attic floors.
When warm moist air get into the attic, it will stay there circulating air ( ventilation ) allows moisture to exit the building through vents ( active or passive ).
In time excess moisture can soak insulation and delaminate sheathing. It starts as water stains, progresses to mold, and can end up as rotted framing.
When it’s cold outside, warm, moist interior air condenses when it get to unconditioned attics. It may be visible as frost on the underside of the sheathing or on roofing nails.
If there is snow on the roof, that warm, rising air will melt it, causing water to run down the roof and then refreeze at the eaves, producing spectacular icicles and destructive ice dams. This is totally avoidable with adequate attic ventilation
Green Attic Insulation installs a solar powered fan with the optional electrical backup for humid overcast days. This fan is super quiet and runs without electrical when placed in ( south facing all day) direct sunlight. The solar fan is the best choice for active mechanical ventilation and ensures healthy air movement. For mechanical ventilation to work correctly, intake vents must be adequately sized. Otherwise power fans create negative pressurization within the house.
Here are ten things to look for when evaluating attic ventilation
- is the attic excessively hot in summer? during winter to icicles form along the eaves
- are there perforated or continuous soffit vents? what other kinds of ventilation exist ridge, gable, turbines, or passive mushroom vents?
- are screened soffit vents painted shut?
- is the attic insulation blocking the soffits
- can you see staining around roofing nails from inside the attic, is the sheathing clean and healthy? are there rusty nails or a cheetah pattern of roofing nails leaving water stains?
- are the ceilings below the attic moldy or water stained ?
- does the attic meet minimum requirements for venting 1sq ft of vents per 300 sq ft of attic?
- are attic fans operational ( most attic powered fans have a 2-3 year lifespan, chances are its not even working anymore)
- can you feel negative pressure sucking conditioned air from the living space when running negative exhaust fans such as bath fans, kitchen fans, whole house fans, etc.
- does the house remain hot upstairs in the summer even with air conditioning running, or the does the a/c turn on and off ( cycle ) more than your neighbor, how does your electric bill compare to your neighbor
Text @2015 by Roger C. Robinson and Michael Litchfield
Passive Ventilation = As air heats beneath the roof, it rises and exits at a ridge or passive mushroom vents or gable end vents.
Active Ventilation = mechanical ventilation provided by solar powered or electrical powered fans. Ideally these have both a humidistat and thermostat to control moisture and temperature. The attic fan should be running any time the temperature of the attic becomes warmer than 10 degrees of outside air.
One last thing about ventilation .......
Keep Critters Out. Vent openings should be screened with mesh fine enough to keep out wasps, mice and other pests that would enjoy a roof over their heads. Attic louvered gable vents, mushroom vents, powered vents have openings large enough for pests to enter. Installing 1/4 in. metal screening on the inside of is usually the best fix.