Attic Ventilation

Lower ambient temperatures and remove humidity. Keep out pests and control air quality. 

attic insulation bath fan exhaust through roof cellulose ventilation
Traditional Attics should be a rain shed only vented well like an army pup tent

There are five main types of attic ventilation.  It is recommended to have as much fresh healthy air as possible moving through the attic. If your home can have all five types of vents, this is great, balanced at 50% inlet 50% outlet. 

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. 

Attic Ventilation is crucial to a healthy Attic
us army pup tent

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. 

Baffles in Every Bay Not Just "where ventilation is present."

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. 

warm air rising attic insulation humidity vapor attic condensation water vapor

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. 

frost on nails green attic insulation
ice dam skokie ice dam removal near me icicles february 2021

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 

Three types of ventilation are 

  • active – mechanically controlled
  • passive – costs nothing to operate 
  • hybrid– combination of both 
active passive hybrid ventilation gaps cracks joints vents exhaust
green attic insulation solar fan install #5

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 

  1. is the attic excessively hot in summer? during winter to icicles form along the eaves 
  2. are there perforated or continuous soffit vents? what other kinds of ventilation exist ridge, gable, turbines, or passive mushroom vents? 
  3. are screened soffit vents painted shut? 
  4. is the attic insulation blocking the soffits 
  5. 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
  6. are the ceilings below the attic moldy or water stained ? 
  7. does the attic meet minimum requirements for venting 1sq ft of vents per 300 sq ft of attic? 
  8. are attic fans operational ( most attic powered fans have a 2-3 year lifespan, chances are its not even working anymore) 
  9. 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. 
  10. 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. 


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. 

attic vent rodent : pest screen green attic insulation