Ventilation

Is my attic properly vented?

The answer depends on these factors. 

  1. Healthy air quality ( mold mildew and moisture free.) 
  2. Comfortable, cozy, conditioned home below the attic that is optimally heated or cooled with minimal energy consumption.
  3. Similar temperature to the exterior. 

Before reading more, consider scheduling a free insulation and ventilation evaluation with our estimators. We will measure temperatures and humidity in the attic, and evaluate the current ventilation as it relates to optimal conditions. 

Attics ventilation draws in fresh outdoor air to balance temperatures and prevent mold growth. 

Traditional Attics should be a rain shed only vented well like an army pup tent

Residential Attics are one of our  specialties, and we see hundreds of them per month. Each home is unique, and each homeowner has specific needs, that being said, there are some simple truths to follow when it comes to ventilation

  1. In a vented unconditioned attic you can never have too much ventilation; the goal of a vented attic is to keep the attic as close to exterior temperature as possible
  2. In a conditioned / semi-conditioned attic, keeping outside air from getting in is equally essential to the air quality and health of the organic building materials

To Create a COZY, COMFORTABLE, CONDITIONED HOME, Ventilation is crucial.

Each category of ventilation is essential and if all 5 can be utilized that would be ideal. However due to structural considerations you may only get two or three types.  

If you have the option cross gable ventilation has a great performance track record. Cross gable ventilation provides the most efficient air flow and can also be utilized with a power vent at one end of the gable. This is often see in grade level large scale parking garages to remove carbon dioxide from vehicle exhaust. 

Soffit vents can be replaced with low profile vents near the bottom of the roof if there are no overhangs for air intake. 

There are 5 categories of unconditioned attic ventilation

1. soffit vents – under the eaves at bottom of attic floor

2. power vents – rely on electrical or solar power

3. gable vents / cross ventilation 

4. ridge vents – at top of attic ( usually continuous) 

5. can vents – sometimes called mushroom vents 

Which vents are right for your attic depends on structural considerations to achieve balanced air flow

Cross Ventilation - In this case Gable Ventilation (Provides Natural Air Flow But Depends On Optimal Natural Air Movement )

Residential ventilation attic vents cross gable vent Cross-gable vent green attic insulaiton gable-vent roof sheathing rafter baffles open ridge vents
cross_ventilation gable ventilation illustration courtesy of tpi polytechniek green attic insulation ventilation
Cross Flow Ventilation
gable vents courtesy of IBEC international institute of building enclosure consultants green attic insulation gable ventilation attic vents
Two Common Locations of Gable Vents

Cross Ventilation depends on natural air flow so if the homes elevation is not (south) facing for example it will not get adequate pressure from one side to move adequate air through the gable vents. This method of ventilation can be supplemented with electrical or solar powered fans. Most older homes relied on gable vents, methods shifted towards  soffits and mushroom vents was taken up, however; the big mistake we see being made contributing to poor ventilation in this method is fiberglass batts or loose-fill fiberglass blocking air intake of the soffits. 

Soffit Vents _ Essential Rules for Optimal Performance

Ventilation 1
Mold Growth Beneath Baffles as Result of Condensation

See here in this photo is our field supervisor Charlie removing an existing baffle to expose black mold growth as a result of soffit air intake meeting warm air from the attic that un-intentionally escaped from the living space in winter, warming the fiberglass enough to create the condensation ( think cold glass of ice water on a picnic table in the hot summer sun. 

Ventilation from the soffits must serve some better purpose than to be trapped behind insulation or to be directed into the wrong areas of the attic with no air flow balance.

Air flow balance is essential to a healthy vented attic. 

Ventilation 2
Prior to insulating, each joist bay gets its own dedicated baffle secured to the sheathing.

Our estimators check to ensure existing soffits are not

  • Blocked by loose fill fiberglass or batt attic insulation because insulation baffles weren’t used in every joist bay or insulation was blown in at high pressure clogging the intended air pathway
  • Clogged with debris from building materials, pests, or landscape materials 
  • Installed in a location where ventilation is not present

In Each Case: there is a standard menu item on our proposal to solve this problem. Fill out our contact form for a free ventilation evaluation today. 

In regard to soffit vents, Green Attic Insulation distinguishes itself from local competitors in one valuable way, we install soffits in every joist bay, not just ” were ventilation is present ” as seen by competitors, leaving the homeowner with less than desirable results. 

Too often this is confused and poorly executed due to a lack of understanding.  Lets be clear, the entire soffits is an air chute designed to pull air through each joist bay, not just where perforated soffits are present ( which is every 4-8 ft) without air flow across the entire soffit the sheathing will not be optimally cooled. 

Power Vents _ Solar or Electrical Power

Power Vents are known as active ventilation. Powered vents can be electrically powered or solar powered. 

Powered vents can provide more air movement but must be installed with consideration of air flow balance. 

Considerations for vents are calculations to determine the minimum required net free ventilating area (NFVA) using the  1:300 ratio or 1: 600 of upper attic area. 

This is only possible when the soffits are open and baffles are properly installed to prevent insulation from clogging the soffits.  

 

Ventilation 3

Continuous Ridge Vents

Ventilation 4

Continuous Ridge Vent is installed at the top of the roof / ridge. This allows outward air flow along the top of the roof.  Look at your neighborhood, each house with a raised 1-2″ peak on the ridge has one already. 

Continuous means end to end ventilation. 

Since air movement is the key to good ventilation, it must have an air intake source in order to be effective. 

Most new re-roofs include the upgrade to continuous ridge vents but must take into account air movement / balance. 

Cap Vents / Mushroom Vents / Passive Roof Vents

Passive vents are less common in new construction as the continuous ridge vent is replacing them as it provides less penetrations and more air flow. Passive vents are also outtake vents and are designed to allow warm air to escape naturally in summer, and prevent a moist environment in winter.

Passive vents are not to be confused with active powered  ventilation. In each case, a vented attic must perform in conjunction with a completely sealed attic floor to prevent air intake from the conditioned living space. 

Ventilation 5

Conclusion

Ventilation depends on active or passive vents which draw fresh outside air into the vented attic space to prevent mold growth from humidity and condensation and prevent uneven temperatures relative to outside temperatures. 

The attic should be the same or as close to outside temperature as possible. 

Schedule a free estimate today and have a member of our team visit your attic and evaluate the humidity and temperature control of your vents. 

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