Insulation in the attic with ridge vent and eaves

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ROOF VENT SOFFIT + RIDGE NEEDED - CONTENTS: How do a soffit intake and ridge outlet vent work together on a roof and why are both needed? Adding a ridge vent alone can increase building heating costs. Adding soffit venting alone is ineffective. How to Correct Inadequate Attic Venting to Stop Attic Condensation, Ice Dam Leaks, Attic Mold, & Roof Structure Damage POST a QUESTION or READ FAQs about attic moisture, condensation & ventilation: why are both soffit intake and ridge outlet needed? REFERENCES

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Here we explain why a functional roof venting system needs both intake venting at the eaves or soffits and outlet venting at the roof peak or ridge.

This article series explains How to Correct Inadequate Attic Venting to Stop Attic Condensation, Ice Dam Leaks, Attic Mold, & Roof Structure Damage.

Our photo at page top shows a...

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Attic ventilation keeps your house cooler in summer, and it prevents moisture from building up in winter and ruining your roof framing and insulation. A passive ventilation system should have air inlets at the base of the roof, usually in the soffits, and outlets in the peak or gables. The total venting space should equal 1/150 of the floor space of the attic. If your roof lacks eaves, you need a substitute for soffit vents.

The Function of Soffit Vents

For proper ventilation, it isn't enough for air to simply get into your attic; it must also circulate. For this reason, the square footage of vent space at the base of the roof and at the peak should be the same. The vents at the base admit cool air, which tends to warm up in the attic space. It rises as it warms and creates an updraft when it is drawn out of the vents higher up on the roof. The roof soffits are at floor level and are usually the most convenient place to install the lower vents.

Problems when...

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Our contractor installed a ridge vent on our roof. We were still getting significant heat build up in the attic, so he then installed a solar roof fan that moves 500 CFM (cubic feet per minute). I noticed you said that these two systems should not be combined. Should we remove the solar vent fan? -Ron

Hi Ron,

Attics are vented using the natural circulation that occurs when hot air rises. Vents in the soffit beneath the eaves at the bottom of the attic draw in cool outside air while gable or ridge vents at the peak of the attic allow heated air to exit. In hot climates, a power vent fan is often mounted behind a gable vent or cut into the roof near the peak to assist this process by forcibly expelling additional hot air from the attic.

Combining an attic power vent fan with a ridge vent is usually not recommended because:

It could reverse the natural flow of hot air out the ridge vent. If air is drawn in through the ridge vent while it’s raining, it might...
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Attic Ventilation Poor

I have a 2500sqft ranch in Tampa, FL that has 42 soffit vents and a full length ridge vent (new), along with two 2x3 ft gable end vents at the roofline. The attic is 15ft tall at the peak and has 12 inches of blown insulation it - but it is still very, very HOT and has almost zero airflow through it. When I open the pull-down attic door in my garage, it feels as if I turned on a BIG fan because of the air being sucked up there. I haven't found any soffit vents that are plugged. My local electric company told me that an attic fan would not be cost efficient (go figure),but I am looking for a solution! Is there something wrong here, or is this somewhat normal? What can I do?

A whole house fan, sucks from your house pushes into the attic (then out the attic vents..ridge, gable ends, and soffits... where ever)
The gable end fan, mounts over your gable end vent and sucks off the attic discharging outside.
This may very well be...

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First, sweep the voids to remove any debris. To stop the loose-fill leaking out under the eaves, create a barrier where the joists meet the rafters using a small section of blanket insulation, as shown here. If your roof is covered with non-breathable felt, leave a 2-in (50-mm) gap between the roof and the blanket to allow air to circulate freely.

Carefully pour loose-fill insulation into the areas between the joists. Pour in enough to reach the top of the joists. It is best to start at the eaves on one side of the roof and work across to the other.

Cut a section of plywood to the same width as the gap between the joists. Sweep the fill away from you, using the offcut to level it off. Move excess loose-fill to areas that need to be built up.

When leveled off, you should have an even coverage across the entire attic space. The blanket insulation at the eaves will prevent "creeping."

The depth of the loose-fill will determine any further requirements...

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Soffit vents sit underneath the eaves of the roof of a house to allow air circulation into the attic; the air is then exhausted through gable or attic vents above the soffits. But not all homes have an overhanging roof line or soffit vents. Without them it is actually easier to insulate your attic, because you do not have to worry about covering up the vents or installing rafter baffles to ensure the vents breathe. In an attic without soffit vents you can add insulation in the corners and the wedges between the slope of the roof and the floor of the attic, which serves as the ceiling for the room below.

Figure out how much insulation you need for the area of the country in which you live by accessing the the U.S. Department of Energy's website and calculating your insulation needs by zip code (see Resources). The R-value of insulation defines the measurement of its resistance to heat movement. For batt insulation, measure the distance between attic joists to determine batt...

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