What is my inspector looking for anyway? Structural Systems – Attic Ventilation Systems, Part 2

PASSIVE SYSTEMS

Passive ventilation is a natural ventilation system that makes use of natural forces, such as wind and thermal buoyancy, to circulate air to and from an indoor space.

These ventilation systems work to regulate the internal air temperature as well as bring fresh air in and send stale air out.

Passive vents require no electricity, but their effectiveness often depends on their being properly designed for a specific home site.

A well-designed passive ventilation system has an intake device located low in the roof, with an exhaust installed near the ridge.

In a balanced system, the net opening of the intake will be approximately the same as the net opening of the exhaust.

Cliff-Bell Home Inspectors – A Texas Licensed Houston Home Inspections Company

Soffit Vents

soffit vent is simply a vent installed into the underside of your home’s eaves (called the soffit) that permits fresh outside air to be drawn up into the attic. Cooler fresh air is drawn up through the soffit at the base of your roof and hot and humid air is expelled through the roof vents at the top.

If the system is out of balance, it’s better to have more ventilation lower in the roof by way of larger intakes. There may be individual vents each serving a rafter bay, or continuous vents, as you see here.

Cliff-Bell Home Inspectors – A Texas Licensed Houston Home Inspections Company

Blocked Vents

As the inspector inspects the attic, the inspector wants to make sure that the soffit vents are not blocked by insulation. This is especially common in attics with blown-in insulation. If blocked vents are observed, a comment will be in your inspection report. If the insulation is not held back the inspector should see baffles installed to create an air space. It’s important that baffles extend through to the exterior so that they actually allow airflow into the attic. Once the siding and soffits are complete, the inspector won’t be able to confirm this visually. Unless you can actually feel air flowing from the baffles, you will not be able to confirm functional airflow, and you should disclaim it.

Cliff-Bell Home Inspectors – A Texas Licensed Houston Home Inspections Company

Gable Vents

Gable vents are usually installed on the exterior wall of your attic in order to create proper air circulation during extreme climate conditions. During the winter, stagnant air can cause condensation to form in your attic as well, once again putting your house at risk for mold, mildew, and leaks. Gable vents are installed in the gabled ends at opposite ends of the attic. They’re most effective when the vents align with the prevailing winds. This allows high air pressure on the upwind side of the home to push air into the attic, and low pressure on the downwind side to pull air out. When prevailing winds blow perpendicular to the vents, the gable vents act as both intake and exhaust. Less air exchange takes place and attic ventilation is not uniform, so it’s less effective.

Cliff-Bell Home Inspectors – A Texas Licensed Houston Home Inspections Company

Roof Vents

Roof vents. Air intake and exhaust vents are used in ventilating steep-slope roof assemblies to provide a means of allowing outside air to enter and exit attics and ventilation spaces. Intake vents should be located along a roof assembly’s lowest eave at or near soffits or eaves.

Roof vents, sometimes called “turtle” vents, should be installed near the roof peak. This illustration shows cool air entering the soffit vents. It rises along the underside of the roof sheathing and absorbs heat before exiting the attic through the roof vent.

Cliff-Bell Home Inspectors – A Texas Licensed Houston Home Inspections Company

Wind Turbine

turbine is installed directly on the top of a roof and uses wind power to suck hot and humid air out of the attic. A turbine has a series of vanes that spin as wind passes through them. A ridge vent is similar to a screen and allows heat to escape up and out of the attic.

Occasionally, you’ll see a turbine vent. Turbines use a series of specially-shaped vanes that catch wind and spin the turbine. As the vanes spin, they create an area of low pressure which pulls air from the attic.

While they’re not as effective as ridge vents, they do provide a low-cost alternative in areas with consistent wind speeds of at least 5 mph. That’s the power cord for the evaporative cooler you see improperly routed through the turbine vent into the attic.

Cliff-Bell Home Inspectors – A Texas Licensed Houston Home Inspections Company

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