Attic Ventilation Problems & Mistakes

Virtually ALL houses can benefit from increased attic ventilation. Even new homes often don’t have adequate ventilation!! #1 Problem – Blocked, Clogged or Dirty Soffit Vents.

Before you do ANYTHING else, check for dirty or clogged soffit vents. This is the NUMBER #1 ventilation problem.
Soffit vent is clogged because of electric fan pulling too hard.











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#1 Dirty Soffit Vents – They once worked and let air through, but now they are so dirty they are blocked and are effectively useless

#2 Blocked Soffit Vents – Something is blocking the soffit vents from inside the attic. Usually old wood shingles after a roof replacement, or insulation was blown over the soffit vents (especially on newer homes).

#3 Inadequate Soffit Vents – Most homes simply does not have enough soffit (intake vents) to properly ventilate the attic.

#4 Soffit Vents Holes Cut Too Small – You may have vents, but the holes behind them are cut very small (see picture at right). You have to get close and look through the vent to see the actual size of the hole. Some houses have vents, but NO HOLES cut behind them.

Soffit Vents – Above is an example of a soffit vent cut too small. This is common even on new homes.


Has anyone ever told you to “Clean your soffit vents?” Probably not. If air is flowing through the vents, the vents will eventually get dirty (just like the lint trap on a clothes dryer). If they become blocked or clogged, they restrict the air flow and will not be effective. Cleaning should be done every couple of years. Watch this short video: How to Clean Dirty Soffits

Always clean your soffits with a DRY nylon brush. DO NOT USE A WATER HOSE!!

If you have an electric attic fan, the soffit vents should be cleaned every year. Otherwise, the soffit vents will get clogged making your electric attic fan useless and the motors will burnout quickly.

Soffit vents that are blocked due to multiple layers of paint should be replaced.

If your house is more than a few years old and the soffit vents are NOT dirty this is another concern. See Tray Ceilings or Mixed Exhaust Ventilation below.

Another problem is that many soffit vents are cut too small, even on new homes. You cannot assume that a soffit vent is providing the correct amount of intake ventilation. If the soffit vents are cut too small, this disrupts the balance of NFA (net free area) needed for proper air flow.

Holes like this are pretty common behind soffit vents.

Common Trouble Spots for Ventilation

Problem Area – Tray Ceilings

Does Your House Have Tray Ceilings? A Tray ceiling is like a mini vaulted ceiling in the corner of the room. Generally the wall goes up about 8 feet then at an angle to the ceiling for a few feet.

With tray ceilings there is often there is no air channel for the air to flow between the sheetrock and the roof deck.

Many homes built before about 1997 have tray ceilings with NO air channel for attic ventilation. The insulation is sandwiched between the sheetrock and the roof deck. The result is that the soffit vents are effectively useless, the air flow is blocked from reaching the ridge or exhaust vents. This can contribute to hot rooms, especially upstairs where interior walls face the attic space.

Problem Area – Electric Attic Fans

Electric attic fans in and of themselves are not the big problem. It’s how they affect the rest of the ventilation system that makes them problematic.

Electric fans should be avoided. Two reasons: First, they usually burn out after a couple of years. Second, once the soffit vents are clogged (see above) they will pull air conditioned air from inside the home into the attic.

An electric fan acts as though you just put a giant vacuum cleaner hose in your attic! Are you starting to get the picture? The fan is going to pull from ALL OPENINGS INTO THE ATTIC. And, since air will travel the path of least resistance, virtually any other opening you have in the attic now becomes the intake vents with the fan being the dominant and primary exhaust vent. How can you fix this?

All other “Exhaust Vents” should be blocked. If you install an electric fan next to a wind turbine, the turbine will now act as an intake vent. The result? Air is being sucked in a few feet away and going out the electric fan. This can actually DECREASE the amount of air flow moving through the attic.

More Soffit Vents Are Needed!! With electric attic fans more intake ventilation is needed. Actually you should OVER-COMPENSATE with more soffit vents to provide unrestricted air-flow. If there are not enough soffit vents, this is what happens: Air will be pulled from INSIDE the house through light fixtures, switches, vents and other passages into the attic. Ironically, the attic might be cooler, but this might be because your cool air conditioned air is now being pulled into the attic! Finally, without enough soffit vents the motors tend to burn out quickly.

Ideally ridge vent or wind turbines are the best exhaust methods.

The Problem – Mixed Exhaust Ventilation

Mixing wind turbines, ridge vents & electric fans can often cause unwanted effects. The theory that “More is Better” is not necessarily true. Read this article.

See the example on this roof with mixed exhaust ventilation. This roof has both a ridge vent & wind turbines. More is not always better.

By mixing different types of exhaust vents “wind-washing” can occur. Wind-washing is air moving IN and OUT of the same vent. If ventilation is done properly, air only flows IN through the bottom soffit vents and OUT through the top vents. Your house may have several attic cavities.

The Problem – Gable Vents

Gable vents were originally designed for wood roofs. If your roof has been converted to a deck and composition roof, gable vents should be blocked. And, more intake ventilation (soffit vents) should be added. This will cause the cool air to enter from the bottom and exit through the top of the attic.

If you have wind turbines or other exhaust vents, the gable vents generally should be blocked to only allow air to enter through the soffit vents.

This eliminates wind-washing through the gable vents. By not blocking the gable vents, the air in the bottom part of the attic can become stagnant. This creates hot zones during the summer, and during the winter the under-ventilated areas can lead to condensation, mold and mildew.