Attic Ventilation – Not So Baffling

By some estimates, 90% of homes in North America are improperly ventilated. Poorly ventilated homes cost more to heat and cool and could be vulnerable to major damage.

Your roof and attic space rely on the natural phenomenon of convection to circulate air through intake and exhaust vents. Without this air circulation, moisture builds, heat is trapped, and serious problems both inside and out can occur.

Bad ventilation:


  • Ages your roof prematurely
  • Warps farming and decking
  • Buckles shingles
  • Rots your roof
  • Damages siding and paint

According to the Energy Star program, proper insulation and ventilation can save as much as 20% every year on your home’s energy costs. Good ventilation reduces load on air conditioning units in the summer and keeps mold-causing moisture from accumulating in the winter.

In cold climates, proper ventilation also keeps ice-dams from forming on roofs. Ice-dams can melt and cause severe water damage to your home.

Insulation performance is closely tied to attic ventilation as well. Excess condensation, heat, or disrupted air-flow all reduce the effectiveness of your insulation, contributing to higher energy bills.

Soffit vents and gable vents

In order to take advantage of the natural way air moves, you need an equal number of intake vents in the soffit and exhaust vents in the gables or peaks of the roof. Soffit vents allow cool air to enter below the roof, while gable vents allow hot air to exit at the top.

If warm air is trapped in your attic, vapors will condense and lead to water damage. Heat will also be trapped, possibly making your home unbearably hot in the summer months.


Baffles are much easier to understand than their name might imply, and they are essential for proper venting and insulation. Baffles allow insulation to cover the top plates of exterior walls to maintain a thermal barrier between your attic and your living space. Baffles also keep insulation from being blown around by strong winds entering through the soffits. Without baffles, insulation can clog vents or shift into an ineffective position.

Image of proper soffit vent and wind baffle

image of soffit vent and exiting gable vent

How many soffit vents do you need?

Before you begin installation, you need to figure out how many vents you need. The general rule is 1 square foot of vent space for every 150 square feet of attic space. Depending on the dimensions of your attic and your chosen vents, this could be a lot of vents or only a few.

Soffit vents are available in long, continuous runs, small circular ports, and rectangular vents like you see in floors.

Gables and ridge vents also come in a variety of sizes and some have extra bells and whistles like fans and solar panels.

Generally speaking, you need an equal number of soffit vents and gable vents to ensure proper air flow through the attic.

Prevent problems now

The damages that could result from poor attic ventilation simply aren’t worth ignoring. It will cost significantly less to install soffit vents now and prolong the life of your roof. Homeowners with some basic DIY skills can even install vents themselves for very little cost.

Want to know more about preventing roof problems before they start? Check out our next homeowner article here

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