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Attic Insulation & Ventilation

Roof it Right with Insulation and Ventilation Services

Attic Insulation and Ventilation

Having the RIGHT amount of attic ventilation and insulation can:

  • Increase the lifespan of your roofing system
  • Increase the comfort and well-being of your family
  • Lower heating and cooling cost
  • Lower costs of future home repairs
  • Keep your roof eligible for an extended warranty
The top of a roof with new shingles

Does my attic have proper ventilation?

Roof and Attic Ventilation

What is the main purpose of attic ventilation?

You might think that it is to manage the temperature. Good guess! But the main purpose of attic ventilation is to control moisture. Here is why it’s so important:

Moisture in your home . . .

  • Makes insulation weak
  • Rots your roof deck
  • Promotes mildew growth, a health hazard

That isn’t to say that temperature control isn’t important. It is. An excessively warm attic transfers heat to the roofing system. This, in turn, can warp the roof deck and prematurely age your shingles. Yet another reason to have an effective attic ventilation system.

An effective ventilation system needs…

  • Intake vents – Cooler outdoor air is drawn in
  • Exhaust vents – Warmer, humid air escapes
  • 1 Square foot of exhaust vent intake area (called net free area) for every 150 square feet of attic space per building code
  • Balance between the intake and exhaust vents

If certain requirements are met, such as balanced ventilation, the ratio of exhaust vents’ net free area to attic square footage can be reduced to 1:300. Owens Corning recommends a 1:150 ratio combined with a balanced intake and exhaust ventilation for optimum results.

It’s easy to calculate how many exhaust vents your roof might need based on the square footage of your attic. And there are several options (see below). But if you have doubts about whether you intake vents are properly working, you may want to ask for a Ventilation Balance Evaluation.

*A Ventilation Balance Evaluation includes a thorough evaluation of the workings of your ventilation system and several hours of calculations. Most roofing companies don’t offer a quality ventilation inspection with a regular roof inspection. Roof It Right offers this service for a fee of $350, which could be waived if you hire us for repairs, if any are needed.

Roof and Attic Insulation

Speaking of ventilation, it works hand-in-hand with your insulation. Ventilation protects your insulation from sucking in too much moisture. Moisture causes insulation to lose its ability to trap heat. Think about it; it would be like trying to warm up while wearing wet clothes. Insulation needs to stay dry in order to keep cool air or heat in.

The measurement of insulation’s ability to Resist  heat transfer is called R-value. The higher the number, the more resistant the insulation is. According to, the recommended level for most attics is R-38 or about 10-14 inches depending on the type of insulation. There are two general ways to install insulation.

Blown-in: Confetti-like, loose-fill material such as cellulose (mostly recycled paper), glass wool, or rock wool that is blown in with a special machine into cavities or covering an attic floor.

Blanket Insulation: Comes in batts (pre-cut panels) or rolls that can be cut and trimmed to fit in between rafters and other spaces.

The big problem that we notice in Kentucky homes is that generally there is not enough insulation to meet the recommended R-value. And, unfortunately, installing an extra vent on the roof will not compensate for insufficient insulation or improve cooling or heating costs. 


Common Intake Vent Options in Louisville Metro:

Soffit Intake Vents (recommended):

Soffit intake vents are installed in the underside of your roof’s eaves.

DA-4 intake vents:

In homes that did not have soffit vents built into them, DA-4, or deck air vents are a viable option. They are installed near the bottom of your roof’s edge as illustrated below.

Gable Vents:

Gable vents are intake vents installed under the peak of a gable. The disadvantage of gable vents is that they miss the warm humid area below the vents.

Common Exhaust Vent Options in Louisville Metro:

Slant vent

A slant vent is also called a turtle or a box vent. It covers 51 square inches of exhaust flow.

Ridge vents

Ridge vents are very elegant looking and leak less, if the roof is not too low pitch. With a net free vent area of 20 square inches per linear foot, they boast outstanding performance. A sufficient length of ridge is required for ridge vents.

Turbine or Whirlybird vents

Turbines or whirlybirds have a higher flow capacity of 95 square inches of net free area airflow each. Another plus is the maintenance-free top and bottom dual bearing system.

Power Vent

A power vent could resolve issues with ventilation, but might require electrician fees to wire or re-connect it. The drawbacks of a power vent are that it draws temperature from the house, is noisy, is costly to replace, and is easy to miss when it’s broken. And a broken vent has a huge impact on the frame, roof deck, and roofing materials.

A common power vent used in Louisville Metro is a 1,500-CFM power vent (It’s 1,500 cubic feet of air flow per minute and handles up to 2,100 square feet of attic space).

Note: Asphalt shingles installed over an insulated roof deck (insulation directly against the roof deck, not the attic floor) without sufficient ventilation (volted ceiling, cathedral ceiling, spray foam roof deck) do not qualify for manufacturer’s extended warranties. Full warranty over such a deck is for 10 years ONLY for residential homes and 5 years for non-residential homes.

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