Roof Ventilation and Insulation: The Basics

Published April 15, 2014 by Whirlwind Team

building ventilation systemPreserving the integrity of your metal building makes roof ventilation and insulation a requirement. Not only does moisture contribute to corrosion and other damage, it can be the proximate cause of mold.

In order to protect the building and its contents from mold and other environmental issues due to water, heat, or cold, your roof must have adequate ventilation designed into it and you should consider the need for insulation depending on the building’s use and location.

Where Does the Water Come From?

Most moisture found in metal buildings is the result of condensation forming on the roof and wall panels as the temperature and humidity change throughout the day and night. Condensation occurs when warm humid air is cooled to the point where the water can no longer be held in the air particles.

Moisture can come from outside, through human respiration, heaters, your HVAC system, or through improper construction techniques.

Some water could, of course, be due to a leak.


Proper ventilation helps deter condensation and keeps the inside environment at more pleasant temperatures. Vents reduce roof and ceiling temperatures in the heat and save you on summer utility bills. In colder climates ventilation actually helps maintain a cold roof to mitigate the formation of ice dams.

A rule of thumb in determining adequate ventilation is to allocate 1 square foot of vent opening for every 150 square feet of insulated ceiling. If the insulation has a vapor barrier the ratio changes to 1:300. The most effective design is a combination of continuous ridge vents along the roof peak and continuous soffit vents at the eave.

To help the flow of air you can also use cap vents, turbines, and gable vents if there is not enough room in the attic.


Insulation is meant to keep heat in or out of whatever area is insulated. Just as you don’t want all your air conditioning leaking through the roof you don’t want a lot of heat coming in the same way… and vice versa in the winter.

The problems with insulation come in when moisture is introduced or the insulation is compressed somehow. Critters like to make nests in insulation, too. Proper roof maintenance and venting can reduce these issues. And insulation works along with venting to keep the temperature at the roof at proper levels.

Types of Insulation

  • Blanket: least expensive, may come with a radiant barrier.
  • Rigid board: can be custom cut, may have weatherproof facing or be made of flame retardant materials,
  • Sag and bag: a combination of blanket and loose fill, good for getting into all the crevices and oddly shaped areas.

With the need for energy efficiency in a world where utility costs always seem to be on the rise, proper ventilation and insulation can result in a significant drop in both your cooling and heating bill. Good ventilation and vapor barriers keep moisture away from the roof panels and out of the insulation so corrosion and rot do not occur.

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