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Cathedral Ceilings Insulation

Cathedral ceilings are open areas high below the roof for architecture and design. They are beautiful but must be properly insulated so as to keep the ceiling temperatures close to the room temperatures. Insulated cathedral ceilings are a relatively recent phenomenon that took off in the 1970s. Prior to the insulated cathedral ceilings invention, cathedral ceilings were thermal disasters since they did leak air and heat, therefore encouraging condensation and decomposition. Even the introduction of ventilation only made it worse. Insulation was the only solution to these problems. There are some special considerations in each area while doing insulation and this article will help you with tips on insulating a cathedral ceiling.


If your cathedral ceiling is built with space between the roof deck and your home ceiling, it will have truss joists or large rafters. This will require you to install batted insulation, often specified thin batts to ensure there is an air space above the batts for ventilation. Here, cellulose insulation is mostly recommended but also fiberglass is used. Your cathedral ceiling may be of another design known as unvented cathedral ceiling or hot roof design. Do not misunderstand the word ‘hot-roof’, since it is not as much hot, maybe 1-5 degrees hotter than in surface temperature. But basically, a hot roof is the one whereby insulation is directly attached to the roof. In this case, no ventilation is required. Building codes do not allow insulation with fiberglass and cellulose in hot roof design. They recommend the use of spray foam –spraying the inside with foam- and foam board. Unlike spray foam, when using foam board you are required to redo your roof.

 Does A Cathedral Ceiling Need To Be Vented?

Building an airtight ceiling is more important than roof ventilation. Though the basics of venting roofs are mostly misunderstood, there are things worth having in mind.

  • Roof ventilation does not lower indoor humidity levels.
  • Migration of water vapor through a cathedral ceiling should be discouraged at all costs.
  • Roof ventilation does no lower the temperature of any roof in significant degrees during the summer
  • Check the flow of heat into the roof ventilation by installing thick insulation to ensure minimal heat loss at home.
  • The flow of water vapor into the roof ventilation should be limited to ensure that the roof sheathing never gets damp.
  • Without an airtight ceiling, roof ventilation is dangerous since it allows indoor air leakages.

How To Establish If Your Soffit Vents And Ridge Vents Provide Adequate Air Flow

This should be simple. Builders should always follow building codes that provide code requirements and formulas for calculating roof ventilation openings. Even while doing attic insulation, these codes are important; follow them to the letter. If you visit companies that deal with home insulation, they will explain most of the codes. Some of the codes require 1 square foot free ventilation area every 300 square feet of attic floor area if you are locating half of the ventilation openings in the soffit area and the other half on the ridge area. But for soffit vents, you require 1 square feet for 150 square feet of attic floor.