Encapsulating an Attic Space

By Robert Robillard on Energy Saving, Home Maintenance

Value of Creating a Conditioned Attic Space

Encapsulating an Attic Space means including the attic in the thermal envelope by installing insulation under the roof sheathing and not in the attic floor, joist bay. While any insulation can be used, we feel the best practice is to use spray foam. Typically, this is done with open cell or closed cell insulation.

Contractor blowing foam insulation

The end result is the attic becomes a conditioned space. This results in stable temperatures inside the attic, as opposed to a ventilated attic, which sees huge seasonal temperature swings.

Benefits of Using Spray foam

Applying an open or closed cell spray foam will encapsulate your attic space. The foam stops the “chimney effect,” most homes have, and can reduce heat loss by 50%.

Another benefit can be found during the warmer summer seasons. The outdoor pollen and humidity is prevented from entering the home through the soffit and ridge vents. This significantly reduces the amount of work the HVAC has to do to dehumidify the home making it much more efficient and comfortable. For those with allergies, this could greatly reduce your seasonal suffering.

Bathroom Remodeling Insulation and Ventilation

Bringing Ductwork into Thermal Envelope

There are more Pros than Cons to encapsulating your attic space. One of the biggest returns on investment is that it helps regulate the attic from temperature fluctuations, resulting in reduced HVAC costs.

In a nutshell, HVAC operation becomes more efficient. It does this by remaining cooler in the summer and warmer in the winter.

Bathroom ventilation and Insulation

Reduction in Air Leaks / Ice Dams

Encapsulating the attic space eliminates the concern of air leaking from the main house into an unconditioned attic. Air leaks often are seen in wire, pipe and access penetrations into the attic floor from below. Heat loss, through air leakage, is one of the ingredients in ice dams.

Eliminate Frost and Mold on the Underside of Roof

In the winter, air leaks show up as frost on the underside of the roof.  Frost gets into the attic from air leaks, or attic bypasses.  Frost eventually melts and leaves plywood, framing and insulation wet. Eventually mold grows. Learn More about frost and mold in the attic.

The best way to prevent frost from accumulating in an attic is to seal off attic air leaks or encapsulate it. Once you seal the air leaks, the attic will be frost free.

Sealed-Combustion Furnaces

It should be noted that “direct-vent” HVAC equipment (sealed-combustion furnaces) are the best choice for an encapsulated attic. When you encapsulate an attic it becomes a sealed “unvented attic assembly.” A sealed-combustion furnace uses a separate air intake and exhaust. This is needed because a sealed attic cannot support a vented HVAC unit.

Conditioned Attics have a Few Drawbacks

Creating a conditioned attic is a solution to a fundamental design flaw (locating ductwork or HVAC equipment outside of a home’s thermal envelope) but come with their own set of drawbacks.

Sealed Attic Disadvantages

Encapsulating an attic with spray foam is more expensive than installing insulation on an attic floor. It’s also  harder to locate roof leaks or repair rotten roof sheathing than in a home with an unconditioned attic. I always recommend that the roof condition be evaluated and uprated as needed.

Resolving Ice Dams

Sealed Attic Space – No Ice Dams

Sealed Attic Advantages

One BIG advantage of sealing the attic is that it prevents whole house air leakage is reduced saving heating and cooling energy costs. Learn more about air leaks here. Increased attic temperature also  means decreased moisture which means decreased, or no mold growth.

Another benefit is that it will significantly reduce, if not eliminate, ice damming in the winter. The spray foam in the rafters, allow you to eliminates air leak sealing in attic floor, sealing around recessed lights or access doors and hatches.  All of which can be difficult to do properly.

Mechanical systems and ductwork in the attic often leak warm air and contribute to ice gaming. If installed in a sealed attic, they operate more efficiently, with less strain on equipment. The controlled attic temperature and humidity, decrease the possibility of condensation and creates a conditioned space for storage.

Spray foam also helps reduce rodents infiltration and seal out insects since it eliminates the need for  roof venting. It is also a great solution for complex roof venting designs which often cause issues with ice damming.

Over the years we’ve used a few different spray foam contractors. It’s taken us a bit to vet them all, but we’ve found a company, InsulationDoneRight.com,  that were pleased to partner with.

InsulationDoneRight uses superior USA made Green Guard approved products, has a highly-trained team that is professional and competent.

When your reputation matters, its important to use good sub contractors and not just go low bid!


Creating a conditioned attic space may cost more up front, but you will reap the rewards over time. When you compare the Pros vs. Cons – you see that the Pros far outnumber the setbacks of cost and damaging roof leaks.

Encapsulating an Attic – Conditioned Attic Space

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About the author

Robert Robillard

Carpenter / Remodeler / Editor

Rob Robillard is “The Concord Carpenter” Rob is a builder, general contractor, carpenter, woodworker, and editor of Concord Carpenter and ToolBoxBuzz As a General Contractor and carpenter, Rob owns and operates Concord Carpenter LLC. A full-service remodeling and construction company. Rob is a recognized leader in home building best practices and a source for how-to information for building professionals. On this website, Rob covers all aspects of home construction, building science, home improvement, woodworking, remodeling, and some of the best product and tool reviews. Rob is in charge of our Tool and Product Review series - Concord Carpenter Videos where we post all of our tool reviews and video tutorials. Rob approaches remodeling and building construction with a pragmatic and problem-solving approach. He enjoys using his knowledge and experience to help and educate building professionals as well as DIYers on best practices in the construction and remodeling industry. He's a strong advocate for "raising the bar" in the construction trades and promoting the trades to youth. #BeAMentor #Green2Great Craftsmanship, quality, and pride guide his journey on this channel The Concord Carpenter's motto: "Well done is better than well said!" : Read more about Rob

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