Best Attic Duct Insulation

An attic that isn’t insulated can have extreme temperature changes depending on the weather outside. If your air conditioning is located in such an attic, then it means you’ll spend much more on your energy bills.

During the cold season, the ducts become cold as well implying that any air passing through them gets cooled. Your heating system will therefore work harder to heat the air raising your energy bills. During the summers, the HVAC system works to cool the air to make your home comfortable. As the warm air passes through the equally hot duct system due to poor insulation, your air conditioning works harder to cool it.

If you have part or all of your Heating and ventilation located in your attic you need to insulate your attic to create a closed system. The best way to create a closed attic system is to use spray foam insulation.

What is a Closed Attic System?

Closed attic systems are un-vented and cannot allow air infiltration or moisture leakages. If the duct-work of your home heating and cooling system is found in a vented attic, several things could happen. Firstly, if the ducts are un-insulated, it could lead to loss of conditioned air in the summer and heated air in winter.

Benefits of a Closed Attic System

There are two main benefits of having an un-vented attic as detailed here.

  • Can act as a living/storage space

Once you’ve fully insulated your attic to make it air impermeable and free from moisture leaks, you can convert it into a storage space. Besides, you can always use a conditioned attic into a living space which actually adds to the value of your home.

  • Saves on energy costs

The other major benefit of having a closed attic system is that the HVAC system doesn’t get affected by extreme temperatures in winter or summer. Your air conditioning system thus becomes sufficient saving on energy.

Spray Foam Insulation for Closed Attic System

Spray foam is made of isocyanate and polyol resin. The two chemicals react when mixed on site rising up to 100 times the original size. Once the chemical components cure on the surface, they foam a rigid layer of insulation that’s air and moisture resistant.

What is used to install spray foam?

To properly install spray foam in the attic and duct-works, you need to have the following items.

  • Spray foam
  • Gun with several nozzles to change 
  • Protective wear
  • Utility knife (for cutting the excess foam)
  • Hose

How to install spray foam to create a non-ventilated attic

You can create a non-ventilated attic system by installing spray foam right under the roof. Spray foam is either an open cell or closed cell. For unvented attic systems, we recommend using the closed cell spray foam because it conforms to all shapes creating an air seal and thermal resistance. With closed cell foam, you can also create more R-value in a small space.

Before you start insulating the attic and the roofing on the inside, it’s important to inspect the roofing first. Check for any signs of rot on the rafter which is a common occurrence due to moisture leakages. You also need to check for any signs of pest infestation. If any of these problems are detected, fix them first before you think of installing spray foam.

The process of insulating your attic can be a simple DIY project that can take only a few hours. The trick is spraying the foam between the rafters. 1 inch layer of closed cell spray foam can form a great insulation because for every inch, you get about 6.5 – 7 inches R-value. Pay close attention to the areas where the decking meets the rafters. Also make sure to spray on the seams found along the roof decks for proper insulation.

Now, depending on where you live, some building codes require that you place ignition and thermal barriers on top of the insulation. Usually, these can be in the form of plastic boards. However, in most places, you don’t have to go through this step.

As you spray foam your attic, some foam may go beyond the required area or may even form uneven layers. Allow the insulation to cure which can take about 24 hours. After that, use a utility knife to cut the excess foam leaving a uniform layer.

What if You Don’t Want to Re-insulate the Whole Attic?

If you don’t want to re-insulate the whole attic, you can use jacketing tape or any other duct insulation. When ducts are located in crawl spaces or the attics that are unconditioned, it can lead to energy inefficiencies due to heat loss or heat gain. Remember ducts carry conditioned air from a central place to all areas of a home.

Jacketing tape for example has an adhesive that helps it stick onto the surface of any duct in the attic. You only have to apply the tape around the duct to acquire a perfect insulation. Insulating ducts prevents condensation on the surface of the ducts due to differences in temperature of the air inside and the air outside.   


Proper insulation of the attic to create a closed system can help you convert the attic into a storage or living space. Besides, insulated attics and ducts can help save on energy costs because it reduces heat gain or heat loss in extreme temperatures. The best way to create a non-ventilated attic system is by using closed cell spray foam. As for the ducts, you can use a jacketing tape or any other duct insulation.