Should I Insulate My Attic Floor Or Ceiling?

You want to insulate your attic. Considering your attic is responsible for about 50% of your home’s energy efficiency, we are thrilled for you. But you can’t decide whether to insulate the floor or the ceiling. You don’t know if there’s a difference or how you should choose. We’ve got you covered.

South Central Services has insulated hundreds of homes with spray foam in and around Greencastle, Pennsylvania. Depending on what our customers need, we insulate either the attic floor or the ceiling. With the right insulation product, both areas can contribute to lower energy bills, better air quality, and a more comfortable home.

You need to know the difference and which is best for you. Specifically, by the end of this article, you will understand:

• The differences between vented and unvented attics
• How to choose between a vented or unvented attic
• The insulation products available for your attic

Don't have time to read right now? Check out everything you need to know at a glance.

The Difference Between Attic Floor And Attic Ceiling Insulation

There are two critical differences between attic floor insulation and attic ceiling insulation: how air flows and which insulation products are available. Let’s examine these in more detail.

1. Airflow In Attics

Ventilation is the process of air exchange. If you open a window, air ventilates into and out of your home. As far as ventilation is concerned, there are two types of attics: vented and unvented.

A vented attic allows for ventilation in the attic. Air can leak into and out of the attic freely. There is no control or airtight seal to prevent ventilation. Most attics already exist as vented attics, but adding insulation on the attic floor can create a barrier between the air infiltration upstairs and the conditioned air downstairs.

An unvented attic does not allow for uncontrolled ventilation in the attic. Insulating the attic ceiling creates an airtight seal. The only permitted ventilation in the attic is mechanical. No air can leak into the attic space or escape through it.

2. Available Insulation Products For Attics

There are many insulation options for homeowners who insulate their attic floor. Spray foam, batt, and blown-in insulations are all options for attic floors. If your attic floor is insulated with a batt or blown-in product, there will still be air exchange between the main floor of your home and your attic. For the lowest energy bills, you’ll want to consider air-sealing the attic floor to create an airtight barrier.

Attic ceilings have fewer options due to the nature of blown-in insulation. Attic ceilings can be insulated with spray foam, which adheres to the ceiling. Other options include dense pack cellulose or batt insulation, which can be stuffed into the rafters.

However, the ceiling must be sealed with an air-sealing product to create an unvented attic. Spray foam insulation both air-seals and insulates, but batt insulation would need to be paired with a separate product to air-seal before installation. Otherwise, the nature of batt insulation would allow air to exchange even with the insulation installed on the ceiling.

There are cases where the ceiling above the insulation is vented using baffles. This method poses a high risk of condensation in-between the roof material and the insulation material.

Should I Insulate Both My Attic Floor And Ceiling?

While it may seem like the more insulation you have, the more energy-efficient your home will be, you do not want to insulate both the attic floor and ceiling.

Insulating the floor and the ceiling would create a separate and conditioned environment, especially if you air-sealed your attic. The goal of insulating your attic is to cut the attic off from your conditioned home environment or add the attic into the conditioned home environment. Insulating both the floor and ceiling creates an isolated attic climate.

Picture the outline of a house with its floor, walls, and roof. That outline is your thermal envelope. That outline represents the only separation between your home and the weather outside.

If you insulate the attic floor, the thermal envelope stops before the roof. If you insulate the attic ceiling, the thermal envelope includes the whole house. But if you insulate the floor and ceiling, there are two thermal envelopes: two separate areas within the house.

Another reason not to insulate both your attic floor and ceiling is the cost. Insulating both areas of your attic would be much more expensive than choosing a single place to insulate.

Do I Need A Vented Or Unvented Attic?

Now that you understand the technical differences between vented and unvented attics, how can you determine which one is best for you? Let’s examine the key indicators that you need a vented or unvented attic.

Signs You Want A Vented Attic

Homeowners who want a vented attic are looking for storage space. You are not worried about temperature control for any of the belongings in your attic. You don’t have ductwork running through the attic. Your goal is to lower your energy bills.

Signs You Want An Unvented Attic

Homeowners who want an unvented attic need temperature control in the attic. You may have items to store that are sensitive to heat, like musical instruments or electronics. You may plan to finish your attic and make it part of your living space. Or, you have HVAC ductwork upstairs and want to help prevent excess heat load on that ductwork in the summer.

Which Is More Affordable: Insulating The Attic Floor Or Ceiling?

No matter which option you choose, insulating your attic will likely cost several thousand dollars. However, one option is more budget-friendly than the other simply due to the quantity of materials.

Creating an unvented attic involves insulating the ceiling of your attic and the gables. A vented attic, by comparison, only needs one insulated surface: the floor. The square footage of an unvented attic is larger than a vented one.

If your biggest concern is the insulation cost, insulating your attic floor is less expensive than insulating the ceiling.

The Bottom Line About Where In Your Attic Is Insulated

Attic insulation is one of the first steps to making an existing home more energy-efficient. You can either insulate your attic floor or your attic ceiling. Insulating your attic floor can create a vented attic, which is ideal for storage and not needing temperature control upstairs. Insulating the ceiling will make an unvented attic, which allows you to control the temperature for temperamental storage items, living space, and HVAC ductwork.

No matter which area you choose to insulate, we recommend air-sealing to maximize energy efficiency. An airtight seal can be provided by air-sealing products and spray foam insulation. Consider a separate air-sealing product if you choose a budget insulation like fiberglass.

Now that you know where in your attic needs insulation, your next step is to:

• Compare best attic insulation options
• Learn the process for spray foam installation in attics
• Calculate a sample estimate for your attic spray foam