Is it more cost-effective to add insulation during construction, or retrofit it after the house is finished? What kind of insulation is best? How does insulation installation work?

In this article, we’ll cover all of the above and more. Keep reading to learn more about:

  1. Types of insulation
  2. Adding insulation during construction
  3. Installing insulation after a house is finished

Types of Insulation

The table below from provides an overview of most available insulation materials, how they are installed, where they’re typically installed, and their advantages.

Types of Insulation

Blanket: batts and rolls Fiberglass

Mineral (rock or slag) wool

Plastic fibers

Natural fibers

Unfinished walls, including foundation walls

Floors and ceilings

Fitted between studs, joists, and beams. Do-it-yourself.

Suited for standard stud and joist spacing that is relatively free from obstructions. Relatively inexpensive.

Concrete block insulation

and insulating concrete blocks

Foam board, to be placed on outside of wall (usually new construction) or inside of wall (existing homes):

Some manufacturers incorporate foam beads or air into the concrete mix to increase R-values

Unfinished walls, including foundation walls

New construction or major renovations

Walls (insulating concrete blocks)

Require specialized skills

Insulating concrete blocks are sometimes stacked without mortar (dry-stacked) and surface bonded.

Insulating cores increases wall R-value.

Insulating outside of concrete block wall places mass inside conditioned space, which can moderate indoor temperatures.

Autoclaved aerated concrete and autoclaved cellular concrete masonry units have 10 times the insulating value of conventional concrete.

Foam board or rigid foam Polystyrene




Unfinished walls, including foundation walls

Floors and ceilings

Unvented low-slope roofs

Interior applications: must be covered with 1/2-inch gypsum board or other building-code approved material for fire safety.

Exterior applications: must be covered with weatherproof facing.

High insulating value for relatively little thickness.

Can block thermal short circuits when installed continuously over frames or joists.

Insulating concrete forms (ICFs) Foam boards or foam blocks Unfinished walls, including foundation walls for new construction Installed as part of the building structure. Cores in the blocks are typically filled with concrete to create the structural component of the wall. Insulation is literally built into the home’s walls, creating high thermal resistance.
Loose-fill and blown-in Cellulose


Mineral (rock or slag) wool

Enclosed existing wall or open new wall cavities

Unfinished attic floors

Other hard-to-reach places

Blown into place using special equipment and, although not recommended, sometimes poured in. Good for adding insulation to existing finished areas, irregularly shaped areas, and around obstructions.
Reflective system Foil-faced kraft paper, plastic film, polyethylene bubbles, or cardboard Unfinished walls, ceilings, and floors Foils, films, or papers fitted between wood-frame studs, joists, rafters, and beams. Do-it-yourself.

Suitable for framing at standard spacing.

Bubble-form suitable if framing is irregular or if obstructions are present.

Most effective at preventing downward heat flow, effectiveness depends on spacing and number of foils.

Rigid fibrous or fiber insulation Fiberglass

Mineral (rock or slag) wool

Ducts in unconditioned spaces

Other places requiring insulation that can withstand high temperatures

HVAC contractors fabricate the insulation into ducts either at their shops or at the job sites. Can withstand high temperatures.
Sprayed foam and foamed-in-place Cementitious




Enclosed existing wall

Open new wall cavities

Unfinished attic floors

Applied using small spray containers or in larger quantities as a pressure sprayed (foamed-in-place) product. Good for adding insulation to existing finished areas, irregularly shaped areas, and around obstructions.
Structural insulated panels (SIPs) Foam board or liquid foam insulation core

Straw core insulation

Unfinished walls, ceilings, floors, and roofs for new construction Construction workers fit SIPs together to form walls and roof of a house. SIP-built houses provide superior and uniform insulation compared to more traditional construction methods; they also take less time to build.


Adding Insulation During Construction

It is more cost-effective to add insulation during construction than to retrofit it after the house is finished. To properly insulate a new home, you’ll need to know where to insulate and the recommended R-values for each of those areas. Use the Home Energy Saver tool to determine where you need to insulate and the recommended R-values based on your climate, type of heating and cooling system, etc.

Once you know where you need to insulate and the recommended R-values, review our information on the types of insulation to help you decide what type to use and where. Before you insulate a new home, you also need to properly air seal it and consider moisture control. Energy losses due to air leakage can be greater than the conductive losses in a well-insulated home.

Consider products that provide both insulation and structural support, such as structural insulated panels (SIPs), and masonry products like insulating concrete forms. You should consider attic or roof radiant barriers (in hot climates), reflective insulation, and foundation insulation for new home construction. Check with your contractor for more information about these options.

Choose a team of local building professionals familiar with energy-efficient home construction in your area. The performance of insulation is very dependent on the quality of the installation; contractors that are familiar with the products you are considering will increase the likelihood that they will be installed properly.

Installing Insulation After a House is Finished

Unless your home was specially constructed for energy efficiency, you can probably reduce your energy bills by adding more insulation. Many older homes have less insulation than homes built today, but even adding insulation to a newer home can pay for itself within a few years.

To determine whether you should add insulation, you first need to find out how much insulation you already have in your home and where it is. A qualified home energy assessor will include an insulation check as a routine part of a whole-house energy assessment. An energy assessment, also known as a home energy audit, will also help identify areas of your home that are in need of air sealing.  Before you insulate, you should make sure that your home is properly air sealed.

If you don’t want an energy assessment, you need to find out the following for yourself:

  • Where your home is and is not properly insulated
  • What type of insulation you have
  • The R-value and the thickness or depth (inches) of the insulation you have.

If you live in a newer house, you can probably get this information from the builder. If you live in an older house, you’ll have to inspect the insulation.

Inspecting and Evaluating Your Insulation

Check the attic, walls, and floors adjacent to an unheated space, like a garage or basement. The structural elements are usually exposed in these areas, which makes it easy to see what type of insulation you have and to measure its depth or thickness (inches).

Inspect the exterior walls by using an electrical outlet:

  1. Turn off the power to the outlet.
  2. Remove the outlet cover and shine a flashlight into the crack around the outlet box. You should be able to see if there is insulation in the wall and possibly how thick it is.
  3. Pull out a small amount of insulation if needed to help determine the type of insulation.
  4. Check outlets on all floors as well as old and new parts of your house. Just because you find insulation in one wall doesn’t mean that it’s everywhere in the house.

At Alamance Insulation and Gutters, we can help with all your insulation installation. We are a leader in the insulation and home performance industries centrally located in Burlington, North Carolina. We provide leading-edge products and services to customers throughout North Carolina – from Greensboro, Burlington, Elon, and Mebane to Chapel Hill, Durham, and Raleigh. Let us help you today!