Restoration Guide: Choosing and Installing Wall Insulation

Rob Sabo

Editor's Note: This is article 6 of 18 in Chapter 2: Exterior Walls of the Old House Web Restoration Guide. This guide was developed and edited for old homes from original material in the U.S. Housing and Urban Development (HUD) Rehab Guide.


Section 1--Overview

The measure of how much thermal resistance is offered by insulation is known as R-value. Increasing the R-value of insulation is an important aspect of any home renovation. A well-insulated home is more energy efficient and offers a higher degree of comfort to the residents.

There are several factors to consider during a home restoration in regards to insulation, primarily:

  • Compressibility
  • Density
  • Air leakage
  • Moisture control
  • Fire safety

This chapter of the Old House Web Restoration Guide discusses three main types of insulation: Fiberglass batts, dry blown-in insulation, and sprayed-on expanding insulation.

(Please also see our article on 10 Green Options for Wall Insulation)

Section 2--R-Values

The thicker the fiberglass batt, the higher it's R-value--an R-15 batt has about 180 percent more material than a R-11 batt. However, compressing batts, for example smooshing thicker batts intended for 2x6 inch framing into 2x4 inch wall cavities, only redcues the batt's effectiveness--and subsequently, its R-value.

With dry blown-in insulation, the installer should blow in more insulation than the required minimum to prevent it from settling, especially in vertical wall cavities. When getting bids for this type of insulation, compare bids by comparing the total number of bags required to reach minimum R-value density.

Note: Blown-in insulation can lead to air leakage at wall top plates since it's difficult to completely fill framed-in vertical cavities. Leakage is not a problem with batts or sprayed-on insulation, because it's usually installed prior to interior wall treatments such as sheet rock or plaster.

Section 3--Installing Fiberglass Batt Insulation

Fiberglass bats are sold in rolls of preset thicknesses for 2x4 inch or 2x6 inch wall construction for 8 foot tall walls. Thicker insulation--as well as continuous rolls--is available to insulate floor joists or roof rafters, which are usually 2x12 inch or 12 inch engineered wood joists. Batts most often are sold in widths to fit between wall studs framed every 16 inches or 24 inches on center.

Batts are sold unfaced, or with a craft paper or aluminum foil face, which includes a 1 inch paper/foil flange or tab that covers wall studs and provides a surface to attach staples. These tabs also can be stapled to the inside of studs depending on builder preference--but face-stapling provides a better vapor barrier and eliminates the possibility of an air cavity between the insulation and interior wall covering.

Fiberglass batts are one of the most popular forms of insulation because they are easy and fast to install, and they completely seal cavities between studs with zero settling.

Certain types of fiberglass batt insulation, such as encapsulated insulation, are idea for remodeling. Encapsulated insulation has craft paper or a plastic layer on both sides to enclose the fiberglass and prevent it from being exposed. It's ideal for insulating attics, where insulation typically is left uncovered.

Section 4--Installing Blown-in Insulation

4.1: Closed Stud Spaces

Loose-fill insulation can be blown into closed wall cavities by drilling holes into the exterior or interior finish, or by removing small amounts of the interior or exterior cladding at the top of the wall line. This is an effective method for increasing the R-value of an old house without removing the wall cladding. Care must be taken by the installer not to let insulation pile up around electrical wires and plumbing, which can prevent the insulation from fully filling the wall cavity. Blown-in holes also may be required at the base of the wall line to achieve minimum density.

Another method is to use a narrow tube inserted into the hole at the top of the wall that extends to the bottom of the wall cavity. Insulation is forced through the tube, which is gradually withdrawn until the cavity is completely filled. This type of "dense-pack" insulation uses special insulation types that help prevent settling and increase fire safety.

4.2: Open Stud Spaces

Blown-in insulation also can be used before the interior cladding is applied by placing a polyethylene barrier over wall studs. The insulation is blown in via slits in the plastic membrane, which later should be sealed with tape. Care must be taken not to overfill cavities, as it can cause the membrane to bulge and hinder application of drywall.

Section 5--Spray-on Foam Insulation

One of the newer forms of insulation that's quickly gaining market share is spray-on foam insulation, such as Icynene. Icynene is certified by the U.S. Green Building Council and also is Energy Star approved. Spray-on foam applied to open wall spaces provides a continuous insulation and air infiltration barrier, and it also adds a level of noise reduction not found in other insulation types. However, electrical panels and windows must be protected from over spray, and excess material must be wiped off stud faces before it hardens.

Spray-on foam costs more than other types of insulation, and it can be extremely messy. However, it reduces air circulation within walls, improves fire safety, and increases R-value.

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