How to Add Insulation to Walls That Are Closed

Cutaway of a wall showing insulation

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Most new construction homes have insulation contained in the wall cavities. Walls of older homes built before the 1970s and even as late as the 1980s often will not be insulated, unless a retrofit project has already solved this problem. Having uninsulated closed walls in a harsh climate results in discomfort and high energy costs. A lack of wall insulation means an overworked heating or cooling system that diligently blows hot or cold air, yet the house envelope is not holding up its end of the deal. Instead, a vast majority of that expensive warm or cool air seeps through hollow wall cavities and uninsulated ceilings.

Retrofit wall insulation is a debatable subject because there is no single right answer for all homes and homeowners. Only a cost-benefit analysis in relation to your own situation can help you arrive at the right answer. In some cases, the cost of adding insulation may exceed the cost of energy needed to heat or cool it. While uninsulated walls are never beneficial from an eco-friendly standpoint, sometimes they can make more financial sense than if your only solution is to remove all of the drywall, insulate, install drywall, and paint again.

Injection Foam

Foam has advantages over fiberglass insulation, chiefly because it resists mold and mildew better than loose-fill, batt, or roll fiberglass. Unlike blown-in cellulose, its strong expansion properties mean that it can force its way into difficult areas, such as around wires, boxes, protruding nails and screws, and other spaces that tend to hang up gravity-fed cellulose.

Foam injection insulation is like those individual cans of foam insulation you can buy at a home center but on a much larger and far more efficient scale. Professional injection foam installation is best, but several manufacturers offer moderately expensive do-it-yourself kits. Foam insulation is probably the best retrofit choice in terms of avoiding wall damage.

  • Pros: Injection foam expands to work into difficult areas that blown-in insulation may ignore.
  • Cons: This process creates holes in your walls that need to be filled, patched, and painted.
  • Brands: Prominent brands include Tiger Foam and Touch 'n' Foam.

Roll Insulation

In a perfect world, you would be able to unscrew invisible bolts, remove drywall panels, install insulation, and reinstall the panels. Our less-than-perfect world of permanently attached wallboard means time-consuming hacking away of gypsum, individually removing drywall screws or nails, installing R-13 or greater fiberglass roll insulation, and re-installing the drywall. It's a mess and it's expensive. Still, for all of the pain and effort involved, the remove-and-reinstall method is simple, straightforward, and can give you the best assurance that all vacancies in your walls are being filled.  

  • Pros: This method ensures maximum wall cavity coverage at a relatively low cost. Also, this can be an entirely do-it-yourself project, if you wish. Only simple tools are involved. No special blowers need to be rented.
  • Cons: It is very messy and labor-intensive, basically the antithesis of a clean retrofit.
  • Brands: Manufacturers of fiberglass roll insulation include Owens Corning, Johns Manville, Knauf, and Guardian.

Loose-Fill Insulation

How do you feel about having a paper product insulating your walls? With boric acid added for fire resistance, shredded, recycled telephone books, tax forms, and newspapers all contribute to making safe cellulose insulation, blown-in cellulose is injected into the wall cavities by a series of holes drilled into either the inside or outside of the walls. Blowing-in attic cellulose is conceivably a do-it-yourself job. But wall cavities are more difficult, so do-it-yourself installation is not recommended.

  • Pros: With no shortage of companies offering blown-in cellulose, competition keeps prices lower for this type of insulation.
  • Cons: Cellulose insulation tends to settle, resulting in hollow spaces above the cellulose. Also, it can hang up on inner-wall obstructions such as wires, boxes, plaster keys, and even spider webs.
  • Brands: Some blown-in cellulose insulation brands include GreenFiber, Applegate, and Nu-Wool.

Blow-In Blanket Insulation

Blow-In Blanket system (BIBS) is the trademarked name for a patented new-construction method of insulating walls with blower-injected insulation that can be used for either open or closed walls. On open walls, a fabric sheath is attached to studs, providing a type of cage that contains blown-in fiberglass (not cellulose) insulation, in pellets and other forms. Unlike loose-fill insulation, the insulation forms a tight, dense, seamless blanket that is highly effective at stopping air infiltration.

  • Pros: BIBS insulation does not settle. The initial volume you fill will remain at that volume. Unlike cellulose insulation, certified BIBS materials do not soak up moisture, so mold and mildew growth is inhibited.
  • Cons: BIBS is a fairly specialized system and is not widely available. It is not a do-it-yourself process.
  • Brand: Blow-In Blanket System is a patented system by Service Partners LLC, which certifies a few insulation products by different manufacturers for use with the BIBS system.