Home Improvement Interior Remodel Walls & Ceilings Drywall

How to Add Insulation to Walls That Are Closed

Front view of a closed wall with fiberglass insulation

The Spruce / Jason Donnelly

Most houses benefit from insulation in the walls. But walls of older homes may not be insulated, especially if they have never been remodeled. Uninsulated closed walls mean an overtaxed heating or cooling system, high bills, and energy waste. Learn the options for adding insulation to walls that are already finished with drywall panels and painted.

Injection Foam

Injection foam is a spray form of insulation used to fill the cavities of a home.

Foam injection insulation is similar to those individual cans of foam insulation found in home centers but on a much larger and far more efficient scale. Professional injection foam installation is best. A few manufacturers do offer moderately expensive do-it-yourself kits. Foam insulation is best left in the hands of professionals, though.

Foam has advantages over fiberglass insulation, chiefly because it resists mold and mildew better than loose-fill, batt, or roll fiberglass. It expands to work into difficult areas that blown-in insulation may ignore.

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.

The injection foam process creates holes in the walls that need to be filled, patched, and painted. Pressure from the foam can damage walls if not applied properly.

Brands

Pros
  • Expands

  • Moisture-resistant

Cons
  • Holes in walls

  • Foam creates pressure

Person applying injection foam insulation

The Spruce / Jason Donnelly

Loose-Fill Blown-In Cellulose Insulation

Loose-fill cellulose is a pellet-like insulation made of recycled paper that is blown in through holes in the walls.

Loose-fill cellulose insulation begins as paper and gets turned into insulation. The key ingredient that makes this work is boric acid. 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. 

Loose-fill cellulose insulation tends to settle, potentially resulting in higher energy bills. While the pellets usually fit around obstructions, this isn't guaranteed. Pellets may clog at key points.

Brands

Pros
  • Affordable

  • Resists pests, mold

  • Fits some obstructions

Cons
  • Tends to settle

  • Requires vapor barrier

  • Holes in walls

Hands holding a pile of loose-fill cellulose insulation

The Spruce / Jason Donnelly

Blow-In Blanket Insulation (BIBS)

Blow-In Blanket System (BIBS) is a method of insulating walls with blower-injected insulation that can be used for either open or closed walls. 

On open walls, a fabric sheath or net 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.

BIBS helps to bridge the gap between injected insulation and roll insulation. The product does not settle. The initial volume you fill will remain at that volume. Certified BIBS materials do not soak up moisture, so mold and mildew growth is inhibited.

The downside is that, like roll fiberglass or rock wool insulation, the walls do need to be opened up in order to attach the BIBS fabric.

Brands

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.

Pros
  • Does not settle

  • Mold and mildew minimal

Cons
  • Specialized system

  • Not DIY-friendly

Blow-in blanket insulation

The Spruce / Jason Donnelly

Roll Insulation

Roll insulation is the traditional method of adding insulation to the cavities in walls. The difference is that the walls are already closed, so the interior drywall needs to be removed and replaced.

Either fiberglass or rock wool is used. Rock wool is a mineral that is heated and then spun into a fiber.

Adding roll insulation ensures full coverage in the wall cavities. The insulation works through or around obstructions like electrical wires, pipes, and cross braces. The insulation itself is inexpensive, though the overall project is not.

The downside of using roll insulation is that the interior drywall must be demolished, hauled away, and disposed of. If the walls were painted in lead-based paint, this is a health hazard. After the insulation has been added, new drywall must be hung, finished, and painted.

Brands

Brands of fiberglass and rock wool insulation include:

Pros
  • Maximum coverage

  • Inexpensive

  • DIY-friendly

  • Simple tools needed

Cons
  • Messy

  • Labor-intensive

  • Disruptive

  • Hazard if lead-based paint

Side profile roll of fiberglass insulation

The Spruce / Jason Donnelly