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Installing Blown Insulation in Existing Walls

Lower Power Bills and Claim an Energy Tax Credit in Older Homes

© 2011 by Kelly R. Smith

Photo of Kelly R. Smith

How blowing insulation works

How blowing insulation works

This article was updated on 06/10/21.

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The purpose of thermal insulation, fiberglass, rockwool, or radiant barrier foil, is to sustain your home’s temperature and provide a thermal barrier between indoors and outdoors. It is one of the most cost-effective methods of saving money over the long term for frugal homeowners.

Properly installed, it can pay for itself in terms of energy conservation by lowering your utility bills. Exterior walls, and sometimes even interior (mostly for sound control), take spray insulation for new construction, and blown-in for existing homes.

Why? In new homes, spray insulation may be sprayed while the exterior walls are still open to the inside. The modern trend is to use green and eco-friendly building products.

Closed-cell spray foam made from soy beans is a great example. However, a lot of older homes were constructed with no exterior wall insulation. Why?

Central Air Conditioners and Heaters were Rare

This is the primary reason. With no HVAC (Heating, Ventilating, and Air Conditioning), it was viewed as a frivolous expense. This seems odd for colder latitudes; insulation certainly would have been a benefit here. Secondly, today’s thermal technology didn’t really exist; available materials were very flammable and considered dangerous.

Third, after HVAC systems became common, utility bills were more affordable than now. It wasn’t until energy bills got so high that the public took an interest and building material manufacturers had incentives to work develop efficient products. Soon, owners of older houses began to retrofit their exterior walls to save money.

Introducing Green, Sustainable Cellulose Insulation

Cellulose has become is a popular material for these retrofits.

  • There are no realistic methods to install fiberglass batts into the the finished wall, save removing the drywall. Bad choice!
  • Mineral fiber like Rockwool is undesirable from an eco point of view. It’s manufactured using natural gas-fired furnaces. These release greenhouse gases into the atmosphere. As an aside, I've installed this stuff before. It's the very devil to work with.
  • Cellulose insulation uses electricity in the production process. This consumes approximately 15% to 20% less energy than the mineral fiber process with a resulting equal R-value.

    According to the Canadian Standards Association (CSA), the entire process of producing mineral fiber, pound per pound, takes 59 times more additional energy than cellulose.
  • Cellulose may be produced using recycled newsprint (lower landfill footprint) to which a flame retardant is added, or organic materials like soy (renewable resource, easy crop to grow).

Option 1: Blow Insulation in from the Interior

To install insulation into finished exterior walls involves creating an opening in order to insert the nozzle. There are two points of entry, either on the inside or on the outside. If your home siding is brick veneer construction, installation must be done from the inside.

Exterior wall wood framing studs are usually 16 inches on center, mandated by the local building code. This means at least one penetration should be made close to the ceiling between each stud, just below the top plate.

You’ll probably have to have this done by a professional insulation company. Because:

  1. They own the right tools, although they may be rented by a knowledgeable DIYer.
  2. There will be obstructions inside your walls like electrical cable,Romex for example, plumbing lines, and firestopping framing (horizontal noncombustible members between studs). Professional installers will have the experience to locate all these items and cut additional holes where necessary.
  3. Following the installation process, the penetrations are plugged up with drywall and the wall texture and paint must be matched.

Option 2: Blow Insulation in from the Exterior

Many homeowners consider this to be the preferred option. It eliminates the extra time-consuming, messy, and expensive steps of plugging holes and then matching the drywall texture and paint.

This option is great for some kinds of exterior siding; vinyl, wood, or in some cases, stucco. One or two runs of siding are taken off under the soffit before cutting holes in the sheathing.

Additional siding will have to be dealt with to address the issue of firestopping. After the job is done, the siding is simply replaced.

Consider the Economic Benefits of Installing Insulation

This is usually the most cost-effective way to reduce your utility bills and carbon footprint. Both wall and attic insulation, along with a foil or painted radiant barrier, will pay for itself quickly.

Also, in the US, homeowners usually may claim an energy tax credit of up to $500 for 10% of qualified energy efficiency improvements including installing blown insulation in existing walls; something to consider. But always check; this changes from year to year. Well, it's the government; some years energy efficiency is more important than others. It depends on which lobbyists are being the most generous.

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About the Author:

Photo of Kelly R. SmithKelly R. Smith is an Air Force veteran and was a commercial carpenter for 20 years before returning to night school at the University of Houston where he earned a Bachelor’s Degree in Computer Science. After working at NASA for a few years, he went on to develop software for the transportation, financial, and energy-trading industries. He has been writing, in one capacity or another, since he could hold a pencil. As a freelance writer now, he specializes in producing articles and blog content for a variety of clients. His personal blog is at Considered Opinions Blog where he muses on many different topics.

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