Professional Blown-in insulation is often the ideal solution for older homes because its installation is minimally invasive and it effectively fills the irregular and obstructed wall cavities common in older construction. Unlike batt insulation, which requires tearing out walls, blown-in material can be installed through small, easily patched holes. This method preserves the original character and materials of the home, like plaster walls, while still delivering a major upgrade in thermal performance. The material flows around old wiring, plumbing, and uneven framing, creating a complete fill that is nearly impossible to achieve with other retrofit methods.
For owners of historic or vintage properties, this approach solves the long-standing problem of how to make their homes more comfortable and energy-efficient without a destructive and costly renovation. This article, based on the experience of insulation professionals, will cover the process and materials involved, starting with the unique challenges that make this method so necessary for older buildings.
The Unique Challenges of Insulating Old Homes
Many homes built before the 1970s have little to no insulation in their walls. They were built at a time when energy was cheap and building science was not well understood. Adding insulation to these homes isn’t as simple as it is with new construction. They often present a number of challenges:
- Irregular Framing: Stud spacing can be inconsistent, and cavities may be different sizes.
- Obstructions: The wall cavities are often cluttered with old fire blocks, wiring, and plumbing that make it difficult to install pre-cut batts.
- Plaster and Lath Walls: Tearing out these durable, character-rich walls is messy, expensive, and results in the loss of a home’s original charm.
- Balloon Framing: Some very old homes have wall cavities that run uninterrupted from the foundation to the attic, creating a massive channel for air and heat loss.
These issues make traditional fiberglass batts a poor choice for retrofitting walls. It would require a full gut renovation, which is often out of the question for homeowners who want to preserve their property’s integrity.
How the Blown-In Process Works
The process for installing blown-in insulation is what makes it so compatible with existing homes. A specialized machine is used to fluff up a compressed insulation material and blow it through a long, flexible hose to where it’s needed.
For an attic, the process is straightforward. A technician takes the hose into the attic and blows a thick, uniform blanket of insulation over the attic floor, covering the tops of the joists and filling in all the nooks and crannies.
For walls, the technique is called “dense-packing.” The crew typically works from the outside of the house to minimize disruption. They will carefully remove a section of siding, drill a small hole (usually 2-3 inches in diameter) into each stud bay, and insert the hose. They then blow the insulation into the cavity under pressure until it’s tightly packed. This density is important to prevent the material from settling over time. Once all the cavities are full, the holes are plugged, and the siding is replaced, leaving little to no visible trace of the work.
Common Blown-In Insulation Materials
There are two main types of material used for blown-in applications: fiberglass and cellulose. Both are effective, but they have slightly different properties.
Blown-In Fiberglass
This is the same material as the familiar pink batts but in a loose, fluffy form. It’s made from molten glass spun into fine fibers. It’s naturally non-combustible and has excellent resistance to moisture and mold growth. Because it’s a very lightweight material, it can be installed in attics without putting too much stress on the ceiling drywall below.
Blown-In Cellulose
Cellulose insulation is made from recycled paper products, primarily old newspapers, that are treated with borates. This treatment makes the material highly resistant to fire, mold, and pests. Cellulose is denser than fiberglass and is known for its excellent ability to fill small gaps and reduce air movement within the wall cavity.
- Bonus Tip: The borate treatment in cellulose insulation provides a great secondary benefit for older homes, which can be more susceptible to pests like ants and cockroaches. Borates are a natural insect repellent.
A Look at Key Material Differences
| Feature | Blown-In Fiberglass | Blown-In Cellulose |
|---|---|---|
| Material Source | Recycled glass, sand | Recycled paper, wood fiber |
| R-Value per Inch | ~R-2.2 to R-2.7 | ~R-3.2 to R-3.8 |
| Fire Resistance | Naturally non-combustible | Excellent (due to borate treatment) |
| Pest Resistance | Fair | Excellent (due to borate treatment) |
| Settling (Walls) | Very low when properly dense-packed | Low when properly dense-packed |
| Moisture Handling | Does not absorb moisture | Can absorb and release moisture |
Key Advantages for Older Structures
The benefits of blown-in insulation service align perfectly with the needs of older buildings.
Preserves Original Finishes
This is the number one advantage. Homeowners can get a fully insulated wall without having to sacrifice their original plaster, woodwork, or wallpaper. The small holes needed for installation are easily patched, making it a respectful way to upgrade a historic building.
Fills Every Gap
The loose nature of the material allows it to flow around all the obstacles inside an old wall cavity. It fills the space completely, eliminating the thermal gaps and voids that would be left behind with batts. This complete fill is what delivers consistent thermal performance across the entire wall.
Improves Sound Control
Older homes can be noisy, with sound traveling easily through uninsulated walls and floors. Both fiberglass and cellulose provide a significant improvement in sound dampening. Filling the empty cavities with insulation absorbs sound waves, making the home noticeably quieter and more peaceful.
- Bonus Tip: Before having insulation blown into your walls, consider having an energy audit performed. An auditor can use an infrared camera to show you exactly where your heat loss is occurring and help you confirm the insulation has filled all the cavities after the job is done.
Things to Consider Before Making a Decision
Before you move forward with a blown-in insulation project for an older home, there are a few important considerations.
- Knob-and-Tube Wiring: If your home still has active knob-and-tube wiring, it is a serious fire hazard to surround it with insulation. This wiring must be decommissioned and replaced by a licensed electrician before any insulation work can begin.
- Existing Moisture Problems: You must fix any roof leaks, plumbing leaks, or foundation water issues before insulating. Insulation can trap moisture against the wood framing if the source of the water isn’t stopped, which could lead to rot.
- Air Sealing is Still Needed: Blown-in insulation does a great job of stopping heat transfer, but it’s not a true air barrier. For the best results, the insulation work should be combined with professional air sealing in the attic and basement to stop drafts.
- The Contractor Matters: The performance of blown-in insulation is highly dependent on the quality of the installation. Choose a contractor with specific experience in dense-packing walls in older homes. They will know how to get the right density to prevent settling and ensure a complete fill.
Questions People Ask About Insulating Older Homes
How long does the installation usually take?
For an average-sized home, insulating the attic and walls with blown-in insulation typically takes one to two days.
Will the insulation settle in the walls over time?
If the insulation is dense-packed correctly by a qualified installer, settling will be minimal to non-existent. The pressure used during installation ensures the material is locked in place within the cavity.
Is the installation process very messy?
Professional crews take steps to control dust, especially when working inside. However, it is an insulation product, and some cleanup will be necessary. Most of the disruptive work can be done from the outside to keep the interior of the home clean.
What is the typical R-value for an old wall after it’s been insulated?
Most older homes have walls framed with 2x4s, which gives about 3.5 inches of space. Filling this with cellulose will result in an R-value of about R-13, and fiberglass will provide about R-9. While lower than new construction walls, this is a massive improvement over an empty cavity.
Can you insulate walls that have plaster and lath?
Yes, absolutely. Experienced installers know how to drill through plaster and lath cleanly. This is one of the main reasons blown-in insulation is so well-suited for these types of homes.
A Smart Upgrade for Classic Homes
For owners of older homes, blown-in insulation offers a practical and effective way to improve comfort and efficiency without compromising the building’s character. It solves the unique structural challenges these homes present and delivers immediate results in terms of stable temperatures and lower energy bills. Before starting, homeowners should ensure any underlying issues like old wiring or moisture are addressed to get the best and safest long-term outcome.
Get a Professional Assessment for Your Older Home
Determining the best way to insulate an older property requires a careful inspection. For homeowners in Kentucky and the surrounding region looking for an expert evaluation, the team at Armored Insulation has extensive experience with retrofit projects in older homes. They can identify potential issues and recommend a safe, effective insulation plan. To schedule a consultation, they can be reached at (270) 727-5566 or by email at [email protected].
Author: Jared Baker, Owner and Director of Business at Armored Insulation, brings deep local insight and strong business expertise to the company. He plays a key role in upholding the company’s focus on delivering top-tier service.
Reviewer: Mia Clark used her 9 years of experience in the spray foam industry to review this article and offered input focused on helping companies make their services easier to understand.