What Is New Construction Insulation?
New construction insulation is installed during the framing phase of a build — after the studs are up but before drywall goes on. With open wall cavities, installers can lay fiberglass batts or spray foam directly into each stud bay, achieving complete, consistent coverage.
It's the gold standard for a reason: full access, no obstacles, and no existing finishes to work around. The downside is obvious — you can only do it once, during construction.
What Is Retrofit Insulation?
Retrofit insulation is added to a home after the walls are already finished — drywall on the inside, siding on the outside. The challenge is accessing the wall cavity without tearing everything apart. There are three main approaches:
- Open-wall method: Remove drywall or siding, install batts, then re-close. Most complete but most disruptive and expensive.
- Blown-in insulation: Drill holes, blow cellulose or fiberglass into the cavity. Less disruptive but can leave voids and tends to settle over time.
- Injection foam: Drill small holes, inject expanding foam that fills the entire cavity. Least disruptive, no settling, best coverage of the three retrofit methods.
How Retrofit and New Construction Compare
| Factor |
New Construction |
Retrofit (Injection Foam) |
Retrofit (Blown-In) |
| Wall access |
Open cavities |
Drill & inject |
Drill & blow |
| Disruption to home |
Only during construction |
Minimal — exterior only |
Minimal — exterior only |
| Coverage completeness |
Excellent |
Excellent — fills entire cavity |
Good, may leave gaps at top |
| Settling over time |
None (batts stay put) |
None (foam is stable) |
Yes — cellulose & fiberglass settle |
| Drywall removal |
N/A |
Not required |
Not required |
| Best for |
New builds |
Existing occupied homes |
Attics, accessible spaces |
Why Injection Foam Is the Best Retrofit Option
Of the three retrofit methods, injection foam comes closest to new construction performance — without the demolition. Here's why:
- Complete cavity fill. The foam expands to fill every corner of the stud bay, including gaps around blocking and wiring that blown-in materials miss.
- No settling. Unlike blown-in insulation, RetroFoam doesn't compact over time. The R-value you get on installation day is the R-value you have 20 years later.
- Works with all siding types. Vinyl, wood, brick, stucco, cedar shake — we drill from the outside and patch color-matched to your siding.
- Lifetime warranty. The foam is stable, non-toxic, and backed by a lifetime product warranty.
- One-day install. Most homes are done in a single day. You stay home; there's no mess inside.
When to Choose Retrofit Insulation
Retrofit insulation makes sense when:
- You already own the home and aren't planning a full gut renovation
- You have cold rooms, drafts, or energy bills that don't match what you're paying for
- You're preparing to sell and want to improve your home's energy performance rating
- Your home was built between 1950 and 1985 — the peak era of uninsulated wall construction
If your home was built between 1950 and 1985, there's a good chance your walls are empty or under-insulated. Retrofit injection foam is the most practical fix — and it can often be completed in a single day without disturbing your daily routine.
What About the Cost Difference?
New construction insulation is cheaper per square foot — but only because the wall is already open. When you factor in the cost of removing and replacing drywall or siding, the open-wall retrofit method quickly becomes the most expensive option. Injection foam retrofit sits in the middle: more complete than blown-in, far less disruptive (and costly) than open-wall.
For homeowners in Washington, PSE utility rebates of $2.50 per square foot on wall insulation can further offset the cost. See available rebates →
