Does blown-in cellulose settle over time in New Brunswick homes? | Insulation IQ?

Yes, blown-in cellulose does settle over time — and in New Brunswick's climate, understanding how much settling to expect and how to account for it is important to ensuring your attic insulation performs as intended over its full service life.

The settling process is a function of gravity and gravity alone. Cellulose is made from densely processed recycled paper fibres that are ground into a light, fluffy mass. When installed at low density (as is typical for open attic blowing), the fibres are not interlocked tightly, and over weeks to months they gradually compress under their own weight. The amount of settling depends on the installed density and depth. In typical open attic applications, cellulose loses roughly 15 to 20 percent of its installed height through settling. So if you blow in cellulose to an initial depth of 18 inches, you can expect it to settle to approximately 14 to 15 inches at equilibrium — which is close to, but still above, the R-50 threshold for a Climate Zone 6 New Brunswick attic.

This is why professional installers always account for settling in their calculations. The CGSB (Canadian General Standards Board) settling factor is built into the bag-count charts provided by manufacturers. When the packaging says "X bags covers Y square feet at R-50," that estimate already factors in settling to the settled depth, not the freshly blown depth. This means if you follow the bag-count instructions correctly, you should still hit your target R-value after settling has occurred. Where homeowners sometimes go wrong is under-installing — stopping when the loose material looks deep enough without counting bags — and then finding after a year that the settled depth falls short of the target.

Depth markers are the standard tool for monitoring this. Stakes or small rulers are placed throughout the attic floor before blowing begins, and they remain permanently in place. After settling, you can poke your head into the attic and read the settled depth at multiple points. For NB Power's Home Energy Savings Program and the Canada Greener Homes Grant, installed depth at settled measurement is used to verify R-value compliance.

One condition that accelerates or worsens settling in New Brunswick is moisture intrusion. Cellulose is treated with borate compounds that give it fire resistance and some resistance to mould, but if the material gets wet — from a roof leak, inadequate vapour control, or condensation due to air leakage — the fibres can mat and compact significantly. This is a concern in older Moncton and Saint John homes where roof flashings may be aging or where the ceiling vapour barrier has gaps. Wet cellulose also loses much of its R-value temporarily, and while it can dry out and recover some performance if the moisture source is eliminated, repeated wetting cycles degrade the material. A roof leak that allows liquid water to reach the cellulose can create a dense, low-R-value mass that sits flat against the ceiling deck.

Compared to blown-in fibreglass, cellulose settles more noticeably but still delivers excellent long-term performance when properly installed. Fibreglass loose fill settles very little (fibres have more internal spring), but it performs at a lower R-value per inch, so you need more depth to start with. In terms of long-term thermal performance per dollar, cellulose remains competitive and widely used by New Brunswick insulation contractors for attic retrofits.

A few practical points worth noting: cellulose handles thermal bridging across framing better than fibreglass batts because it fills irregularly shaped spaces and flows around obstructions. It also has better sound attenuation properties, which some homeowners in denser urban areas like Fredericton or Saint John find valuable. Its environmental footprint is low — it's one of the highest recycled-content insulation products available.

If you're doing a top-up over existing insulation in an older New Brunswick home, cellulose is generally compatible with any existing loose-fill material and most batt products. Just ensure the existing material is dry before adding on top, and verify that the total installed system will reach R-50 or better after settled depths are accounted for.

For a proper assessment of what your attic needs and how much material to install, a consultation with a local insulation professional is the most reliable approach. New Brunswick Insulation can connect you with experienced contractors through the New Brunswick Construction Network.

---

Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• Brunswick insulation & roofing
• Arctic Fox Construction Inc.
• moose luxury painting
• 3Tone Construction Ltd
• Gionetterenovations