When Mice Move Out, Your Insulation Might Never Recover

In the Lehigh Valley, a lot of homes share the same story:

• older cape or colonial

• a past mouse problem in the attic

• “We had someone bait and trap them a few years ago, it’s fine now”

Then winter hits and the house still feels drafty, the heat runs nonstop, and there’s ice sitting along the edge of the roof. You pop your head into the attic and see insulation everywhere and assume it’s not the problem.

The science says otherwise.

The Fisher (1984) Study: What Happened When Mice Lived In Insulation

In a controlled experiment in 1984, researcher Fisher set up insulated wall panels and allowed house mice to live and breed in them for six months. At the end of the test period, the panels were evaluated for thermal performance.

The fiberglass batt insulation had lost 46.4% of its R-value.

No one ripped it out. No one removed big sections. The material was still there, but it wasn’t functioning the same way.

That is the key idea homeowners are almost never told:

insulation does not have to be missing to stop working. It only has to be disturbed enough that it can no longer hold still air.

What Mice Actually Do To Your Insulation

When mice move into an attic, they treat your insulation as building material, bedding, and a highway system.

Over time they:

• tunnel through the same paths night after night

• pack fibers into dense nests

• dig down to the drywall in some areas and heap insulation in others

• contaminate the material with urine and droppings

From the attic hatch, it still looks like “a lot of insulation.” In reality, the layer now has channels where air can move freely, thin spots with very low R-value, and contaminated pockets that transfer heat faster.

Insulation works by trapping still air between fibers. Once mice have carved runways and crushed sections, the efficacy of that insulation drops, even though it hasn’t “gone anywhere.”

That is why a home can have:

• cold bedrooms on the second floor

• a hot roof deck in winter

• ice damming along the gutters

even though it technically has a full layer of insulation.

Why Just “Adding More” Isn’t Always The Answer

A common suggestion is to just blow more insulation over the top. That can help in clean attics. In rodent-damaged attics, it often just buries the problem.

The old layer underneath still has tunnels, compression, and contamination. Air and heat will still move through those pathways. You end up paying to cover failed material without restoring performance.

In those cases, the honest fix is:

1. remove the damaged insulation

2. clean and sanitize the attic

3. seal rodent entry points

4. install new insulation that actually meets the R-value target for our climate zone

That is exactly where County Pest’s CleanStart division and TAP insulation come in.

Why County Pest Uses TAP Insulation After Rodent Cleanouts

Once we remove contaminated insulation and address the rodent issue, we install TAP cellulose for a few specific reasons that matter in our climate and your use case.

Better real-world performance in Zone 5A

Here in the Lehigh Valley, we sit in climate zone 5A. Winters are cold, summers are humid, and air movement through the attic matters just as much as stated R-value on paper. TAP cellulose settles into and around framing, wiring, and small gaps, which helps control air movement and improves the effective performance of the attic as a system.

Fire resistance

TAP is treated with borate minerals that provide added fire resistance. In an attic full of wiring, bath fan ducts, and recessed lights, having an insulation that helps slow flame spread is a real benefit.

Built-in pest resistance

Those same borates are not friendly to many insects and make the attic less attractive as a nesting site. It does not replace rodent exclusion or good IPM, but it supports the work our pest control side is already doing by making the space less appealing habitat.

Higher R-value with less material compared to what you had

Because TAP is dense and controls air movement effectively, we can reach the recommended R-values for zone 5A without needing impractical depths. You get a continuous thermal blanket that actually does its job, instead of a patchwork of disturbed fiberglass from old mouse activity.

Most importantly, you are getting a system that was designed as pest control and insulation working together, not just another layer on top of old damage.

What A County Pest CleanStart Energy Audit Looks Like

When someone in the Lehigh Valley calls County Pest about a past rodent issue and comfort or energy problems, here’s what we actually do during a free energy audit:

• Inspect the attic for rodent damage, tunneling, nesting areas, and droppings

• Check the depth and consistency of the existing insulation and estimate current R-value

• Look for obvious bypasses and air leaks, like open chases, bath fan discharge issues, and unsealed penetrations

• Take photos so you can see exactly what we’re seeing

• Go over options, including full CleanStart removal, sanitation, sealing, and TAP insulation installation if it makes sense

You get clear information and a written estimate. No pressure, no scare tactics, just a real look at how your attic is performing after the mice have had their way with it.

Ready To Find Out If Your Insulation Still Works?

If your home has a history of mice in the attic, and you’re tired of cold rooms, ice along the roof edge, or a heating system that never seems to shut off, it may not be the furnace at all. It may be insulation that lost nearly half its effectiveness years ago.

County Pest can help you fix both sides of that problem: the pests and the insulation they damaged.

Schedule your free CleanStart energy audit today at countypest.net or call our local office at 610-965-4399.

We’ll show you exactly what is going on above your ceiling and what it would take to get your attic working for you again.