Rodent Contamination Cleanup Across a 1,420 Square Foot Norwalk Basement
1 / 12The unfinished side before any work began. Insulation in this condition reads as a whole ceiling job, not a spot repair.
See How the Work Was Done
Real photos from this Norwalk project: the soiled ceiling insulation, the nesting inside it, the containment and negative air, and the cleaned joist system.
What Happened
A buyer taking over this Norwalk, CT home found mouse droppings through the basement ceiling. The assessment confirmed the problem was not a corner of the space but the whole of it: nesting cavities burrowed into the fiberglass batts between the joists, droppings across the slab, and soiled insulation running the full 1,420 square feet over both the finished and unfinished sides. Because dried rodent droppings become airborne the moment contaminated material is pulled down, the crew built the job around containment before touching anything. A zippered access door went into the containment barrier so technicians could enter and exit without breaking the seal, and three HEPA negative air scrubbers ran on 24 hour cycles to keep the work zone under negative pressure and capture airborne particulate for the duration. The crew worked in Tyvek suits, N95 respirators, goggles and gloves. All 1,420 square feet of soiled insulation came down and went straight into sealed bags inside the confined space. The 850 square feet of drop ceiling tile over the finished side came out with it, and 250 square feet of drywall on the unfinished side was cut out where spore growth had taken hold behind it. With the cavity fully open, the entire joist system was bio cleaned across the same 1,420 square feet, then the space was fogged with a plant based antimicrobial using an ULV cold fogger to reach the framing gaps a wipe cannot. Roughly four tons of debris left in a 20 yard dumpster. The basement was left stripped, cleaned, treated, and ready for new insulation.
Scope of Damage
Ceiling Insulation
SevereMice had burrowed nesting cavities into the fiberglass batts between the joists, with droppings worked through the material itself. All 1,420 square feet was removed and bagged in the confined space.
Finished Basement Ceiling
Moderate850 square feet of drop ceiling tile over the finished side was removed to reach the contaminated cavity above it.
Unfinished Basement Drywall
Moderate250 square feet of drywall affected by mold spores on the unfinished side was cut out, bagged and disposed of.
Joist System & Slab
SevereDroppings and nesting debris across the framing and the basement floor. The full 1,420 square foot joist system was bio cleaned once the cavity was open.
How We Solved It
- 1
Containment & Zipper Access
A containment barrier went up with a single zipper access door positioned so technicians could enter and exit and the seal could be closed behind them every time.
- 2
HEPA Negative Air
Three HEPA negative air scrubbers ran on 24 hour cycles, holding the work zone under negative pressure and capturing airborne particulate from the first removal through the final treatment.
- 3
Insulation & Ceiling Tear Out
1,420 square feet of soiled insulation and 850 square feet of drop ceiling tile removed and bagged inside the confined space, in full PPE.
- 4
Affected Drywall Removal
250 square feet of drywall on the unfinished side cut out where mold spore growth had taken hold behind it.
- 5
Joist System Bio Cleaning
With the cavity fully open, the entire 1,420 square foot joist system was bio cleaned surface by surface.
- 6
Antimicrobial Fog
A plant based antimicrobial applied as an ULV cold fog across 1,420 square feet to reach framing gaps and cavities a wipe cannot, with no harsh chemicals or solvents.
- 7
Disposal
Roughly four tons of contaminated material removed from the property in a 20 yard dumpster staged on site.
Tools & Equipment Used
Questions Homeowners Ask
Why did all 1,420 square feet of insulation have to come out?
Rodent droppings and urine soak into fiberglass rather than sitting on top of it, so soiled insulation cannot be cleaned in place. In this Norwalk basement the mice had burrowed nesting cavities through the batts across the full ceiling, on both the finished and unfinished sides, which is why the removal covered the entire 1,420 square feet rather than a patch. Hard surfaces are different. The joist system underneath was bio cleaned and kept.
Why run negative air for a cleanup rather than just bagging the material?
Dried rodent droppings and nesting material break apart and go airborne the moment contaminated insulation is pulled down. Three HEPA negative air scrubbers ran on 24 hour cycles here so the work zone stayed under negative pressure for the whole job, meaning air moved into the contained space and through HEPA filtration rather than out into the rest of the home.
Why was the finished basement ceiling removed too?
The contaminated insulation sat in the joist cavity above the drop ceiling. There is no way to remove and clean what is above a ceiling without opening it, so 850 square feet of ceiling tile came down over the finished side. Tile is a removable system, which is what makes this practical rather than destructive.
What does the antimicrobial fog do, and what does it not do?
After the physical removal and the bio cleaning of the joist system, a plant based antimicrobial was applied as an ULV cold fog across 1,420 square feet. Fogging reaches framing gaps and cavities that a wipe cannot get into. It is a treatment applied at a point in time as part of the cleaning, and it is not a barrier or a warranty against future activity. The removal and the cleaning do the real work.
Does this job stop the mice from coming back?
No, and it is important to be straight about that. This scope was removal, cleaning and treatment. It did not include sealing entry points or exclusion work, which is a separate trade. A cleanup takes away the contamination and the nesting material that made the space attractive, but keeping rodents out means closing the routes they use, which your pest control contractor handles.
What happens to the basement after a cleanup like this?
It is left stripped, cleaned, treated and open. The joist bays are bare, which is the correct state to hand off in, because new insulation should only go into a cavity that has been cleaned first. Reinsulating was not part of this scope.
