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Cellulose & Loose Fill Fiberglass
A machine chops and fluffs cellulose or fiberglass, then a hose carries it into your attic where a technician distributes it across the entire floor rather than fitting individual pieces into individual cavities. For an open, unfinished attic floor in Hollywood or Sunrise, that speed and evenness is usually the whole reason to pick this method over anything cut to length.
Two very different products get blown in through the same style of hose, and they should not be confused with each other. Cellulose is made mostly from recycled newsprint that has been shredded into a fine, fibrous texture and treated with a fire retardant, most commonly borate compounds, which also happen to discourage insects and rodents from nesting in it. It is gray or off white, dense compared to fiberglass, and it packs down into gaps and around obstructions with a thoroughness that loose fiberglass does not always match.
Blown fiberglass, sometimes called loose fill fiberglass, is spun glass fiber broken into small tufts rather than the long strands used in batts. It is lighter than cellulose by volume, does not absorb moisture into its fiber structure the way cellulose does, and tends to hold its loft a bit better over time in a dry attic. Neither material is inherently better in every situation. Cellulose generally edges out fiberglass on air flow resistance and on filling irregular nooks tightly, while fiberglass edges out cellulose on moisture tolerance if the attic sees any humidity swings, which in a South Florida attic is close to guaranteed at some point in the year.
The machine itself sits on a trailer or in a truck bed outside the house, loaded with bales of compressed material. An operator feeds those bales into a hopper where an agitator breaks the compressed block apart, and from there the loosened material is metered into an airstream moving through a long flexible hose, sometimes over one hundred feet of it, that snakes up through the attic access and into the space above the ceiling. Air pressure alone is what carries the material that distance and fluffs it back up to its intended loft once it exits the hose nozzle.
Inside the attic, a second technician holds the nozzle and walks the space methodically, moving in a pattern that covers every section of the floor rather than dumping material in one spot and hoping it spreads. Getting this right requires reading the attic as you go: material has to be worked into tight corners near the eaves, held back from ventilation baffles so soffit airflow is not blocked, and layered evenly rather than piled high in the middle of the floor and thin at the perimeter, which is the single most common shortcut a rushed crew takes.
Depth is measured with marked rulers, called depth gauges, set upright at intervals across the attic before blowing begins, so the technician can see at a glance during the job whether coverage is reaching the target thickness everywhere rather than just in the middle of the floor. A quoted R value assumes a specific settled depth across the entire surface, and a floor that averages the right depth but has thin patches near the perimeter and thick patches near the hatch is not actually delivering that R value uniformly, even though a casual glance from the attic access might look fine.
Coverage around recessed lighting, plumbing vent stacks, and electrical junction boxes needs particular attention, since material blown carelessly around a non IC rated recessed fixture can create a fire hazard, and material blown over an open junction box violates electrical code. A careful crew either builds a dam around fixtures that require clearance or confirms the fixtures are IC rated and sealed before blowing over them at all.
Cellulose in particular settles after installation, typically losing something in the range of fifteen to twenty percent of its initial loft over the following months as the fibers compress under their own weight and shift slightly with attic temperature swings. A competent installer accounts for this by blowing to a higher initial depth than the final target, so that after settling occurs the attic still meets or exceeds the R value called for in the original scope. If a crew blows only to the bare minimum depth on day one, the attic will underperform once settling finishes, and there is no way to catch that shortfall without going back up and checking depth again later.
Fiberglass loose fill settles less dramatically than cellulose in most cases, which is one reason some installers favor it for attics where the floor will not be revisited or topped off for years. Neither material should be expected to hold its exact installed depth forever, particularly in an attic that sees any airflow disturbance, foot traffic during other repairs, or water intrusion from a roof leak that was not caught quickly.
| Method | Speed of install | Best fit | Long term behavior |
|---|---|---|---|
| Blown in cellulose | Fast on open floors | Open attic floor, irregular framing, topping off existing material | Settles, absorbs water if wetted |
| Blown in fiberglass | Fast on open floors | Open attic floor where moisture swings are a concern | Holds loft slightly better, does not absorb moisture into fibers |
| Fiberglass batts | Slower, piece by piece | Joist bays, additions, tight retrofit cavities | Can compress or gap at seams over time |
| Spray foam | Slower per square foot, more setup | Roof deck, air sealing combined with insulating | Does not settle, adheres permanently |
The single most frequent scenario is an older Pembroke Pines or Miramar home built with attic insulation that was adequate decades ago but never topped off, leaving depth well under current recommendations. Rather than removing intact, dry, uncontaminated existing material, blowing new cellulose or fiberglass directly over it is often the fastest way to bring depth up to target, provided the existing layer is actually clean and dry, which a technician should verify before starting rather than assuming.
A second common pattern is a house with a large, simple, open attic floor and no ductwork or major obstructions up there, where the labor cost of hand fitting individual batts into every joist bay would run far higher than simply blowing loose fill across the entire plane in a fraction of the time. Homes with attic floors like this, common in many Broward subdivisions built during large development pushes, are close to the ideal case for blown in material.
Blown insulation is also frequently used to correct wind damaged or storm disturbed attics where prior insulation shifted, compacted in spots, or was partially removed for roof repair access and never fully restored. Rather than patching with batts that were never designed to blend seamlessly with loose fill, blowing fresh material across the repaired section brings the whole floor back to a consistent depth.
Before the job, a homeowner should expect to see thin, compressed, or uneven material when they look into the attic access, sometimes down to bare ceiling drywall visible in spots near the perimeter. After a properly done blow, the entire floor should show a uniform, fluffy layer at a consistent depth from the hatch to the farthest eave, without visible bare patches or piles. The comfort change most homeowners notice first is a reduction in how quickly upstairs rooms heat up in the late afternoon, since a thin or gapped attic floor lets heat radiate down into the ceiling much faster than a properly depthed one.
An open attic floor is the ideal setting for this method, but plenty of South Florida homes do not have one. If the attic has significant ductwork, HVAC equipment, or storage platforms crowding the floor, blowing loose fill around and under all of that obstruction becomes far harder to do evenly, and a combination approach or a switch to attic insulation planning that considers the whole space usually serves better. If the framing is a series of narrow, separated joist bays without a continuous open plane, hand fitting batt insulation to each cavity can actually be more precise and less wasteful of material than trying to blow loose fill into tight, broken up spaces.
Blown insulation is also the wrong first move if the attic currently has water damage, active roof leaks, or signs of rodent activity, since new material blown over any of those problems only buries them rather than resolving anything.
Both perform well when installed correctly. Cellulose fills irregular spaces tightly and resists airflow slightly better, while fiberglass tolerates humidity swings without absorbing moisture into its fibers. The better choice often comes down to the specific attic's obstructions and moisture history rather than a blanket rule.
Yes, provided the existing layer is dry, free of mold, and not contaminated by rodent activity. A technician should check the existing material before blowing, since covering a hidden problem does not make it go away.
Most single story attics can be completed in a matter of hours once setup and containment are in place, since the blowing process itself moves quickly across an open floor. Larger or more obstructed attics take longer to distribute material evenly.
A properly sealed attic access and careful containment during the job should prevent material from entering living space. Some fine dust is normal in the attic itself during blowing, which is why crews wear respirators and ventilate the space.
Cellulose treated with borate discourages some insect activity, but neither cellulose nor fiberglass is a substitute for sealing actual entry points. If pests are already active, that access needs to be addressed separately from the insulation itself.
There is no fixed schedule, but any attic showing visibly thin or compacted material compared to when it was installed is a candidate for a top off. Checking depth every few years, especially after any roof work, is a reasonable habit.
Loose fill fiberglass can still cause skin irritation on contact, which is why installers wear long sleeves and protective gear in the attic. Once installed and undisturbed, it does not present the same handling irritation to occupants below.
Before a single bag of material is opened, a competent installer works out how many bags a given attic needs based on the square footage of the floor, the target settled depth, and the coverage chart printed on the specific product being used, since bag coverage rates vary between brands and between cellulose and fiberglass. Skipping this calculation and simply blowing until the truck runs low is how attics end up with inconsistent depth, because a crew running short partway through a job under time pressure tends to thin out coverage near the end of the attic rather than stopping the job and ordering more material.
A careful crew calculates bag count with a margin built in above the bare minimum, accounting for settling and for the reality that corners, eaves, and areas around obstructions consume more material per square foot than open floor space does, since material has to be worked into those tight spaces rather than simply dropped and leveled. Leftover bags at the end of a job are a reasonable sign of a properly planned installation, not wasted material.
Access to the attic hatch needs to be clear, and any stored items directly beneath or immediately around the access point should be moved before the appointment, since the crew will be running a long hose through that opening repeatedly during the job. If the attic currently has any personal belongings stored on the floor, those need to be relocated before blowing begins, since loose fill material will bury anything left in place and make it difficult to retrieve afterward without disturbing the new insulation.
Homeowners should also plan for some noise during the job, since the blowing machine itself runs on a gas or electric motor positioned outside or in a garage, and that motor needs to run continuously throughout the application. Pets sensitive to noise or to strangers moving through the house to reach the attic access should be secured in a separate area for the duration of the appointment.
Cellulose in particular is sensitive to moisture during and immediately after installation, since freshly blown material that gets wet from an active roof leak or from condensation forming during an unusually humid stretch can clump and lose loft before it ever has the chance to settle normally. A responsible crew checks the roof condition before starting a job and will flag any active leak for repair before insulation goes in, rather than blowing new material over a wet spot and hoping for the best.
Timing a blow in job is generally more flexible than timing spray foam, since loose fill does not depend on a chemical reaction that behaves differently at different temperatures the way foam does. That said, scheduling during the cooler parts of the day, particularly for larger attics that take longer to complete, keeps the crew working in the attic safer and more comfortable, which in turn supports a more careful, evenly distributed application.
Homeowners should expect blown insulation to meaningfully improve an attic that was previously thin or unevenly covered, particularly in terms of how quickly the ceiling below heats up during peak afternoon sun. It will not address duct leakage, poor ventilation, or air infiltration around the attic hatch and top plates on its own, since those are separate problems that loose fill insulation was never designed to solve. A thorough evaluation before the job should identify whether any of those additional issues exist so they can be addressed as part of the same visit or as a clearly identified next step.
Attics with wide, uninterrupted floor spans are common across large subdivisions built during the major development pushes throughout Pembroke Pines, Miramar, and parts of Sunrise, where builders framed roofs with simple trusses over a single open floor plate rather than the cut up, custom roof lines seen in older, more architecturally varied neighborhoods. Homes in these subdivisions are frequently strong candidates for blown insulation precisely because the floor plan overhead matches the conditions where a blowing machine performs at its best, covering long, unobstructed runs quickly and evenly.
Older homes throughout Davie and unincorporated parts of Broward sometimes present a mixed picture, with an original section of the house holding a simple open attic and a later addition introducing a more complicated roofline. In those cases a crew may blow the original open section while handling the addition separately with fitted batts, treating the attic as two distinct zones rather than forcing one method across the whole space.
Describe what you can see from the attic hatch and we will tell you what it likely needs.