How to Install Blown-In Insulation: DIY Step-by-Step (2026)
How to Install Blown-In Insulation: DIY Step-by-Step
Blown-in insulation is the most cost-effective way to insulate an attic floor, and it's a realistic DIY project for anyone comfortable working in a confined space. A 1,000 sq ft attic costs $600–$1,100 in materials, takes 4–8 hours with two people, and the blowing machine is often free with your insulation purchase. This guide covers material selection, coverage charts, machine operation, and the step-by-step process — plus a clear explanation of why wall installations are NOT a DIY job.
Quick Answer: Rent a blowing machine (free with 20+ bags at Home Depot/Lowe's), budget $600–$1,100 for a 1,000 sq ft attic to R-49, and plan for 4–8 hours with two people. Air seal the attic floor first. Wall cavities (dense-pack) require professional equipment and technique — hire a contractor for walls.
Table of Contents
- Choosing Your Material: Cellulose vs Fiberglass
- Coverage Charts
- Getting the Machine
- Tools & Materials Checklist
- Attic Installation: Step-by-Step
- Wall Installation: Why It's a Pro Job
- Tips for Better Results
- Common Mistakes
- Key Takeaways
- FAQ
Choosing Your Material: Cellulose vs Fiberglass
| Property | Blown-In Cellulose | Blown-In Fiberglass |
|---|---|---|
| R-Value/Inch | R-3.2–3.8 | R-2.2–2.7 |
| Depth for R-49 | ~14" settled (install 16–18") | ~20" (minimal settling) |
| Settling | ~20% over first 2–3 years | 1–3% |
| Bags per 1,000 sq ft (R-49) | 30–36 | 25–35 (varies by product) |
| Cost per bag | $12–$15 | $10–$14 |
| Dust | Heavy (N95 essential) | Moderate (N95 still essential) |
| Coverage around obstructions | Excellent | Good |
Our pick: Cellulose for most attic jobs — higher R-per-inch means less depth needed, better coverage around wiring and plumbing. Fiberglass if you want minimal settling or less dust. The head-to-head at fiberglass vs. cellulose covers every angle.
Coverage Charts
Always check the coverage chart on the bag you purchase — it specifies bags per 1,000 sq ft at each R-value target for that specific product. Owens Corning and GreenFiber both publish detailed coverage tables. These are general reference numbers.
Blown-In Cellulose (Settled Thickness)
| Target R-Value | Settled Depth | Install Depth (+20%) | Bags per 1,000 sq ft |
|---|---|---|---|
| R-30 | 8.5–9" | 10–11" | 18–22 |
| R-38 | 10.5–11" | 13–14" | 23–28 |
| R-49 | 13.5–14.5" | 16–18" | 30–36 |
| R-60 | 16.5–17.5" | 20–21" | 37–43 |
Blown-In Fiberglass
| Target R-Value | Depth Needed | Notes |
|---|---|---|
| R-30 | 11–14" | Minimal settling — installed depth ≈ final depth |
| R-38 | 14–17" | — |
| R-49 | 18–22" | Significant depth — verify attic clearance |
| R-60 | 22–27" | — |
How to calculate: Measure your attic square footage → find your target R-value by climate zone (R-49 for zones 2–3, R-60 for zones 4–8) → read bags per 1,000 sq ft from the chart → multiply by your area (e.g., 1,200 sq ft = 1.2 × 33 bags = ~40 bags of cellulose for R-49). Buy 10% extra. The insulation thickness chart has cross-material comparisons.
Getting the Machine
Where to rent: Home Depot, Lowe's, and independent equipment rental shops carry insulation blowing machines.
Free rental deal: Most Home Depot and Lowe's locations offer free 24-hour machine rental with purchase of 20+ bags of blown-in insulation. At 30–36 bags for R-49 in a 1,000 sq ft attic, you'll easily qualify. Without a purchase, rental is ~$100/day.
What the machine is: A large hopper (chest-high) on wheels with a motorized agitator inside that breaks up compressed insulation, plus a blower that pushes the loose material through a flexible hose (typically 50–100 feet long). It runs on a standard 120V outlet (15–20 amp circuit).
Transporting it: The machine fits in a pickup truck bed or SUV cargo area. Some stores help load it. You'll also need to transport 30+ bags of insulation — a standard pickup handles this in one trip; a car/SUV requires two.
Two-person operation:
- Person 1 (ground, at the machine): Opens bags, feeds material into the hopper at a steady rate, monitors the machine, adjusts air speed. Communicates with the person in the attic.
- Person 2 (attic): Directs the hose, controls insulation placement, checks depth markers. This is the more physically demanding role.
Pro Tip: Test the machine before going into the attic. Feed a bag through, blow a small amount onto the ground, and verify the material is breaking up into loose, fluffy fibers (not clumps). Adjust the agitator and airflow settings. Five minutes of calibration prevents clogging problems mid-job. Home Depot has machine operation guides at the rental counter.
Tools & Materials Checklist
- Blowing machine (rental)
- Insulation bags (coverage chart quantity + 10% extra)
- N95 or P100 respirator
- Sealed safety glasses or goggles
- Headlamp + battery work light
- Long sleeves, long pants, gloves, knee pads
- Plywood walkboards (2–3 pieces, 2' × 4')
- Utility knife (opening bags)
- Tape measure and ruler (depth checking)
- Depth markers (wire rods, paint sticks, or purchased rulers)
- Rafter baffles (one per soffit vent bay)
- Staple gun + staples (for baffles)
- Extension cord (100 ft, 12-gauge for machine)
- Air sealing materials ($100–$300 — see how to air seal an attic)
Attic Installation: Step-by-Step
This is a condensed version — our full how to insulate an attic guide has expanded detail on every step.
Step 1: Air Seal the Attic Floor
Seal every penetration, top plate, recessed light, duct boot, and chase BEFORE insulating. This step saves 15–25% on energy bills by itself. Full instructions at how to air seal an attic. Don't skip this.
Step 2: Install Soffit Baffles
Staple a rafter baffle between every rafter pair at the eaves. These maintain a 1–2 inch ventilation channel so blown insulation doesn't block soffit vents. One baffle per bay, pushed up against the roof deck, stapled to rafter sides.
Step 3: Set Up Depth Markers
Position wire markers, paint sticks, or rulers at 4–6 foot intervals across the attic, marked at your target install depth (e.g., 17" for cellulose at R-49). These are your visual reference while blowing.
Step 4: Position the Machine and Feed the Hose
Place the machine near the attic access (garage floor, exterior). Route the hose up through the access and toward the far end of the attic. Keep the hose as straight as possible — kinks cause clogs.
Step 5: Start at the Far End
Blow from the farthest point back toward the access. You never want to walk through fresh insulation. Direct the hose in a slow, sweeping pattern, building material to the depth markers. Hold the nozzle 2–3 feet from the surface.
Step 6: Fill Evenly and Completely
Work in sections. Make sure insulation covers all penetrations, wiring, and plumbing — this is where blown-in excels over batts. Ensure material extends fully to the eaves, over the top plates, right up to the baffles.
Step 7: Check Depth and Bag Count
Verify depth at every marker before declaring the job done. For cellulose, installed depth should be 20–25% above the settled target. Compare bags used against the coverage chart — if you used fewer bags than specified, you're short somewhere.
Step 8: Insulate the Attic Access
Add 2" rigid foam + weatherstripping to the attic hatch. For pull-down stairs, build an insulated box or install a pre-made cover.
Pro Tip: Don't rush the blowing. The most common DIY error is uneven coverage — thick in some areas, thin in others. Move the hose slowly in wide sweeping arcs, building up depth uniformly. Pause periodically to check depth at markers. A well-blown 1,000 sq ft attic should take 3–5 hours with two people — if you're done in 90 minutes, you went too fast and coverage is probably uneven.
Wall Installation: Why It's a Pro Job
Dense-pack wall insulation requires specific pressure (3.0–3.5 lb/ft³ density), calibrated commercial equipment, and technique that comes from experience. This is NOT a DIY project.
Why consumer machines can't do it: Rental blowing machines are designed for open attic loose-fill — low pressure, high volume. Dense-pack wall installation requires high pressure, low volume. The material must be packed tightly enough that you can't push a finger into the finished cavity. Under-packed walls settle, leave voids, and don't air seal. Over-packed walls bow drywall and push out siding.
The professional process (brief):
- Drill 2–3" holes through exterior siding between each stud bay
- Insert a fill tube to the far end of the cavity
- Blow cellulose at high pressure, slowly withdrawing the tube as the cavity fills
- Monitor fill density by feel and pressure gauge
- Plug holes, patch, repaint
Cost: $1.50–$3.00/sq ft installed for dense-pack cellulose. A typical 1,500 sq ft home: $1,500–$3,000. Full details at wall insulation and insulate walls without removing drywall.
Tips for Better Results
- Keep material fluffy. Don't tamp down or compress blown-in insulation — compressed material loses R-value proportionally. Let it sit naturally at full loft.
- Work in cool conditions. Heat exhaustion is the #1 attic safety risk. Work in fall, spring, or early morning. If you start sweating heavily or feel dizzy, get out immediately.
- Two people minimum. One at the machine, one in the attic. Trying to solo the job means constantly climbing down to refill the hopper — it triples your time and produces worse results.
- Check depth frequently. Stop every 100–200 sq ft and check several markers. It's far easier to add more material as you go than to re-enter the attic to fill thin spots later.
- Don't skip the far eaves. Insulation coverage at the eave line (directly above exterior walls) is the most thermally critical area. This is where ice dams form if insulation is thin. Make sure full-depth material extends to the baffles.
Troubleshooting Common Machine Issues
If the blowing machine gives you trouble (it happens, especially with rental units):
- Clogging in the hose: Usually caused by damp material or feeding bags too fast. Disconnect the hose at the machine, clear the blockage, and slow down the feed rate. Keep bags dry and stored indoors before use.
- Uneven output: The machine's speed gate controls material flow. If output seems inconsistent, adjust the gate and check that material is feeding evenly into the hopper. Break up any clumps before they enter.
- Machine won't start: Check the circuit breaker — these machines pull significant amperage. Use a dedicated 20-amp circuit with a 12-gauge extension cord no longer than 50 feet. Avoid household extension cords.
- Hose too short: Standard rental hose lengths are 50–100 feet. If your attic access is far from where you can park the machine, ask about extra hose sections at pickup. Running out of hose length mid-project is frustrating.
Common Mistakes
1. Skipping air sealing. Air sealing before insulating saves 15–25% on energy bills. Blown-in loose-fill insulation does NOT stop air leakage. Seal first, insulate second — always.
2. Blocking soffit vents. Without rafter baffles, blown insulation migrates into soffit vent channels, blocking ventilation and causing moisture problems. Install baffles in every bay before blowing.
3. Uneven coverage. "It looks about right" isn't a measurement. Thin spots dominate the assembly's thermal performance — R-49 with a 4-inch thin spot performs far worse than consistent R-38 everywhere. Use markers and check depth systematically.
4. Attempting DIY dense-pack walls. Consumer blowing machines can't generate the pressure needed for proper wall dense-pack (3.0–3.5 lb/ft³). Under-filled walls settle and leave gaps. This is the one blown-in application that's strictly professional.
5. Running out of material. Running back to the store mid-project wastes half a day and the machine rental clock is ticking. Calculate from the coverage chart, buy 10% extra, and have it all on site before starting.
Key Takeaways
- DIY blown-in attic insulation: $600–$1,100 for 1,000 sq ft to R-49. Machine rental free with 20+ bags.
- Two-person job: 4–8 hours for blowing, plus 2–4 hours for air sealing beforehand.
- Air seal the attic floor first — this step alone saves 15–25% on energy bills.
- Cellulose: R-3.2–3.8/inch, install to 16–18" for R-49 (settles to 14"). Fiberglass: R-2.2–2.7/inch, install to 20" for R-49 (minimal settling).
- Install soffit baffles before blowing. Use depth markers. Check depth at 6–8 locations.
- Wall dense-pack is strictly a professional job ($1.50–$3.00/sq ft installed).
- Start at the far end, work toward the access. Don't walk through fresh insulation. Don't compress the material.
FAQ
How hard is it to install blown-in insulation yourself?
Moderate difficulty. The machine operation is straightforward — feed bags into the hopper, direct the hose, build up to target depth. The physical challenge is working on your knees/belly in a hot, dusty attic for several hours. No specialized skills are needed, but you should be comfortable in confined spaces and physically able to navigate attic joists. Two people make the job manageable.
How much material do I need?
Use the coverage chart on the bag. For a 1,000 sq ft attic: cellulose to R-49 needs 30–36 bags ($360–$540). Fiberglass to R-49 needs 25–35 bags ($250–$490). Measure your attic square footage, find your climate zone's R-value target, and calculate from the chart. Buy 10% extra. Full coverage data at the insulation thickness chart.
Can I add blown-in over existing insulation?
Yes — R-values are additive. Blow new material directly over old insulation as long as it's dry, mold-free, and not vermiculite/asbestos. If existing insulation has kraft facing, slash it with a utility knife so moisture doesn't get trapped. No removal needed for insulation in good condition. The R-value chart shows target values by zone.
Should I use cellulose or fiberglass?
For attic floors, both work well. Cellulose delivers more R-value per inch (less depth needed) and conforms better around obstructions. Fiberglass settles less (1–3% vs 20%) and is non-combustible. Cost difference is minimal. We slightly favor cellulose for attic work — the full comparison is at fiberglass vs. cellulose and blown-in insulation.
How much money will I save?
The DOE estimates that upgrading from R-19 to R-49 saves $200–$400/year on heating and cooling for a 1,500 sq ft home. At $600–$1,100 DIY cost, payback is 2–3 years. Adding air sealing brings the total savings to 15–25% of heating and cooling costs — on a $2,000/year energy bill, that's $300–$500/year. Full ROI analysis at attic insulation cost.