You don't need a crew for this. A 1,000 sqft attic floor can go from R-19 to R-49 in a single day with blown-in insulation and a rented machine. The real secret is air sealing first — plugging every gap and hole before you add a single inch of insulation. This guide walks you through the whole process, start to finish, with exact materials and quantities.
Difficulty
Beginner–Inter.
Time
4–6 hrs (blown)
Cost (1,000 sqft)
$400–$800
| Item | Est. Cost | |
|---|---|---|
| Blown-in cellulose or fiberglass | $300–$560 | |
| Insulation depth rulers/markers | $10–$15 | |
| Foam board or metal flashing (fixture dams) | $20–$40 | |
| Weatherstripping and caulk (air sealing) | $15–$30 | |
| Baffles/ventilation chutes | $30–$60 | |
| Rigid foam board (attic hatch) | $15–$25 | |
| Fire-rated caulk or foam | $10–$20 | |
| Total | $400–$750 |
Calculate exact quantities for your attic with our Insulation Calculator.
Seal every hole, gap, wire penetration, pipe, light fixture box, and top plate gap you can find. The big ones: chimney chases (use metal flashing and fire-rated caulk, NOT spray foam — fire hazard), plumbing vents, electrical wire holes, recessed light cans (build a dam around non-IC-rated cans), and the attic hatch or door. A can of fire-rated foam and a caulk gun handle 90% of the gaps. Air leaks waste more energy than missing insulation.
Staple a ventilation baffle in every rafter bay where the roof meets the attic floor. These keep your soffit vents open so air can flow from the soffits up to the ridge vent. Blocked soffits cause ice dams in winter and mold in summer. Push each baffle all the way down to the top plate.
Any recessed light, exhaust fan, or junction box needs clearance. Build a box around each one using foam board or sheet metal, at least 3 inches away on all sides. This is a fire safety requirement. If your recessed lights are IC-rated (check the label inside the can), you can insulate over them — but still leave the dam for airflow.
Park the machine outside or in the garage. Feed the hose up through the attic hatch. Solo tip: load 5–6 bags into the hopper, go up and blow until it runs out, come back down and reload. It’s a workout, but it’s manageable alone. Have a helper feed bags if you can.
Blow insulation evenly across the attic floor, filling between and over the joists. Use your depth markers so you know when you’ve hit the target. For R-49, you need about 16–17 inches of cellulose or 19–20 inches of fiberglass. Walk only on planks laid across the joists. Never rush this step.
Walk back through the attic on your planks and check the depth with a ruler in 10–15 spots. Pay extra attention to corners and edges where coverage tends to be thin. Overfill slightly — blown-in insulation settles 10–15% over the first year or two.
Glue a piece of rigid foam board to the back of the hatch door — 2 inches thick gives you about R-10. Add self-adhesive weatherstripping around the frame so it seals when closed. The attic hatch is one of the biggest heat loss points in most homes, and people forget it every time.
Your foot goes right through the drywall ceiling below. Walk only on planks or boards laid across the joists. Every single time.
If insulation covers the soffit openings, you lose attic ventilation. That means ice dams in winter and trapped moisture in summer. Baffles prevent this.
Insulation slows heat transfer. Air sealing stops air movement. Without air sealing, you lose 30–40% of the insulation’s effectiveness. Always seal before you insulate.
Non-IC-rated recessed lights get hot. Piling insulation directly on them is a fire hazard. Check the rating. Build a dam if they’re not IC-rated.
If you run out of bags and stop short, you won’t hit your target R-value. Measure as you go. Buy an extra 5 bags — you can always return unopened ones.
For blown-in cellulose, you need about 16–17 inches of depth. For blown-in fiberglass, plan on 19–20 inches. The number of bags depends on your attic square footage — roughly 30–40 bags for a 1,000 sqft attic. The bag label tells you coverage per bag at your target R-value.
Yes, in most cases. If the existing insulation is dry, mold-free, and not vermiculite (possible asbestos), you can blow right over it. You just need enough new material to reach your target R-value total. Remove any old vapor barriers on top before adding more — they can trap moisture.
Blown-in wins for most DIYers. It fills gaps and odd spaces automatically, covers over joists for fewer thermal bridges, and you can rent the machine for free. Batts work fine but take longer, require precise cutting, and leave more gaps if you rush.
In most climates, no — not on top of the insulation. A vapor barrier goes on the warm side (the ceiling below). If you already have one on the ceiling drywall, you're good. Adding a second vapor barrier on top of attic insulation can trap moisture and cause mold.
Fiberglass and cellulose insulation lasts 20–30 years or more if it stays dry. The main enemies are moisture, pests, and settling. Blown-in cellulose settles 10–15% over the first year or two, which is why you overfill slightly during installation.
Yes, as long as you take basic precautions. Wear an N95 mask, safety glasses, long sleeves, and gloves. Walk only on planks across the joists — never step between them. Check for knob-and-tube wiring and vermiculite before starting. If you find either, call a pro.