Blown-In Insulation: A Homeowner’s Guide (US)

Materials & tools

Materials

• Insulation: cellulose or fiberglass (per code and assembly).

• Interior smart vapor retarder: Oskorp VARISMART DUO+ — ideal for dense-pack/blow-in walls and sloped ceilings. Its mesh reinforcement resists ballooning and tearing during injection, holds staples securely, and keeps the cavity under uniform pressure for consistent density and fewer voids.

• Air-sealing tapes & sealants: use an acrylic construction sealant and an all-weather tape (e.g., ONE 4 ALL Tape) for seams, penetrations, and to close injection ports.

• Patches/finishes as needed.

Step-by-step (updated excerpts)

1) Assess & plan

• Plan your air & vapor control layer on the interior. For dense-pack, choose VARISMART DUO+ to allow seasonal drying while providing robust reinforcement during blow-in.

2) Create access (for membranes & drill points)

• Install VARISMART DUO+ across studs/rafters (smooth, taut surface).

  • Overlap seams per spec and tape all seams/edges (ONE 4 ALL Tape works well).

  • Staple to framing; the integrated mesh gives superior staple pull-out resistance and minimizes bulging when the cavity is pressurized.

• Injection layout: Mark injection locations on the membrane (one high per bay; add a lower port if needed for complex cavities). Use a hole saw or membrane nozzle to make clean ports you can re-tape later.

3) Blow the insulation

• Insert the hose through the VARISMART DUO+ injection port.

• Dense-pack from the bottom up, slowly backing out as you feel steady back-pressure. The membrane’s mesh reinforcement helps maintain target density across the full bay.

4) Close & finish

• Close ports: remove the hose and tape the injection openings flush to restore airtightness and vapor control (again, ONE 4 ALL Tape).

• Patch interior finishes if you drilled through drywall elsewhere (not needed if you injected through the membrane only).

FAQ

Do I really need a special membrane for blow-in?
For best results, yes. VARISMART DUO+ combines a smart vapor retarder with mesh reinforcement, so it both manages moisture and stands up to the pressure of dense-pack installation. You’ll get more uniform density, fewer blow-outs, and a tighter assembly.

Is blown-in right for my house?
Often ideal for older homes with empty wall cavities, under-insulated attics, and framed floor/ceiling cavities. Confirm moisture control strategy (air sealing + appropriate vapor retarder) for your climate and assembly.

Can I do it without a pro?
Yes - attic top-ups are very DIY-friendly. Dense-pack walls require more care to avoid voids, manage moisture, and maintain exterior/interior finishes. If in doubt, hire a pro for the walls and DIY the attic.

Do I need a vapor retarder?
It depends on climate zone and assembly. In most U.S. climates, a smart vapor retarder on the interior side of walls/ceilings is preferred to manage seasonal moisture while allowing drying. Always follow local code and product instructions.

What about lights and heat sources?
Keep insulation clear of non-IC-rated recessed lights, flues, and other heat sources. Use proper chutes/baffles to maintain attic airflow from soffits.