The best type of attic insulation for an older home is usually blown-in cellulose or blown-in fiberglass, because they can be added over existing insulation without major demolition and conform to irregular joists and wiring common in older homes. Older homes built before 1970 often have low attic insulation levels like R11 to R19, no air sealing, and many penetrations where plumbing, electrical, and chimney chases leak air. The most cost-effective approach is to first air seal all top plate gaps, wire penetrations, and can lights with caulk and spray foam, then blow in cellulose or fiberglass to reach R49 to R60. Cellulose is often preferred for older homes because it is denser at R3.5 per inch, provides better resistance to air movement, is treated with borate for pest and fire resistance, and is made from recycled newspaper, making it eco-friendly. It costs about $0.60 to $1.20 per square foot DIY with free blower rental. Blown-in fiberglass like Johns Manville Climate Pro is lighter, so it is better if your ceiling drywall is older plaster that cannot support heavy loads. Avoid installing new fiberglass batts over old batts if the old insulation is uneven, as it creates gaps. If your older home has knob-and-tube wiring, vermiculite insulation that may contain asbestos, or mold, you should have an electrician and abatement professional evaluate before insulating. Never block soffit vents.
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