Retrofit insulation is more complex than new construction — different access, different code rules, different priorities. Here's how to approach it.
New construction insulation is straightforward — open cavities, no existing materials, full access. Retrofit and remodeling insulation is more complex: existing finishes may be in place, cavity depths vary, and code compliance for existing buildings differs from new construction. Here's how to navigate it.
| Location | Approach | Product | Access |
|---|---|---|---|
| Exterior walls (open) | Standard batt installation | R-13, R-15 HD, R-19, R-21 | Wall open during remodel |
| Exterior walls (closed) | Dense-pack blown-in or injection foam | Not our product range | Drill through exterior or drywall |
| Attic floor (accessible) | Add batts over existing if present | R-19, R-30, R-38, R-49 | Walk-in attic access |
| Crawl space floor | Batt between floor joists from below | R-19, R-30 | Crawl space access |
| Basement rim joist | Cut batt or rigid to fit each bay | R-15, mineral wool cut pieces | Inside basement |
| Interior partitions | Acoustic batts for sound | R-11, R-13, mineral wool AFB | Open during remodel |
The most common retrofit move: the existing attic has R-11 or R-19 from original construction, and you want to bring it up to R-49. You can lay new unfaced batts over the existing insulation — run them perpendicular to the joists to cover the joist tops. If the existing insulation is damaged or has moisture problems, remove it first. Never put faced batts on top of other insulation with the facing sandwiched in the middle — the facing acts as a vapor retarder and can trap moisture between the two layers.
Remodels frequently have non-standard cavity sizes — 24" OC framing mixed with 16" OC, odd-depth cavities from old framing, or partial-height walls. We supply 15" batts (for 16" OC) and 23" batts (for 24" OC) in all R-values. For non-standard depths, batts can be cut lengthwise or split in thickness — no waste when you know what you're doing.
Building additions must meet current energy code requirements for new construction in your jurisdiction. Existing portions of the building being remodeled may qualify for prescriptive exceptions depending on the scope — check with your building department. For additions, specify the full R-value for your climate zone. See our climate zone guide for zone-specific requirements.
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