Install Insulation
Insulation is your addition's thermal barrier—it keeps heat in during winter and out during summer. But insulation only works if it's installed correctly with proper air sealing. This step covers R-value requirements, insulation types, and the air sealing that makes it all work.
Quick Summary
Typical cost
$1.50-$4.00/sq ft
Time needed
1-2 days
Professional help
DIY possible or insulation contractor
Why This Step Matters
Insulation is one of the best investments in your addition. Proper insulation reduces heating and cooling costs by 20-40%, makes rooms more comfortable by eliminating hot/cold spots, and reduces noise transmission. Under-insulated spaces are uncomfortable year-round and cost more to heat and cool for the life of the building.
Critical Point
Insulation and air sealing work together. Even R-60 insulation is almost worthless if air can bypass it through gaps and cracks. Air sealing first, then insulation—never the other way around.
R-Value Requirements by Climate Zone
R-value measures insulation's resistance to heat flow. Higher numbers mean better insulation. The minimum required R-values depend on your climate zone and the part of the building you're insulating.
| Climate Zone | Ceiling | Walls | Floor |
|---|---|---|---|
| Zone 1-2 (Hot) | R-30 to R-49 | R-13 to R-15 | R-13 |
| Zone 3 (Warm) | R-30 to R-60 | R-13 to R-20 | R-19 to R-25 |
| Zone 4-5 (Mixed) | R-38 to R-60 | R-13 to R-21 | R-25 to R-30 |
| Zone 6-8 (Cold) | R-49 to R-60 | R-20 to R-21+5 | R-30 |
Find your zone: Visit the Department of Energy website and search for "insulation zones" or ask your building inspector. Your permit will specify the minimum R-values required.
Insulation Types Compared
Fiberglass Batts (Most Common)
Pre-cut panels that friction-fit between studs. Available in various R-values and thicknesses to match standard stud spacing.
Specs
- • R-value: R-2.9 to R-3.8 per inch
- • Cost: $0.50-$1.00/sq ft
- • DIY-friendly
Best For
- • Standard stud walls
- • Attic floors
- • Budget-conscious projects
Caution: Batts must fill cavities completely without compression. Gaps and voids drastically reduce effectiveness.
Blown-In (Cellulose or Fiberglass)
Loose insulation blown into cavities using special equipment. Conforms to irregular spaces and fills around obstacles better than batts.
Specs
- • R-value: R-2.2 to R-3.7 per inch
- • Cost: $1.00-$1.50/sq ft
- • Requires equipment rental
Best For
- • Attics (excellent coverage)
- • Walls with many penetrations
- • Existing walls (through holes)
Pro: Cellulose is made from recycled paper and is one of the most environmentally friendly insulation options.
Spray Foam (Open or Closed Cell)
Liquid foam sprayed into cavities that expands and hardens. Provides both insulation AND air sealing in one application. Closed-cell also adds structural strength and moisture resistance.
Open Cell
- • R-value: R-3.5-3.8 per inch
- • Cost: $1.50-$2.50/sq ft
- • Good for interior walls
Closed Cell
- • R-value: R-6-7 per inch
- • Cost: $2.50-$4.00/sq ft
- • Best for exterior walls, crawlspaces
Key benefit: Spray foam air-seals as it insulates, often eliminating the need for separate air sealing work. This can make the higher cost worthwhile.
Rigid Foam Board
Solid foam panels (XPS, EPS, or polyiso) used on exterior walls, foundations, or as continuous insulation over sheathing. Excellent for thermal bridging.
Specs
- • R-value: R-3.8 to R-6.5 per inch
- • Cost: $0.75-$1.50/sq ft
- • Requires sealing at seams
Best For
- • Exterior continuous insulation
- • Basement/foundation walls
- • Breaking thermal bridging
Critical: Air Sealing Before Insulation
Air leaks can account for 25-40% of heating and cooling loss in a typical home. Before installing any insulation (except spray foam), seal all air leaks:
Common Air Leak Locations
- • Rim joists and sill plates
- • Around windows and doors
- • Electrical boxes and penetrations
- • Plumbing and wiring holes
- • Recessed lights (if not IC-rated)
- • Duct boots and HVAC penetrations
- • Top plates (wall-to-attic connection)
Air Sealing Materials
- • Caulk: Small gaps (<1/4")
- • Expanding foam: Medium gaps (1/4"-3")
- • Foam board + caulk: Larger openings
- • Weatherstripping: Doors and hatches
- • Gaskets: Electrical boxes
- • House wrap tape: Sheathing seams
Energy Audit Tip
Consider a blower door test after air sealing to verify you've addressed the major leaks. Some utilities offer free or subsidized energy audits that include blower door testing.
Frequently Asked Questions
Can I install insulation myself?
Fiberglass batts are very DIY-friendly—cut to fit, press into place, staple the facing. Blown-in requires equipment rental but is manageable for attics. Spray foam should be professionally installed due to equipment complexity, safety concerns, and the precision required.
Do I need a vapor barrier?
It depends on your climate. In cold climates (zones 5-8), a vapor retarder on the warm (interior) side prevents moisture from condensing in walls. In hot-humid climates, the vapor retarder goes on the exterior. In mixed climates, use a "smart" vapor retarder that adjusts with humidity. Your local code will specify.
Should I exceed minimum R-values?
Often yes. Energy codes set minimums, but exceeding them provides ongoing savings. The incremental cost to go from R-19 to R-30 walls, for example, is relatively small during new construction but pays back for decades. Attic insulation is especially cost-effective to upgrade.
What about thermal bridging?
Wood studs conduct heat much faster than insulation, creating "thermal bridges" that reduce overall wall performance by 20-30%. Address this with continuous exterior insulation (rigid foam over sheathing) or advanced framing techniques.
Ready for the Next Step?
With insulation installed, the next step is roughing in smart home and networking infrastructure. This is your last chance to run low-voltage wiring before drywall goes up.