Install Insulation and Air Sealing
This is your one chance to achieve superior energy performance. With walls open during a whole home remodel, you can install spray foam or high-quality batts with complete air sealing, creating a comfortable, efficient home for decades.
Quick Summary
Typical Cost
$5,000 - $20,000
Whole home, varies by material
Time Required
1 - 3 days
After rough-in passes
Difficulty Level
DIY Possible / Professional
Batts DIY, spray foam professional
Why This Matters
Insulation and air sealing together determine your home's energy performance, comfort, and durability. They work as a system: insulation slows heat transfer, while air sealing stops the uncontrolled movement of air that can bypass even the best insulation. A perfectly insulated wall with air leaks performs poorly; a well-sealed wall with poor insulation still loses energy. You need both.
During a whole home remodel with walls open, you have unrestricted access to install insulation and air sealing correctly. This is dramatically easier and more effective than any retrofit approach. The choices you make now affect heating and cooling bills, comfort, indoor air quality, and even the durability of your home for the next 50 years or more.
Modern building science has greatly advanced our understanding of building envelopes. The goal is not just more insulation, but a complete air barrier with proper vapor management. Get this right, and your remodeled home will be more comfortable, use less energy, and have fewer moisture-related problems than virtually any existing home.
Step-by-Step Guide
Step 1: Complete Rough-In Inspections First
Never insulate until all rough-in work passes inspection. Changes to electrical, plumbing, or HVAC after insulation are expensive.
- Verify electrical rough-in has passed inspection
- Confirm plumbing rough-in has passed inspection
- Ensure HVAC rough-in has passed inspection
- Complete any required framing corrections
- Install any remaining blocking or backing
- Photograph all systems for future reference
Step 2: Plan Air Sealing Strategy
Identify all air leakage pathways and determine how each will be sealed before insulation installation.
- Map all penetrations through the building envelope
- Identify electrical boxes, plumbing pipes, and ducts through exterior walls
- Note rim joist areas, sill plates, and top plates
- Plan sealing around windows and doors
- Identify any dropped ceilings or soffits connecting to attic
- Select appropriate sealants: caulk, foam, or gaskets
Step 3: Seal Major Air Leakage Points
Address the biggest air sealing targets before installing any insulation.
- Seal rim joist areas with spray foam or rigid foam and caulk
- Seal sill plate to foundation with appropriate sealant
- Seal top plates, especially in interior walls connecting to attic
- Seal around all penetrations with fire-rated caulk or foam
- Seal electrical boxes with air-tight boxes or foam gaskets
- Seal any chases, soffits, or other pathways to unconditioned space
Step 4: Choose Insulation Materials
Select insulation types appropriate for each location in your home based on performance needs and budget.
- Walls: Spray foam, high-density batts, or dense-pack cellulose
- Attic: Blown cellulose or fiberglass for unfinished areas
- Cathedral ceilings: Spray foam or rigid board with venting
- Floors over unconditioned: Spray foam or batts with air barrier
- Basement walls: Rigid foam or spray foam
- Consider continuous exterior insulation for high performance
Step 5: Install Exterior Wall Insulation
Install wall cavity insulation with careful attention to complete coverage and proper fit.
- For batts: Cut precisely to fit cavities without compression
- Split batts around electrical wires and boxes
- Fill completely around plumbing and other obstructions
- For spray foam: Install per manufacturer specs with proper lifts
- Avoid gaps, voids, and compression that reduce effectiveness
- Install vapor retarder if required by code in your climate
Step 6: Insulate Rim Joists and Basement
Rim joists are a major source of air leakage and heat loss. Proper treatment is critical.
- Spray foam rim joists: provides both insulation and air sealing
- Alternative: Cut rigid foam to fit, seal edges with caulk
- Insulate basement walls if conditioned space
- Use rigid foam or spray foam to avoid moisture issues
- Do not use batt insulation against basement walls
- Address any moisture issues before insulating
Step 7: Insulate Attic
The attic is typically the most important area to insulate well, as heat rises and escapes through the top of the house.
- Complete all air sealing of attic floor before insulating
- Install wind baffles at eaves to maintain soffit ventilation
- Blow cellulose or fiberglass to R-49 to R-60 (check local code)
- Build up around attic access hatch and insulate lid
- Ensure even coverage throughout attic floor
- Install depth markers to verify insulation level
Step 8: Insulate Cathedral Ceilings
Cathedral ceilings require special attention to prevent moisture problems while achieving good R-values.
- Maintain ventilation channel from eave to ridge if using batts
- Install rafter vents to create air space
- Fill remaining cavity with high-density batts
- Alternative: Spray foam fills entire cavity, no venting needed
- Consider unvented assembly with spray foam for best R-value
- Verify approach meets local code requirements
Step 9: Insulate Floors Over Unconditioned Space
Floors over garages, cantilevered floors, and floors over vented crawlspaces need careful insulation.
- Install air barrier on bottom of floor assembly
- Fill joist cavities completely with batts or spray foam
- Support batts with insulation supports or mesh
- Seal around all penetrations through floor
- Consider closed crawlspace approach as alternative
- Pay special attention to cantilevered sections
Step 10: Verify and Inspect Installation
Before closing walls, thoroughly inspect all insulation for completeness and quality.
- Check every wall cavity for complete fill with no gaps
- Verify insulation is not compressed or bunched
- Confirm vapor retarder installation where required
- Inspect attic for consistent depth and coverage
- Consider blower door test to verify air sealing
- Schedule insulation inspection if required by code
Insulation Materials Comparison
Closed-Cell Spray Foam
Highest R-value per inch, provides air barrier and vapor retarder.
- R-value: R-6 to R-7 per inch
- Cost: $1.50-2.50 per board foot
- Pros: Highest R-value, air seals, adds strength
- Cons: Most expensive, requires professional, off-gasses
- Best for: Rim joists, thin walls, flash and batt
Open-Cell Spray Foam
Excellent air sealing, more affordable than closed-cell, good sound control.
- R-value: R-3.5 to R-4 per inch
- Cost: $0.75-1.50 per board foot
- Pros: Air seals, fills irregular spaces, sound reduction
- Cons: Lower R-value, absorbs water, requires professional
- Best for: Full wall fill, attic rooflines
Fiberglass Batts
Most common insulation, affordable and DIY-friendly with proper installation.
- R-value: R-3.2 to R-4.3 per inch
- Cost: $0.40-1.00 per square foot
- Pros: Affordable, DIY-friendly, widely available
- Cons: Does not air seal, easily installed poorly
- Best for: Wall cavities with good air sealing
Blown Cellulose
Recycled content, fills irregular spaces, good for attics and dense-pack.
- R-value: R-3.2 to R-3.8 per inch
- Cost: $0.50-1.25 per square foot
- Pros: Recycled content, fills gaps, fire treated
- Cons: Settles over time, can absorb moisture
- Best for: Attics, dense-pack walls
Cost Breakdown
Pro Tips
Air Seal Before You Insulate
Air sealing is impossible or much harder after insulation is installed. Complete all air sealing first, then insulate. This sequence ensures you can access and seal every penetration and gap. Insulation does not stop air; only an air barrier stops air.
Consider Flash and Batt
Flash and batt combines 1-2 inches of closed-cell spray foam on the sheathing (for air sealing) with fiberglass batts filling the rest of the cavity (for cost-effective R-value). This hybrid approach provides excellent performance at moderate cost.
Do Not Compress Batts
Batt insulation works by trapping air in its fibers. When compressed, R-value drops significantly. Cut batts precisely to fit cavities. Split batts around wires - never stuff them over wires. A poorly installed R-19 batt might perform like R-10.
Get a Blower Door Test
A blower door test measures your home's air tightness and helps identify remaining leaks. Test after air sealing but before insulation to catch issues while you can still fix them easily. Target 3 ACH50 or better for an efficient, comfortable home.
Add Exterior Insulation
Continuous exterior insulation (1-2 inches of rigid foam over sheathing) eliminates thermal bridging through studs, which can account for 25% of wall heat loss. It also keeps wall sheathing warm and dry. This is a high-impact upgrade during re-siding.
Plan for Ventilation
Tight homes need mechanical ventilation for healthy indoor air. As you improve air sealing, plan for an HRV or ERV to provide fresh air while recovering energy. This is not optional for well-sealed homes - it is a code requirement in many areas.
Common Mistakes to Avoid
Insulating Without Air Sealing
Insulation alone does not stop air movement. Air carries both heat and moisture through the building envelope, bypassing insulation entirely. You must have a continuous air barrier working with your insulation for the system to perform. This is the most common and costly insulation mistake.
Vapor Barrier in Wrong Location
A vapor barrier on the wrong side of the wall traps moisture and causes rot. In cold climates, vapor retarders go on the warm (interior) side. In hot-humid climates, no interior vapor barrier. In mixed climates, use vapor retarders, not barriers. Get this wrong and you will have mold and structural damage.
Missing the Rim Joists
Rim joists are often the leakiest part of a home's envelope. Many installers skip or poorly treat these areas. Spray foam the entire rim joist area, or use cut-and-cobble rigid foam with thorough caulking. Do not just stuff in some batts and call it done.
Ignoring Thermal Bridging
Wood studs have R-1 per inch, far less than insulation. In a standard wall, 25% of the surface is studs, significantly reducing effective R-value. Consider wider stud spacing, staggered studs, or exterior continuous insulation to address thermal bridging in high-performance assemblies.
Poor Attic Air Sealing
The attic floor has more air leaks than any other surface: electrical and plumbing penetrations, duct chases, dropped soffits, partition wall top plates, and attic access. Seal all of these before adding insulation. Insulation blown over leaky attic floors provides minimal benefit.
Frequently Asked Questions
Should I use spray foam or fiberglass insulation?
Spray foam provides both insulation and air sealing in one step and works well in irregular spaces, but costs 2-3 times more than fiberglass. High-quality fiberglass or mineral wool batts with careful air sealing can achieve similar performance at lower cost. Many remodels use a hybrid approach: spray foam at critical air sealing locations (rim joists, around penetrations) with batts filling the main wall cavities. This balances cost and performance effectively.
What R-value do I need for my climate?
Recommended R-values vary by climate zone and building assembly. For climate zones 4-8 (most of US), current Energy Star standards recommend: R-49 to R-60 in attics, R-25 to R-30 in walls (using continuous insulation), and R-25 to R-30 in floors over unconditioned spaces. Check IECC requirements for your specific zone. During a whole home remodel, exceeding minimums often makes sense for long-term energy savings.
What is the most important place to air seal?
Focus air sealing on the biggest leakage pathways: attic access hatches, recessed lights in insulated ceilings, plumbing and electrical penetrations, rim joists over foundation walls, dropped soffits and ceilings, duct chases, and around windows and doors. The top and bottom of the thermal envelope (attic floor and foundation) typically have the largest air leakage. A blower door test can identify specific leaks in your home.
Do I need a vapor barrier?
Vapor barrier requirements depend on your climate zone. In cold climates (zones 5-8), a vapor retarder (like kraft-faced batts or polyethylene) on the warm side prevents moisture from condensing in wall cavities. In hot-humid climates, no interior vapor barrier is recommended as it can trap moisture. Mixed climates require careful analysis. Modern thinking favors vapor retarders (semi-permeable) over vapor barriers (impermeable) in most cases to allow some drying.
How do I insulate an older home with shallow wall cavities?
Older homes often have 2x4 walls with only 3.5 inches of cavity depth. Options include: dense-pack cellulose (R-13 in 3.5 inches), high-density fiberglass batts (R-15), closed-cell spray foam (R-24 in 3.5 inches), or adding continuous rigid insulation on the exterior (R-5 per inch for XPS). The exterior insulation approach is excellent for remodels as it increases total R-value, eliminates thermal bridging through studs, and protects the wall sheathing.