Insulation and Weatherproofing Guide

A well-insulated, air-sealed home is more comfortable, quieter, and significantly cheaper to heat and cool. This guide covers insulation types, air sealing techniques, and weatherproofing projects you can tackle yourself to improve your home’s energy efficiency.

Understanding Heat Transfer

Before diving into insulation, understand how heat moves.

Three Types of Heat Transfer

Conduction: Heat moves through solid materials (like heat traveling through a metal pan handle)

Convection: Heat moves through air currents (warm air rising, cold air sinking)

Radiation: Heat travels as infrared energy through space (like warmth from the sun)

Insulation primarily addresses conduction, while air sealing addresses convection. Radiant barriers address radiation.

Where Heat Escapes

In a typical home, heat loss/gain occurs through:

• Attic/Roof: 25-30%
• Walls: 25-30%
• Air leaks: 25-40%
• Windows: 10-15%
• Basement/Floor: 10-15%

This is why attic insulation and air sealing provide the best return on investment.

Understanding R-Value

R-value measures insulation’s resistance to heat flow.

What R-Value Means

• Higher R-value = Better insulation
• R-values are additive (R-19 + R-19 = R-38)
• R-value doesn’t measure air sealing ability
• Same R-value, different performance with air leaks

Recommended R-Values by Location

Climate Zone 1-2 (Hot):

• Attic: R-30 to R-49
• Walls: R-13 to R-15
• Floors: R-13

Climate Zone 3-4 (Mixed):

• Attic: R-38 to R-60
• Walls: R-13 to R-21
• Floors: R-19 to R-25

Climate Zone 5-7 (Cold):

• Attic: R-49 to R-60
• Walls: R-13 to R-21
• Floors: R-25 to R-30

Check the Department of Energy’s recommendations for your specific zone.

Types of Insulation

Different insulation types suit different applications.

Fiberglass Batts

The most common insulation type:

Pros:

• Inexpensive
• DIY-friendly
• Widely available
• Non-flammable

Cons:

• Requires careful installation (gaps reduce effectiveness)
• Irritating to skin, eyes, lungs
• Doesn’t air seal
• Loses effectiveness when compressed

Best for: Attics, walls (new construction), floors

R-value per inch: R-2.9 to R-3.8

Blown-In Fiberglass

Loose fiberglass blown into cavities:

Pros:

• Fills irregular spaces well
• Good for adding to existing attic insulation
• Less irritating during installation than batts

Cons:

• Requires equipment
• Can settle over time
• Doesn’t air seal

Best for: Attic floors, enclosed wall cavities

R-value per inch: R-2.2 to R-2.7

Cellulose

Made from recycled paper, treated for fire resistance:

Pros:

• Environmentally friendly
• Fills cavities completely
• Some air sealing qualities
• Pest-resistant when treated

Cons:

• Can settle over time (blown-in)
• Can hold moisture if wet
• Requires equipment for blown-in

Best for: Attic floors, dense-packed walls

R-value per inch: R-3.2 to R-3.8

Spray Foam

Expands on application, creating both insulation and air barrier:

Open-cell foam:

• R-value: R-3.5 to R-3.7 per inch
• Less expensive than closed-cell
• Allows moisture to pass through
• Good for interior applications

Closed-cell foam:

• R-value: R-6 to R-7 per inch
• Acts as vapor barrier
• Adds structural strength
• More expensive

Pros:

• Excellent air sealing
• Fills irregular spaces
• High R-value per inch (closed-cell)

Cons:

• Expensive
• Requires professional installation
• Off-gassing during installation
• Difficult to modify later

Best for: Rim joists, cathedral ceilings, irregular spaces

Rigid Foam Boards

Solid foam panels:

Types:

• EPS (Expanded Polystyrene): R-3.6 to R-4.2 per inch
• XPS (Extruded Polystyrene): R-5 per inch
• Polyisocyanurate: R-5.6 to R-6.5 per inch

Pros:

• High R-value per inch
• Moisture resistant
• Can serve as vapor barrier
• DIY-friendly installation

Cons:

• Must be cut to fit
• Joints need sealing
• Fire barrier required when exposed

Best for: Basement walls, exterior sheathing, under slab

Mineral Wool (Rock Wool)

Made from rock or slag fibers:

Pros:

• Fire resistant (rated to 2000°F)
• Water resistant
• Sound dampening
• Doesn’t support mold

Cons:

• More expensive than fiberglass
• Heavier
• Can be irritating to handle

R-value per inch: R-3.3 to R-4.2

Best for: Fire-safety applications, soundproofing, around chimneys

Air Sealing Basics

Air sealing is often more impactful than adding insulation.

Why Air Sealing Matters

Air leaks account for 25-40% of heating and cooling loss:

• Conditioned air escapes
• Unconditioned air enters
• Creates drafts and cold spots
• Can carry moisture into building cavities
• Reduces insulation effectiveness

Finding Air Leaks

Common leak locations:

• Around windows and doors
• Electrical outlets on exterior walls
• Where pipes and wires penetrate walls
• Recessed lighting fixtures
• Attic hatches
• Chimney and flue penetrations
• Where walls meet foundation
• Dryer vents
• Kitchen and bathroom exhaust vents

Detection methods:

Visual inspection: Look for gaps, daylight, dirty insulation (air flow deposits dust)

Feel method: On a cold, windy day, feel for drafts around suspected areas

Smoke test: Hold incense stick near suspected leaks; smoke moves toward leaks

Blower door test: Professional test that pressurizes home to measure and locate leaks

Air Sealing Materials

Caulk: For gaps up to 1/4 inch

• Silicone: Durable, flexible, not paintable
• Acrylic latex: Paintable, easy cleanup, less durable
• Polyurethane: Durable, paintable, harder to apply

Spray foam: For gaps 1/4 inch to 3 inches

• Expanding foam for larger gaps
• Low-expansion foam for around windows/doors

Weatherstripping: For movable joints (doors, windows)

Rigid foam: For large openings (can combine with foam sealant)

Metal flashing: Required around heat sources (chimneys)

Air Sealing Safety

Fire safety: Use fire-rated materials around heat sources:

• Furnace flues
• Chimneys
• Recessed lights (unless IC-rated)

Ventilation: Don’t seal combustion appliance vents or makeup air intakes

Moisture: Understand vapor barriers and where moisture can accumulate

Attic Insulation

The attic is typically the highest-priority area.

Assessing Current Insulation

Measure what you have:

1. Safely access attic (use proper lighting)
2. Measure insulation depth in several spots
3. Identify insulation type
4. Calculate approximate R-value

Fiberglass batts: Measure depth × R-value rating on bag Loose fill: Measure depth and consult R-value charts

Before Adding Insulation

Air seal first:

1. Seal around plumbing and electrical penetrations
2. Seal around chimney with metal flashing and high-temp sealant
3. Seal recessed light fixtures (or replace with IC-rated airtight fixtures)
4. Seal attic hatch
5. Seal duct penetrations
6. Seal where walls meet attic floor

Check for hazards:

• Knob-and-tube wiring (needs air space, consult electrician)
• Vermiculite (may contain asbestos, test before disturbing)
• Moisture problems (fix source before insulating)
• Pest evidence (address before insulating)

Adding Attic Insulation

Blown-in insulation (most common for adding):

1. Install depth markers to gauge thickness
2. Ensure soffit baffles are in place for ventilation
3. Work from edges toward access point
4. Maintain uniform depth
5. Don’t block ventilation paths

Batts over existing:

1. Lay perpendicular to existing batts or joists
2. Don’t compress—compression reduces R-value
3. Cut carefully around obstacles
4. Don’t cover recessed lights (unless IC-rated)

Attic Access

Insulating the hatch:

1. Attach rigid foam to hatch back
2. Install weatherstripping around perimeter
3. Add latches to hold hatch tight against weatherstripping

Attic stairs (pull-down):

1. Build insulated box over stairs
2. Or install commercial attic stair cover
3. Weatherstrip around perimeter

Maintaining Ventilation

Proper attic ventilation is critical:

• Keeps attic cool in summer (extends shingle life)
• Removes moisture in winter (prevents ice dams, mold)
• Requires air path from soffits to ridge

Install soffit baffles:

1. Place baffles at each rafter bay at soffit
2. Extends from soffit vent to above insulation
3. Maintains air channel even with deep insulation

Wall Insulation

Walls are challenging in existing homes.

Checking Existing Wall Insulation

Electrical outlet method:

1. Turn off power to outlet
2. Remove cover plate
3. Carefully feel inside wall cavity with finger
4. Look for insulation with flashlight

Thermal imaging: Camera shows temperature differences indicating missing insulation

Options for Existing Walls

Dense-pack cellulose:

• Holes drilled in wall (exterior or interior)
• Cellulose blown in at high density
• Holes patched
• Professional installation required
• Most common retrofit method

Injection foam:

• Similar process to cellulose
• Higher R-value per inch
• More expensive
• Good for smaller cavities

Interior rigid foam:

• Foam boards attached to interior walls
• Covered with drywall
• Reduces room size slightly
• DIY-friendly but labor intensive

Exterior foam sheathing (during re-siding):

• Rigid foam applied to exterior
• New siding installed over
• Most effective but expensive

New Construction Walls

Standard methods:

• Fiberglass batts (most common)
• Cellulose (blown or dense-pack)
• Spray foam (best performance)

Key installation points:

• Fill cavities completely
• No gaps or compression
• Proper vapor barrier placement

Floor and Basement Insulation

Over Unconditioned Spaces

Floors over garages, crawl spaces, or cantilevered areas:

Fiberglass batts:

1. Install with paper/foil facing up (toward heated space)
2. Don’t compress against subfloor
3. Support with wire or mesh if needed
4. Air seal any penetrations

Spray foam:

• Applied to subfloor from below
• Excellent air sealing
• Professional installation

Basement Wall Insulation

For conditioned basements:

Rigid foam on walls:

1. Attach foam boards to wall
2. Seal joints with foam or tape
3. Cover with code-required thermal barrier (drywall)

Spray foam:

• Professional application
• Excellent air sealing
• Moisture resistance (closed-cell)

Important: Don’t use fiberglass batts against basement walls—moisture problems result

Rim Joist Insulation

The rim joist (where floor meets foundation) is a major heat loss area:

Spray foam method:

1. Spray foam directly on rim joist
2. Creates air seal and insulation
3. Professional or DIY (canned foam for small areas)

Rigid foam method:

1. Cut foam to fit each joist bay
2. Caulk or foam around edges to air seal
3. Stack pieces if needed for R-value

Crawl Space Approaches

Vented crawl space (traditional):

• Insulate floor above
• Maintain ventilation
• Moisture barrier on ground

Conditioned crawl space (often better):

• Seal vents
• Insulate walls instead of floor
• Install vapor barrier on floor and walls
• May need dehumidifier or conditioned air supply

Window and Door Weatherstripping

Weatherstripping seals gaps around operable windows and doors.

Weatherstripping Types

Adhesive-backed foam:

• Inexpensive
• Easy to install
• Compresses to fill gaps
• Deteriorates in 1-3 years
• Best for: Light-use doors, windows

V-strip (tension seal):

• Plastic or metal
• Long-lasting
• Works on side and top of doors
• More complex installation
• Best for: Doors, double-hung windows

Door sweeps:

• Attaches to bottom of door
• Various styles (brush, vinyl, rubber)
• Easy installation
• Best for: Exterior doors

Threshold seals:

• Replaces or enhances door threshold
• Works with door sweep
• Best for: Exterior doors

Tube gaskets:

• Vinyl or rubber tube
• Compresses to fill gap
• Medium durability
• Best for: Doors

Interlocking metal:

• Most durable
• Complex installation
• Professional recommended
• Best for: Entry doors

Weatherstripping Doors

Door jambs (sides and top):

1. Clean existing surfaces
2. Remove old weatherstripping
3. Measure gap size
4. Choose appropriate weatherstripping
5. Install per product directions
6. Check door still opens/closes freely

Door bottom:

1. Install door sweep on interior
2. Adjust threshold if present
3. Check seal when door closed

Common mistake: Installing weatherstripping too tight—door should close easily

Weatherstripping Windows

Double-hung windows:

1. Install V-strip in channels where sashes slide
2. Apply foam tape to bottom of lower sash
3. Install compression strip where sashes meet

Casement windows:

1. Check existing weatherstrip condition
2. Replace worn sections with matching type
3. Adjust hardware if needed for proper seal

Window Treatments

Beyond weatherstripping, window coverings add efficiency.

Interior Options

Cellular (honeycomb) shades:

• Trap air for insulation
• Single, double, or triple cell options
• Good balance of cost and performance

Insulated curtains:

• Multiple layers including insulating material
• Must seal at edges to be effective
• Close at night, open for solar gain during day

Interior storm windows:

• Plastic or glass panel inside existing window
• Creates insulating air space
• Removable for summer

Exterior Options

Storm windows:

• Adds insulating air gap
• Reduces drafts
• Extends life of older windows
• Can be permanent or seasonal

Awnings:

• Block solar heat gain (reduces cooling load)
• Best for south and west windows
• Retractable allows winter solar gain

Duct Sealing and Insulation

Duct leaks waste significant energy.

Why Ducts Matter

• Leaky ducts can waste 20-30% of heated/cooled air
• Duct losses often occur in unconditioned spaces
• Sealing and insulating ducts provides significant savings

Sealing Duct Leaks

Common leak locations:

• Connections between duct sections
• Where ducts meet registers
• Where ducts connect to equipment
• Seams in duct runs

Sealing methods:

1. Clean duct surfaces
2. Apply mastic sealant to all joints and seams
3. For larger gaps, use mesh tape with mastic
4. Or use foil tape (not cloth duct tape, despite the name)

Insulating Ducts

In unconditioned spaces (attics, crawl spaces, garages):

1. Seal ducts first
2. Wrap with duct insulation (R-6 minimum, R-8 preferred)
3. Seal insulation seams
4. Don’t compress insulation

Energy Audit

Consider a professional energy audit.

What Auditors Do

• Blower door test (measures total air leakage)
• Thermal imaging (finds insulation gaps)
• Duct testing (measures duct leakage)
• Safety testing (combustion appliances)
• Prioritized recommendations

DIY Assessment

Walk around looking for:

• Gaps around penetrations
• Missing or damaged weatherstripping
• Inadequate insulation (attic is easiest to check)
• Single-pane windows
• Uninsulated ducts in unconditioned spaces

Utility bills: Compare usage to similar homes for your climate

Rebates and Incentives

Many efficiency improvements qualify for rebates:

• Utility company rebates
• State energy programs
• Federal tax credits
• Manufacturer rebates

Check the Database of State Incentives for Renewables and Efficiency (DSIRE) for programs in your area.

Prioritizing Improvements

If budget is limited, focus in this order:

1. Air sealing: Highest return, lowest cost
2. Attic insulation: Major impact, relatively easy
3. Duct sealing: Often overlooked but impactful
4. Weatherstripping: Low cost, immediate results
5. Basement/rim joist: Good return in cold climates
6. Wall insulation: Higher cost, harder to do

When to Call Professionals

Some work requires professional help:

• Spray foam insulation: Equipment and expertise required
• Dense-pack wall insulation: Specialized equipment
• Anything involving asbestos: Vermiculite, old insulation
• Electrical issues: Knob-and-tube wiring
• Major moisture problems: Fix source before insulating
• Combustion safety: If sealing a tight house with gas appliances

Measuring Success

After improvements, verify results:

• Utility bills: Compare heating/cooling costs year over year
• Comfort: Notice fewer drafts, more even temperatures
• Follow-up blower door test: Measures actual improvement
• Thermal imaging: Confirms insulation effectiveness

A well-insulated, air-sealed home is more comfortable, healthier, and significantly cheaper to heat and cool. The improvements often pay for themselves in energy savings while making your home a better place to live.