1. Insulation

Insulation plays a crucial role in maintaining the internal temperature of the ADU by reducing heat transfer between the inside and outside. This ensures the space stays warmer in winter and cooler in summer, while also reducing energy consumption and costs.

Types of Insulation:

1. Fiberglass Batt Insulation:some text
   • Description: The most common type of insulation, made from fine glass fibers. It comes in large rolls (batts) and is usually installed between studs, joists, and rafters.
   • R-Value: R-values typically range from R-11 to R-38, depending on the thickness and density of the batt.
   • Use Case: Best for standard stud walls, floors, and ceilings where cavities need to be filled.
   • Pros: Cost-effective, easy to install.
   • Cons: Less effective at preventing air leakage and moisture movement.
2. Spray Foam Insulation:some text
   • Description: A liquid foam that expands and hardens when applied. It is excellent for filling gaps and creating an airtight seal.
   • Types:some text
     • Open-cell spray foam: Lightweight, flexible, and provides a lower R-value (typically R-3.5 to R-4 per inch).
     • Closed-cell spray foam: Denser, more rigid, with a higher R-value (R-6 to R-7 per inch).
   • Use Case: Ideal for irregularly shaped areas, small gaps, or spaces where airtightness and moisture control are essential.
   • Pros: Excellent air sealing, high R-value, moisture-resistant.
   • Cons: More expensive than traditional insulation, requires professional installation.
3. Blown-in Insulation:some text
   • Description: Loose insulation material (either fiberglass or cellulose) that is blown into wall cavities, attics, and other hard-to-reach areas.
   • R-Value: Varies depending on the material, typically R-2.2 to R-3.8 per inch.
   • Use Case: Commonly used for attics and retrofitting existing walls.
   • Pros: Fills irregular spaces well, good for retrofits.
   • Cons: Requires specialized equipment for installation.
4. Rigid Foam Insulation:some text
   • Description: Sheets or boards made from polystyrene, polyisocyanurate, or polyurethane. Rigid foam is often used in walls, roofs, and foundation applications.
   • R-Value: Offers high R-values per inch (typically R-5 to R-6).
   • Use Case: Ideal for exterior walls, basements, and crawl spaces.
   • Pros: High R-value, moisture-resistant, durable.
   • Cons: More expensive and harder to install than fiberglass batts.

Best Practices for Insulation Installation:

• Air Sealing: Before installing insulation, make sure that any gaps, cracks, or holes in the building envelope are sealed to prevent air leakage.
• Moisture Barrier: In areas with high moisture potential (such as bathrooms or basements), install a vapor barrier (e.g., plastic sheeting) to prevent moisture from accumulating within walls and causing mold or rot.
• Insulating Walls, Floors, and Roofs: Ensure that all exterior-facing walls, the roof, and the floors are properly insulated to maintain energy efficiency.

Cost of Insulation:

• The cost of insulating a typical ADU (around 500-1000 sqft) ranges from $1,500 to $6,000, depending on the type of insulation and the area being insulated.

2. Drywall

After insulation is installed, drywall (also known as plasterboard or gypsum board) is applied to create smooth, finished surfaces for the interior walls and ceilings.

Types of Drywall:

1. Standard Drywall:some text
   • Description: Regular drywall (often ½ inch thick) is the most commonly used for interior walls and ceilings.
   • Use Case: Ideal for general-purpose rooms such as living rooms, bedrooms, and hallways.
   • Pros: Inexpensive, easy to install and finish.
   • Cons: Offers little resistance to moisture or fire.
2. Moisture-Resistant Drywall (Green Board):some text
   • Description: A type of drywall with a water-resistant coating, often used in areas with high moisture exposure.
   • Use Case: Bathrooms, kitchens, laundry rooms.
   • Pros: Better resistance to mold and moisture than standard drywall.
   • Cons: More expensive than standard drywall and not suitable for direct water exposure (like in shower stalls).
3. Fire-Resistant Drywall:some text
   • Description: Also known as Type X drywall, this material has fire-retardant additives that help delay the spread of fire.
   • Use Case: Used in areas requiring enhanced fire protection, such as garages or between shared walls in multi-family units.
   • Pros: Offers greater fire resistance than standard drywall.
   • Cons: Heavier and harder to cut than standard drywall.
4. Soundproof Drywall:some text
   • Description: A specialized type of drywall designed to reduce noise transmission between rooms.
   • Use Case: Home theaters, bedrooms, or spaces where sound insulation is critical.
   • Pros: Effective at dampening sound.
   • Cons: More expensive and harder to install than regular drywall.

Drywall Installation Process:

• Cutting and Hanging: Drywall is cut to size and hung on the framed walls and ceilings using screws or nails. Sheets are typically hung horizontally to minimize seams.
• Taping and Mudding: After hanging, joints between sheets are covered with drywall tape and then coated with joint compound (mud). Multiple layers of mud are applied to achieve a smooth finish.
• Sanding: Once the compound has dried, the surface is sanded to eliminate rough spots or imperfections.
• Priming and Painting: After sanding, the drywall is primed to seal the surface, followed by painting or adding texture if desired.

Best Practices for Drywall Installation:

• Moisture Control: In moisture-prone areas, use moisture-resistant drywall or install a vapor barrier behind the drywall.
• Seam Management: Properly tape and mud seams to prevent cracking or visible lines in the finished walls.
• Fire-Resistant Drywall in Key Areas: Use Type X drywall in locations that require enhanced fire protection, like garages or shared walls.

Cost of Drywall:

• Drywall cost per square foot ranges from $1.50 to $3.50, including materials and labor. A typical ADU might cost between $1,500 to $4,000 to drywall, depending on the size and complexity of the space.

Conclusion

Insulation and drywall are essential for the energy efficiency, comfort, and aesthetics of an ADU. Insulation helps regulate indoor temperature, improves energy efficiency, and reduces noise, while drywall provides a smooth, paintable surface for interior walls and ceilings. Proper installation of both materials is crucial to ensure durability and long-term performance.

Sources:

• Energy.gov: Insulation Materials

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