Roofing Installation
Your roof is your ADU's first line of defense against the elements. A properly installed roof protects your investment, controls energy costs, and can last 20-50+ years depending on materials. Getting the roof on quickly after framing protects all your work from weather damage.
Quick Summary
Timeline
3-7 days
Cost range
$3,000-8,000
Lifespan
20-50+ years
Understanding Roofing Layers
A roof isn't just shingles or panels on top. It's a complete system with multiple layers working together to keep water out and protect your ADU. Understanding each layer helps you make informed decisions and spot quality issues.
Roof Decking/Sheathing
Plywood or OSB panels nailed to trusses or rafters. This creates the solid base for everything above. Typically 1/2" or 5/8" thickness.
Underlayment
Water-resistant barrier over sheathing. Synthetic underlayment is superior to traditional felt paper—it's more durable, lies flatter, and resists tearing during installation.
Drip Edge & Flashing
Metal pieces that direct water away from edges, valleys, and penetrations. Critical for preventing water intrusion at vulnerable points.
Finish Roofing Material
Shingles, metal panels, or membrane that forms the visible, weather-facing surface. Material choice affects cost, longevity, and aesthetics.
Ridge Vents & Ventilation
Proper ventilation extends roof life by preventing moisture buildup and reducing heat. Ridge vents at the peak combined with soffit vents create airflow.
Roofing Material Options
Composition (3-Tab) Shingles
The most affordable option, composition shingles are flat with uniform tabs. They're lightweight and easy to install but have a shorter lifespan than architectural shingles.
Cost
$2-3 per sq ft installed
Lifespan
15-25 years
Architectural (Dimensional) Shingles
The most popular choice for residential construction. Multiple layers create depth and shadow lines for a more attractive appearance. Better wind resistance and longer warranty than 3-tab shingles.
Cost
$3-5 per sq ft installed
Lifespan
30-50 years
Standing Seam Metal
Premium option with excellent longevity and modern aesthetics. Raised seams connect panels and create clean, contemporary lines. Great for shedding snow and rain. Higher upfront cost but minimal maintenance.
Cost
$8-14 per sq ft installed
Lifespan
40-70 years
Flat/Low-Slope Roofing (TPO, EPDM, Modified Bitumen)
For ADUs with minimal roof slope, membrane roofing systems are required. TPO and EPDM are popular single-ply options. Proper drainage is critical—flat roofs need tapered insulation or crickets to direct water to drains.
Cost
$5-10 per sq ft installed
Lifespan
20-30 years
Matching Your Main House
If your ADU is visible from the street or adjacent to your main house, matching or complementing the existing roof creates a cohesive property appearance. This often affects property value and may be required by HOA or design review.
Pro tip: If your main house has old shingles, you may not find an exact match. Get a sample from the main house roof and bring it to roofing suppliers. A close match in color and style is usually sufficient. Consider whether it makes sense to re-roof the main house at the same time for better pricing and a perfect match.
The Installation Process
Install roof sheathing
Plywood or OSB secured with proper nailing pattern to trusses/rafters
Install drip edge at eaves
Metal edging directs water into gutters, prevents rot at edges
Apply underlayment
Synthetic or felt paper provides secondary water barrier
Install ice and water shield (if needed)
Self-adhering membrane at valleys, eaves, and penetrations in cold climates
Install flashing
At valleys, walls, vents, and any roof penetrations
Install finish roofing material
Shingles, metal panels, or membrane applied per manufacturer specs
Install ridge cap and vents
Ridge vent allows attic ventilation while keeping water out
Common Roofing Problems to Avoid
Improper Flashing
Most roof leaks occur at flashing points—where the roof meets walls, vents, or other penetrations. Ensure flashing extends under shingles above and over shingles below.
Inadequate Ventilation
Poor attic ventilation causes heat buildup (damaging shingles from below), ice dams in cold climates, and moisture problems that can rot sheathing.
Wrong Nail Placement
Shingle nails placed too high won't secure properly in wind. Nails driven too deep tear through shingles. Follow manufacturer's nailing zone specifications exactly.
Insufficient Slope for Material
Each roofing material has minimum slope requirements. Shingles need at least 2:12 pitch. Below that, you need a membrane system designed for low slopes.
Frequently Asked Questions
Should I install gutters on my ADU?
Usually yes. Gutters direct water away from the foundation and prevent erosion. They're especially important if the ADU is close to the main house or property lines. Budget $500-1,500 for aluminum gutters with downspouts on a small ADU.
Is metal roofing noisy when it rains?
With proper installation over solid sheathing and adequate insulation, metal roofing is no louder than other materials. The old "tin roof" noise came from metal installed directly over purlins without underlayment—modern installation eliminates this issue.
Can I add solar panels later?
Yes, but plan for it now. Ensure your roof framing can support the additional weight (typically not an issue for residential solar). Metal roofing is ideal for solar attachment. With shingles, solar installers work around existing material but may need to remove and replace shingles under mounting brackets.
What warranty should I expect?
Material warranties: 25-50 years for quality shingles, 40-50+ years for metal. Workmanship warranties from installers: 5-10 years is reasonable. Always get warranty documentation in writing and understand what's covered vs. excluded.
Ready for the Next Step?
With the roof complete, your ADU is protected from weather. Next up: windows and exterior doors to fully enclose the building and let natural light flood in.