Install Dormer Roofing
Sheathing, flashing, and shingling your dormer to create a weatherproof roof that integrates seamlessly with your existing roofing.
Why Proper Dormer Roofing Matters
Dormer roofing is more complex than standard roof installation because of the multiple intersections with the main roof. Every valley, every corner where walls meet roof, and every transition point is a potential leak source if not properly flashed. Water follows gravity and will find any gap in your defense. The flashing work on a dormer is more important than the shingles themselves - proper flashing with average shingles will outperform poor flashing with premium shingles every time. Take extra care with these details and you'll have a leak-free roof for decades.
Tools & Materials You'll Need
Step-by-Step Guide
Install Roof Sheathing
Cover the dormer rafters with structural sheathing:
Sheathing Options: Use 1/2" or 5/8" CDX plywood or 7/16" OSB. Plywood is stronger and more moisture-resistant. Check local code for requirements.
- Start at the lower corner and work up and across
- Stagger seams so joints don't align between rows
- Leave 1/8" gap between panels for expansion
- Nail every 6" along edges, every 12" in field
- Extend sheathing to meet existing roof sheathing
- Use H-clips between panels if rafters are 24" on center
Apply Underlayment and Ice Shield
The first layer of waterproofing goes directly on sheathing:
Ice & Water Shield Areas:
- • All valley intersections (full length)
- • Eaves - extend 24" past interior wall
- • Around all penetrations
- • Where dormer walls meet main roof
Synthetic Underlayment:
- • Cover all remaining sheathing
- • Overlap ice shield by 4 inches
- • Overlap courses by 6 inches
- • Staple or cap nail in place
Critical Detail: Ice and water shield must extend under existing shingles at valleys. Lift existing shingles carefully and slip the membrane underneath.
Install Valley and Step Flashing
Flashing at intersections is the most critical waterproofing step:
Valley Flashing:
- • Use pre-formed W-valley metal (minimum 24" wide) or open metal valley
- • Lap metal sections at least 6" with sealant between
- • Never nail through the valley center - only on edges
- • Extend valley flashing onto main roof under existing shingles
Step Flashing (Side Walls):
- • Use individual 4x4" or 5x7" pieces for each shingle course
- • Bend flashing 90° - half under shingle, half up wall
- • Each piece overlaps the one below by shingle exposure
- • Nail only the top corner into wall sheathing
Install Drip Edge
Drip edge protects fascia and directs water into gutters:
- Install drip edge along eaves first (under underlayment)
- Overlap sections by 2 inches
- Nail every 12 inches along top edge
- Install drip edge along rakes (over underlayment)
- Miter or overlap at corners
- Use color-matched drip edge for finished appearance
Order Matters: At eaves, drip edge goes under the ice shield and underlayment. At rakes (sides), drip edge goes over the underlayment.
Install Shingles
Now apply the visible roofing material:
- Start with a starter strip along the eaves (tabs facing up or use starter shingles)
- Begin first course with a full shingle at the rake
- Offset each subsequent course by 6 inches for proper stagger
- Use 4 nails per shingle (6 in high-wind areas) in the nailing zone
- At valleys, trim shingles to follow valley line and seal cut edge
- Weave or overlap courses with main roof shingles at valleys
- Install ridge cap at peak using specialized ridge shingles
Valley Treatment: For open valleys, keep shingles 3" back from valley center. For woven valleys, alternate shingles from each roof plane. Apply roofing cement under cut shingle edges at valleys.
Pro Tips
- ✓Buy 10-15% extra shingles for waste, matching, and future repairs
- ✓Work on cool days when possible - hot shingles are soft and damage easily from foot traffic
- ✓Use a chalk line to keep shingle courses straight - even small deviations become visible
- ✓Apply roofing cement liberally under shingles at all flashings and cut edges
- ✓Photograph all flashing details before covering with shingles - useful for warranty claims
Frequently Asked Questions
How do I match new shingles to an existing roof?▼
Matching shingles perfectly is challenging because roofing fades over time. If your roof is more than 5 years old, an exact match is unlikely. Options include: re-roofing the entire main roof slope that connects to the dormer for uniformity, choosing a complementary color that looks intentional, or accepting a slight color variation that will fade together over time. Bring a sample shingle to multiple suppliers to find the closest match.
Is ice and water shield necessary for dormer roofing?▼
Yes, ice and water shield is critical at all valley intersections and along the eaves. Dormers create multiple valleys where the dormer roof meets the main roof - these are prime locations for ice dams and water infiltration. Code typically requires ice shield extending 24 inches past the interior wall line. In cold climates, many contractors extend coverage further. The material is self-sealing around nail penetrations, preventing leaks.
What type of flashing should I use for dormer valleys?▼
For dormer valleys, use either woven shingles, closed-cut valleys, or open valleys with metal flashing. Open valleys with aluminum or copper flashing are most durable and easiest to maintain. The metal should be at least 24 inches wide (12 inches each side of center). For woven or closed-cut valleys, follow manufacturer specifications. Step flashing is required where the dormer side walls meet the main roof - use individual pieces under each shingle course.
Can I install dormer roofing myself or should I hire a roofer?▼
While shingle installation is straightforward, dormer roofing involves complex flashing details that are critical for waterproofing. Poor flashing is the leading cause of roof leaks. If you have roofing experience, you can likely handle this project. If not, consider hiring a professional roofer for the flashing work at minimum. Many homeowners install sheathing and underlayment themselves, then hire a roofer for flashing and shingles.