ADUs are booming—your roof plan matters more than you think
California has leaned hard into ADUs as a housing solution, and homeowners across Southern California are building backyard units and converting garages at record pace. Cal HCD+1
But here’s what many owners learn the hard way: the roof is where ADU projects most often get delayed, red-tagged, or hit with surprise costs—especially when you’re tying new construction into an older home.
ADU roofing is different from “just a small roof”
Even a small ADU roof has to handle the same performance requirements as a house:
- Waterproofing and drainage
- Proper ventilation (or correctly designed unvented assemblies)
- Weather and heat exposure
- Fire-rated materials where required
- Inspections and permit compliance
And because ADUs are often built close to fences, trees, and other structures, they can be more vulnerable to debris buildup and drainage problems.
The #1 ADU roofing issue: the tie-in
If your ADU/garage conversion connects to an existing roofline, the “tie-in” detail is mission-critical:
- Roof-to-wall transitions
- Valleys and dead zones
- Roofing-to-stucco interfaces
- Step flashing / counterflashing sequences
- Underlayment continuity and slope changes
A bad tie-in can leak even when the shingles (or membrane) are brand new.
Drainage: small roofs can create big problems
ADU projects often have:
- Limited slope
- Tight setbacks that force odd gutter/downspout routing
- Hardscapes that don’t absorb runoff
So the drainage plan should be intentional:
- Where does the water go in a heavy downpour?
- Do gutters overflow near doors or windows?
- Is runoff directed away from both the ADU and the main home foundation?
Don’t forget heat + comfort (especially in SoCal)
ADUs can get hot fast. Your roof choices affect comfort and operating cost:
- Roof color/reflectivity
- Insulation strategy
- Ventilation strategy
- HVAC placement and penetrations (each penetration is a leak opportunity if done wrong)
And because California continues to update ADU guidance and related housing rules, it’s smart to work with contractors who keep up with the latest handbook updates and local permitting expectations. California State Assembly+1
Pro tip: plan your roof penetrations early
ADUs often include:
- Bathroom exhaust vents
- Kitchen vents (sometimes)
- Mini-split linesets
- Solar conduit (if planned)
- Plumbing vents
The best way to prevent future leaks is to design penetrations up front, then flash them correctly—rather than “patching in” after finish work.
If you’re building an ADU or converting a garage in Southern California, Rocket Roofing can inspect the existing roof, coordinate tie-in strategy, and help you avoid the “finished inside, leaking outside” nightmare.
Owens Corning Roofing Products
Owens Corning Roofing Products
Rocket Roofing is proud to be selected as an Owen’s Corning Approved Roofing Contractor.
Owens Corning is a leader in roofing shingles, underlayment and components products. The look of a roof can have a significant impact on the overall design and perceived value of a home. After all, the roof can make up half of a home’s exterior.
Owens Corning systems look better, last longer and offer more choices to perfectly fit your project.
Rocket Roofing is proud to be selected as an Owen’s Corning Approved Roofing Contractor.
Owens Corning is a leader in roofing shingles, underlayment and components products. The look of a roof can have a significant impact on the overall design and perceived value of a home. After all, the roof can make up half of a home’s exterior.
Owens Corning systems look better, last longer and offer more choices to perfectly fit your project.
