Fall Garage Conversion Guide: Convert Before the Rainy Season

Why Fall Timing Matters for Garage Conversions

Garage conversions are different from purely interior projects like kitchen or bathroom remodels. The most visible change in a garage conversion is right at the front: removing the garage door and replacing it with a framed, insulated, and finished exterior wall. That work, along with foundation waterproofing and any slab modifications, requires dry weather.

The Bay Area’s rainy season typically begins in late November and runs through March. That gives homeowners who start construction in September or early October a comfortable window to complete all weather-sensitive exterior work before the first significant rains arrive.

Once the exterior envelope is sealed, the remaining work happens entirely indoors. Insulation, electrical, plumbing, drywall, flooring, paint, and finishes are all unaffected by what is happening outside. But getting to that point requires dry conditions for the critical first phase of construction.

The Weather-Sensitive Phases of a Garage Conversion

Understanding which parts of the project need dry weather helps you prioritize the construction sequence during a fall build.

Garage Door Removal and New Wall Framing (Week 1)

The first step is removing the existing garage door and its tracks, hardware, and header (if the header is being modified). This creates a large opening in the building envelope that must be closed as quickly as possible.

Your contractor frames the new exterior wall, installs a structural header (if the original is not sufficient), and sets the window and door openings. At this point, the opening can be covered with sheathing and house wrap to provide temporary weather protection, even before siding and trim are installed.

Fall priority: Get the opening sheathed and wrapped within the first week to provide a weather barrier.

Foundation and Slab Work (Weeks 1-2)

Most garages have concrete slabs that sit lower than the main house floor level. Depending on your project, the slab may need to be raised, a new moisture barrier installed, or a subfloor system built over the existing concrete.

These are some of the options:

Vapor barrier installation. A polyethylene moisture barrier is laid over the existing slab before a new subfloor is built on top. This prevents ground moisture from migrating into the living space.

Slab leveling or raising. If the garage floor is significantly lower than the house floor, self-leveling concrete or a raised subfloor system brings the levels closer together. Concrete work requires dry conditions for proper curing.

Drainage improvements. If the garage currently slopes toward the door for water runoff (as most garages do), the drainage pattern may need to be modified. French drains or channel drains along the exterior redirect water away from the converted space.

Fall priority: Complete all concrete and moisture barrier work during the dry weeks of September and October.

Exterior Finishing (Weeks 2-3)

With the wall framed and sheathed, the exterior needs siding, trim, and paint or stain to match the rest of the house. Stucco, which is common on Bay Area homes, requires several days of dry weather for application and curing. Lap siding and board-and-batten siding are less weather-sensitive but still benefit from dry installation conditions.

Fall priority: Complete all exterior finishing, including caulking, flashing, and painting, before the rains arrive.

Roofing Modifications (If Needed)

Some garage conversions require roofing work, particularly if the garage roof needs insulation, new sheathing, or tie-ins to the main house roof for an addition above the garage. Any roofing work should be scheduled early in the fall timeline.

Fall priority: Address roofing first if your project requires it. A compromised roof during the rainy season causes cascading problems.

Moisture Management: The Most Important Technical Consideration

Garages were designed to store cars, not to house people. They typically lack the moisture protection that livable spaces require. Converting a garage into a comfortable, healthy living space means addressing moisture from every direction.

Ground Moisture

Garage slabs are often poured directly on compacted soil without a vapor barrier. In the Bay Area, where groundwater levels can be high in certain neighborhoods, moisture wicks through the concrete and into the space above. This moisture causes flooring problems (warping, mold under vinyl or carpet), musty odors, and poor indoor air quality.

The solution is a continuous vapor barrier between the slab and the finished floor. During a fall conversion, this work happens in dry conditions, which is ideal for proper installation and adhesion.

Rain and Surface Water

The former garage door opening is the most vulnerable point for water intrusion. Proper waterproofing at this location includes:

• A raised threshold at the base of the new wall to prevent water from flowing under the wall
• Flashing that directs water away from the wall-to-slab connection
• Grading that slopes away from the new wall, not toward it
• Gutters and downspouts that direct roof water away from the conversion

Fall is the time to test these systems before the rainy season puts them to work. A heavy rain in December will reveal any waterproofing shortcomings.

Interior Humidity

A converted garage is a tighter space than it was as an open garage. Without proper ventilation, indoor humidity from cooking, bathing, and occupancy can build up and cause condensation on windows and walls.

Your conversion plan should include adequate mechanical ventilation, either through an HVAC system with fresh air intake, exhaust fans in bathrooms and kitchens, or an energy recovery ventilator (ERV).

The Fall Garage Conversion Timeline

Here is a realistic timeline for a Bay Area garage conversion starting in September.

Before Construction: Design and Permits (2-4 Months Prior)

Design your conversion, prepare construction documents, and submit for permits during the summer months. Garage conversion permits in the Bay Area typically take 4-8 weeks for review and approval.

Weeks 1-2: Demolition and Exterior Envelope

• Remove garage door, tracks, and hardware
• Modify or reinforce the structural header
• Frame the new exterior wall with window and door openings
• Complete any slab modifications and install vapor barrier
• Sheath and wrap the exterior wall
• Install windows and exterior doors

Weeks 3-4: Rough-In

• Run electrical circuits, switches, and outlets
• Install plumbing supply and drain lines (if adding a bathroom or kitchenette)
• Install HVAC ductwork or mini-split line sets
• Frame any interior partition walls
• Install insulation (walls, ceiling, and floor as needed)

Weeks 5-6: Exterior Finish and Inspections

• Install exterior siding, trim, and paint
• Complete roofing modifications (if any)
• Schedule and pass rough-in inspections (electrical, plumbing, mechanical, insulation)

Weeks 7-9: Interior Finish

• Hang and finish drywall
• Install flooring
• Paint walls and ceiling
• Install cabinets and countertops (if applicable)
• Set plumbing fixtures
• Install electrical fixtures, outlets, and switches
• Install interior doors and trim

Weeks 10-12: Final Details

• Install appliances
• Complete HVAC commissioning
• Final inspections and certificate of occupancy
• Touch-up paint and punch list items
• Final cleaning

This timeline assumes a two-car garage conversion with a bathroom. A simpler single-car conversion without plumbing can finish 2-4 weeks faster.

Cost Considerations for a Fall Garage Conversion

All pricing is approximate, reflects 2026 Bay Area market conditions, and is subject to change. Every project is unique. Final costs are determined on a project-by-project basis during our design phase.

Bay Area garage conversion costs depend on the size, scope, and features of the project.

A basic single-car garage conversion (approximately 200-250 square feet) without a bathroom typically ranges from $80,000 to $120,000. A two-car garage conversion (400-500 square feet) with a full bathroom and kitchenette runs $120,000 to $200,000. A high-end conversion with premium finishes, a full kitchen, custom built-ins, and extensive sitework can exceed $200,000.

Fall-specific costs to plan for:

• Waterproofing and moisture management: $3,000 to $8,000 for proper vapor barriers, drainage, and flashing
• Expedited exterior work: Contractors may schedule additional crew to close the envelope quickly, which can affect labor costs
• Material staging: Fall projects benefit from ordering materials early, since any delays push work into the rainy season

The cost of proper waterproofing is not optional. Cutting corners on moisture management in a garage conversion leads to expensive remediation within the first few years of occupancy.

The Cost of Waiting Until Spring

Some homeowners consider waiting until spring to start their garage conversion. While spring offers excellent weather for the entire project, waiting has real costs:

Opportunity cost. Six months of potential rental income, living space, or home office use is lost while waiting for better weather.

Contractor availability. Spring is the busiest season for Bay Area contractors. Lead times for scheduling are longer, and some popular contractors are booked months in advance.

Market timing. Construction costs tend to increase year over year. Starting sooner locks in current pricing.

A fall start, with proper planning and prioritized waterproofing, gets your conversion completed months sooner than waiting for spring.

Your Fall Garage Conversion Checklist

• Complete design and submit permits by July or August
• Confirm permits are approved before September
• Pre-order windows, exterior doors, and siding materials
• Schedule construction start for early September
• Prioritize exterior envelope closure in the first 2-3 weeks
• Complete all slab and foundation work during dry weather
• Install waterproofing, drainage, and vapor barriers before rain arrives
• Continue interior work through the rainy season without interruption
• Target completion by late November or December

Why Custom Home for Your Garage Conversion

Custom Home Design and Build has extensive experience with Bay Area garage conversions, including the moisture management challenges specific to this region. Our design-build process ensures that waterproofing, drainage, and ventilation are engineered into the project from the beginning.

We understand fall construction scheduling and prioritize the weather-sensitive phases of work so that rain does not delay your project. Our team manages every trade, from structural engineering and exterior finishing to plumbing and electrical, under one coordinated plan.

Start Your Conversion This Fall

If a garage conversion has been on your list, fall is the time to act. Every week you wait compresses the timeline for completing exterior work before the rains.

Contact Custom Home Design and Build to discuss your garage conversion project. We will assess your garage, review your goals, and map out a fall timeline that gets the weather-sensitive work done on schedule.