A 400-square-foot family room addition typically takes 4 to 7 months from the day you submit permit drawings to the day you sign off on the final walkthrough. A second-story addition or a larger footprint, say 800 square feet with a new bathroom, can stretch to 9 or 12 months. These numbers assume no major surprises: no rock in the excavation, no rotted framing hiding behind old siding, no permit office backlog. Here’s what actually happens during each phase and why the timeline moves the way it does.
Design and Permitting: 6 to 12 Weeks
Before a contractor touches a shovel, you need stamped drawings and a permit in hand. If you’re working with an architect, expect 3 to 6 weeks for design development and another 2 to 4 weeks for construction documents, depending on how many revisions you request. Structural engineering, required for load-bearing changes or foundation work, adds 1 to 2 weeks.
Permit review times vary enormously by jurisdiction. Some suburban building departments turn around a straightforward addition permit in 2 weeks. Cities with high volume, like parts of California or the Northeast, can take 6 to 10 weeks, especially if the project triggers zoning review for setbacks, height limits, or lot coverage. If your addition requires a variance because it doesn’t meet setback rules, add another 4 to 8 weeks for a hearing before the zoning board.
Homeowners in HOA communities often forget this step: architectural review committees can take 2 to 4 additional weeks and sometimes run in parallel with, sometimes before, city permitting. Check your HOA bylaws before you finalize a schedule with your contractor.
Bidding and Scheduling: 2 to 6 Weeks
Getting three contractor bids, comparing scope, and negotiating a contract takes real time, even though it’s tempting to rush this step to get started. Reputable contractors are usually booked 4 to 8 weeks out, sometimes longer in spring and summer when addition and remodel demand peaks. If your chosen contractor tells you they can start next week, that’s worth asking about directly. Good crews have a backlog.
This is also when you finalize material selections that have long lead times. Windows, especially custom sizes, can take 4 to 8 weeks to arrive. Cabinetry runs 6 to 10 weeks for semi-custom lines. If you’re adding a bathroom, tile and fixtures should be ordered now, not when the framing is done, because backorders on popular tile patterns can add a month to your finish schedule without warning.
Site Work and Foundation: 1 to 3 Weeks
Once permits are approved and the contractor’s crew is mobilized, site work moves fast compared to design and permitting. Excavation and foundation work for a standard addition takes 5 to 10 working days: excavating, forming, pouring footings, curing (which takes a minimum of 48 hours before stripping forms, though structural strength continues developing for 28 days), and backfilling.
Weather causes the most common delays here. Frozen ground in winter, saturated soil after heavy rain, or a hot dry spell that cracks curing concrete can push this phase out by a week or more. If your addition requires connecting to existing sewer or water lines, add 2 to 4 days for utility trenching and inspection.
Framing Through Rough-In: 4 to 8 Weeks
This is the phase where the addition starts looking like a building, and it’s also where inspections start controlling your calendar. A typical sequence:
- Framing: 1 to 2 weeks for walls, roof structure, and sheathing
- Framing inspection: scheduled 1 to 3 days after request, depending on the department
- Rough plumbing, electrical, and HVAC: 2 to 3 weeks, often overlapping
- Rough-in inspections (separate for each trade in most jurisdictions): 3 to 7 days total for scheduling and passing
- Insulation and vapor barrier: 2 to 4 days
- Insulation inspection: 1 to 2 days
Failed inspections are common and not a sign of a bad contractor. A missed nailing pattern or an electrical box that’s slightly too deep can trigger a correction and re-inspection, adding 2 to 5 days each time. Building in buffer time for at least one failed inspection is realistic planning, not pessimism.
Drywall to Final Walkthrough: 5 to 9 Weeks
Drywall hanging, taping, and mudding takes 1 to 2 weeks, with 3 to 5 days of drying time between coats depending on humidity. Priming and paint add another week. Flooring installation runs 3 to 7 days depending on material (engineered hardwood is faster than tile, which needs curing time for thin-set and grout).
Trim carpentry, interior doors, and cabinetry installation take 1 to 2 weeks. If you added a bathroom or kitchen extension, plumbing and electrical fixtures go in during this window too, followed by a final plumbing and electrical inspection.
The final building inspection, sometimes called a certificate of occupancy inspection for additions that add habitable space, is usually scheduled within a week of substantial completion. After it passes, your contractor should walk the space with you, generate a punch list of small defects (paint touch-ups, a sticking door, a caulking gap), and give you 5 to 10 days to complete those items before calling the job fully closed.
If you’re planning an addition and want a realistic schedule instead of a hopeful one, ask your contractor for a written timeline broken into these same phases, with specific week ranges for each. Then ask what has caused delays on their last three projects. Their answer will tell you more about your actual timeline than any average ever could.
Related articles: Bathroom Remodel Planning: Getting the Layout, Budget, and Work Order Right · Choosing Flooring That Holds Up in Entryways, Kitchens, and Hallways · Residential Construction Estimating