Addition Cost Calculator Project Checklist

Introduction

Home additions fail in the gaps between phases — the soil test nobody ordered, the inspection nobody scheduled, the finish selection nobody made until the drywall was up. A phase-by-phase checklist closes those gaps by turning the whole project into a sequence of verifiable tasks. Work through it in order; each phase’s completion is the green light for the next.

Use this checklist alongside your budget from the Home Addition Cost Calculator: many checklist items (zoning verification, systems capacity, soil testing) directly feed the estimate’s accuracy. The estimating guide maps these phases to budget line items.

Open the Home Addition Cost Calculator

Phase 1: Feasibility (Weeks 1–3)

Define the scope: room type, approximate size, must-haves vs. nice-to-haves.
Verify zoning: setbacks, height limits, lot coverage — confirmed with the building department.
Check HOA architectural rules independently of zoning.
Verify systems capacity: electrical panel slots and spare amperage, HVAC load margin, water heater capacity.
Walk tie-in points: roof junction, wall junctions, plumbing/electrical/HVAC routing.
Run a preliminary budget in the calculator; confirm the project is financially viable before spending on design.
Decide DIY scope now (see the DIY vs pro guide), not mid-project.

Phase 2: Design and Permitting (Weeks 4–12)

Hire a designer/architect; confirm whether structural engineering is required.
Complete schematic design; lock the footprint — changes after this get expensive.
Order a boundary survey if required; order soil testing if conditions are uncertain.
Select structural materials and exterior finishes that match the existing house (see the material guide).
Finalize construction documents: site plan, floor plans, elevations, structural details.
Submit the permit application with complete plans; track plan-review comments and respond in one revision cycle if possible.
Pay permit fees; confirm the inspection sequence and scheduling process with the AHJ. Permit realities are detailed in the code compliance guide.
Order long-lead materials (windows, specialty doors, custom cabinetry) as soon as the permit is approved.

Phase 3: Bidding and Contracting (Overlaps Phase 2)

Write a one-page scope summary: dimensions, room type, finish level, permit status, who’s supplying what.
Solicit at least three bids on the identical scope document.
Compare bids line by line — labor vs. materials, allowances vs. fixed prices, exclusions.
Verify contractor licensing, insurance, and references; check for complaints with the licensing board.
Sign a written contract: fixed scope, payment schedule tied to milestones (never large upfront deposits), change-order procedure, timeline, and warranty terms.
Confirm builder’s risk insurance is in place.

Phase 4: Site Work and Foundation

Confirm utility locates (call-before-you-dig) are complete before excavation.
Verify excavation dimensions against the approved plans before concrete.
Pass the footing inspection before pouring footings.
Confirm foundation waterproofing and drainage are installed per plan — this is buried and unforgiving.
Pass the foundation inspection before backfill.
Photograph all underground work (footings, drainage, waterproofing) for your records.

Phase 5: Framing, Roofing, and Exterior Shell

Verify framing matches the structural plans: load paths, beam sizes, shear-wall nailing, hold-downs.
Pass the framing inspection before any rough-in work is covered.
Complete the roof tie-in with proper flashing; verify shingle/material match with the existing roof.
Install windows and exterior doors; verify flashing and weatherproofing at every opening.
Complete siding and exterior trim; confirm the weather envelope is continuous before interior work advances.
Photograph every wall cavity — framing, with a tape measure visible — before insulation.

Phase 6: Rough-Ins (Plumbing, Electrical, HVAC)

Complete all rough-in work per plan: supply/drain lines with proper venting, circuits and boxes, ductwork or mini-split lines.
Verify any panel upgrade or new circuits are complete and labeled.
Pass all rough-in inspections (plumbing, electrical, HVAC) before insulation — no exceptions.
Pressure-test plumbing lines where required; document results.
Photograph all rough-in work with measurements visible before it’s covered.

Phase 7: Insulation, Drywall, and Interior Finishes

Install insulation to the specified R-values; pass the insulation inspection where required.
Hang, tape, and finish drywall; verify a paint-ready surface in good lighting before priming.
Complete flooring, interior trim, doors, and hardware.
Install fixtures: plumbing trim, light fixtures, switches, and devices.
Paint after drywall is fully cured and sanded; protect finished floors during painting.
Complete any DIY finish tasks (see your Phase 1 DIY scope) without blocking the contractor’s critical path.

Phase 8: Final Inspections and Closeout

Schedule and pass the final building inspection; obtain the certificate of occupancy/completion.
Walk the punch list with the contractor: every defect noted in writing, with a completion date.
Verify all fixtures, outlets, switches, windows, and doors operate correctly.
Collect warranties, manuals, and the approved plans for your records.
Confirm final grading and drainage direct water away from the foundation.
File the completion certificate with your insurer; notify the tax assessor as required locally.
Release final payment only after the punch list is complete and the certificate is issued.

Ongoing: The First Year

Watch the roof tie-in through the first heavy rains — the highest-risk detail in the project.
Monitor for settlement cracks at the junction between old and new foundations; hairline cracks are common, growing ones are not.
Exercise the warranty: report defects in writing within the warranty period.
Keep your cavity photographs with the house records — future projects will thank you.

Skipped steps are how budgets die — the common mistakes guide catalogues the expensive ones, and the pro tips guide covers the field habits that keep each phase on track.

Related Guides

Complete Guide — the full budgeting overview behind this sequence.
Estimating Guide — the budget process that parallels these phases.
Code Compliance — the permit and inspection requirements in each phase.
Pro Tips — field wisdom for executing each phase well.
DIY vs Pro — deciding your role in each phase.
FAQ — quick answers on timelines and process.

Get Your Number

A checklist turns a daunting project into a sequence of small, verifiable wins — and every phase you complete on this list protects the budget you built in the Home Addition Cost Calculator. Print it, work it in order, and don’t start a phase until the previous one’s inspections are signed off.

Disclaimer: This checklist is general planning guidance for typical US residential additions. Actual phases, inspections, and requirements vary by jurisdiction and project. Verify requirements with your local building authority and consult licensed professionals for structural, code, or permit decisions.