What a Whole-House Gut Renovation Actually Looks Like: A Project Plan for Westchester Homeowners

Mar 11

Most homeowners who take on a whole-house gut renovation start with a rough idea of what they want—new kitchen, updated bathrooms, open up the floor plan, maybe finish the basement while we’re at it. Some are also thinking about converting an attached garage into a self-contained living space for aging parents or rental income. It all sounds straightforward until you realize that every one of those decisions affects the others, and the order you do things in can mean the difference between a project that runs smoothly and one that costs an extra six figures in avoidable mistakes.

This post walks through what an actual project plan looks like for a comprehensive gut renovation of a typical Westchester home—a 2,500-square-foot colonial or split-level on a quarter-acre lot, with the scope expanded to include finishing the basement and converting an attached two-car garage into a living space that functions as an accessory dwelling unit (ADU). It’s the sequencing logic that determines how a project like this actually gets built. (For town-level cost context, see whole-house gut cost in Mount Kisco and Briarcliff.)

Before Anything Gets Demolished: The Pre-Construction Phase

This phase takes longer than most homeowners expect, and rushing it is the single most expensive mistake you can make. For a project of this complexity in Westchester, plan for three to five months of pre-construction work before a single wall comes down.

Assembling the team

A whole-house gut with a basement finish and garage conversion needs a NY-licensed architect for work of this scope. You’ll also need a NY-licensed structural engineer (the garage conversion and any load-bearing wall removals require one under NYS Education Law and the Office of the Professions). Depending on your lot, a civil engineer for site work. If you’re on septic rather than municipal sewer—which many Westchester properties are—you need a septic assessment early, because adding habitable space (especially bedrooms in the ADU) can trigger a Westchester County Department of Health review and potentially require system upgrades. (See septic capacity for northern Westchester bedroom additions for the specifics.)

Your architect should be local to Westchester. The permitting process varies town by town. An architect who works regularly in your municipality knows the code officials, what triggers additional review, and what the building department will flag before you submit. (See when you actually need a structural engineer for the engineering thresholds.)

Design and construction documents

For a project of this scope, expect the design phase to take eight to twelve weeks. Your architect will produce schematic designs first (the big-picture layout), then design development drawings (material selections, detailed room layouts), and finally construction documents—the full technical drawing set that your contractor bids from and your building department reviews. Cutting corners on construction documents to save time guarantees problems during construction. Every ambiguity in the drawings becomes a question on site, and questions on site become change orders. (See how to stop renovation change orders for the math on why scope discipline matters.)

The garage conversion needs particular design attention. You’re creating a self-contained living space—separate entrance, bathroom, kitchenette, sleeping area—inside a structure that was built to house cars. That means insulating walls and ceiling to current energy code (NY State Energy Conservation Construction Code), bringing the floor up to habitable grade if needed, running new plumbing for the bathroom and kitchenette, designing the electrical system as an independent zone, and providing fire separation between the ADU and the main house per IRC R302.3 (two-family dwelling fire separation).

Permitting and zoning

In Westchester, a project of this scope requires building permits, and the drawings need to be stamped by a NY-licensed architect or PE. Depending on the municipality, you may also need zoning approval for the garage conversion—ADU regulations in Westchester vary significantly by town. Some towns have adopted ADU-friendly ordinances following Westchester County’s ADU model provisions; others require special use permits; and a handful effectively prohibit ADUs through restrictive lot-size or parking minimums. There is no statewide pre-emption—each Westchester town controls its own rules. Your architect should pull the zoning code for your specific property before you commit to the garage conversion scope. (See the northern Westchester ADU reality check for what actually goes through.)

Permit review timing varies by town; some are faster, some slower. Budget for at least one round of comments and resubmission—first-pass approval is possible but not something to count on. (See permit speed in northern Westchester for town-by-town review timelines.)

Contractor selection and pricing

While permits are in review, your architect (or you) should be soliciting bids from general contractors. For a whole-house gut with a basement finish and garage conversion, you want a GC who has done projects of this scale and complexity, not someone whose experience is limited to kitchen remodels. Get three bids. Expect significant spread between them—20% to 30% variation is normal on complex projects—and don’t automatically take the lowest number. The cheapest bid is often the one with the most exclusions. (See the 12 scope items contractors leave vague for the items that disappear from bids.)

For a project of this scope in Westchester—2,500-square-foot gut renovation plus basement finish plus garage-to-ADU conversion—total construction costs are substantial. Benchmark against current contractor quotes on similar Westchester projects rather than relying on a generic per-square-foot multiplier; finish level, foundation type, structural complexity, and town premium all materially affect the number. Plan a budget that includes contingency separate from contract value (15–25% on most projects, higher on pre-1940 housing stock).

Phase 1: Demolition and Discovery (Weeks 1–3)

Demolition on a whole-house gut is both the most dramatic and most informative phase. Everything comes out—cabinets, flooring, drywall, old plumbing, old wiring—and for the first time, you and your contractor can see what’s actually behind the walls.

This is where surprises live. Knob-and-tube wiring that wasn’t visible during the pre-purchase inspection. Undersized structural headers over window openings. Water damage to framing behind a bathroom. Asbestos-containing material in floor tiles or pipe insulation (which requires AHERA-licensed abatement under EPA rules, not GC laborer work). Lead paint on pre-1978 surfaces (which requires EPA RRP-certified contractors). A good contractor budgets time in the demolition phase for assessment. (See the true all-in cost of older homes for what era-by-era surprises tend to be.)

In the basement, demolition is typically lighter—you’re not gutting finished space in most cases, you’re preparing an unfinished space. But you may be removing old mechanical equipment, relocating the water heater or furnace, and addressing any water intrusion issues. Basement waterproofing needs to happen before you frame walls and install finishes; the scope of waterproofing work can’t be fully determined until the space is cleared. (See finishing a basement in Westchester for the full waterproofing-to-finish sequence.)

In the garage, demolition means stripping the space to the studs (if it has studs—some garages are CMU block), removing the garage doors, and prepping the slab. If the garage slab is lower than the main house floor level, your contractor needs to either pour a new slab at the correct height or build a framed floor system on top of the existing slab. This decision has structural and budget implications, and it needs to be made before framing begins.

Critical sequencing note: Demolition should happen across all three zones—main house, basement, and garage—simultaneously. You want all the discovery done at once so your team can assess the full picture before committing to the construction sequence. Finding a structural issue in the garage after you’ve already framed the basement wastes time and money.

Phase 2: Structural Work (Weeks 3–6)

Once demolition is complete and the team knows what they’re working with, structural work begins. This is when load-bearing walls come down (with temporary shoring in place), new beams and headers go in, and the structural engineer’s specifications get built.

For the main house, this typically involves opening up the floor plan—removing walls between the kitchen, dining room, and living areas is one of the most common requests in Westchester colonials. Each removed wall requires a steel beam or engineered lumber header sized by the structural engineer per IRC tables R602.7 or by separate calculation, and installed by the framing crew.

In the basement, structural work may include underpinning or bench footings if you need to lower the floor to achieve the IRC R305 minimum ceiling height of 7 feet for habitable space (6′8″ for bathrooms; 6′4″ allowance for beam projections). This work is expensive and the per-square-foot range varies widely with site conditions; benchmark against current quotes on your specific project.

In the garage, the structural phase includes framing the new exterior wall where the garage doors were, reinforcing any existing walls that weren’t built to habitable structural standards, and installing the subfloor system if you’re raising the floor height. The structural engineer’s involvement is critical here—you’re changing the use of the space, and the structural requirements for a habitable space are meaningfully different from those for a garage.

Phase 3: Mechanical Rough-Ins (Weeks 6–10)

This is the phase where the house becomes a construction site full of plumbers, electricians, and HVAC technicians all working simultaneously. Rough-in means installing everything that goes inside the walls, floors, and ceilings before they get closed up.

Plumbing

New supply lines and drain lines get run to every bathroom, the kitchen, and the laundry room in the main house. In the basement, plumbing for a bathroom typically requires a sewage ejector pump (since the drains are below the sewer line), which adds cost and a maintenance consideration. In the garage ADU, plumbing is being run from scratch—supply, drain, and vent lines for the bathroom and kitchenette, tied into the main house system or run independently depending on the design.

Electrical

A whole-house gut is the opportunity to bring the electrical system up to current National Electrical Code (NEC) standards (NY adopted the 2020 NEC via the 2020 Uniform Code). Many Westchester homes built before 1980 have panels that are undersized for today’s loads. If you’re adding an ADU with its own kitchen appliances, HVAC, and lighting, you may need a service upgrade or a separate subpanel for the ADU. Confirm with a NY-licensed electrician based on your specific load calculation. All new circuits, outlets, GFCI/AFCI protection per NEC Article 210, switches, and lighting rough-in happen during this phase.

HVAC

The main house typically gets a new forced-air system or a combination of ducted and ductless units, sized via ACCA Manual J load calculation. The basement needs its own zone—basements have different heating and cooling characteristics than above-grade space. The garage ADU is often well served by a ductless mini-split system, which provides both heating and cooling without requiring ductwork, and can be installed as a completely independent system from the main house.

Critical sequencing note: All three zones—main house, basement, and garage—need to be roughed in before any inspections are called. The building department will inspect mechanical rough-ins before you’re allowed to close up walls, and it’s far more efficient to have one inspection visit cover the entire project than to schedule them piecemeal.

Phase 4: Insulation, Drywall, and Closing Up (Weeks 10–14)

After rough-in inspections pass, insulation goes in everywhere—exterior walls, interior walls where sound transmission matters (like between the ADU and the main house), basement walls, and the garage conversion. In the basement, insulation type matters: closed-cell spray foam on foundation walls is widely used in Westchester basements because it serves as both insulation and vapor barrier, helping prevent the moisture problems that plague finished basements. Confirm insulation specifications meet the current NY State Energy Conservation Construction Code for your climate zone.

Once insulation is in, drywall gets hung, taped, mudded, and sanded—typically to Gypsum Association GA-214-2021 Level 4 finish for paint, Level 5 for critical lighting and gloss/semi-gloss surfaces. This is the phase where rooms start to look like rooms again. It’s also where you realize how important it was to get the mechanical rough-ins right; once drywall goes up, accessing anything behind it means cutting it open.

Phase 5: Interior Finishes — Main House (Weeks 14–22)

This is the longest and most detail-intensive phase. Finishes go in roughly in this order:

Cabinetry and built-ins get installed first, because countertops are templated off of installed cabinets, and tile work in kitchens and bathrooms needs to meet the cabinetry. If you ordered custom or semi-custom cabinets, they should have been ordered during the design phase—lead times routinely run two to four months, sometimes longer for custom shops with tight backlogs.

Tile work in bathrooms, the kitchen backsplash, and any other tiled surfaces comes next. Then countertop templating and installation, which takes two visits—one to measure, one to install—with a one to two week gap between them.

Flooring goes in after cabinets and tile but before final trim, so that baseboard and door casings sit on top of the finished floor. Painting happens in stages—primer and first coat before flooring, final coat after trim is installed.

Plumbing and electrical fixtures get set last: toilets, sinks, faucets, light fixtures, outlets, and switches. Appliances are installed and connected. Hardware goes on cabinets and doors.

Phase 6: Basement Finish (Weeks 16–22, Overlapping)

The basement can be finished concurrently with the main house interior work, which is one of the scheduling advantages of tackling everything at once. While the kitchen cabinets are going in upstairs, the basement is getting flooring, built-ins, and its bathroom finished out.

Basement-specific considerations: flooring should be moisture-resistant (luxury vinyl plank is widely used over hardwood for below-grade applications), lighting needs to be planned carefully because basements have limited natural light, and egress is critical. If the basement includes a bedroom, IRC R310 requires an emergency escape and rescue opening: minimum 5.7 sq ft net clear (5.0 sq ft at grade), 24″ minimum height, 20″ minimum width, sill no more than 44″ above floor. Below-grade openings need a window well meeting R310.2.3 (36″ minimum projection, 9 sq ft area; ladder required if >44″ deep). This requirement needs to be addressed in the design phase, because adding an egress window after the fact means cutting through the foundation wall.

Phase 7: Garage-to-ADU Conversion (Weeks 14–22, Overlapping)

The garage conversion can also run in parallel with the main house finishes, though it may lag slightly because the ADU is effectively a small apartment and needs the same sequence of finishes as the main house—cabinets, countertops, tile, flooring, fixtures—just on a smaller scale.

The garage conversion has a few unique finish requirements. The new exterior wall where the garage doors were needs to match the existing house facade—siding, trim, and architectural details should be consistent so the conversion doesn’t look like a conversion. The separate entrance needs to be welcoming and functional, with proper lighting, a landing, and code-compliant steps if there’s a grade change. The kitchenette, even if small, needs to be planned as a real kitchen because the livability of the ADU depends on it. Fire separation between the ADU and the main house under IRC R302.3 (1-hour rated assembly typical for two-family dwellings) is non-optional.

If the ADU is intended for aging parents, accessibility considerations should be designed in from the start: wider doorways (36 inches minimum), a curbless shower in the bathroom, lever-style door handles instead of knobs, and blocking in bathroom walls for future grab bar installation even if you don’t install them now. The 2010 ADA Standards aren’t mandatory in private homes but are a useful design reference.

Phase 8: Punch List, Final Inspections, and Closeout (Weeks 22–26)

The last phase is the one that tests everyone’s patience. Punch list is the process of walking through every room—main house, basement, and ADU—and identifying everything that isn’t quite right: a paint drip on a door casing, a cabinet door that doesn’t close flush, a light switch that controls the wrong fixture, a grout line that’s uneven. On a project of this scale, the initial punch list will routinely have 50 to 100 items. That’s normal.

Your contractor addresses the punch list, and then the building department does a final inspection—or more accurately, a series of final inspections. In Westchester, expect separate inspections for building, electrical, plumbing, and fire safety. The ADU may require its own Certificate of Occupancy update or letter of completion, depending on your municipality’s classification.

Once inspections pass and the CO is issued, the project is officially complete.

The Full Timeline, Realistically

For a project of this scope—whole-house gut, basement finish, and garage-to-ADU conversion in Westchester—here’s what the timeline actually looks like:

Pre-construction (design, permits, contractor selection): 3 to 5 months. Construction: 6 to 8 months. Total: typically 9 to 13 months from the day you hire your architect to the day you move back in. That assumes no major surprises during demolition, no significant permit delays, and no extended material lead times. Add a month if any of those things happen. Add two if more than one does.

The homeowners who have the smoothest experience are the ones who accept this timeline at the outset rather than fighting it. Trying to compress a 10-month project into 6 months doesn’t save time—it creates the conditions for mistakes, and mistakes take longer to fix than doing it right the first time.

What Most People Get Wrong

The biggest mistake isn’t choosing the wrong tile or overspending on appliances. It’s starting construction before the plan is fully baked. Homeowners who rush through the design phase—or skip the architect and let the contractor figure it out—end up making expensive decisions on the fly during construction. Industry data put residential change orders at around 10% of contract value on average and past 25% on poorly-managed projects. Most of that variance is avoidable with better upfront planning.

The second biggest mistake is treating the basement and garage conversion as afterthoughts—deciding to “add them on” after the main renovation is already in progress. This creates coordination problems, extends the timeline, and can trigger permit complications that wouldn’t exist if the full scope had been submitted together. If you’re going to do all three, plan all three from the start.

How to Frame the Budget and Approach

Start with PermitWut for the full town-specific approval list including ADU rules. CostWut calibrates the line-item budget to your specific town and finish tier. RiskWut flags older-home, environmental, and zoning exposure on your address. The full Design and Biz tools page ties them together.

Sources

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Brandon Cavanagh