Remodel

Basement Finishing & Conversions

Turning unfinished space into living space.

An unfinished basement is the cheapest square footage in your house — it already has a roof and walls. We convert basements into bedrooms, suites, media rooms, and legal ADUs, handling the egress, moisture, and ceiling-height issues that make basements tricky.

Basements come with real constraints: egress windows for bedrooms, moisture control, ceiling height, and where the plumbing can go. We solve those first — waterproofing, proper egress, and insulation — then build out warm, dry, code-compliant living space that doesn't feel like a basement.

What's included

  • Egress windows and code compliance

    Every basement bedroom needs an egress window or door sized and placed to code; we cut the opening, build the well and make the room legal.

  • Moisture control and waterproofing

    We find and fix the water first — grading, drainage, sealing and vapor control — so the finished space stays dry, then insulate for a warm floor and walls.

  • Framing, insulation, and drywall

    Framing, insulation and drywall that turn concrete walls into finished rooms, with ceiling height, soffits and ductwork planned around the structure above.

  • Bathrooms and wet bars (in-house plumbing)

    Our own plumbers add bathrooms and wet bars below grade, including the ejector pump when the fixtures sit below the sewer line.

  • Legal basement ADUs

    A basement apartment with its own entrance, kitchen and bath, permitted as a legal ADU where your city allows it.

  • Lighting and mechanical

    Recessed lighting that doesn't eat ceiling height, extended heating and cooling, and the electrical a media room or suite needs.

How it works

  1. 1
    Free advice visit

    We check ceiling height, moisture, egress options, where the plumbing can go and what you want the space to do — then leave you a scoped range.

  2. 2
    Complimentary 3D model

    The finished basement on your actual plan — rooms, ceiling, lighting — before anything is framed.

  3. 3
    Design and permits

    Drawings, egress and energy-code details, structural engineering when the floor is lowered or a beam changes, and the building and trade permits.

  4. 4
    Moisture, egress and structure

    Water solved first, egress openings cut, any underpinning or slab work done.

  5. 5
    Rough-ins, insulation and drywall

    Plumbing, HVAC and electrical inspected, then insulation and drywall.

  6. 6
    Finishes and walkthrough

    Flooring, doors, trim, paint, fixtures and the final inspection.

The same ten-step process runs every project we build — see how we work.

What it costs

Finishing a basement is priced per finished square foot, with the wet rooms, egress and any structural work moving the range the most: a bathroom below the sewer line adds an ejector pump and more plumbing, a bedroom adds an egress window, and lowering the slab for ceiling height is a structural project of its own. Finish level and whether the space becomes a legal ADU with its own kitchen and entrance also set the number.

Price my project

Timeline

  1. Design and permits

    Layout, 3D model, egress and energy-code details, drawings and permits.

  2. Water, egress and structure

    Drainage and sealing, egress windows cut and wells built, underpinning or slab work where ceiling height requires it.

  3. Framing and rough-ins

    Walls, soffits, plumbing, HVAC and electrical, each inspected.

  4. Insulation, drywall and finishes

    Insulation, drywall, flooring, doors, trim, paint, fixtures and lighting, then the final inspection.

Permits and codes

Finishing a basement adds habitable space, so it needs a building permit with egress, insulation and ceiling-height details, plus plumbing and electrical permits for a bathroom, wet bar or new circuits. Lowering the floor or changing a beam adds structural engineering, and a legal basement ADU adds land-use review.

Our engineering and permitting team produces the drawings and engineering — our Redmond basement theater included a full floor dig-out, underpinning and a new structural slab to win back ceiling height — and we schedule every inspection from framing to final.

Where we offer it

Basement Conversions across Washington, Idaho, Montana and Arizona

Reviewed on Google and Yelp

What clients say

  • "Sebastian and his team did an exceptional job restoring my garage — both its structural integrity and the finish — after a car plowed into it. They prioritized the structural restoration within one day of visiting the…" Read more

    Fedon M.
    Garage Restoration · SeaTac · May 2024
    via Yelp
  • "I had a great experience with ID Builder Construction. I discovered a load-bearing beam in the house was compromised due to water damage, which would have prevented me from renting it. Sebastian came in at a reasonable…" Read more

    Nikhil A.
    Structural Repair · San Jose · Apr 2024
    via Yelp
  • "This company came out to bid and actually showed up at the date and time agreed upon. Once they quoted the work (at a competitive price) they had guys working that same day. They kept to their quote, and we even added…" Read more

    Jake P.
    Remodel & Drywall · Puyallup · Mar 2024
    via Yelp

Questions, answered

Yes. A bedroom below grade needs an emergency escape opening — an egress window with a well or a door to the outside — sized and placed to code. We cut the opening in the foundation, build and drain the well, and the room becomes a legal bedroom.

Water first, finishes second. We look at grading, downspouts and drainage outside, seal and manage vapor inside, and only frame once the space stays dry; insulation then goes against a dry wall. A finished basement over an unsolved leak is the most expensive mistake in this work.

Habitable rooms need code-minimum ceiling height, with limited allowances for beams and ducts; many older basements fall short. Where the height isn't there, we can lower the slab — our Redmond project included a full dig-out, underpinning and a new rebar-tied structural slab to win back the height — and we tell you at the visit whether your basement needs it.

Yes. When the fixtures sit below the main sewer line, the drains run to a sealed ejector pit and pump that lifts the waste to the sewer. Our own plumbers rough it in, and it's planned with the slab work so the floor is only opened once.

Where your city allows it, yes — its own entrance, kitchen, bath, egress and fire separation, permitted as an accessory dwelling unit. See our ADU and DADU page for how the rules work; a basement conversion is often the least expensive ADU because the shell already exists.

Yes — a building permit plus plumbing and electrical permits, and engineering if the floor is lowered or structure changes. We handle the package and the inspections.

Design and permitting first, then construction that depends on moisture work, egress, structure and the wet rooms in the plan. We give you a phased schedule at contract rather than a guess at the first meeting.

Square footage, bathrooms and wet bars (and whether they sit below the sewer line), egress windows, ceiling-height work, finish level and whether the space becomes a legal ADU. The free advice visit prices it against your actual basement.

Financing available — pre-qualify in minutes, no credit score impact.

Pre-qualify through Acorn Finance ($1,000–$100,000, 20+ lenders) or HFS Financial (up to $450,000, no home equity required).

Book your free professional advice visit

Free estimate. Free 3D design model. Free on-site advice from the builder who prices the job. No obligation.