Subfloor & Prep
The finish floor everyone walks on tomorrow only lays flat, glues down, locks together, and stays quiet because of the four prep services that happen first. The 1960s ranch in Ballard where the kitchen subfloor dips three-quarters of an inch from one cabinet run to the other and the new luxury vinyl plank reads every dip like a topographic map. The Madison Park 1924 craftsman where the downstairs powder room toilet has been weeping at the flange for years and the OSB underlayment is black with mildew. The Wallingford bungalow where the crew that installed the previous engineered hardwood in 2008 left the 4 mil polyethylene off the slab because the rolls were on a different truck and now the boards cup in every winter. The Ravenna split-level where the pulled-up carpet revealed a layer of 1972 vinyl glued to 1956 vinyl glued to original 1948 fir, and no flooring contractor will quote the install until somebody else demos the stack. Subfloor and prep is the trade family that resolves all of it before the finish goes down — subfloor leveling, subfloor repair and replacement, old flooring removal and disposal, and moisture barrier and underlayment. Handis self-performs every prep scope as core finish-carpentry work. From $500 for a small moisture barrier and underlayment install in a single room to $4,000 for a full repair-and-replacement scope on a sagging laundry-room sheathing.
Services
What Subfloor & Prep Covers
Subfloor and prep is the four-service family that resolves every condition under the finish floor before the install crew rolls in. Each service stands alone (a flat, sound, dry, debris-free subfloor with the right underlayment is the precondition for every hardwood, engineered, laminate, vinyl plank, and tile install), and most projects pick up two or three together when an old floor comes out. Handis self-performs every prep scope — leveling compound and shimming, joist sistering and sheathing replacement, full demo and disposal of carpet/vinyl/wood/laminate/bonded tile, and vapor retarder plus underlayment install per the finish-floor manufacturer spec. No licensed-trade handoff is required for subfloor work; this is core Handis finish-carpentry scope. From $500 for a small underlayment install to $4,000 for a full sagging-sheathing replacement on a laundry or kitchen.
Subfloor Leveling
Self-leveling underlayment (Ardex K 15, Mapei Ultraplan, Henry 555), sanding and shimming on plywood, sistering joists where the dip is structural, and pre-pour priming of the existing substrate. A long aluminum straightedge gets walked across every direction first so the dip pattern is documented and the right pour depth is calculated. Typical floors in 1940s-to-1970s Seattle homes settle three-eighths to three-quarters of an inch across a 12-foot run; modern luxury vinyl plank flags anything over a quarter inch in ten feet, hardwood flags anything over three-sixteenths in ten feet. From $800 for a small bath or laundry to $3,500 for a full kitchen or main level with deeper dips and a sistering scope.
Subfloor Leveling — self-leveler, shimming, joist sistering
Subfloor Repair & Replacement
Rotted or sagging plywood and OSB sheathing replacement on intact joists, joist sistering or sister-and-replace for joists that have cracked, twisted, or rotted at the bearing point, and cut-and-patch sheathing scopes around toilet flanges, tub aprons, and exterior-wall sill plates where a long-standing leak has eaten the underlayment. Tongue-and-groove plywood (3/4-inch APA-rated sheathing for residential subfloor, 1/2-inch for underlayment over existing sheathing), structural screws into joists at the manufacturer-specified pattern, and full sealing of the new substrate before the finish floor goes on. From $900 for a small bath patch around a toilet flange to $4,000 for a full laundry-room sagging-sheathing replacement with two sistered joists.
Subfloor Repair & Replacement — sheathing, sistering, cut-and-patch around flanges
Old Flooring Removal & Disposal
Full tear-out and haul-off for every common Seattle-home flooring layer — carpet and pad, sheet vinyl and tile vinyl (including the layered stacks common in 1950s and 1960s kitchens and bathrooms), hardwood (nail-down face-nailed, tongue-and-groove glue-down, engineered click-lock floating), laminate (glueless click-lock), and bonded ceramic and porcelain tile. Includes staple and nail extraction, mastic and adhesive scrape-off, dust control with a HEPA negative-air scrubber on tile and old vinyl work, and same-day debris removal in our own truck so the demo does not sit in the driveway over the weekend. Asbestos-containing 9x9 or 12x12 tile in pre-1985 homes is identified on the booking call and routed to a licensed abatement contractor before any Handis demo begins. From $700 for a small room carpet pull and pad demo to $2,500 for a full main-floor mixed-stack tear-out and haul-off.
Old Flooring Removal & Disposal — carpet, vinyl, hardwood, laminate, tile demo and haul-off
Moisture Barrier & Underlayment
Vapor retarder and underlayment install matched to the finish-floor manufacturer spec — 6 mil polyethylene over concrete slabs for engineered or laminate floating floors, asphalt-saturated kraft (rosin) paper or felt under nail-down hardwood on plywood, foam underlayment with integrated vapor barrier (Bestlaminate Pro Vapor 3 in 1, Roberts Super 60) under laminate and floating engineered, cork underlayment for sound dampening under hardwood on upper floors, and decoupling membrane (Schluter DITRA, Wedi Subliner) under tile to break shear stress. Includes seam taping, edge wrapping at the perimeter, and a written confirmation of the underlayment matched to the specific finish-floor warranty spec. From $500 for a small bath or laundry underlayment install to $1,800 for a full main-floor vapor barrier and cork underlayment scope.
Moisture Barrier & Underlayment — vapor retarder, foam, cork, decoupling membrane
Subfloor & Prep Pricing
Final pricing depends on the room size, condition of the existing subfloor and finish floor, the depth of any dip or rot found on site, and the underlayment matched to the finish-floor warranty spec. Each child page lists detailed pricing for that prep family. Asbestos abatement (pre-1985 9x9 and 12x12 vinyl tile) is identified on the booking call and routed to a licensed abatement contractor; that scope is never quoted by Handis. Request a free estimate for an accurate quote.
Tell us the room and the condition under the old floor — we will quote leveling, repair, demo, and underlayment as one prep package before the finish floor goes down.
Why Seattle Homeowners Book Handis for Subfloor & Prep
Every failed flooring install we are called back to repair traces to a single shortcut at the prep stage. The flooring contractor who skipped the moisture meter on a slab and the new engineered hardwood cupped through the first wet Seattle winter. The big-box install crew who laid laminate over a half-inch dip and used the existing carpet pad as underlayment, and the boards now click apart at the seams under the table. The DIY tile job that went over the original 1956 vinyl without a decoupling membrane, and every grout line opens by year three. Subfloor and prep is the trade family that decides whether the finish floor lasts the full warranty life or fails inside five years — and it is the cheapest place to spend money on a flooring project because it never has to be done twice. Handis self-performs every prep scope; we name the underlayment and the manufacturer spec on every quote.
Flat to the finish-floor flatness spec, documented before the pour or shim
A long aluminum straightedge gets walked across every direction of the room before any prep quote is firm — corner to corner, wall to wall, and diagonally across the longest run. The dip pattern is photographed and the depth at each low point is recorded in sixteenths. We size the self-leveler pour or the shim plan to the actual deviation, not a guess. The flatness target on the final substrate is the published spec of the finish floor being installed (luxury vinyl plank, hardwood, laminate, tile — each has a different tolerance), not a vague 'flat enough'.
Sheathing replaced with rated material, screwed to the manufacturer spec
Subfloor patches and replacements use APA-rated tongue-and-groove plywood (3/4-inch for primary subfloor on joists, 1/2-inch for underlayment over existing sound sheathing) — never OSB on a wet area, never bargain 5/8-inch on a 16-inch joist span. Structural screws into the joists at the manufacturer-specified pattern (typically 6 inches on edge, 12 inches in the field), every joint sealed at the perimeter, every fastener set flush so the new substrate is dead flat to the existing.
Real dust control on demo — HEPA negative-air on tile and old vinyl
Tile demo and pre-1985 vinyl demo run with a HEPA negative-air scrubber to capture silica dust and contain it to the work zone. Plastic zip wall at every doorway out of the demo room. Asbestos-containing 9x9 or 12x12 tile from the 1950s through the early 1980s is identified on the booking call before any Handis demo starts and routed to a licensed abatement contractor — we never demo a suspected ACM tile to 'see what is under it'.
Moisture barrier and underlayment matched to the finish-floor warranty
Vapor retarder, foam, cork, or decoupling membrane is sized to the specific finish-floor manufacturer warranty — 6 mil poly over slabs for engineered floating, rosin paper or felt under nail-down hardwood, integrated-barrier foam for floating laminate, cork on upper floors for sound, Schluter DITRA or Wedi Subliner under tile. The wrong underlayment voids the floor warranty on day one; we name the spec on the quote and confirm it against the finish-floor manufacturer's installation guide.
Insured, background-checked, one-year project warranty on prep workmanship
Handis carries general liability and workers' compensation; every technician has cleared a background screening. Our one-year project warranty covers the prep workmanship — leveler pour, shim plan, sheathing replacement, sistering, underlayment install. A finish floor failure traced to our prep gets the prep redone at no cost. The finish-floor manufacturer warranty covers the floor itself; we name both warranty paths on the quote so the customer knows which company to call for what.
Estimate
Tell us the room (kitchen, bath, laundry, main floor, basement, upstairs), the rough square footage, what is on the floor now (carpet, vinyl, hardwood, laminate, tile, painted concrete, bare sheathing), and what is going down next (luxury vinyl plank, engineered hardwood, laminate, nail-down hardwood, tile). A phone photo of the existing floor and any visible dip or soft spot helps us quote leveling and repair scope without a site visit. We send a clear estimate with the prep package itemized — demo, leveling, sheathing repair, underlayment — separately or as a bundle.
What Our Customers Say
Recent subfloor and prep reviews from verified Seattle-area customers.
1962 ranch in Ballard. We pulled the carpet ourselves to save the demo fee and were going to do the new vinyl plank install ourselves too. Handis walked the floor with a straightedge and showed us a five-eighths-inch dip across the kitchen-dining run that we had not seen. They did a self-leveler pour, two sister boards on the joists at the worst spot, and the new floor went down flat. We would have read every dip through the plank for ten years.
Madison Park craftsman. The downstairs powder-room toilet had been weeping at the flange for years and the OSB under the tile was black. Handis cut out a four-foot square section, replaced the sheathing with 3/4-inch plywood, sealed it with the right primer, then retiled. No more soft spot, no more mildew bloom in the closet next door.
Wallingford bungalow kitchen demo. Pulled-up carpet revealed three layers — carpet pad, 1972 sheet vinyl, 1956 tile vinyl, original 1948 fir. The flooring installer said he would not quote the new floor until somebody else did the tear-out. Handis did the demo in two days with a HEPA scrubber, hauled everything in their truck, left the original fir subfloor clean and ready for the new install.
Ravenna split-level basement. We were laying engineered hardwood directly on the slab and the flooring shop sold us 3-in-1 underlayment with vapor barrier. Handis confirmed the slab moisture reading with a calcium chloride test before they laid the polyethylene under the foam, then installed both layers. First wet Seattle winter and the floor is dead quiet, no cupping at the perimeter.
Queen Anne 1924 second-floor renovation. We were installing nail-down hardwood and the contractor recommended cork underlayment for sound. Handis ordered the cork to the right thickness, rolled it tight over the rosin paper, taped every seam. Downstairs neighbor heard nothing during install and hears nothing now when we walk across the room.
Frequently Asked Questions
Common questions about Handis subfloor and prep work — scope, pricing, scheduling, what triggers a sheathing replacement versus a leveler pour, asbestos identification, and how prep ties into the finish floor warranty.