Subfloor Leveling
Handis subfloor leveling brings a settled Seattle subfloor flat to the finish-floor manufacturer spec — self-leveling underlayment pours on plywood or concrete, mechanical shimming under nail-down hardwood, and sistered joists where the dip is structural — from $800 for a small bath or laundry pour to $3,500 for a full kitchen with sistering and deeper dips. The 1962 ranch where the kitchen floor reads three-quarters of an inch low at the dishwasher base. The 1947 craftsman where the dining-room hardwood is high at the chimney chase and low at the doorway to the kitchen. The 1971 split-level where the basement slab has a half-inch sag at the floor-drain pour. Every leveling quote starts the same way — a long aluminum straightedge gets walked corner to corner, wall to wall, and on the diagonals, the dip is photographed and measured in sixteenths at each low point, and the matching pour depth or shim plan is sized to the published flatness spec of the finish floor going down on top. Hardwood needs 3/16 inch in 10 feet. Luxury vinyl plank flags anything over 1/4 inch in 10 feet. Large-format tile needs 1/8 inch in 10 feet. We pour to the spec, prime where the leveler manufacturer requires it, and cure to the published window before any underlayment touches the floor.
Service
What Does Subfloor Leveling Include?
Subfloor leveling is the scope that brings a settled, uneven, or out-of-spec substrate flat enough for the next finish floor to install per the manufacturer warranty — covering a straightedge walk of every direction of the room to document the dip pattern, calculation of the required pour depth or shim thickness against the finish-floor flatness spec, self-leveling underlayment pour on plywood or concrete (Ardex K 15, Mapei Ultraplan, Henry 555), mechanical shim on nail-down installations, joist sistering where the dip is structural, substrate priming where the leveler manufacturer requires it, and full cure to the published spec window before underlayment or finish floor goes on top. Handis covers leveling from $800 on a small bath or laundry to $3,500 on a full kitchen with sistering and deeper dips. The pour or the shim is matched to the finish floor — wrong leveler for the floor manufacturer warranty is rejected on the booking call before any product is ordered.
Self-Leveling Underlayment Pour
Cementitious self-leveling underlayment poured on plywood or concrete to fill dips up to one inch in a single pour (deeper requires staged pours per the manufacturer spec). Ardex K 15 is the premium pour for hardwood and tile underlayment (high compressive strength, finishes flat without polishing). Mapei Ultraplan and Henry 555 are reliable mid-range pours for laminate and luxury vinyl plank underlayment. Includes substrate priming with the matched manufacturer primer, full mixing per the published water ratio (a too-wet mix segregates the aggregates and cracks at cure), and a perimeter dam at every wall opening so the leveler stays in the room.
Mechanical Shimming on Nail-Down Hardwood
Tapered wood shims (cedar or yellow pine, never softwood pine that compresses under load) layered between the existing sound subfloor and the new hardwood sleeper plane to bring a dip flat without pouring leveler. Used under nail-down hardwood where the homeowner does not want the added height of a leveler pour. Each shim seated with construction adhesive and pinned, every shim location photographed in writing before the finish floor goes on. Handles dips up to 1/2 inch on a single-pass shim.
Joist Sistering for Structural Dips
Sister joist (a full-length new joist fastened alongside an existing joist) when the dip is structural — a joist that has settled at the bearing point, cracked at a notch from a previous plumbing run, or twisted from long-term moisture loading. Sized to the existing joist depth and species (2x8, 2x10, 2x12 in fir or hem-fir), structural screws or 16d common nails per the prescriptive code spec, and shimmed up to bring the top of the sister joist to the existing subfloor plane. The joist work happens before the leveler pour so the structural fix is done first.
Substrate Prep and Priming
Existing substrate inspected for paint, mastic, adhesive, or contaminant that interferes with the leveler bond. Old paint mechanically scraped to bare plywood, adhesive scraped or solvent-cleaned to a sound bond surface, dust HEPA-vacuumed, and the matched manufacturer primer rolled to the published coverage rate. Skipping the primer is the most common cause of leveler failure (debonding, hairline cracking, dust-up at the surface); we never pour over an unprimed substrate.
Cure Window Before Finish Floor Install
Self-leveling underlayment is walkable in two to four hours per the manufacturer spec, but the published cure window for installing finish floor on top is 24 to 72 hours depending on the pour depth, the ambient temperature, and the slab moisture. We hold the cure window in writing on the quote and confirm the schedule with the finish-floor installer so the next trade does not arrive early. Pouring leveler on Tuesday and asking a hardwood crew to lay floor on Wednesday is a published warranty void on most products; we do not allow the schedule slip.
How a Subfloor Leveling Job Works
Six sequential steps from straightedge walk to final cure — the actual sequence on every Handis subfloor leveling project.
Straightedge Walk and Dip Documentation
Long aluminum straightedge (8-foot or 10-foot) walked corner to corner, wall to wall, and on both diagonals. Every dip photographed with the straightedge in frame and the gap measured in sixteenths at each low point. The dip pattern goes on the quote alongside the finish-floor flatness spec being targeted.
Match the Pour, Shim, or Sister to the Dip
Surface dip under 1/4 inch on sound sheathing — shim plan or shallow self-leveler pour. Dip 1/4 to 1 inch on sound sheathing — single-pass self-leveler pour at the matched depth. Dip over 1 inch or structural sag at a joist — sistering plus staged leveler pour. The plan goes on the quote with the leveler product named.
Substrate Prep, HEPA Vacuum, Primer
Old paint, mastic, adhesive, and contaminant scraped to a sound substrate. Surface HEPA-vacuumed twice — once after the scrape, once before the primer rolls. Matched manufacturer primer rolled to the published coverage rate (Ardex P 51 under Ardex K 15, Mapei Primer L under Ultraplan, Henry 547 under Henry 555). Primer flashed to the manufacturer-specified dwell before the pour starts.
Sister Joists First if the Dip Is Structural
Full-length sister joist set alongside the existing joist, sized to the existing depth and species, structural-screwed or 16d nailed per the prescriptive code, and shimmed up to bring the top of the sister to the existing subfloor plane. Sheathing patch over the joist work if any was opened to expose the bearing point. Structural fix completes before the leveler mixes.
Mix and Pour the Self-Leveler to Spec
Powder mixed with the published water ratio in a 5-gallon bucket on a paddle drill for the manufacturer-specified mix time (typically 2 to 3 minutes). Mixed product poured continuously across the dip, spread with a smoothing trowel and a gauge rake to the matched depth. Perimeter dammed at every wall opening to keep the leveler in the room. Self-leveler self-levels in the next 10 to 20 minutes — we do not over-trowel.
Cure Window, Post-Pour Flat Check, Sign-Off
Walkable in 2 to 4 hours per the product spec. The straightedge walk repeats post-cure and the new flatness measurement is photographed for the customer file. Finish-floor install holds for the published 24 to 72 hour cure window depending on pour depth and ambient temperature. We coordinate with the finish-floor installer so the next trade does not arrive early and void the warranty.
Subfloor Leveling Pricing
Final pricing is labor plus self-leveler product (typical 50-pound bag of Ardex K 15 covers 30 square feet at 1/4 inch depth and runs $45 to $55 per bag at trade pricing; product passes through transparently on the quote). Joist sistering and structural sheathing repair are quoted as separate add-ons. Asbestos in pre-1985 vinyl or mastic under an existing floor is identified on the booking call and abated by a licensed contractor before any Handis leveling work begins. Request a free estimate for an accurate quote.
Send a phone photo of the room with a level or straightedge across the worst dip — we will quote the pour, shim, or sistering plan against your finish floor spec.
Why Handis for Subfloor Leveling
Most flooring warranty claims we are called to investigate trace to one number — the flatness reading at the substrate. Hardwood specs 3/16 inch in 10 feet. Luxury vinyl plank specs 1/4 inch in 10 feet. Large-format tile specs 1/8 inch in 10 feet. The flooring installer who lays product over a half-inch dip is not just doing rough work — he is voiding the manufacturer warranty on day one, and the customer finds out three years later when the boards click apart at the seams or the grout opens at every joint. Subfloor leveling is the cheapest insurance on a flooring project because it is the line between a warranty-valid floor and one that has no real coverage. Handis walks every dip with a straightedge before quoting, sizes the pour or shim to the published finish-floor spec, and documents the post-pour flatness in writing so the manufacturer warranty stays valid.
Straightedge walk before any quote, dip measured in sixteenths
Every leveling quote starts with a long aluminum straightedge walked across every direction of the room — corner to corner, wall to wall, and on the diagonals. Each low point gets a sixteenth-inch measurement at the straightedge gap, photographed for the customer file. The pour, shim, or sistering plan is sized against that real dip pattern, not against a guess.
Matched leveler product for the finish floor warranty
Ardex K 15 for hardwood and tile underlayment because its high compressive strength and dust-free finish meet the warranty requirements of every premium finish-floor manufacturer. Mapei Ultraplan and Henry 555 for mid-range laminate and luxury vinyl plank installs. The wrong leveler is rejected before product is ordered — a budget leveler under a Bona-sealed white oak floor voids the warranty before the boards arrive.
Primer rolled to the published coverage rate, never skipped
Substrate primed with the matched manufacturer primer (Ardex P 51 under Ardex K 15, Mapei Primer L under Ultraplan, Henry 547 under Henry 555) rolled to the published coverage rate and flashed to the spec dwell time. Skipping the primer is the most common cause of leveler failure — debonding, hairline cracking, dust-up at the surface — and we never pour over an unprimed substrate.
Cure window held to the manufacturer spec, not the calendar
Self-leveler is walkable in 2 to 4 hours but the cure window for installing finish floor on top is 24 to 72 hours depending on depth, ambient temperature, and slab moisture. We hold the cure window in writing on the quote and coordinate with the finish-floor installer so the next trade does not arrive early. A floor laid into a green pour is a warranty void on most products.
Joist sistering when the dip is structural, not just a surface fix
A dip that traces to a settled or cracked joist gets the structural fix first — full-length sister joist alongside the existing joist, sized to the existing depth, structural-screwed or 16d nailed per code, and shimmed up to plane. Pouring leveler over a sagging joist masks the structural problem for a year or two and then the floor sags again at the same spot. We sister first, level second.
Insured, background-checked, one-year project warranty
Handis carries general liability and workers' compensation; every technician has cleared a background screening. One-year project warranty on the leveling workmanship — leveler pour, primer bond, shim plan, sistering installation. A finish floor failure traced to our leveling (boards over a missed dip, leveler debond from a missed primer, cracking from a wrong-depth pour) gets the prep redone at no cost.
Estimate
Tell us the room, the rough square footage, and what finish floor is going down next (luxury vinyl plank, engineered hardwood, laminate, nail-down hardwood, tile). Send a phone photo of the room with a level or a straightedge across the worst dip so we can size the pour or shim plan. We send a written estimate with the matched leveler product named and the cure window for the finish-floor install confirmed against the manufacturer warranty spec.
Customer Reviews
Subfloor leveling reviews from real Handis customers.
1962 Ballard kitchen — five-eighths-inch dip across the run from the fridge to the dishwasher. Tech walked it with an 8-foot straightedge, photographed the dip, came back with a pour plan and a sistering recommendation for one joist. Ardex K 15 pour, one sister, and the floor reads dead flat now. The new luxury vinyl plank locked together at every seam with no rocking.
Madison Park 1924 craftsman dining room. The old hardwood had heaved up at the chimney chase and dropped at the doorway. Handis shimmed under the new white oak nail-down install (we did not want to add the height of a leveler pour) and the floor came out flat across the whole 22-foot run. The boards lay down clean and quiet.
Basement slab in our 1971 Ravenna split-level had a half-inch sag near the floor drain. Tech ran a moisture test on the slab first, confirmed it was within engineered hardwood spec, then poured the leveler and held the 48-hour cure window before the floor install rolled in. No cupping, no edge lift, perfect floor.
Wallingford kitchen renovation. The flooring installer would not start the luxury vinyl plank install until the substrate measured within 1/4 inch in 10 feet. Handis did a staged self-leveler pour across the kitchen and the breakfast nook, primer first, two pours because the deepest dip ran almost an inch. Final measurement came in at 3/16 in 10 feet — better than the spec.
Queen Anne second-floor renovation. The room had a structural sag in two joists from a previous bathroom remodel that pulled out a key brace. Tech sistered both joists with full-length 2x10 fir, structural-screwed per code, shimmed to plane, then poured a thin Ardex layer on top. The fix held — five years later the floor is still dead flat.
Frequently Asked Questions
Common questions about subfloor leveling — pricing, the difference between leveler and shim, joist sistering, cure windows, and how leveling protects the finish-floor warranty.