Why Is My Hardwood Floor Bulging? Causes, Fixes and When to Call an Inspector
Updated: 10 hours ago
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A bulge in a hardwood floor is a raised spot or ridge where boards have pushed up out of plane with the rest of the floor. It can be a soft hump under a rug, a ridge along a wall, or a section that rocks when you step on it. In almost every case the floor is telling you that the wood has taken on moisture or has run out of room to move. Here is how an NWFA certified inspector looks at a bulging floor and what you can do about it.
What Does A Bulging Hardwood Floor Look Like?
Bulging usually shows up as one of these patterns:
A raised hump in one area, often near a sink, dishwasher, refrigerator, exterior door or bathroom.
A long ridge running across the boards, sometimes near the middle of a room.
Boards lifted along a wall, cabinet or doorway where the floor meets a fixed object.
A spongy or hollow feel when you walk over the area, even if the bulge is small.
Bulging Vs Buckling Vs Crowning
These words get used for the same thing, but an inspector separates them. Bulging is a general raised area. Buckling is the extreme version, where boards lift completely off the subfloor, sometimes several inches. Crowning is when individual boards are higher in the center than at the edges, often after a cupped floor was sanded flat. If your floor has a dramatic lift, read our guide to hardwood floor buckling. If each board is domed, see hardwood floor crowning.
What Causes A Hardwood Floor To Bulge?
Wood expands across its width as it absorbs moisture. When the boards swell and have nowhere to go, they push up. The source of that moisture, or the lack of room, is what an inspection has to find.
Water Leaks And Spills
Dishwashers, ice maker lines, sinks, toilets, radiators and pet accidents are common sources. A leak does not have to be visible on the surface. Water can travel under the floor and show up as a bulge several feet away.
Moisture From Below: Slabs And Crawlspaces
Concrete slabs that were not tested or sealed, and crawlspaces without a proper vapor retarder or ventilation, can feed moisture into the floor from underneath. The result is often a slow, widespread bulge rather than one spot. See what moisture content is normal for hardwood for the readings inspectors compare against.
Missing Expansion Space
Industry installation guidelines call for an expansion gap around the perimeter and at fixed objects. When boards are installed tight to walls, cabinets, stair nosings or door jambs, normal seasonal swelling has nowhere to go and the floor lifts.
Subfloor And Installation Problems
Uneven subfloors, wrong fasteners or spacing, poor adhesive coverage on glue-down floors, and flooring that was not acclimated before installation can all contribute. These are often the questions behind warranty and contractor disputes.
Can A Bulging Hardwood Floor Be Fixed?
Usually, yes, but the fix depends on the cause and how long the floor has been wet. The order matters:
Find and stop the moisture source, or restore the missing expansion space.
Dry the floor and subfloor slowly while monitoring moisture readings.
Give the wood time to settle before deciding what needs replacing.
Repair or replace damaged boards, then refinish if needed.
Sanding or replacing boards before the floor is dry often leads to cupping, gaps or crowning later.
What To Do Right Now
Look for and shut off any active leak.
Take dated photos and video of the bulge, with a ruler or coin for scale.
Run air conditioning or a dehumidifier to bring indoor humidity into a normal range. Avoid blasting heat directly on the floor.
Lift rugs and mats from the area so it can dry.
Do not nail, sand or cut boards until the cause is confirmed.
When To Call An Independent Inspector
Call an inspector when the cause is not obvious, when the floor is new or under warranty, when an insurance claim is involved, or when the installer and manufacturer disagree. An NWFA certified inspector takes moisture readings in the wood and subfloor, checks job-site conditions and installation methods, and writes a report that documents the cause. Learn what a hardwood floor inspection includes.
Quick Answers About Bulging Hardwood Floors
Will A Bulging Hardwood Floor Go Back Down On Its Own?
Sometimes. A slight bulge can flatten once the moisture source is fixed and the floor and subfloor dry out slowly. Boards that have pulled loose from the subfloor, cracked, or been crushed at the edges usually need repair or replacement.
Is A Bulging Floor Covered By Homeowners Insurance?
It depends on the cause and your policy. Sudden events like a burst pipe are more often covered than long-term humidity, slow leaks or installation problems. An independent inspection report documents the cause, which is what adjusters and manufacturers look at.
How Quickly Can A Wood Floor Bulge After A Leak?
Wood absorbs water fast, so swelling can show up within days of a leak or flood. Slower sources, like a damp crawlspace or a concrete slab that was never tested, can take weeks or months to show.
Should I Nail Down A Bulging Floorboard?
Not before the cause is found and the floor has dried. Fastening a swollen board can split it, crush neighboring edges, or simply move the problem to another spot once the wood shrinks back.
Seeing A Bulge In Your Floor?
National Wood Floor Consultants provides NWFA certified hardwood floor inspections nationwide. Call (908) 232-6600 or book a consultation with Joe Avila to find out what is causing your floor to bulge.
Looking for hardwood flooring inspectors you can trust? Our guide explains how to find one and check their NWFA certification.
About The Author
Joe Avila is the founder and lead consultant of National Wood Floor Consultants, with 26 years in wood flooring. He is an NWFA Certified Wood Flooring Inspector, installer and sander, and teaches accredited AIA, ASID and IDCEC continuing education for architects and designers. His project experience includes Montclair University, One Wall Street, institutional and landmark buildings, and luxury residences and penthouses, and he pioneered subfloor sound-attenuation systems for New York City apartments. Read Joe's full profile.
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