The industry standard for subfloor flatness is 3/16″ of variation over a 10-foot span. At Soleil Floors, we hold to 1/16″ — three times tighter — because that extra precision is what prevents the pops, clicks, and hollow sounds homeowners complain about after installation. Flatness is not the same as levelness; it is the local highs and lows across the surface that cause planks to flex underfoot and eventually fail. Skipping or rushing subfloor prep is one of the most avoidable and most expensive mistakes in a flooring project. We find Austin homeowners get the best long-term results when subfloor prep is treated as part of the installation, not an afterthought — see common flooring mistakes to avoid before your project starts.
Quick Facts:
- Industry standard: 3/16″ flatness over 10 feet — that is nearly a quarter inch gap, enough to cause flex and creaking underfoot
- Soleil Floors standard: 1/16″ over 10 feet — significantly tighter and the reason our floors feel solid and quiet for years
- Concrete slabs: Moisture testing is required before any hardwood goes down; Central Texas humidity shifts affect slab conditions seasonally
- Warning signs: Soft or springy spots, visible dips, and existing squeaks all need to be addressed before new flooring is installed
Top 3 Questions to Ask Your Installer:
- What flatness tolerance do you use? — A specific number matters; if they cannot give you one, that tells you something about the quality of work you can expect
- Is subfloor prep included in the quote? — Prep work billed as a surprise add-on mid-project is a common source of budget overruns; get it in writing upfront
- Do you perform a moisture test before installation? — On concrete slabs especially, this step is non-negotiable; our solid vs. engineered hardwood guide explains why moisture matters more for some products than others
Ready to Plan Your Installation? Contact Soleil Floors for honest advice or talk through your subfloor situation at our Round Rock showroom.
The industry standard for subfloor flatness is 3/16″ of variation over a 10-foot span. At Soleil Floors, we hold our work to 1/16″ over 10 feet, three times tighter than what most installers require. That extra precision is what prevents the pops, clicks, and hollow sounds that homeowners complain about after a hardwood installation that looked fine on paper.
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What Does Subfloor Flatness Actually Mean?
Flatness and levelness are not the same thing, and this trips people up.
Level means the floor is perfectly horizontal relative to gravity. Flat means there are no high spots or low spots across the surface. For hardwood installation, flat is what matters. A floor can be slightly off-level from one side of the room to the other and still be perfectly suitable for hardwood. What causes problems is local variation: a ridge here, a dip there, any spot where the subfloor rises or drops within a 10-foot stretch.
Those variations become the pressure points that make a hardwood floor creak underfoot.
Why Is the 3/16″ Standard Not Enough?
The industry’s 3/16″ tolerance sounds tight until you think about what it means in practice.
Three-sixteenths of an inch is almost a quarter inch. That’s a meaningful gap for a wood floor plank to bridge. When a plank spans a low spot, it flexes slightly with every step instead of resting firmly on the subfloor. Over time, that flex creates the popping and clicking sounds that feel like something has gone wrong.
At Soleil Floors, we use a 1/16″ standard because the goal isn’t to meet industry minimums. It’s to install a floor that behaves like a floor should: solid, quiet, and consistent underfoot.
What Are the Signs My Subfloor Needs Work Before Installation?
You don’t need to be a flooring professional to spot the warning signs. A few things to look for:
Walking across the existing floor and feeling soft or springy spots suggests the subfloor may be compromised, especially in areas near plumbing or older parts of the home. Visible ridges or dips you can see from a low angle across the floor usually mean the surface will need grinding, self-leveling compound, or both before installation. Squeaks from the existing floor can point to fastener issues or separation between the subfloor and the joists below. Current squeaks that aren’t addressed before new flooring goes down will still be squeaks after.
The NWFA’s problem prevention guidance specifically identifies moisture and structural movement as the primary causes of hardwood floor failure. A good pre-installation assessment addresses both.
How Do You Check Subfloor Flatness?
The practical method is a long straightedge, typically a 10-foot level, laid across the floor in multiple directions. Any gap between the straightedge and the floor surface is the deviation. If that gap exceeds your tolerance threshold, the area needs correction before flooring is installed.
On concrete slabs, which are what most Austin-area homes sit on, high spots are typically ground down, and low spots are filled with a self-leveling compound. On wood subfloors, high spots may be sanded or planed, and low spots shimmed or filled. Both processes add time and cost to the project, but they are not optional steps. Installing hardwood over an out-of-spec subfloor is one of the most common and avoidable mistakes in a flooring project.
Does Subfloor Prep Differ for Engineered vs. Solid Hardwood?
Both require the same flatness standard, but concrete slabs add a moisture consideration that applies specifically to hardwood installations.
Before any hardwood goes down over a concrete subfloor, a moisture test should be performed. Concrete is porous and can hold residual moisture that migrates upward, especially in Central Texas, where seasonal humidity shifts are significant. Texas A&M AgriLife Extension research on indoor humidity and organic materials makes clear that moisture management is one of the most important environmental factors for any wood product installed in a Texas home.
For engineered hardwood over concrete, a moisture barrier is standard. For solid hardwood over concrete, the requirements are stricter, and the margin for moisture error is smaller, which is one of the key reasons engineered wood is the preferred option for slab homes in this area.
What Happens If the Subfloor Is Not Properly Prepped?
The problems show up fast and are fully preventable.
Pops and clicks are the most common complaints. These happen when planks have nothing firm beneath them at a low spot and flex with foot traffic. Echo sounds, where the floor has a hollow ring in certain areas, point to the same issue. In more serious cases, gaps can develop between planks, or boards can develop a slight rock underfoot.
The NWFA’s buying process guide emphasizes working with a flooring professional who evaluates subfloor conditions before installation begins. Once the wood is down, fixing subfloor issues means pulling the floor up. That is an expensive lesson.
What Should I Ask My Installer About Subfloor Prep?
This is a question we get asked on a regular basis, and the answer matters a lot when you are comparing quotes.
Ask what flatness standard they use. Ask whether subfloor prep is included in the quote or billed separately. Ask whether a moisture test is performed before installation. If an installer cannot give you a specific flatness tolerance, or if prep work is treated as an afterthought, that is useful information about the quality of work you can expect.
Our post on solid vs. engineered hardwood explains which option makes the most sense depending on your subfloor type. The NWFA’s durability guidance is also worth reading to understand how installation quality directly affects how long your floor performs.
If you are planning a hardwood project in the Austin area and want to understand exactly what subfloor prep will involve in your home, stop by our Round Rock showroom or schedule a visit to talk through your project before you commit to anything.