No subfloor is perfectly level, but any signs of unevenness and high or low spots must be remedied. Please follow these requirements: Subfloor unevenness cannot be greater than 3/16 of an inch over a 10-foot span or 1/8 inch over a 6-foot span.
If you do not level the subfloor to manufacturers specifications you will not only void the warranty but the flooring will fail. The uneven subfloor allows too much flex in the flooring and it will break the locking system apart in short time.
The Standard simply defines the required flatness of a concrete subfloor. The subfloor, or 'underfloor' as I like to call it, “shall not deviate more than 3/16 of an inch in ten feet.” Photo 1 shows a ten straight edge being used to gauge the undulation of the floor.
It is totally normal. In fact if you have a house more than a couple years old that has completely flat floors you should be very proud. See houses are made out of things that shrink a bit and settle a bit and unless you have the foundation on bedrock there is no way that is going to happen completely evenly.
Hi Emma yes you can install ply to level floor but I would recommend a DPM first for under the ply. Also you would be far cheaper to use a tanking product to seal concrete them use a self level compound. Hope this is a help to yourself.
Subfloor unevenness cannot be greater than 3/16 of an inch over a 10-foot span or 1/8 inch over a 6-foot span. Subfloors must not slope more than ½ inch per 6 feet (25 mm per 1.8 m) Subfloors must be structurally sound. When making a concrete substrate level, use a portland cement or gypsum-based floor patch.
Using a flat-edged trowel, apply the floor leveling compound. Fill in all dips and uneven spots in the subfloor. Allow the leveler to dry as is instructed by the manufacturer's product label. Remove hills or humps using a floor sander until the entire floor is level.
The acceptable tolerance for subfloor unevenness for laminate flooring is typically 3/16 inch over a 10-foot span. If any areas exceed this tolerance, they will need to be addressed before proceeding with the installation.
Uneven floors are rarely caused by problems with the floor itself. The cause is usually settling or shifting of the foundation underneath the floors.
Uneven floors pose a serious risk of slips, trips, stumbles and falls. Our feet instinctively know to expect even and consistent flooring. Have you ever walked onto uneven flooring? It's a jarring experience, even if you don't fall down.
A subfloor needs to be clean, dry, level and structurally sound. Use a level to determine if the floor is level within 3/16-inch change per 10 feet. Mark any high or low spots with a pencil or marker. If you're gluing the new floor to the subfloor, use a sander to remove oil, wax, paint, adhesives or other materials.
For parts under 36” in both width and length, flatness should not exceed ¼”. For parts whose length is between 36” and 72”, the flatness variation should not exceed 75% of the flatness of a 10' sheet for that given width.
Tolerances are 1/8” within a 6' radius, or 3/16” within a 10' radius.
Step 4: Use a flooring underlayment to smooth out any remaining inconsistencies. A flooring underlayment can help to smooth out any remaining peaks and valleys in the subfloor and prevent problems down the line. However, remember that an underlayment can't work miracles, so don't count on it as your only solution.
Liquid Leveler is still the best option
As Steller Floors have grown in popularity, we have heard of many, many ways to level subfloors but by far, the best way is by using liquid floor levelling compound. It is the fastest, easiest, most cost-effective solution in the bunch.
Use a spirit level (the longer, the better) and lay it on the floor. Look to see whether the bubble is central. You can measure your slope by lifting the spirit level until the bubble is central and then measuring the gap between the level and the floor.
In general, if a floor slopes ½ inch to 1 inch for every 20 feet of the floor, it may require you to watch the situation, but it may not be a big concern. Sloping or sagging floors of more than 2 inches will indicate a problem. Sometimes, original builders slope the floor to allow for drainage.
Most flooring manufacturers specify a flatness tolerance, typically 1/8” over a 6-foot span, or 3/16” over 10 feet. However, tolerances can be much tighter especially for industrial and healthcare applications. In the level areas, we needed to achieve a near-zero deviation—less than 1/8” over 10 feet.
One of the primary causes of uneven floors is foundation issues. If the foundation of your home is unstable or has settled over time, it can cause the floors to become uneven. This is particularly common in older homes that were built on pier and beam foundations.
Use an underlayment, floor leveler or floor patch product to fix low spots in a wood or concrete subfloor. An underlayment is a thin layer of material sandwiched between two other materials. It's used to help insulate, absorb sound and reduce wear on your floor. It can also serve as a vapor barrier.
For added strength and stability, a double-layer subfloor is often recommended. In this configuration, two layers of plywood are installed, with the top layer offset from the seams of the bottom layer. By staggering the seams, the subfloor's overall strength is enhanced, reducing the risk of deflection or squeaks.
Before you put down your new floors, underlayment is a great way to ensure your subfloor will be level.
Fill any gaps or seams between the plywood sheets with a wood filler, leveling compound, or self-leveling compound. This will provide a smooth and even surface, eliminating any visible discrepancies.
The best solution for uneven flooring is a latex floor screed. It is a powder mix that you can pour down on the uneven flooring and let it settle down by itself. Then you can use the wooden screen to even out the floor. A self-levelling compound like latex floor screed is excellent for a wide range of flooring.
Moderate damage: For areas with uneven joists or minor subfloor issues, repairs could cost between $1,000 and $5,000, depending on the extent of the damage and the repair technique used. Major structural repairs: If the problem stems from foundation issues or severely damaged joists, costs can climb significantly.