Basement subfloors are crucial intermediary layers of the flooring system in a basement. Subfloors support the finished floor by offering a flat continuous surface. The most popular choices for a basement subfloor are rigid foam subfloor, floating subfloor, basement subfloor panels, and sleeper subfloor.
It is important to distinguish between underlayment or cement board, which goes between the subfloor and finished flooring, and the subfloor itself.
Basement Subfloor Options
| Basement Subfloor Options | Description |
|---|---|
| Rigid Foam Subfloor | Durable, easy to cut and install, and has drainage passageways. |
| Floating Subfloor | Float above a corrugated or “cleated” waterproof underlayment |
| Basement Subfloor Panels | Pre-made panels installed on the foundation |
| Sleeper Subfloor | Protect laminate and hardwood flooring |
Rigid Foam Subfloor
Durable, dense sheets of specific types of foam are used to create rigid board insulation.
The most common foam compounds include polyurethane, polystyrene, or polyiso.
Sold in 4-feet by 8-feet sheets(the same size as plywood), they are typically 1 to 2 inches thick and provide outstanding insulation.
Rigid foam boards are also easy to cut and install.
Additionally, it has drainage passageways, allowing for under-floor drainage action in the event of a leak.
This is possible due to the elevated, rounded feet that extend downwards from the underside of the panels, creating a gap for drainage.
EPS and XPS rigid foam boards are waterproof, making them an ideal choice for subfloor.
Due to their hardness and water resistance, rigid foam insulation has a lifespan of 100 years or longer.
Floating Subfloor
The term “floating subfloor” refers to a method of installation in which glue, nails, or staples are not used to attach the flooring to the subfloor.
Instead, each panel or plank is connected to the others by a locking mechanism or glue and sits on top of the subfloor, appearing to “float” on top of it.
This method is made possible by the weight of individual planks, which lock together and distribute the weight over a large surface.
As a result, the subfloor functions as one large, heavy object.
Typically floating subfloors are made of plywood or oriented strand board(OSB) and never touch the floor.
Instead, they float above a corrugated or “cleated” waterproof underlayment, which creates an air gap above the concrete.
The air in this space, in combination with the wooden panels, acts as an insulating layer that keeps floors and rooms comfortable.
Moreover, channels in the underlayment help to quickly drain and evaporate moisture.
This ensures that the subfloor and the flooring above it remain dry and stable, prolonging their lifespan.
Basement Subfloor Panels
Basement subfloor panels are pre-made sheets of material, that are installed on the foundation before building the floor.
They come in many varieties, including plastic-bottom, foam-bottom panels, and foam-only panels.
Plastic-bottom panels consist of tongue-and-groove oriented strand board attached to stiff plastic components.
These panels have hard plastic layers that prevent moisture from entering.
In contrast,foam-bottom panels have extruded polystyrene foam bonded to OSB.
Of the three types, foam-only panels are the least expensive, which work only with foam.
Their primary advantage is insulation.
Although prefabricated subfloor panels like DRICORE® are expensive, they are simple to install and are strong enough to support any flooring.
In fact, they can sustain up to 6,000 lbs. per square foot.
The DRICORE subfloor features air gap technology which helps prevent mildew, mold, moisture, and minor water leaks.
These panels measure 23.25” x 23.25′′ and are 3/4” thick.
Sleeper Subfloor
You can install subfloor sleepers in basements to safeguard flooring materials, including laminate and hardwood.
The sleeper is designed to stop warping and mold growth, which extends the lifespan of your floor.
To begin the process, place a vapor barrier over the concrete slab using a 4 to 6-mil polyethylene film, making sure the edges overlap by 4 to 6 inches.
The sheeting should reach under the baseboard on all sides.
Then, construct a sleeper frame and level it on top of the moisture barrier.
Afterward, lay the sleepers out along the area of the subfloor in the proper locations, making any necessary length modifications.
To prevent the sleeper from shifting as the house settles, safely secure the frame to the floor with concrete fasteners.
To build the floor of the sleeper frame, utilize plywood with tongue and groove joints.
Fasten each 4-by-8-inch sheet to the frame with deck screws that have a thickness of 5/8 inch.
Before laying the finished floor, add an additional layer of polyethylene to the sleepers.
Thickness of the Basement Subfloor: How to Decide
The thickness of a subfloor is determined by joist spacing, underlayment options, and the type of subfloor materials used.
If you’re using plywood, it needs to be at least 5/8 inches thick, while OSB needs to be thicker, with at least 23/32 inches, because it doesn’t hold fasteners.
If you increase the joist spacing, the thickness requirements rise to at least 7/8 inches for plywood subflooring and 1 inch for OSB.
For laminate flooring, plywood of 3/4 inches will do the job, but adding an extra underlayment of thinner plywood gives the floor even more support.
For a concrete slab, subflooring should be at least 4 inches thick.
Cost of Basement Subfloor
Costs for subfloor installation vary depending on labor costs, the kind of materials used, and the size of the area to be covered.
Typically, the cost per square foot for subfloor installation ranges from $3 to $10.
Plywood is the most cost-effective material option for a subfloor.
How to Prepare Basement Subfloor for Floor Installation
To prepare the subfloor for flawless floor installation, many elements must be taken into account.
Clean Subfloor
First, thoroughly clean any debris, oil, dirt, and other contaminants from the subfloor.
Check for Flatness
Next, it is important to check the flatness of the subfloor.
According to ASTM F-710, subfloors must not deviate more than 3/16″ in 10′.
There should be no pronounced highs or lows.
Prevent Moisture
Moisture prevention is also a key factor.
To prevent water from leaking through the concrete slab, seal it and place a moisture barrier between the concrete and the subfloor.
The concrete subfloor’s relative humidity (RH) should not exceed 65%.
Check Structural Integrity
Finally, a trained installer should inspect the space before installation.
Subfloors should not have fractures, instability, or a lot of deflection.
How to Install a Basement Subfloor
To prepare for laying the subfloor, measure and clean the area.
Next, use a circular saw to cut the subfloor to the appropriate size.
Once cut, begin installing the subfloor by starting in a corner and working outward.
Set down each piece of the subflooring in a staggered pattern with at least one inch of overhang from the piece before it.
Attach the subfloor to the concrete slab using construction adhesive.
Additionally, place a foam underlayment between your flooring and the subfloor to increase insulation and reduce noise.
Is a Vapor Barrier Required Between the Subfloor Layers?
Vapor barriers are important to prevent moisture from penetrating the subfloor and reaching the underlayment.
Regardless of the type of floor you are installing, it is important to use a vapor barrier for any flooring that is susceptible to moisture damage.
Different types of vapor barriers include:
- Class 1: plastic sheets, glass, and rubber
- Class 2: asphalt-coated paper, bitumen-coated kraft paper, and polystyrene
- Class 3: gypsum board, brick, and fiberglass
The strongest moisture barriers are class 1, while class 3 barriers are typically porous.
Is it Worthwhile to Install a Basement Subfloor?
Since you most likely have concrete installed, subfloors are not an absolute necessity in basements.
But a basement subfloor can help transform your unfinished basement into a livable one.
It also helps to insulate your basement and act as a moisture barrier while also providing a flat, long-lasting surface for your flooring installation.
You can choose from various basement subflooring materials, such as plywood, concrete, and OSB.
The type of material you use and the size of the space you cover will affect the price of your basement subflooring.
Frequently Asked Questions(FAQ)
Are Tongue-and Groove Plywood Sheets Better than Regular Plywood?
Though regular plywood can be used for subfloors, tongue-and-groove sheets that interlock at the rims are a better option.
This is because tongue-and-groove plywood reduces drooping at the joist seams.
But they are also more difficult to install due to the tight-fitting joints.
Is it Necessary to Ventilate the Subfloor?
In order to prevent excess moisture and promote airflow, ventilation is essential for the subfloor.
To create a crossflow, vents must be placed on both sides of the subfloor.
What is the Best Basement Subfloor?
Rigid foam is the best subfloor option since it has outstanding insulation capabilities.
This type of subfloor is also easily achievable with readily available materials.
