Subfloors are designed to provide a stable base for your floorcoverings. They seldom need replacement, but this may be required if you have a serious water problem that leads to rot or mold or if your floor is damaged by insects. You may also have to remove and ultimately replace a subfloor during a remodel to gain access to the floor joists for running utility lines or strengthening the floor structure. Or if you are replacing your flooring with another type, such as upgrading from sheet vinyl to ceramic tile, you may need to stiffen the floor with new subflooring to prevent cracked tiles.
The materials for a new subfloor cost about $1.60 to $2.10 per square foot of floor area. Professional labor for the job costs an average of $0.58 per square foot. That's a grand total of about $2.18 to $2.68 per square foot.
Basics of Subflooring
Subflooring is fastened to the tops of your home's floor joists to create a structural platform for your floor. The subfloor often is topped by one of various types of underlayment, followed by the floorcovering. Most subfloors in modern houses are made from 3/4-inch-thick plywood or oriented strandboard (OSB) with tongue-and-groove edges. Subfloor panels are sometimes referred to by the more common brand names, such as Sturdifloor. Older homes (pre-World War II) may have subfloors fashioned from 3/4-inch-thick lumber planks.
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Installing a new subfloor is a labor-intensive job, but it is not complicated or highly technical. It is messy work that requires lugging around heavy materials as well as furniture. If you are taking a DIY approach, the cost primarily consists of materials and disposal fees. Alternatively, if you decide to hire out the project, you'll have the additional cost of labor and any markup and profit the contractor adds to the bid. A pneumatic coil nailer will reduce the time and effort required to fasten the panels to the joists, but using screws instead of nails will give a more secure and squeak-free result.
Subfloor Panel Sizes
Most building centers and lumberyards carry 3/4-inch-thick plywood and OSB subfloor panels. These are intended for joists that are set 16 inches apart on-center, which is almost universal in residential housing. If your floor joists are 24 inches on-center, the local building code likely will require that you upgrade to 7/8-inch-thick panels, which are considerably harder to locate. Plywood and OSB subflooring fluctuates in cost (like most wood materials), but these days the typical range is $25 to $50 for a 4 x 8-foot panel.
Some building suppliers still carry 1 1/8-inch-thick plywood subfloor panels. These are intended mostly for extremely heavy flooring products, such as thick marble or polished concrete. They are a bit of a relic from the 1970s and do not constitute a significant part of the retail market.
The most common exception to standard subfloor panels is engineered panels designed for basements. These have a hard plastic base and an OSB top layer, and they come in 2 x 2-foot squares. The plastic base rests on the concrete basement floor and protects the OSB and finish flooring above from moisture. One leading product is the DRICORE panel, which costs about $10 per 2 x 2-foot panel, or $2.50 per square foot.
Plywood Subflooring Material
The most common subfloor material is plywood. Plywood panels with tongue-and-groove edges are recommended, since they create a more stable surface and are less likely to squeak or bounce than standard plywood. Suppliers offer several different types of plywood subflooring:
- Standard sanded fir panels: These have a smooth top surface, which may allow you to skip additional underlayment for sheet vinyl, vinyl tile, or carpeting. A 3/4-inch-thick, 4 x 8-foot panel costs about $42, or $1.31 per square foot.
- Fire-retardant panels: Fire-retardant subflooring may be required in multistory or multifamily homes. A 3/4-inch, 4 x 8-foot tongue-and-groove panel costs around $90, or $2.81 per square foot.
- AC2 pressure-treated panels: These may be required for exposed floors or other applications requiring rot-resistance. Cost for a 3/4-inch, 4 x 8-foot panel is around $90, or $2.81 per square foot.
- Water-repellent panels: Builders may opt to use these to prevent subfloor damage while a home is under construction and the subfloor is exposed to weather. They cost about the same as standard sanded fir subflooring.
Oriented Strandboard (OSB) Subflooring
OSB is a versatile sheet material made with thin strips of wood bonded under pressure with resin and wax. OSB subflooring is often used interchangeably with plywood. It is sold in similar thicknesses and panel sizes and typically has tongue-and-groove edges. OSB panels cost about 10 to 20 percent less than plywood subflooring. It is generally less durable than plywood during transport, but it performs about the same once installed. A 3/4-inch-thick, 4 x 8-foot panel with tongue-and-groove edges costs around $45, or $1.40 per square foot.
Subfloor Fasteners and Materials
You can use either screws or nails (driven with a hammer or an air nailer) to attach your subfloor. There are pluses and minuses to both. Most building codes recommend spacing nails or screws 6 inches apart along all joists and edges, so for a 4 x 8-foot panel, you'll need around 170 screws or nails. Recommended nailing patterns are subject to local codes, so be sure to check with your city's building department for specifications.
Screws hold better than nails but cost more and take a lot longer to install (unless you have a coil screw gun). And if you ever need to remove the subfloor, you'll have to unscrew them all, instead of simply prying off a nailed subfloor. For 3/4-inch-thick tongue-and-groove panels, use 2-inch screws, the stronger the better. Look for a #9 x 2-inch construction screw, preferably with Torx or star drive and a bugle head. These drive faster and strip less easily than Phillips-drive screws, and the bugle head helps the screws countersink neatly. Unfortunately, they cost at least three times more than standard Phillips construction screws.
Nails go in faster than screws and are removable, but they don't hold as well, making the subfloor more susceptible to movement and squeaks. Just about any 8d (8 penny) nail will do, although ring-shank nails grip better than standard smooth nails. There are pneumatic nail coils made for subfloors, most with a ring shank. You'll need a coil (roofing-style) nailer, though, not a finish nailer. Look for round-head, 13-gauge nails that are 2 1/2 inches long.
In addition to screws or nails, it is a good practice to lay a bead of construction adhesive on each joist top before placing the subfloor panel. This helps eliminate squeaks and stabilizes the floor. All-purpose construction adhesive costs about $2 per tube, so this material will not add significantly to the overall cost of replacing a subfloor.
Estimating Subflooring Amounts and Costs
Figuring out the quantity of subfloor panels, fasteners, and adhesive you'll need is pretty easy. Simply calculate the square footage of the room (length x width) in feet, divide by 32 square feet (the area of one 4 x 8-foot panel), and round up to a whole number.
For example, if a room measures 10 x 20 feet (200 square feet), divide by 32 to get 6.25. Rounding up, you'll need seven 4 x 8-foot panels. It's always a good idea to have about 15 percent for waste. It's also a good idea to sketch out a panel layout plan, keeping in mind that the end seams between panels must fall over joist locations.
So for a 200-square foot room you're looking at around $250 to $300 for subfloor panels, plus $50 to $100 for fasteners and maybe $20 for adhesive, making a grand total of $320 to $420 for materials. If you replace the subfloor yourself, this may be your entire cost. However, if you need to rent a dumpster to get rid of the old materials or you have to rent a truck or pay for delivery of the panels, you may be in for another $150 to $200.
Hiring out the job to a contractor certainly adds to the cost, but it might add less than you think. Labor rates vary widely by location, but the national average labor rate for a basic subfloor replacement ranges from $100 to $250 for a 306-square-foot room, according to HomeAdvisor.