The subfloor is the decking installed on top of flooring joists; the finished floor is then installed on top of the subfloor. The thickness of plywood panels in a subfloor is regulated by the spacing of the joists.
This number is known as a span rating. When installing a plywood subfloor on top of the slab at grade, the thickness is governed by how long the fasteners for the flooring will be. Floor joists are made from 2-byinch or 2-byinch lumber, or from engineered quiet beams, which are made from a thin layer of chipboard on edge between two lumber caps forming an "I" shape.
Floor joist spacing has traditionally been 24 inches on center, or from center to center of the joists. Newer construction has floor joists spaced at 16 inches on center.
You will need to determine the spacing before installing the joists, or measure the distance between joists for existing construction. CDX plywood is traditional wood plywood made from thin layers of lumber, known as veneers. Glue is sprayed between each layer and the sheet is hot pressed. Oriented strand board, or OSB, is a wood structural panel that can also be used for flooring. It is made from shredded strands of wood pressed together with wax and a special adhesive, then hot pressed into a panel with up to 50 layers of strands.
Sturd-I-Floor is a specialized engineered wood structural panel expressly designed for single-layer flooring installations on upper floors, where carpet will be laid directly over the subfloor. These panels are more rigid than either traditional plywood or OSB.
Mark Morris started writing professionally in Morris specializes in many topics and has 15 years of professional carpentry experience. He is a voice, acting and film teacher. He also teaches stage craft and lectures on playwriting for Oklahoma Christian University.
By Mark Morris Updated December 19, About the Author.Plywood underlayment is a thin plywood material that is most commonly used under resilient flooring materials, such as vinyl and linoleum sheets and tiles. It can also be used under hardwood, laminate, and carpet, but this is much less common these days because subflooring is typically smooth enough for these materials, many of which are installed with a different type of underlayment or pad.
Plywood underlayment provides a smooth, flat surface, without voids from knots or other surface imperfections common with subflooring. Often, the terms "subfloor" and "underlayment" are used interchangeably.
Underlayment is a thinner material that lies over the subfloor. While underlayment may add a modest amount of stiffness to a floor assembly, it does not strengthen a floor or enhance it structurally. Plywood is only one type of underlayment. Other common types include cementboard or tile backer used under ceramic or stone tilefoam underlayment used under laminate and engineered wood "floating" floorsand rosin paper used under solid hardwood flooring.
There are also engineered subfloor panels designed for covering concrete slabs in basements. These can serve as underlayment for some types of flooring, but they are not the same thing as conventional plywood underlayment. It's easy to find conflicting advice about underlayment, especially plywood underlayment. Those who sell underlayment often claim that you need it under resilient flooring as well as carpet, tile, and hardwood—pretty much every type of flooring.
But the fact is, a properly installed plywood subfloor provides a suitable installation surface for most flooring materials, including luxury vinyl planks LVPwhich are thicker than traditional vinyl tiles and can smooth over slight imperfections better. Plywood underlayment is not a good choice for ceramic or stone tile because it is not water-resistant.
For floor tile in any room, use cementboard or a similar tile backer instead. To simplify your decision, consider plywood underlayment if it is recommended by the flooring manufacturer. In some cases, the use of underlayment may be required to satisfy the product warranty. Plywood underlayment is typically needed when a floor material must have a very smooth, flat surface. For example, if you install resilient tiles or sheet flooring over a subfloor, any bumps, dips, or voids in the subfloor may be evident in the finished flooring.
Underlayment covers subfloor flaws for the best possible results. It typically comes in 4 x 8-foot sheets. For many years, the standard option was lauan plywood, also called Philippine mahogany or luan plywood, which is made with an inexpensive tropical hardwood, and therein lies its problem.
Lauan products have been responsible for massive deforestation in the Philippines, Indonesia, Malaysia, and other countries.
Today, a much better option is a plywood specifically designed as underlayment and made with sustainably forested wood. You can also use AC exterior-grade plywood, which has one smooth face and one rougher face.
Always install underlayment with the smoother face up. If you have any questions about the suitability of an underlayment material, contact the flooring manufacturer for recommendations. Plywood underlayment is easy to install. The sheets are lightweight and have perfectly uniform dimensions and edges. You can cut sheets with a circular saw, jigsaw, table saw, or handsaw, just like any wood sheet material. While underlayment traditionally was glued down to wood subflooring, most manufacturers today recommend installing it without glue, which greatly simplifies the installation.
Thorough fastening of the underlayment panels is key to a successful installation. The easiest and best fastening option is galvanized staples driven with an air-powered stapler available for rent at home centers and rental outlets.
You can also fasten underlayment with galvanized or coated screws or nails. Do not use standard, uncoated fasteners because they are prone to rust, which can discolor some types of flooring.
The installation process starts with storing the underlayment panels in the room where they will be installed for at least 72 hours. Once the subfloor is thoroughly cleaned, the underlayment panels are installed one at a time directly over the subfloor.
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Your password has been updated. Current Password. Sign in New to USG? All Inspiration. Installation Installation Installation Guides. Drywall Ceilings Never Sounded so good.Oriented strand board, or OSB, is a sheet panel product, similar to plywood, made from layers of wood strands that are oriented in opposite directions. Builders use OSB to sheath the roofs and sides of homes and to build subfloors. OSB is made from small-diameter logs that are easily and quickly regrown, making it an ecologically sustainable product.
The proper installation of OSB depends on how and where it is used. Local building codes vary. Always check with your building department for specific local requirements. When OSB is used as a structural panel, it must adhere to specific span ratings specified by the manufacturer.
For example, unless a panel is span rated for flooring, do not use it to build a floor. Manufacturers specify span ratings for floors, roofs and exterior wall sheathing.
On roofs and floors, manufacturers supply an additional specification for supported and unsupported edges. Edges are supported by a tongue-and-groove system or by specially made clips that install along the edges of the OSB.
The minimum OSB panel size is 24 inches in any direction and each sheet end must rest on a rafter. Lay sheets in rows with the long edge horizontal to the roof bottom. Nail the panels to the rafters with 8d common nails spaced 6 inches apart on the ends and 12 inches apart in the middle. Install H-clips between adjacent rows of panels every 12 to 16 inches, but not over framing members.
Space joints on adjoining rows by two framing members. Select OSB sheets rated for use as a wall sheathing that meet or exceed the stud spacing on your walls. You may use a sheet rated for a inch span when studs are spaced 16 inches apart, but not a sheet rated for just 12 inches. Install sheets vertically with the long edges on studs. Fasten panels to studs with 8d common nails spaced 6 inches along edges and 12 inches in the middle. OSB subfloor panels have tongue-and-groove edges that fit together and significantly reduce flex in the floor.
Use OSB panels rated for the distance between the floor joists. Run a bead of construction adhesive along each joist and lay the OSB panel on the joists. Stagger adjacent rows of panels by two joists.
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By Michael Logan. Span Ratings When OSB is used as a structural panel, it must adhere to specific span ratings specified by the manufacturer. Roofs The minimum OSB panel size is 24 inches in any direction and each sheet end must rest on a rafter.
How to Install a Plywood Subfloor
Exterior Walls Select OSB sheets rated for use as a wall sheathing that meet or exceed the stud spacing on your walls. Subfloors OSB subfloor panels have tongue-and-groove edges that fit together and significantly reduce flex in the floor. Photo Credits. About the Author.Finding the number of sheets of plywood needed for a floor, wall, ceiling, or cabinet begins with finding the area that needs to be covered. Area can be found by multiplying the length and width of the space in feet.
Find the square footage of each space and add together to find the total square footage needed. Divide by the total square footage by the square footage of a sheet of plywood to find the number of sheets required to cover the space. For example, if the area to be covered in plywood is ft 2 then 25 sheets of plywood will be needed to cover it.
Plywood is actually composed of several layers of wood glued together. Plywood is commonly composed of 3 or 5 layers.Loft Conversion (Animation) by Wasim
Oriented strand board OSB is composed of wood strands or flakes compressed with glue. OSB commonly used in framing to sheath roofs, floors, and walls. Medium density fiberboard MDF is composed of small wood fibers compressed with glue. The smaller fibers offer neat edges and a smooth surface. MDF is commonly used in cabinetry. Particle Board is composed of small wood particles compressed with glue. Particle board is often used for floor sheathing, shelving, and furniture.
Block board is a panel composed of boards glued edge to edge and then sandwiched between sheets of veneer. It is very strong and rigid and is often used in furniture. The thickness needed will depend on the purpose and use-case. Thicker panels are more rigid and durable but are also heavier and more expensive. Keep in mind that the actual thickness of plywood is often slightly thinner than the nominal thickness, learn more about the actual thickness of plywood. In most cases this will not be an issue, but it is important to keep in mind for projects that require more precision such as fine carpentry.
Our calculators can simplify your woodworking project layout and estimation. Add and subtract feet, inches, fractions, centimeters, and millimeters with ease. Get results in imperial and metric measurements. Get hassle-free estimates from local trim carpentry professionals and find out how much your project will cost.
That said, I have also read that I should not screw the underlayment into the joists, but this seems mostly to come into play when folks are talking about installing tile.
Do I really need to be careful about not hitting the joists with the screws? I am planning on 6" spacing on the edges and 8" spacing in the field. Also, should there be a gap between the underlayment plywood butt joints? First, I'd counter your plans to orient the second layer perpendicular to the subfloor.
Plywood and OSB have a strength axis that should run across the joists. Instead of turning the top layer, simply stagger its joints with respect to those of the subfloor. Start with a ripped half sheet and stagger the butt joint by two joists. I've never heard the advice you mention about avoiding joists with underlayment fasteners. It's probably not critical to run screws into joists, but there are a couple reasons why you would.
Running through between the joists creates some possibility that you'll hit something underneath that shouldn't have holes in it. You may find your screws stripping at the threads before the heads are completely sunk.
They should be at or below flush, and that takes quite a bit of pull from the threads. I wouldn't worry about gapping butt joints with plywood. It's stable enough that it shouldn't be a problem unless you happen to be installing very dry wood in a very humid environment. OSB is usually undersized to allow for swelling, but not plywood.
You are referring to the "decoupling principle" which allows the surface to move independently from the substrate what's underneath. It's generally not necessary with wood, because wood can slowly change shape as the house ages. Tile is rigid and crystalline and will never change shape, therefore decoupling is essential. If both layers of sub-flooring and the hardwood flooring were all anchored into the joists, it would prevent the house from deforming. If the upper layers are separated from a settling house, the upper layers will not deform as quickly, but will not add to the structural integrity of the floor.
Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Plywood underlayment over plywood subfloor - how to secure Ask Question. Asked 2 years, 5 months ago. Active 2 years, 5 months ago. Viewed 6k times. Active Oldest Votes. Simply, your floor can hold up your home, or your floor can outlast your home.
It only takes a minute to sign up. In my particular case, I'm building a tiny shed. According to Table R Use 10d common or 8d deformed nails, spaced 6" apart on edges and 12" apart in the field. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. How many screws do I need in my subfloor?
Ask Question. Asked 4 years, 5 months ago. Active 2 years, 4 months ago.
When and How to Use Plywood Underlayment
Viewed 25k times. I'm not sure what the relevant units are either. Pounds per square foot? Screws per 4'x8' sheet? Ryne Everett Ryne Everett 1 1 gold badge 1 1 silver badge 8 8 bronze badges. I think the answer to every how many So this is a bad question because the answer is "it's arbitrary"?
It depends on a lot of factors - what is going over the plywood? There are also several other assembly questions that come into play which you may have already dealt withsuch as expansion spacing, sealing, type of screws, etc. Active Oldest Votes. Use 6d common nails, spaced 6" apart on edges and 12" apart in the field. Use 8d common nails, spaced 6" apart on edges and 12" apart in the field. If you're building from a kit, you should follow the manufacturer's installation instructions.
Tester Tester k 66 66 gold badges silver badges bronze badges. Use the above specs as minimums and upgrade to screws to avoid squeaks. And use construction adhesive between the joist and subfloor, too. Hello, and welcome to Stack Exchange. This is interesting, but hard to understand; would you add a few sentences and make your post clearer? Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.
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