Do you need vapor barrier on plywood subfloor? (2024)

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Do I need a vapor barrier over plywood?

Your plywood would most likely be on a sleeper system (floating wood planks on concrete). Having a vapor barrier below the sleepers is ideal as moisture will not get to the plywood. Regarding on-grade applications, if their is a basem*nt underneath, then you will not need a vapor barrier on top of the plywood.

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Do I need a vapor barrier over wood subfloor?

Moisture can destroy hardwood floors. It causes cupping, warping, and even mildew if not treated. You must install a moisture barrier to protect your flooring from water wicking up from below.

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Do you need underlayment on plywood subfloor?

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.

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Do I need a moisture barrier under laminate on wood subfloor?

No matter which underlayment you choose, if you are installing on a moisture prone subfloor or concrete subfloor, you really need a moisture barrier underlayment. Protect your laminate flooring from moisture for years to come by installing moisture barrier underlayment.

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What happens if you don't install vapor barrier?

Without poly beneath the drywall, water vapor hits the drywall and diffuses through to the drier (in summer) indoor air. By installing a sheet of poly there, you cut off that drying mechanism and water that finds its way into walls can stay there longer and do more damage.

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Do I need a vapor barrier between subfloor and underlayment?

Very often, particularly in a below-grade installation on a concrete basem*nt floor, a vapor barrier is recommended in addition to the underlayment. That vapor barrier would go between the subfloor and the underlayment.

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What should I put between plywood and subfloor?

Different types of flooring require different kinds of underlayment. For hardwood floors, you want to use plywood underlayment, while stone and tile flooring requires a cement backer board. Laminate, on the other hand, will look great on top of a thin layer of foam.

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Should I leave gaps in plywood subfloor?

To avoid buckling, subfloor panels should be spaced with a 1/8-inch gap at all edges and ends to provide room for naturally occurring expansion.

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Can you use regular plywood as subfloor?

Plywood. Plywood is considered the most popular material used for subflooring, it has been used since the 1950s and remains one of the top choices for contractors. Standard plywood works perfectly fine as a subflooring material, but the best option is ¾” tongue-and-groove plywood subflooring.

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Can I use plywood instead of subfloor?

You can use standard plywood for subfloors, but it is more common to use tongue-and-groove sheets that interlock along the edges. The spacing of the joists governs the recommended thickness of the plywood subfloor.

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Can you use plywood subfloor as floor?

Plywood is generally considered to be a subflooring wood choice but can be used as finish flooring in some situations, especially when painted. You want to install high-quality plywood flooring that won't warp or be easy to damage.

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What happens if there is no vapor barrier under slab?

Without a vapor barrier, moisture would continually wet the bottom of the slab, as vapor will continuously drive from the high humidity below slab to the relatively low humidity above the slab.

Do you need vapor barrier on plywood subfloor? (2024)
What happens if you lay laminate without underlayment?

Without underlayment to add a layer between these damp subfloors and the surface flooring, your laminate can quickly become wet, warped, and mildewy, harming its overall integrity. Moisture over time can also break down floor adhesive which causes the floor to start warping.

What goes under a plywood floor?

Plywood Subflooring

Quality installation of a plywood subfloor includes gluing the plywood panels to the floor joists with construction adhesive. The panels are also screwed to the joists or nailed with ring-shank or fluted subflooring nails. Plywood subflooring also comes in 1/2-inch and 5/8-inch thicknesses.

How do I know if I need a vapor barrier?

A vapor barrier is likely required if the building is cladded with absorptive material and if the structure is in United States climate zones 4C, 5 through 8. If you are building in a colder climate, check local laws or consult with your architect if a vapor barrier is required.

Do I need a vapor barrier in an unheated space?

The majority seem to agree that insulated, unheated garages, should be allowed to breathe. If the garage is heated, you will need a vapor barrier, otherwise you will get frost and mold.

Can you insulation without vapor barrier?

Not every type of insulation needs a vapor barrier. But if it does, the barrier should face inside in northern, heating climates, and outside in humid southern climates.

How do I protect my subfloor from moisture?

What steps should you take to prevent subfloor moisture?
  1. Take proper measurements before, during, and after installation of the moisture level. ...
  2. Add a flooring underlayment with a vapor retarder barrier, also known as a moisture barrier. ...
  3. Make sure that your contractors don't penetrate the vapor barrier.
20 May 2021

Where should I put my vapor barrier on the floor?

Above-Slab Vapor Barriers

Applying a vapor barrier on top of the slab and under the flooring underlayment prevents moisture (and the alkaline salts that moisture can pull from the concrete) from diffusing through the concrete slab. It slows or prevents water in the concrete from damaging the floor.

Do you need underlayment on top of subfloor?

Underlayment for laminate flooring is a must. Since laminate is a floating floor, it must be evenly distributed across your subfloor. Underlayment is what allows the floor to float, gives it stability, support, noise reduction, and supports the locking systems in between planks to assure the sturdiest flooring project.

How thick should plywood subfloor be?

The minimum thickness of plywood for subflooring is about 5/8 inch. Since it does not hold fasteners as well as plywood, OSB must be a little thicker, or at least 23/32 inch. There are several factors that determine what subfloor thickness is optimal for added benefits like insulation.

Should you screw or nail plywood subfloor?

Screws are preferred over nails for subfloor and underlayment installations as they provide strong and tight connections that help prevent the floor from squeaking. Before starting your next subfloor or underlayment installation, make sure you have the right subfloor screw gun for the job.

What grade of plywood is best for subfloor?

When choosing a grade for your plywood flooring I'd stick with CDX if it's a subfloor. Higher grade plywood is typically used for cabinet and furniture making. If your joists are spaced at 16 inch on center go with at least a 5/8 inch plywood. Use two layers of plywood when building a fiberglass floor.

Should I glue plywood to subfloor?

The answer: Glue. Although using a subfloor adhesive (or subfloor glue) is not required by code, it is a standard practice that can help prevent floor squeaks by reducing the chance for movement at the panel-to-joist connection. A quality subfloor adhesive will also increase the overall stiffness of the floor.

How long can you leave subfloor exposed?

“Adequately protected from moisture, most subfloor materials can be expected to last for the lifespan of the home.” However, if the subfloor is consistently exposed to moisture, you may need to replace it after 20 to 30 years or sooner.

Should you glue second layer of subfloor?

Second Layer Installation

The second layer should also be installed perpendicular to the floor joists. First layer must be dry prior to laying the second layer. Place a layer of 15-lb felt on top of the subflooring prior to installing second layer. Adhesives should not be used to fasten the two layers together.

Is black vapor barrier better than clear?

White/Black Vapor Barriers

Black barriers are more effective at stopping moisture evaporation, compared with the clear barrier. The black color hinders the growth of plant seeds that may reside beneath a home's crawlspace. Plants naturally send moisture into the air, creating more moisture.

Do vapor barriers cause mold?

The Problem With Vapor Barriers

This can lead to significant moisture problems and mold; problems occur when walls get wet during construction or more often throughout the home's life. These wetting cycles can be from air flow, window leaks, pressure imbalances, and a host of lifestyle issues.

Is vapor barrier enough?

There's a layer of flooring and insulation between you and the crawl space- isn't that enough? Unfortunately, the answer to that is a very big, very loud, shout-it-through-a-megaphone NO. A vapor barrier, also known as a moisture barrier, is actually the bare minimum protection you should have in your crawl space.

Does plywood subfloor need to be tongue-and-groove?

Tongue-and-groove plywood is superior to regular plywood for floor decks because it creates a stronger, more rigid subfloor, and helps eliminate sagging and "bounce" at the seams between the joists. But it is also more difficult to install because the tight-fitting joints don't always go together easily.

Is plywood or OSB better for subfloor?

This evolved plywood may claim an overall advantage over OSB, since plywood is a stiffer, longer-lasting subfloor option. It will also hold up better under flooring accidents like leaks or flooding, and has greater nail withdrawal strength to hold the nail in under stress.

How many layers of plywood do you need for a subfloor?

Just 1 layer of 3/4 “ or 5/8” will do for most applications. If your finished floor is going to be heavy ceramic tiles, natural stone, and alike it may need to be thicker and or have more supports.

What is the best flooring to put over plywood?

Laminate floors can be installed over any wooden subfloor as long as it's in good repair. If the subfloor is uneven, you can add a layer of thin plywood over the subfloor. The laminate is laid down over a thin underpayment layer. The boards typically lock together.

How do you seal a plywood subfloor?

Sealing The Subfloor Surface

Step 1: Sand the total plywood surface down to make it as smooth as possible. Step 2: Wipe down the floor surface to ensure it is clean and smooth. Step 3: Apply a quality sealer with even strokes and allow the floor to dry.

What happens if you don't have a vapor barrier in a crawl space?

Oftentimes, moisture can seep through the dirt floor of your crawl space when you do not have a vapor barrier installed. Additionally, poor grading and improper vapor barrier installation can lead to rainwater leaking into your crawlspace, causing a huge standing water issue.

When did vapor barrier become code?

Although building code requirements for vapor barriers were totally unjustified when they were first established in 1948, there have been three technical developments since then that have changed the way interior vapor retarders affect wall performance.

Do vapor barriers trap moisture?

Vapor barriers are supposed to stop vapor diffusion through roofs, walls, and floors. But they can also can trap moisture, causing rot and mold.

Can you lay laminate directly on plywood?

Laminate floors can be installed directly over concrete, plywood, OSB, parquet, vinyl and tile. The underlayment must be applied to the original flooring surface first, and then the floating floor can be installed.

Do I need underlayment for laminate flooring on plywood?

So do we recommend an underlayment for laminate flooring on plywood? Yes, underlayment provides compression, sound absorption and insulation value. The moisture protection isn't really a concern unless it is above a crawl space.

Which is better laminate with pad or without?

Laminate flooring manufacturers typically recommend an underlayment. What happens if you don't put padding under laminate flooring is moisture coming through the subfloor can cause it to warp and mildew. And footsteps on the floor will be louder.

Can I use plywood as underlayment?

Plywood underlayment is the layer of plywood that is fastened over the structural subfloor. It creates a uniform, smooth surface for resilient flooring, vinyl tile, ceramic tile, carpet, engineered flooring, and wood floors.

Is plywood considered an underlayment?

Underlayment is a special grade of APA plywood that is attached on top of the subfloor to provide a durable and resistant layer under finish flooring. Underlayment's special face and inner-ply construction resist dents and punctures from concentrated loads.

Do I need a vapor barrier if I use foam board?

There are a number of reasons why you need an air and moisture barrier over foam sheathing. Airtight exterior wall systems are critical to maximizing energy efficiency and gaining LEED points. However, certain characteristics of foam sheathing conspire to compromise airtight construction.

Do all walls need a vapor barrier?

Not every wall does. A vapor retarder is a material used to prevent water vapor from diffusing into the wall, ceiling or floor during the cold winter. Whether or not you need a vapor retarder hinges on three main factors your climate, your home and the location of the wall you're insulating.

Where are vapor barriers required?

The IRC requires Class I or Class II vapor retarders on the interior side of most above-grade frame walls in Climate Zones 5, 6, 7, 8, and Marine 4. It is permitted to use Class III vapor retarders if continuous exterior insulation is installed in accordance with IRC Table R702.

Can you use plastic sheeting as a vapor barrier?

Reinforced polyethylene plastic sheeting (poly) comes in a variety of thicknesses and strengths. A 6 mil thick poly is commonly used as a vapor barrier and offers short-term savings to the homeowner.

Is foil faced foam board a vapor barrier?

Foil faced insulation is the best type of insulation for retaining heat in the winter and keeping heat out in the summer. This insulation product is designed to slow heat transfer and enhance acoustical performance. It also works as a barrier for methane, radon, vapor, termites and other vermin.

Can open cell foam act as a vapor barrier?

Open cell spray foam is not a moisture vapor barrier, and will allow moisture to pass. So, if you're considering spraying foam to the roof deck of your new or existing home, you want open cell. If there's a roof leak, water will pass through the foam, and you will quickly be able to find your problem.

Is foam board better than plywood?

More effective insulation

With R-values ranging from 3.6 to 8.0, rigid foam sheathing has much better insulation per inch than other materials (i.e. plywood has an R-value of 1.25 and fiberglass batts have an R-value of 3.14).

Is Tyvek a vapor barrier?

No, DuPont Tyvek is not a vapor barrier. It is breathable, allowing moisture vapor to pass through it.

Does drywall work as a vapor barrier?

The permeance of unpainted drywall is very high, generally between 20 and 90, so it's not a vapor retarder at all. Meanwhile, air leakage through a 1 square inch hole in a sheet of drywall allows 30 quarts of water vapor to pass through the drywall under the same conditions.

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