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Can You Use OSB for Deck? (How To)

OSB is a very common and well liked material used in the building industry. There are a few types of ways that the word deck can be used to refer to different parts of a building. In this article, I will explain how and where OSB can be used for a deck.

Overall, OSB should not be used for an outdoor deck. But, can be used for a ceiling/roof deck, and mezzanine deck (indoor decks). But, it can only be used as sheathing and should not be installed where it will be exposed to the elements, particularly any moisture.

Wooden house deck

There are a range of options for sheathing that can be used, and there are some materials that are highly recommended to use for an exposed deck, and for a ceiling/roof deck. Below, I will explain if it’s a good idea to use OSB for both of these types of decks, what prep is required to use it, as well as, how to use OSB for these two different types of decks.

Should You Use OSB for Deck?

Wooden house deck

OSB was invented after plywood and has a range of advantages over plywood. However, they are similar enough that often how expensive or cheap one is compared to the other will ultimately decide which is best. But, this is whether you should use OSB for a deck, or if there’s a better option.

In general, you should not use OSB for an outdoor deck, but it’s commonly used for a ceiling and roof deck which is not exposed to rain and humidity. OSB swells, and degrades after about 6 months or less outside. According to the Engineered Wood Association, it can only be used as sheathing.

And therefore, needs to be waterproofed. There are 3 common waterproofing methods used for OSB when it’s used for building applications. These are:

  • Waterproof underlayment (a wrap that is stapled to the OSB)
  • A waterproofing system (complex, requires specialist training and many different types)
  • Plastic building wrap (for walls)

The main reason OSB should not be used for a deck that is exposed to rain is that it swells, and never returns to its original shape again, even after drying out. This swelling degrades how strong it is, and ruins its appearance, particularly on the edges. While it can be used if it’s waterproofed using various products. It’s the wrong material for this kind of job.

It’s best to use a proper decking material such as Composite or PVC. Composite and PVC decking are the best products to use for an outdoor deck. They are more durable than hardwood, look virtually identical, and are made in part with recycled materials.

These provide a far better appearance, are less time consuming – because you don’t need to waterproof them first, and are incredibly strong underfoot.

Copyright article owner is for this article. This post was first published on February 15, 2023.

For a ceiling deck, however, it’s thoroughly recommended to use OSB, and is very commonly used. As you may know a ceiling deck is the area on the underside of a deck that is on the second story. OSB is good to use for:

  • Sheathing ceiling/deck
  • Wood I-joists
  • Single-layer flooring
  • Wall and roof sheathing
  • The interior of industrial containers
  • Mezzanine decks
  • Furniture
  • Subflooring

What Preparations Do You Need to Use OSB for Deck

Wooden house deck

OSB is fairly versatile but it’s important to install it correctly, with buildings there are often a lot of minor details that make all the difference, and therefore, below I will cover what preparations you need to use to use OSB for a deck.

In general, it should be acclimated to your climate for 5 days in a place where it will be completely dry. After installation it should be kept completely dry until it is covered with waterproof underlayment, plastic wrap, or waterproofing.

Doing so will ensure it won’t change dimensions too much in response to changes in humidity. Other than that there is nothing extra that needs to be done to prepare it before installing it.

How to Use OSB for Deck

Wooden house deck

OSB comes in sheets of varying thickness and size and for these reasons it can be used for a bunch of different applications. But, below is how it’s used for a deck, and exactly how to install it on a deck.

OSB is used as sheathing for a ceiling-deck or roof deck. But, not for a deck that is exposed to the elements (regular deck). You nail each OSB sheet to the studs or framing. The exact number of nails differs based on the building codes in your region. But, below are the general guidelines.

To know the exact amount of nails to use to meet building codes you should contact the building codes office in your jurisdiction over email or phone. Regardless of how many nails you need, each board needs to have a space that is ⅛ inch (0.32 cm) to allow for the expansion and contraction. They also should be staggered to provide greater structural integrity, and you should install each row of nails from one end of the OSB sheet to the other.

There are a lot of very specific details for how to nail OSB to framing to use it as a ceiling-deck or roofing deck. Below, is a really good video that shows the very common measurements to be aware of, how to place each sheet, what nails to use, and how to install and space the nails to attach to the framing or studs:

For a ceiling deck, you cover it with a siding such as vinyl siding. For a ceiling deck it’s best to waterproof it with a waterproof underlayment or plastic sheeting, another option is to simply finish it using a sealer, which you paint on. Doing so will make it last much longer, especially in climates that get very humid.

And in some jurisdictions it may be a requirement to meet building codes. After that install what you are finishing it with. Such as vinyl siding. OSB generally looks very bad if you paint it or plaster it, but it can be done.

If you do, it can be waterproofed using a waterproof paint-type primer product instead of waterproof underlayment or plastic sheeting. There are a large number of these, and any of them will work provided it’s designed for waterproofing wood.

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ReadyToDIY is the owner of this article. This post was published on February 15, 2023.

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