Should I use CDX or OSB for roofing plywood?
When planning to redo your roof or repair some damages, you might come across different grades and types of wood, such as OSB and CDX and start wondering what
those abbreviations mean. What are the differences? Is one better for roofing than the other? Should I use CDX or OSB for roofing plywood? OSB and CDX do not only look different, but they have unique characteristics that make one better than the other in specific applications.
Lets learn the differences between CDX and OSB so you can make a more informed decision when it comes time to choose one or the other for your roofing project.
About CDX Plywood
CDX is a type of veneer plywood that is fabricated by gluing then pressing sheets of wood together to strengthen them. The grains run in the opposite direction of the layer below. C and D stand for the grades on either side of the plywood while X means ‘exposure.’
CDX is very stable, since the manufacturing process is built upon the idea of checks and balances.
Compared to CDX, oriented strand board (OSB) is made very differently. OSB is made by combining glue, resin, and wood chips and pressing them into the shape of a plywood sheet then baking everything together. Because of this manufacturing process, OSB is at least half the cost of CDX plywood.
Earlier types of OSB were known as waferboard, which is now considered a sub-standard version of oriented stand board. Fortunately, performance has been increased exponentially.
Differences Between OSB and CDX For Roofing Plywood
Now, let’s have a look at some of the main differences between CDX and OSB as roofing plywood.
One of the major differences between OSB and CDX plywood is how well each holds up against water. Going back to the X in CDX, you may recall that it means ‘exposure.’ Many people think the X stands for ‘exterior,’ but that’s a common misconception. In reality, CDX plywood can only withstand water for a short period of time. An example is when CDX is used for subflooring. Though it will resist water for a few months, it will need to be covered with a sheath for long term use (and that sheath is oftentimes OSB).
Only use CDX plywood for the interior of a house, where water damage is far less likely. Do not use CDX for roofing, sheds, or other places that are exposed to moisture consistently. The sole exception to this is pressure treated CDX, which can survive for decades without even a protective coating.
When building a house, OSB makes for excellent sheathing. Many contractors will use OSB for roofing and subfloors. There are even variants of OSB that come with building wrap already in place, so installation is as easy as taping the seams together.
OSB is much more waterproof than plywood and CDX plywood. The glue and resin that is mixed in with the wood chips makes it much less permeable, so OSB holds up longer in harsher conditions. That is why OSB is sometimes used to secure houses when a hurricane draws near.
Now, even though OSB is thought to be waterproof, there is a downside to its resilience. OSB will not absorb water easily, but when it does, it takes a long time to lose that water and dry out. Because of this, OSB struggles to revert back to its original state.
On the other hand, CDX is hardly waterproof and will absorb water readily, but it also will shed that water quickly and reverts to the original shape and thickness effortlessly. In short, CDX has better dimensional stability, which is why it is used for integral interior sections of a structure.
If you are looking to cut some corners, then you will want to select OSB for more applications than CDX. As mentioned earlier, OSB is usually much cheaper than CDX and is also easier to locate in stores and lumberyards.
With all previously stated information in mind, let’s answer the biggest question people usually have when faced with choosing between OSB and CDX plywood: Which is better for roofing? Although some people will ultimately choose CDX, many experts argue that OSB is better overall for roofing.
OSB is far less likely to expand and contract when exposed to humidity and moisture, even though it will take longer to dry. With wrapping, though, it can withstand the elements without issue. Plus, with shingles, OSB gets enough protection. Comparatively, CDX covered in shingles will still be exposed to too much moisture and will eventually delaminate and warp, increasing the chances of water damage elsewhere in your home.
CDX vs. OSB: Which is Best For You?
Understanding the differences between CDX and OSB is important because you want your home to be protected from the elements throughout the year. The differences, such as moisture resistance and cost and even how CDX and OSB are manufactured lend them unique characteristics. Most homeowners opt for OSB because it is cheap, while others may prefer sturdier CDX.
Why not discuss your options with our professional and knowledgeable team? We will be able to give you more information and provide insight on your roofing project. Get in touch with us by filling out the contact form. We look forward to hearing from you.