Setting things straight...

A couple of days ago I blogged about avoiding getting a lemon if you are buying a new build home. Portions of that post were taken from a story that first appeared on the MSN Real Estate Web site. One line in the article that I used contained the line - OSB is much less water-resistant than plywood. It tends to absorb and retain water, which leads to dry rot.

Well, that drew an immediate email from the APA (formerly called the American Plywood Association) which represents plywood and OSB manufactures, who took exception to that characterization of their product. I certainly didn't mean to impugn OSB and pointed out to them that the line in question was in fact a quote attributed to a fellow out in California who works with homeowners associations (hardly a strong qualification to be quoted on building materials, I will admit). I had gone on in the post right after that line to wonder about building sites where building materials like flooring or roofing are left exposed to the elements for any length of time.

Anyway, I decided that, since I'm certainly not a building materials expert either, I would see what's out on the Internet about OSB and its water proof characteristics. One good article that I found is by Tim Carter, a nationally syndicated newspaper columnist who also authors the Web site Ask the Builder. Tim wrote in an article about Plywood and OSB -

Rain falls on many, many homes as they are being built. In fact, rain storms left standing puddles of water on my own home's plywood sub-floors for days. The plywood was not affected long term because I used the right grade. Make sure that you use plywood or OSB that is stamped EXPOSURE 1. This labeling is your guarantee that waterproof resins and glues were used to bond together the wood. EXPOSURE 1 plywood and OSB are made to withstand repeated rainfall with little or no damage during a normal time frame construction project. To prevent rot and loss of strength, they must be allowed to dry and then have permanent protection from moisture. If you want plywood or OSB that can be permanently exposed to weather and rain, then purchase those products that bear the EXTERIOR stamp or label.

Some OSB panels react differently from plywood when they get wet. When OSB is manufactured the cut edges are sealed with a special waterproof paint. Carpenters destroy the watertight integrity of OSB each time they make a cut that exposes wood fiber edges. These cut edges are prone to swelling after they get wet. It is possible to seal these edges after they are cut, but it may be tough to find a carpenter willing to take the time to perform this extra step.

To read the entire article, which also includes how OSB is made and how it compares to plywood and other building materials, go to the Ask the Build site via this link

http://www.askthebuilder.com/304_Plywood_and_OSB_-_Which_One_Is_Better_.shtml

Hopefully that will clear things up for my readers and square things with the APA folks. What Tim says makes sense and it makes sense too that exposed edges might be an issue, if not properly sealed. We certainly have seen that problem with wood siding on homes, at least with some defective wood siding from Louisiana Pacific years ago. MUch of that siding is still out there on homes and still causing problems.

OSB is now the most commonly used sheeting material in new construction and is even used to build up floor joices. So, it is a fact of life and it would appear from my research that it is a good product with characteristics manufactured into it for the various jobs that it is used for. Maybe the best advice comes out of Tim's article that the buyer should watch to make sure that the right type of OSB is being used for the various places that it is deployed in the build.