Saturday, March 8, 2014

Tiny Home Building: OSB vs. Plywood + Formaldehyde In Homes

A major decision while building our house was whether we should use OSB or plywood. So I turned to the internet, did a bunch of research, and ultimately went with plywood. I wanted to share my research for others out there trying to decide between the two. Plus there's a little info on formaldehyde found in homes and how to protect yourself from it. 

While plywood and OSB both off-gas formaldehyde, OSB off-gasses more of the carcinogenic gas. Plywood, OSB, and other engineered wood products that contain glue can be stored outdoors for several weeks before construction so that much of the dangerous gasses are vented safely into the outdoors.

In favor of OSB: 

OSB can be manufactured into panels that are larger than plywood. 
OSB is more uniform, so there are fewer soft spots, such as those that can occur in plywood. 
OSB is less expensive than plywood. To build a typical 2,400-square foot home, OSB may cost $700 less than plywood.
OSB is considered by many to be a “green” building material because it can be made from smaller-diameter trees, such as poplars, that are often farmed. Plywood production, by contrast, requires larger-diameter trees from old-growth forests.
Plywood has a tendency to delaminate, especially in hot climates such as Florida. 

In favor of Plywood: 

OSB weighs more than plywood. One 23/32-inch 4x8-foot plywood piece weighs approximately 67 pounds, while a piece of OSB of the same dimensions weighs approximately 78 pounds. The increased weight of OSB means that it is harder to install and it will put more stress on the house.
Compared to plywood, OSB swells more when it comes into contact with water, especially at panel edges. Swell is generally greater in OSB than in plywood due to the release of compaction stress in OSB created during the pressing of wood chips into panels. Swollen plywood will return to its nominal thickness as the wood dries, while OSB will remain permanently swollen, to some degree. Swelling is a nuisance because it can uplift whatever materials lie above, such as tile or carpet.
Plywood floors are stiffer than OSB floors by a factor of approximately 10%. As a result, OSB floors are more likely to:

squeak due to floor movement;
cause hard floor surfaces to crack (such as tile); and
result in soft, spongy floors. 

Nails and screws are more likely to remain in place more firmly in plywood than in OSB.
OSB retains water longer than plywood does, which makes decay more likely in OSB than in plywood. Of course, tree species plays a large role in this determination. OSB made from aspen or poplar is relatively susceptible to decay. In one of the biggest consumer class-action lawsuits ever, Louisiana-Pacific (LP), a building materials manufacturer, was forced to pay $375 million to 75,000 homeowners who complained of decaying OSB in their homes.

Sources of Formaldehyde

In homes, the most significant sources of formaldehyde are likely to be pressed wood products made using adhesives that contain urea-formaldehyde (UF) resins. Pressed wood products made for indoor use include: particleboard (used as sub-flooring and shelving and in cabinetry and furniture); hardwood plywood paneling (used for decorative wall covering and used in cabinets and furniture); and medium density fiberboard (used for drawer fronts, cabinets, and furniture tops). Medium density fiberboard contains a higher resin-to-wood ratio than any other UF pressed wood product and is generally recognized as being the highest formaldehyde-emitting pressed wood product. 

Pressed wood products (hardwood plywood wall paneling, particleboard, fiberboard) and furniture made with these pressed wood products. Urea-formaldehyde foam insulation (UFFI). Combustion sources and environmental tobacco smoke. Durable press drapes, other textiles, and glues.

How can people limit formaldehyde exposure in their homes?

The EPA recommends the use of “exterior-grade” pressed-wood products to limit formaldehyde exposure in the home. These products emit less formaldehyde because they contain phenolresins, not urea resins. (Pressed-wood products include plywood, paneling, particleboard, and fiberboard and are not the same as pressure-treated wood products, which contain chemical preservatives and are intended for outdoor use.) Before purchasing pressed-wood products, including building materials, cabinetry, and furniture, buyers should ask about the formaldehyde content of these products. Formaldehyde levels in homes can also be reduced by ensuring adequate ventilation, moderate temperatures, and reduced humidity levels through the use of air conditioners and dehumidifiers. 

Here is something I found that can seal in off-gassing so that it doesn't affect you and your indoor air quality: 

Wherever possible and appropriate, we incorporate surface sealing properties into AFM Safecoat products such as paints and clear finishes. Many chemically sensitive individuals have successfully controlled off-gassing materials using Safecoat, to the extent that they can tolerate environments that were intolerable before.

Every indoor air quality problem, and every surface, is different, so there are no guarantees. But follow these basic rules and critical steps for the best chance of success: 

Formaldehyde off-gassing reduction analysis using SafeCoat products
Sample         Primer Coat                             Finish Coat                        Formaldehyde Evaporation mg. Per liter
A                  Uncoated Plywood                 Uncoated Plywood                                 3.20
B                  Transitional Primer                 0 VOC Semi-Gloss                  .                .03
C                  0 VOC Semi-Gloss                  0 VOC Semi-Gloss                                   .04
D                  Polyureseal BP Gloss             Polyureseal BP Gloss                               .02

I'm probably going to use these in our home: 
IMG_5162 copy