Factors Which Affect Lifespan of Plywood

Plywood products are considered some of the best wood used to construct houses and office buildings. However, despite its many features and qualities, there are some concerns regarding the structural integrity and lifespan of plywood in people’s minds. Questions like, how long would the plywood last and When will I have to make repairs or replace the plywood are commonly asked by people when thinking about using it in their homes.

We must remember that when talking about “plywood,” we’re talking about a whole family of products, not just traditional multi-layer wood plywood made of layers of wood veneer glued together perpendicular to each other. The life expectancy of plywood products will vary considerably, depending upon the type of construction, adhesives used, and environmental conditions to which the plywood is exposed.

Pick Your Materials Wisely

Even materials considered “equivalents” may not have the same life expectancy. One example of this is OSB, which the building code allows to be used in place of ¾” thick softwood plywood for floor sheathing. This decision was made because the strength of the two products is similar, with OSB having greater shear strength. However, OSB is nowhere near as strong as impact strength. It is also much more easily damaged by water.

This potential weakness has caused the buyers to view homes with OSB flooring as sub-par, causing contractors to stop using OSB subfloors in home construction. You can still find it used extensively for wall and roof sheathing, but you will only find it used as subflooring on the cheapest homes.

This illustrates that while there may be various plywood products that can be used effectively for a particular product, they won’t all perform the same or have the same lifespan. The various environmental conditions the products are subject to, and the physical stresses will affect the lifespan differently for different plywood products.

I built a garden shed many years ago using standard ¾” CDX plywood for the floor. Since the shed itself would protect the flooring, I was not concerned about the plywood rotting. However, wet grass on the bottom of the lawnmower provided sufficient moisture that the plywood rotted through in about four years. I had not considered that when I built the shed. If I had done so, I would have used pressure-treated plywood, which I used when replacing the floor.

Expected Lifespan of Plywood

It is almost impossible to ascertain the lifespan of any wood accurately. Much depends on the plywood product used, how it is installed and finished, and the environment it is subject to. You can expect a few averages, but they depend on these factors. Plywood siding, such as T-111, should give at least a 35-year life expectancy if finished properly, but there are many cases of it lasting over 50 years. Roof sheathing should last 30 to 40 years or, to put it another way, two roofs.

Plywood used for smaller indoor projects, such as children’s furniture, could last forever. In that case, it isn’t the environment that makes a difference, but wear and tear that does. While children can be rough on furniture, they don’t have the strength to damage most plywood products. That would require them to use a rock to pound on it or a pocket knife to carve their initials.

On the other hand, children can be extremely hard on the paint finish used on that plywood furniture. As with any painted part of your home, you should consider periodic painting as part of normal maintenance. How often you need to paint depends largely on the surface preparation and priming, how many coats, and the paint quality you use.

Many factors determine how long the plywood panels will remain in their true form and will not degrade. The following are some factors that might affect the lifespan of plywood.

Quality

The quality of the plywood plays a very important role in determining the lifespan. If you have bought your plywood from a good supplier and are certain it is of high quality, then you can expect it to last far more than its guaranteed life expectancy. However, if the plywood is purchased from a discount store or even from one of the big box home improvement centers, it will likely not last.

Such plywood can usually be identified because it has a lumpy surface from the presses and rollers and voids in the inner veneers. The presence of these is a hallmark of its inferior quality. Buying plywood for any project from a hardwood trim supplier, cabinetmaking supplier, or general plywood supplier rather than one of the discount houses or home improvement centers will help ensure the quality of your materials.

The problem with this lower-grade plywood stems from the voids in the inner veneers. These voids mean that there are places where the plywood starts its life delaminated. Anything made from those sheets of plywood will have those voids, which are a prime place for any delaminating to begin. Moisture can gather in those places, causing mold growth, attacking the adhesive, and furthering the process of delaminating the wood.

Moisture

Moisture is one of the biggest factors that can affect the endurance of any plywood product. If the plywood is regularly exposed to high levels of moisture, then there is no way for it to sustain its quality for a long period. This is why plywood used in houses in humid areas does not last that long and degrades much more quickly. If you are building in such an area, buying plywood with a high level of water repellency is important.

However, the moisture in the air isn’t as much of an issue as allowing the plywood to be in direct contact with water. This can happen in several ways, but if a home is properly built, it shouldn’t occur.

• Roof edges are highly susceptible to moisture, especially if OSB is used for roof sheathing. A metal drip edge should be installed on all edges of the roof, beneath the shingles, to protect against the water flowing around the edge of the shingle and soaking into the edge of the roof sheathing. 
• Wood siding is particularly susceptible to water at ground level if the siding reaches the ground. It should be installed several inches off the ground to protect it from direct contact with the soil and wet grass. Avoid stacking bricks, stones, or dirt against the house’s side. 
• When building a home, it is important to dry in the home as quickly as possible, installing a waterproof wrap over the sheathing, even if it is exterior grade plywood. Exterior grade only means that it can withstand some water, not waterproof. The longer it is exposed, the greater the chance for damage. 
• Plywood used for bars, furniture, or directly as flooring is susceptible to damage from spills when left unfinished. It should always be painted or varnished to protect the wood. When the finish becomes scarred and damaged, it should be refinished. 

The biggest problems with moisture usually aren’t with plywood used in the construction of our homes but rather with projects we construct to go with our homes. Plywood is often used in building doghouses, sheds, and storage bins, all regularly exposed to the elements. Yet we don’t take the same care with building those projects as we would in building a home. Therefore, it’s common to see water damage on them, even within a few short years. Remember my garden shed? 

Chemicals and Treatment Process Used

Plywood products are all engineered wood products. This means that as part of manufacturing these products, they pass through chemical treatment processes. The chemicals and treatment process for making a particular type of plywood determines its qualities, features, and life span.

For instance, pressure-treated plywood has a life expectancy of about 20 years; but this is with constant exposure to water, such as being left out in the rain. On the other hand, MRF and OSB have an expected life of around ranging from under 30 to 60 years. But those products are not intended for constant exposure to water. Marine-grade plywood has a life expectancy of 15 to 25 years.

RTD Plywood, one of the newest additions to the family, is gradually taking over from exterior grade softwood plywood. The improved manufacturing process in making this plywood allows for more exposure to moisture than traditional CDX plywood. This should also lead to a greater lifespan.

Conclusion 

These are only a few factors that affect plywood’s life expectancy. Many other factors might play a role in determining the lifespan of plywood used in your home. However, if you take care of it and protect it from moisture abuse, it might last longer than its expected lifespan.