Plywood products are considered to be some of the best forms of wood used for construction of houses and office buildings these days. However, despite the many features and qualities that it possesses, there are some concerns regarding the structural integrity and lifespan of plywood in the mind of the people. 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 making use of plywood in their homes.
We must remember that when we’re 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, dependent upon the type of construction, adhesives used and environmental conditions that the plywood is exposed to.
Pick Your Materials Wisely
Even materials which are considered “equivalents” may not have the same life expectancy. One example of this is OSB, which the building code allows to be used in the place of ¾” thick softwood plywood for floor sheathing. This decision was made because the strength of the two products is similar, with OSB actually having greater shear strength. However, OSB is nowhere near as strong when it comes to 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 being sub-par, causing contractors to largely 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 made.
This illustrates that while there may be various different 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 that the products are subject to, as well as the physical stresses, will affect the lifespan differently for different plywood products.
A number of years ago, I built a garden shed, using standard ¾” CDX plywood for the floor. Since the flooring would be protected by the shed itself, 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 taken that into consideration when I built the shed. Had I done so, I would have used pressure-treated plywood, which is what I used when I replaced the floor.
Expected Lifespan of Plywood
It is almost impossible to accurately ascertain the lifespan of any wood. Much depends on the plywood product used, how it is installed, how well it is finished and the environment it is subject to. There are a few averages you can expect, but they are dependent 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 projects which are kept indoors, such as children’s furniture, could last virtually forever. In that case, it isn’t the environment which makes a difference, but wear and tear that does. While children can be rough on furniture, they just don’t have the strength to damage most plywood products. That would require them using a rock to pound on it or a pocket knife to carve their initials in it.
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 a part of normal maintenance. How often you need to paint depends largely on the surface preparation and priming, as well as how many coats and what quality of paint you use.
There are many factors that determine how long the panels of plywood are going to remain in their true form and would not degrade. The following are some of the factors that might have an effect on the lifespan of plywood.
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 you are certain that it is of a 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 is highly likely that it is not going to last.
Such plywood can usually be identified because it has a lumpy surface from the presses and rollers, as well as voids present in the inner veneers. The presence of these is a hallmark of its inferior quality. Buying plywood for any kind of 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 the growth of mold, attacking the adhesive and furthering the process of delaminating the wood.
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 of time. This is the reason why plywood used in houses that are located in humid areas does not last that long and degrades much more quickly. If you are building in such an area, it is important to buy plywood which has a high level of water repellency.
However, the moisture in the air isn’t as much of an issue as allowing the plywood to be in direct contact with water. There are a number of ways this can happen; but if a home is properly built, they 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 all the way to the ground. Properly installed, it should be several inches off the ground, not only to protect from direct contact with the soil, but also with wet grass. Avoid stacking bricks, stone or especially dirt against the side of the house.
- 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 that it is waterproof. The longer it is exposed, the greater a 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 that is used in construction of our homes, but rather with projects we construct to go with our homes. Plywood is often used in the building of doghouses, sheds and storage bins, all of which are regularly exposed to the elements. Yet we don’t take the same sort of care with building those projects, as we would in building a home. Therefore, it’s not uncommon to see water damage occurring 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 the manufacture of these products, they pass through chemical treatment processes. The specific chemicals and treatments process used for making a particular type of plywood determine the qualities and features it would have and consequently its 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 up 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 plywood family, is gradually taking over from exterior grade softwood plywood. The improved manufacturing process used in making this plywood allows for more exposure to moisture than traditional CDX plywood. This should also lead to a greater lifespan.
These are only a few of the factors that affect the life expectancy of plywood. There are a number of other factors that 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 then there is a chance that it might last longer than its expected lifespan.