How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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What is the average life expectancy of wood siding?
Friday, July 27, 2018
Wood siding should last 20 to 40 years, with an average of 30 years, but can remain in good condition much longer with meticulous maintenance of the paint and caulking to keep water from entering the wood. Here are six variables that will increase or decrease the life of your wood siding compared to the average:
1) Type of wood - Wood decay fungi, commonly called wood rot, is the #1 enemy of wood siding. When the moisture level of the wood rises above 20%, colonies of the fungi form and began eating—literally digesting—the wood, from the surface inward. Redwood, western cedar and cypress are examples of woods that are naturally resistant to wood rot. They eventually succumb if not protected with a waterproof coating, but it happens later rather than sooner.
Also, woods like pine, which have lower rot-resistance, can be pressure-treated with chemicals that prevent wood fungi growth. “Yellawood” is one one popular national brand of pressure-treated wood.
2) Location on home - Siding on walls that are in shade most of the day, either due to their orientation to the sun or overhanging trees, is more likely to deteriorate sooner because the surface stays moist longer. Conversely, siding in a Florida climate that faces the blazing sun in a southern exposure all day may be prone to early wood rot because the waterproofing or paint finish deteriorates faster if not maintained. Siding near the ground suffers due to splash-back of rain falling from the drip edge of any roof without gutters.
3) Maintenance of paint finish and caulking - Dry wood does not rot. It’s that simple. Keeping a waterproof barrier between the wood surface and the weather, using paint or another waterproof coating on the surface of the wood and caulk at any seams, is important. Although siding with rustic, weather-worn paint has lots of “character,” it’s also the most vulnerable to wood rot.
What is commonly called “dry rot” is a misnomer. The term has been used to describe decayed wood that has since dried and ceased decay. Some people erroneously assume that the wood is still in the process of decay but, because moisture is required for wood rot, no literal “dry rot” exists.
4) Water traps - When wood siding and trim is installed improperly, so that a surface is created that is not slanted or sealed properly, if it holds even a small puddle of water after a rainfall, that’s called a “water trap.” Construction professionals diligently avoid them because wood rot always starts at the water traps first. Examples of water traps would be an exterior window sill that does not sland away from the wall and any uncaulked seams at exterior wood trim.
5) Siding profile - Some of the fancier profiles for wood lap siding seem to have a shorter life. The one shown in the photo at the top of this page, called “novelty” siding, is an example. The scoop shape under each lap tends to lose it’s paint finish sooner, making it slightly more vulnerable to rot in that area.
6) Type of wood - Although any wood siding has a long life if kept meticulouly painted and sealed from moisture intrusion, some types can handle wetness better over time. Solid wood and “engineered” are better, and composite wood and plywood not as good at resisting moisture. See our blog posts What is the difference between "composite" and regular wood siding? and What is Z flashing? for more on this.
What can you do to make your wood siding last longer? Carefully maintain the paint finish and caulking around openings, and eliminate any water traps. Dry wood will theoretically last forever; but, of course, that never happens.
Here’s a bar graph that compares the life expectancy of wood to other types of residential siding.
Go to our blog post What is the average lifespan of the parts of a house? for rating of other house components. To understand the basis, potential use, and limitations of lifespan ratings, see our blog post ”How accurate are the average life expectancy ratings of home components? Are they actually useful?”
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To learn more about exterior walls and structures, see these other blog posts:
NOTE: These life expectancies are based on data provided by InterNACHI, NAHB, FannieMae, and our own professional experience. Because of the numerous variables that can affect a lifespan, they should be used as rough guidelines only, and not relied upon as a warranty or guarantee of future performance.
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