Last wood wont load
Specify “all-heart” and you may be in for a dose of sticker shock. Heartwood lumber is essentially unavailable in many species. We now harvest smaller second-growth material that contains a high percentage of sapwood. Large old-growth trees are a thing of the past. You can expect a short service life if you use sapwood in decay-producing exposures. Untreated sapwood of virtually all species has very little decay resistance. Only the heartwood of certain species is naturally decay resistant. Not all siding, decking and trim made from cedar, redwood or other species famous for durability are in fact rot resistant. Like fingernails on a blackboard, homeowners bubble, “I have cedar siding.” Don’t get me wrong cedar is my choice for siding too, but let’s get something straight. The USDA Forest Products Laboratory in Madison has a pamphlet (FPL-RN-0268) listing outdoor EMC’s for about 350 cities worldwide. In Tucson, a 6% MC would be a better mark. Wood used in exterior applications is a different story – it depends on where you live. Wood used inside of homes as finished trim, cabinets and flooring, should be installed at a MC close to 8%. The in-service MC or equilibrium moisture content (EMC), can be benchmarked to relative humidity: It is important to match the MC of the wood you are using with the equilibrium conditions it will see in service. Spot check the lumber you are using with a moisture meter. A KD stamping means very little if the lumber has been left sitting in the rain at a distribution center, reload yard, retail yard or building site. Lumber stored in a very humid environment like next to the ocean can sponge water too. The MC of lumber can soar when is stored at a lumber yard without a protective cover and/or stacked over wet ground. You don’t know its current moisture condition! But these designations only indicate the MC of the lumber when it was manufactured. Other choices are lumber stamped MC 15 or KD 15 for lumber surfaced at 15% MC or lower. This means that the lumber was surfaced when it was at or below 19% MC. The installed MC was over 50%! The remedy was expensive.īuilders can also specify lumber stamped S-DRY (surfaced dry) or KD (kiln dry). In a recent case, S-GRN Douglas Fir 2×10’s were shipped from the west coast, box-piled for months and then installed in a rotted state. Believe it or not, I have been called to examine rotten joists in brand new homes.
S-GRN indicates that the wood was surfaced to its finished shape when the MC was above 19%. But they’re buying shrinkage problems and callbacks. Builders may think they’re getting a deal buying the least expensive S-GRN (surfaced green) lumber. We pay manufacturers to remove at least some moisture. Seldom do we buy “green” fully swollen lumber. Wood shrinks and swells in response to liquid water and relative humidity. But wood will only shrink and swell below its fiber saturation point, which is around 28% moisture content (MC). Conventional wisdom tells us when wood absorbs water it swells and when wood dries it shrinks. Peeling paint, rot, warp, cracks and general shrinkage are all related to water in wood. Virtually all problems with wood-based building materials are moisture problems. 1) Kiln dry (KD) and S-DRY lumber means dry lumber. In the following article, we’ll consider some common notions about wood, and see how they compare with the cold, hard facts. But even experts can be mistaken, and you may be surprised to learn that some of what you know about wood is wrong.
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As builders, we spend much of our time cutting wood, carrying it around or pounding it full of nails. If you say something loud enough and often enough, somehow it becomes true. Setting the record straight on common misbeliefs about the material we use everyday. Some information contained in it may be outdated. Please note: This older article by our former faculty member remains available on our site for archival purposes.