Taking another crack at this, one aspect is that many conifers take what's left after the angiosperms, with their typically-faster growth rate, have taken the better sites. Let me offer just one example, that of Thuja occidentalis up at my land in NE Wisconsin: A part of this land is straight-up swamp, that is, a forested wetland. The "cedar"-the colloquial name for this species,is able to colonize areas having water table essentially within an inch of the surface. I kid you not, when we dig there, the holes immediately fill with water. This coniferous species also grows well on higher, more well-drained sites, but is easily surpassed in growth in such locations by pioneering aspens, birch, maple, etc. So in this one case, the Thuja is taking what's available to it-water-logged soils. Tamarack, another well-known swamp species is exactly the same way. Plant tamarack on an upland site and protect it from encroaching hardwoods, and it will grow very well. but it has essentially no shade tolerance, and left to its own devices would quickly become overtopped by the same hardwood species mentioned earlier. Now do realize, nature is full of niches and diverse situations. What I've described here is just one such item-there are many more. Pyric plant communities are another area where certain conifers, usually pines, can dominate, so long as that fire is not withheld for too long. Think of the great pine woods (whatever is left) of the SE coastal plain of the US. Fires would periodically go through these areas, killing off shrubby species as well as non-fire-adapted tree types, but the pines, with their specialized bark, would survive these fires. The result was the beautiful rather open woods of these areas, replete with saw palmetto understory, etc. If you want to see what happens when man's activities interrupt this process, throwing in some exotic invasive species, look at the demise of the slash pine woods of S. Florida, now with "ladder fuels" allowing fire to climb up into the tops of the pines and thus killing them too. Sad situation, but nobody wants the Walmart to catch fire-well, maybe most don't! In this case, it's man's control of fire, along with the invasion of primarily Malaleuca-an Australian species now virtually extinct in Australia-that is effecting this changeover. Those woods are doomed. There are as many more explanations as there are forest cover types....and that's a lot of types! +oM

brickeyee Your point about RH of winter air seems well taken. What was missing from the Carson Dunlop explanation, I think, is that attic air in a home is often more humid than air outside the attic due to leakage from the conditioned to unconditioned space. Here's how another P.E. describes truss uplift: "A problem that can occur with this system causes cracks in wallboard over time. In recent years, attic insulation usage has increased, which ends up covering the bottom chord of the truss. This tends to keep the bottom chords warm and dry while the top chords absorb moisture and expand. The top cord expansion causes the top chords to lift, pulling up the bottom chord as shown in Figure 1, hence the term truss uplift. " Charles C. Roberts, Jr., Ph. D., P.E. My untrained guess would be that the lengthwise shrinkage of grain does not relate to the length of the wood but to which portion of the tree the wood was cut from. Here's a longer explanation: "Truss uplift is caused by wood's natural response to moisture exposure. This response occurs when humidity changes differentially in two areas (an attic floor and attic ceiling, for example). A truss's top chords expand as their moisture content increases. Problems resulting from truss uplift are most common with flat-bottomed trusses in homes during winter when a truss's bottom chords, often covered by insulation, are kept warm and dry while its top chords are exposed to moisture from condensation. During winter months, warm, humid air emanates from buildings' interior use and occupants. The uplift movement occurs because, as the truss's upper components resize themselves under the differential moisture conditions, internal tensile stress occurs in the truss's web members, which then pulls up the bottom chords (and the attached ceiling drywall), resulting in a separation along the wall-to-ceiling juncture of the drywall. To put this into perspective, consider a truss with top chords made of two members, each measuring 30 feet in length. The total movement anticipated from winter swelling caused by the truss's moisture content increasing is a 0.72-inch expansion per side, or a 1-inch total rise of ridge above the bottom chords. And once a crack forms inside a home, additional moisture generated by occupants and their activities can escape into the attic, travel to the cold attic ceiling surface, condense on the truss's top chords and cause further truss uplift. " Lucas J. Hamilton manager of building science applications, CertainTeed Corp.'s Insulation Group For interest, I will forward this thread with a request for comments to Carson Dunlop. lzerarc As I said, different places, different practices. I've changed only reluctantly. Seeing those spindly stuck-together 2x2s gives me a visceral reaction and I have to rationalize using roof trusses. However, my engineer says they're much better done now than ever and with wall lengths less than 50 feet uplift is rare. None of this applies to warm climate homes.

Count me in for the engineered wood plank floors too. I have Robbins Passeggiata 3 1/4" ash flooring, and I absolutely love it. I live in NH - arid winters and malarial summers, no AC and forced-hot-water heat so the moisture levels swing drastically). Others I knew with solid hardwood floors got gaps every winter and that just drives me NUTS because the cracks between the boards can collect dirt and expose unfinished wood where moisture can infiltrate and spoil the finish. People are very stubborn here about "solid wood has done us fine for 300 years, it'll be fine for another 300!" so I had to fight to get engineered instead of site-finished solid that is the standard here. Site finishing was not an option because we couldn't move out for installation! Besides, I do believe that the factory finishes are more durable than site-applied finishes, since they have the benefit of controlled conditions, kiln curing, etc. (We bought an extra bundle because we knew we'd have to patch the spot by the dog's bed since his nails grow at turbo speed and the floor's pretty gouged.) I adored the look of the extra wide planks, especially the distressed and handscraped types in 7"-plus widths, but they were just SO expensive! I paid $9/sf installed for my Robbins flooring while many of the wide-plank floors I looked at ran much more than that just for the materials for a good quality product. *choke* Bruce has some relatively-inexpensive 5-7" plank floors at around $6-7/sf uninstalled but I'm just not knocked out by their finish quality, the planks were either square-edge (sock-catchers if your floors are not perfectly flat) or had a deeper bevel than I liked, and their veneer layer is thinner than Robbins. Robbins warrants for three full refinishings! As of early 2005 they had the thickest veneer layer in the industry, a full third of the board's thickness. I like their extremely small microbevel as well because it doesn't catch dirt, it sweeps out fine and you don't catch your socks (or worse chip the floorboards where there's raised bits due to subfloor imperfection). I'm not one for strip floors, I find them too busy. Besides, I am an old-house nut, and old New England houses had wide-plank floors, not these stingy little strips! I visited one early-1800s house on the town's historical society house tour where the narrowest board on the floor was 12", many were 16" and even 20", all rock-hard pine. Had I had gobs of greenbacks and a house that could carry it, I'd have gone for wide planks in reclaimed wood. *swoon*

Plastic does not last a lifetime. What utter crap. Take windows. Wood, single-pane windows will easily last 100 years with maintenance. Vinyl windows will last no more than 20. Hardwood floors can be refinished 3-4x and scraped and recoated innumerable times, also frequently lasting well over 100 years. LVP? 20 is a HUGE stretch. Try 5, 10 if you're lucky. People use plastic because they have been sold on the fact that it is "durable" and "low maintenance" and "cheaper," which may be true if you're speaking in terms of 5 or 10 years. But the costs - actual and environmental - are much higher when you acknowledge that its life cycle is much shorter than natural wood products that can last 3-10x longer. Then add in the fact that manufacturing new plastic on that shorter cycle is terrible for the environment, too, and the real costs become obvious. The idea that LVP is used in "high end" homes is an odd one. Where I live, it's only used in the basement of high-end houses, where hardwood obviously isn't suitable. It would be a huge red flag to see LVP anywhere on the main floors of a house, even under $1m.