GREENER OR BROWNER?

Back in the not-so-Jolly Old England of the Middle Ages, where many of America’s  building traditions originated, no one had ever heard of structural engineering. Instead, carpenters used common knowledge gleaned from trial and error and handed down over the centuries. With no way to analyze the strength of their buildings, they just built them as stoutly as they could, using massive timbers hewn from lots and lots of trees. 

For example, records show that one six-room, two story house built in Cambridgeshire around 1600 required seventy-two small oak trees to be cut down for the framing lumber alone. Seven more mature oak trees (which yielded wider planks) were sawn into floorboards. The total wood used was equivalent to about 68 acres of oak forest. A larger house could easily consume over 300 trees--more than 280 acres of woodland as it then existed.

Given the rate at which these houses gobbled timber, the English were already managing their forests for harvesting by 1200. Even so, over the next few centuries, the island famed for Sherwood Forest became the sparsely wooded place it is today.

Fast forward to America during the postwar Baby Boom era. Our houses are constructed with a light framework of slender wooden studs, doing away with the need for heavy timber. It’s a relatively efficient system--an average house of 1950 uses about 9000  board feet of framing lumber, or about 9 board feet per square foot (a board foot is a hypothetical quantity of lumber twelve inches by twelve inches by one inch thick). At a crude average of perhaps 200 board feet per tree, this means we cut down something on the order of 45 trees--mostly softwoods--to build a house. No matter how we, er, slice it, it’s quite a bit less lumber than your average English house of the Middle Ages required. 

But fast forward once again to the present, and you find a strange irony: Today, even though we manage to use even less lumber per square foot than in 1950--only about 8 board feet--the amount of wood we use has nearly doubled, to about 17,000 board feet per house. That’s back up to about 85 trees--even more than were used during the Middle Ages. 

What gives?

For one thing, modern building codes require wood-framed structures to withstand much higher wind and earthquake forces than before, and that takes more lumber and plywood. For another, houses also have more rooms, and hence more interior walls. 

But the main reason we’re back to gobbling wood is simply this: Today’s average house is much bigger--over double the size of a typical house of 1950. In short, we’ve wiped out all the gains we’ve made in using wood more efficiently, simply by using a whole lot more of it. 

Now, one bright spot in cutting down so many of England’s oaks is that some wonderful houses of the Middle Ages are still with us. How many McMansions will still be standing in 2500 A.D.?