Exterior Wood Siding

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People generally think that wood is the least durable of all sidings, and some of what I’ve written would support that. However, certain woods known for moisture resistance will weather very well.

Walnut

A fable for today’s homebuilder: Not far from my place stands a clapboard house whose exterior wood is entirely black walnut. Some of the interior framing is black walnut, too. The house has stood empty for many years, but it's still square, straight, and undecayed. If you know your woods, this will not surprise you. Black walnut is at least as resistant to decay in the weather as cedar and redwood (See R. Bruce Hoadley’s book Understanding Wood, The Taunton Press, for a good grasp of the properties of various kinds of wood.) But who would be so stupid or rich to use such valuable wood for siding?

The answer is that black walnut was once common and plentiful in the Midwest , from Pennsylvania to Iowa , and could still be with a little foresight. We cut down most of the forest where black walnut likes to grow because that’s where corn grows best, too. Now we have such a surplus of corn that the government pays billions of dollars in subsidies (read tax payer money) to keep corn farmers from going broke, while the price of black walnut rises until some foresters refer to it as black gold. The tree will grow literally like a weed, if given half a chance. Where there is an old tree to produce seeds, the seedlings will spring up as if by magic in old pastures, as they are doing on land I am taking back to forest.

Recently I walked a wooded creek valley that just 16 years ago was clear pasture. To my amazement, the young woodland was studded with black walnut trees already 6 to 8 inches in diameter and 20 feet high or more to the first limb. Thousands and thousands of acres of such little valleys cultivated for corn every year (they flood out three out of four years) should be growing black walnut, enough even for beautiful, long-lasting house siding.

But what is that to a modern homebuyer who can only shed so many tears for the past while he worries about his present alternatives? Not much perhaps, but eventually the same tragedy will occur with cedar and redwood, about the only available woods left that will endure as house siding without regular painting. Secondly, a lucky few in the right place with the right knowledge might be able to buy black walnut logs too defective for the high veneer price or even the high-grade furniture market and buy them reasonably for random board siding or for shingles. Sounds fantastic, but I had a couple of logs that timber buyers wouldn’t even pay firewood prices for. They would have made fine shingles.

Mesquite

In northern Mexico and some parts of our own Southwest, there are stone houses dating from the latter 1700s with exposed lintels over doors and windows made of mesquite—still solid. Mesquite is a very durable wood, as these lintels prove. And why is that of special note? Because in the Southwest, especially in west Texas, ranchers have been trying (unsuccessfully) to kill about 58 million acres of mesquite to make pasture for cattle whose red meat is not only in surplus but also now of questionable dietary value. In addition to its low-maintenance durability, mesquite machines well, takes a beautiful finish, and makes quality parquet floors. All it needs to become commercially valuable is to grow larger in size, which it has not been able to do in the last half century because of ranchers hell-bent on playing cowboy at the expense of the ecology of west Texas.

Black Locust

The best example I can give of a really durable low-maintenance wood is black locust, all but ignored in this country. Black locust will last in contact with moist soil for 30 or 40 years, no preservatives needed. Aboveground, it will outlast a human life, or two. Researchers have discovered it contains a natural fungicide. The wood is, in addition, very strong and very hard when thy. It makes excellent hardwood and parquet flooring. When it bums, it puts out a lot of British thermal units (Btu), so it makes good firewood. Black locust grows relatively fast; is a legume that enriches the soil it grows in; will tolerate a wide range of soil types and climates; and its prodigious blossoms produce a superior honey.

America, the native home of this tree, has nevertheless lost interest in it since the 1930s, when much work was done by the U.S. Department of Agriculture to develop superior strains. But in Europe and Asia, led by Hungary where today the main research efforts are underway, man planted forests of black locust increased from 337,000 hectares to 1,890,000 hectares between 1958 and 1978. And that doesn’t take into account huge forestation projects with black locust in China.

What scientists are particularly excited about is the strain discovered in 1936 in the United States, referred to as “shipmast locust” because of its habit of growing a straight, tall trunk, excellent for commercial lumbering. Thousands of these trees have been planted in other countries and work continues. But not in the United States. I suppose when redwood and cedar finally become too expensive to use for home exteriors, we will import locust from Hungary.

Be that as it may, there is plenty of black locust around yet. If you are a do-it-yourselfer looking for a really long-lasting siding for your house, have some black locust sawed into planks and strips for board-and-batten siding. You’ll have to go to local sawmills—commercial lumberyard dealers will stare strangely at you and tell you how hard it's to pound nails into locust. When I hear that, I stare back just as strangely and say it’s hard to pound nails into masonry, too, but we have the nails to do it and it’s done all the time.

Cedar and Redwood Sidings

Western red cedar and redwood are, for all practical purposes, the choices you have for a durable natural wood exterior that you don’t have to spend lots of time painting or staining regularly. Redwood is better and more expensive, but both are good, so long as they come from big trees with lots of heartwood. Wood from the heart of a tree is more decay resistant, and wood from the heart of a big old tree is the most resistant of all as long as the tree is healthy. Thus, you will see many old barns with siding over a century old, weathered gray but solid. That wood came from the virgin forests, trees you will not see in our day unless you visit remnant old-growth forests protected by law. Second- and third-growth lumber, 50 to 70 years in the growing, or even 100 years, can’t match wood from trees 200 to 300 years old or more.

In the dry West, redwood siding will easily last a lifetime without any treatment at all, and cedar-shingled houses in cold New England have resisted decay for over a century. Cedar shingles are especially adaptive to seaside environments, which is why you see so many cedar-shingled houses along the New England coast. All woods resist salt spray better than metal, but the salt actually improves the rot-resistance of unpainted cedar shingles. That’s why they last 100 years along the coast of Maine.

But given that I live in a landlocked state, there is no salt air to help preserve the cedar siding I just bought for a new building. And because the siding has quite a few “tight knots,” as they call them, I intend to put on an initial coating of a penetrating stain and preservative to make sure it lasts a lifetime.

Other Woods

Green rough-sawn board and batten from a local sawmill, a full inch thick, is strong, insulative, and durable. And a great buy. Expect to pay, right now, 704: to 804: a board foot, maybe less if you deal sharply. Of the commonly available woods, oak is best in my part of the country.

For whatever kind of siding you decide to use, the following list contains those woods that are very resistant to decay. If you are not using pressure-treated wood, these are the ones for low maintenance. Most of them, unfortunately, are not available for siding. Catalpa, for example, is becoming a rare wood, as all the old catalpa orchards, grown for fence posts a century ago, have mostly been bulldozed away for corn. Catalpa will last nearly as long as black locust, but has the added advantage of taking nails easily after it's dry. Wood-carvers love it. Chestnut, of course, is almost gone, and it would be difficult to find logs of some of these woods, like Pacific yew, large enough for siding possibilities.

  • Bald cypress (especially old growth)
  • Black locust
  • Black walnut
  • Black or wild cherry
  • Catalpa
  • Cedars (especially Atlantic white cedar, much used for shingles in the East; Northern white cedar, much used for log homes; and Western red cedar, the principal source for cedar shakes and shingles)
  • Chestnut
  • Junipers (Eastern red cedar is a juniper)
  • Mesquite
  • Mulberry (especially red mulberrry)
  • Osage orange
  • Pacific yew
  • Redwood
  • Sassafras
  • White oaks (including bur oak, chestnut oak, gambel oak, Oregon white oak, and post oak)

The following woods are moderately resistant to decay, requiring regular maintenance when used as house exteriors:

  • Bald cypress (young growth)
  • Douglas fir
  • Eastern white pine
  • Honey locust
  • Southern yellow pine (longleaf pine, slash pine)
  • Swamp chestnut oak
  • Tamarack
  • Western larch

Board and Batten

Board arid batten came into vogue precisely because many hard woods when dry are very hard to drive nails into. When the wood is green, however, nails can be driven in as easily as they can in pine. But green boards shrink as they thy, opening cracks wide enough to let a blizzard inside. So strips wide enough to cover any shrinkage cracks were nailed over the junctures between boards. The vertical boards and the diagonal boards so popular today also shed water better and resist rotting better than horizontally lapped boards, although with black locust as with other rot-resistant boards, lapped horizontal siding works nearly as well if put on green. The pattern of board and batten appealed to many people decoratively, and so a favorite American house style was born. The supreme compliment: it’s imitated in metal and other man-made sidings now.

Board and batten is a very practical siding. Thinner boards that cover the gaps between wider boards allow the wood to expand and contract without cracking or leaving gaps exposed to the weather. This is a particularly good siding to use with green wood.

Board and batten is one of the most forgiving ways to build an exterior wall. Precise, professional fitting of boards is not necessary since the battens cover any slight misalignment between boards, and trim over the top plate covers slight mistakes in measurement made there. Varying thickness and width of boards sawed by the somewhat crude machinery of local sawmills does not much matter either. Board and batten is a good siding for a beginner. Just remember to nail the battens onto just one side of a crack or the shrinking boards will crack the batten in two. Always remember that wood moves—swells during humid weather, shrinks during dry. Board and batten is one of the simplest and cheapest solutions to this characteristic of wood. (The shrinkage is mostly lateral, through the width of a board. The lengthwise shrinkage is very small and negligible in board-and-batten construction.)

Penetrating Oils and Stains for Cedar, Redwood, and Other Sidings

The Red Cedar Shingle and Hand Split Shake Bureau ( 515 116th Avenue NE, Suite 275, Bellevue, WA 98004) says a penetrating oil alone will protect cedar. It would also protect other natural woods noted as very resistant to decay in the list on page 59 used in a dry climate, but an oil with a preservative fungicide is advisable in warm, damp climates like Florida. The Bureau recommends Wood Guard and Wood Life, available in most paint stores. A little checking will familiarize you with many other good products, especially Cuprinol and the Olympic Stain products.

Even if you aren’t worried about decay or mildew problems, another reason for treating natural wood siding with a penetrating stain is to preserve the fresh appearance of the wood. I like the fresh-cut look of red cedar, not the weathered gray, and would use a stain that darkens it a bit toward brown. There are scores of colors to choose from.

Penetrating oils and stains can be brushed or sprayed on, but the best way on rough sidings like cedar is to spray and follow up immediately with a brush, working the liquid well into the wood. You want to get plenty on, as the raw wood will soak up the stain like a thirsty blotter. Each product has its own instructions to follow.

Since the basic ingredient is often linseed oil with pigment added, in theory, the more coats applied over the years the better. But several coats are not really necessary with wood siding. Once every five years is not a bad idea in humid climates, if you wish the siding to last indefinitely. But one good soaking coat that gets into all the cracks and crevices, coupled with a good job of sealing joints around windows and doors with caulking or putty, should suffice. In very humid climates, wood siding as I have tried to convey, is not a good low-maintenance alternative. People, especially younger people, don’t like to hear that it’s not a good choice if they are very fond of wood because to them 20 years seems like a long time. Ah, if only that were true.

If you do have to paint, or repaint, or restain, there’s a product on the market to make that horrid job of scraping off loose old coatings a lot easier. Called Restore-X (Restech Industries, Inc., P.O. Box 2747, Eugene, OR 97402), it uses buffered, sodium hydroxide-based compounds to re move deteriorated paint, stain, and even the graying effects of weathering. It is biodegradable, water soluble, and environmentally safe. It will not remove well-bonded paint—just the loose stuff you normally have to scrape or sand off. It dissolves old loosened paint or stain on wood, stucco, brick, concrete, metal and aluminum, but doesn’t work for epoxy, baked enamel, or urethane coatings. You can apply it with a synthetic bristle brush, mop, or roller. Apply in a thick coat and then wait for the liquid to work on the old paint. When the old paint is ready, simply hose it off.

The Rodale Technical Group has independently tested Restore-X with good results. “Both the paint remover and the wood renewer do the job,” they reported. “The former is powerful but biodegradable; the latter keeps water from soaking into wood decks. Both make maintaining wood products easier.” In applying Restore-X, use eye protection and wear rubber gloves for safety.

Between the lines, Restore-Xis really high maintenance. It’s what you use when exterior painted and stained surfaces start giving you a head ache. Olympic’s ads show peeling paint of its competitors beside its own unpeeling brand. Cuprinol shows a deteriorating stain on a wood siding in its ad with a question: “If all oil stains protect, what happened here?” The bottom line is that if you want the beauty of wood, high-maintenance is your inheritance.

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Updated: Tuesday, April 14, 2009 15:55