A word on Exterior Wood Joinery Techniques

Charles Prowell's articles on joinery have appeared in Fine Woodworking, Fine Homebuilding, Woodwork, Old House Journal, and This Old House, among others.

There has been a fair amount of hullabaloo recently regarding the joinery best suited for not only the stile and rail garden gates developed by CPW in the early 90's, but exterior assemblies in general. Exterior joinery is all about the properties of specific woods and their corresponding dimensional stability. There are emphatic do's and don't's far beyond what the site carpenter might understand, with his stackable designs. This is all we saw, for so many centuries, and continue to see day in and day out from renderings and blueprints sent to us from architects all over the country. Levels of an assembly applied to one another in a stacking sequence. This applies most traditionally to exterior pergolas and trellises and arbors, but as well to the Wood Fence and the Wood Gate. In time, and very little time at that, the various applied levels separate from one another. They cup and bow and warp and open to unsightly joints, while offering virtually no integrity to the lateral stability of the design itself. Large cumbersome 45-degree corbels and braces are incorporated into the design to help serve this end, and yet because they are jointed by nothing more than nails or screws, their effectiveness is, well . . . limited, not to mention downright unsightly.

For an eternity it was a struggle between the builder, raised for the most part under the scope of structures. Or the architect schooled in stress loads and spans and form. This pitted against the classical woodworker, apprenticing toward an entirely different genre. Two very distinct trades, crossing paths to some degree centuries ago with the traditional post-and-lintel framing methods of the New England Puritans and Amish, but long since separated and exasperated dramatically in the late 1940's with the onset of housing tracks that stressed speed and a nominal integrity for the sake of affordable housing.

To be sure, there are excellent contractors and carpenters among us today. Hold-outs who once served adequate apprenticeships and who offer a high level of workmanship and acumen within their trade. These however are an increasing minority. Over the past twenty years an entire generation has migrated into the tech industry for quick monetary returns, leaving a vacuum that is only now beginning to have an impact. Furthered by a prolonged economic drought that began in 2007 to reduce even more. Acknowledging those remaining builders and carpenters who are held to their own high standards, what remains is a slough of Johnny-come-latelies, ill-trained and ill-equipped to neither meet, nor carry on, the standards of their predecessors less than one generation removed.

For decades CPW has dealt with hundreds and hundreds of builders and carpenters over the years as potential installers for the assemblies shipped all over the country. You might say we, more so than most, have our finger on the pulse of a changing trade. A trade where the norm is now fielded by those who have simply not served an adequate apprenticeship to perform their work at a professional level. And when we do stumble upon the rare tradesman of an irreproachable workmanship and experience, they are immediately entered into the redox and referred happily to those prospective patrons in need of such.

Much the same with the sister trade of woodworking, cabinet-making, even furniture-making. For those who can afford a two-year apprenticing guild, their schooling is largely relegated to a tolerance that eschews the large rambling structural scope of a builder. We might compare it to the poet and the novelist. The poet fixated on the minutia of words and phonetics and the cadence of a phrase, whereas the novelist sees the large sweeping storylines and relevant themes and by the nature of this, is far less focused on the minutia of linguistics.

The woodworker understands tight joints and an array of joints appropriate for various purposes and a method of construction that has almost no commonality with the builder beyond the criteria of an end product that is structurally sound. They do not work in the same woods nor share the same toolry nor even a common ground on their workplaces; one in the field and all the unforeseen problems of site work, and the other in the controlled environment of a shop, where everything is within reach and there are few distractions and almost never the head-scratching issues that develop from retrofitting an old existing structure known specifically to the remodeler--who in our litany of tradesman within a trade, is as distinct from the builder as the short story writer from the novelist.

I was raised by a builder. A step-father who arrived on the scene when I was 6 or 7. A remodeler who turned builder who exposed me to every aspect of both the remodeling and home-building trades from the time I was a boy all the way through college. A builder who spent weekends and evenings on the phone scheduling electricians and plumbers and roofers and sheetrockers and painters and cabinetmakers and concrete crews and stone masons and tilers and who somehow managed to now and again strap on his tool belt and swing his hammer. Immersed in this world as a little kid left with the crews who took their lunch brakes to wallow in conversations as guttural as those of a longshoreman. Pornographic utterances, followed by a wink to the boss' 8-year old son.

But also, my step-father's father, who had a woodworking shop in his basement in Champaign, Illinois. A part-time furniture-maker who worked alone and without the confusion of coordinating others and from him, on Saturday mornings, I absorbed by comparison an almost Zen-like focus of an entirely different trade. A trade of 64ths of an inch and dry-fitted joints and re-cutting joints until the dry-fitting was a melding puzzle and the properties of wood itself. Properties that were largely of no concern to the builders in the field. What I learned is that the two trades seldom communicated with one another and how to the builder, the woodworker was another sub-contractor no different than the plumber or painter.

So it's no wonder their trade secrets remained secrets. It's no wonder the woodworker never understood the nature of assemblies and structures and stress loads and working on site with portable tools drawn from a toolbox mounted to a pick-up truck. The very idea of their constructions being subjected to sleet and snow and hurricanes and tornadoes and urinating dog is beyond the acceptable scope of the woodworker. And the builder, who who could no more conceptualize the notion of a controlled interlocking haunch tenon than a layman plucked from the crowd. The notion of matching grains for glue-ups and constructing an assembly without fasteners or brackets and the exorbitant time it required to create something so small, if compared to . . . to a barn.

And perhaps this alone explains why exterior assemblies and structures have remained the domain of the builder. A methodology following the same methodology practiced in building a porch or a deck or a framed wall. Layers upon layers stacked upon one another and fastened by screws or nails or bolts and later, by screwguns and nailers driven by compressed air. Accomplishing their structural and lateral rigidity with cumbersome 45-degree corbels or heavy-gauge iron bracketing as if a pergola or trellis were a barn. The heavy, muscular, over-wrought aesthetics of generations upon generations of exterior assemblies built on the predicate of builders who are not woodworkers or woodworks who are not builders and how the two traded methodologies as if they were Republicans and Democrats. How the woodworker might be confused with something he built in his shop being shipped from the temperate climate of San Francisco to Mississippi or Hawaii, where the relative humidity is a major, major factor on just how long his work will survive the dramatic expansions and contractions of regional climates. The dramatic disparity of regional climates separated often by 3,000 miles from the shop where it was built. My step-grandfather's shop did not pay.

Nor did languishing in the attic beside my mother, an artist and painter, enthralled by the act itself of brush strokes and the accumulations of enough strokes developed into a concept and of course, the drunken odor of oil paints. it was the job sites that paid. Job sites that changed like revolving doors until by the time I was of college age, I could frame a house--it's walls and jack rafters and stairs. I could shingle a roof, pour and smooth a concrete driveway, lay a stone wall, shingle a side-wall, sheetrock and tape the walls, lay the stone or linoleum tile, build the cabinets for the kitchen and bath, run the romex, hand-cut the miters for the casings and trim, and build the gate and fence. By that time I leaped at the opportunity to leave it all and relished the idea of five years in college. Five years bouncing from architecture to art to design under Buckminster Fuller to anything at some juncture that kept me and everyone I knew from being drafted. But graduation from Southern Illinois University came and three days later I left for a San Francisco where I knew no one. Not a soul. Where in those days Folsum Street was one long string of woodworking shops when shops could actually afford to locate in San Francisco. A mecca of woodworkers who owned and controlled what is now known as the trendy SOMA district.

Years passed, experimenting and gathering techniques and slowly learning to combine the apprenticeship that began as a boy, sharing his tutelage between the ancestry of a builder and that of a woodworker. Developments were accomplished. Innovations in design were made. Backlogged schedules. By the mid-80's, children were arriving, cute as buttons, and Charles relegated himself to the shop exclusively, closer to the 'Buttons', and concentrated on developing a line of studio furniture, along with the help of the newest Prowell apprentice, #2 son Benjamin, swaddling about the shop in his diapers.

Missing the encounters of site work and all that that entails, Charles returned to the landscape of job sites in the mid 90's with the eventual development of what began with the stile and rail Garden Gate. The result of more than two years of prototypes. Who would think such a simple premise would take two years? A simple premise that was apparently too complex to have been initiated by anyone else. The right wood and the right grade of wood; the right joinery to bear the gravity-laden weight of the product for decades; the right joinery to allow expansion/contraction; the right methodology to allow self-drainage; to allow free expansion/contraction that would alleviate the stress compounding from variable climates as a free and floating entity; the proper hardware at a time when there was no proper gate hardware; and not to overlook the medley of designs that mimicked a signature that spoke from a single aesthetic source. And quickly, the same methodology was brought to a modular fence panel and to a driveway gate and to an arbor and to a bench and swing and to lighted columns and about the only thing braking the growth was the dependency on site builders to what they could and could not be expected to reliably install on the site.

Let's have a look at a hierarchy of joints, drawn from Charles' decades of indentured apprenticeship. Some of them common and recognizable, and some of them closer to performance art.

But first, let's start with this. An image of Charles' left hand. As a lefty, it's a fairly important hand. And if you'll notice, after decades of cutting joints, all his fngers are in their proper, original place. On this, his left hand, as well as his right hand.

Missing digits and surgically repaired digits are always the result of one of two factors:
#1) An increasingly hurried pace of work. (Learn to work at one pace, and only one pace, no matter the time of day or the urgency of a deadline. When they speak of Zen and the art of woodworking, it's all about pace. Establishing your pace.)
#2) Attempting a procedure that simply feels wrong. An odd cut or unorthodox approach alerted by your sixth sense. A warning you should listen to. Stop, step away, and reconfigure how better to set up the procedure. Templates? Jigs? It's often the odd manuever that results in what we call a freak accident.

A Gate illustrating the Butt Joint and diagonal bracing.

Early on, while more or less still in test mode, this joint was utilized on all the CPW gates, illustrated thoroughly in an article for Fine Homebuilding magazine. But we came to realize the limitations of the half-lap.
Advantages:
1) A fairly simple joint to fabricate, providing a large mating area, or what might be called the 'glue-mass.'
Disadvantages
1) Wood breathes with the seasons. The red arrows indicates in what direction the wood will breath, expanding and contracting in wet and dry weather. This breathing occurs perpendicular to the direction of the wood grain. The stile, which is the vertical stock of the gate, breathes left and right, or horizontally. This is why there is a 3/8" clearance configured between the net width of your gate and the post or jamb. Now . . .the rails, which are the horizontal stock between the stiles, is going to breath vertically, or perpendicular to the vertical rail. In direct contrast to the stile's movement.
------In furniture design, this is a principle that cannot be slighted, as the result can often lead to a tug of war that results in one of the two members suffering the severe damage of checks and fissures. Why? Because one of the two members is trying desperately to simply breath, which is it's organic right, and yet it is being held in check by the half-lap of the corresponding member. The result, again, is stress. Stress is bad. Stress is at the root of not only schizophrenia and paranoia and a whole bevy of nervous disorders, but it can also result in this half-lap joint opening, loosening, and the opposing member checking and cracking just as a seemingly sane soul begins to slip from sanity.
2) The second issue that arises with the half-lap joint is how the top of the joint is essentially exposed to the rainfall. This in itself is not the most favorable scenario in that a golden rule in exterior carpentry and woodwork is to avoid allowing end-grain to ever be exposed to the vertical fall of the weather, such as rain and snow and the heat of sunlight.
3) The third issue is that the top of the exposed half-lap joint has nothing to thwart it's placement beyond the strength of the adhesives. As we see in the far right illustration, once the joint opens from the exposure to direct weather, then checks and cracks from the opposing grain directions, the rail begins to crack and check under the stress and drops, or sags, with nothing to prevent the lure of a beckoning gravity.

Here we double the glue mass, or mating surface, by having each side of the tenon, or male segment, mating to the inside surfaces of the milled stile. Assuming you are using the right glue, doubling glue mass is good.
Advantages:
1) Double the mating surface--an improvement over the half-lap.
2) Easy to fabricate.
Disadvantages:
1) We have already covered the issues with grain direction and seasonal breathing, and this joint is not exempt from the faults discussed in the above example. Like furniture-making, dimensional changes are not pervasive, but if you are in the business of creating high-end work, you avoid techniques that allow even the slightest margin of error. The Through Tenon joint is the sort of joint you'll see from carpenters and cabinetmaker who have not met the rigors of a proper woodworker's apprenticeship. The Through-Joint, to a contractor, is high art.
2) We have also covered the issue of nothing between the top of the two joint seams and the falling weather.
3) And finally, the right side illustration resulting in our gate giving way, once again, to the madness of gravity. The Through Tenon has no top shoulder, which is a major component of a joint that weighs against the omnipresence of gravity. Whereas the leg-to-apron joint of a dining or coffee table will perform admirably as a through-tenon, the table, unlike the gate, displaces its weight to the floor.

The traditional furnituremaker's joint. Here we have a male tenon milled from the same stock of the horizontal rail. The tenon consequently mates to a corresponding mortise milled into the vertical stile. Assuming a good tight fit has been fabricated, this is a reliable and long-standing favorite among woodworkers and furniture-makers, as well as traditional timber frame homes.
Advantages:
1) The top of the joint is concealed from the falling weather.
2) The top of the joint has what we call a 'shoulder' above the tenon, preventing, by a matter of simple physics, the tenon dropping to the ravages of gravity.
3) No exposed joints or wood seams. If you're going to expose a joint, be sure it's a world-class joint.
Disadvantages:
1) The issue of breathing in opposing directions is debatable. Not so dramatically as our first two examples, but nevertheless we have a tenon that is an extension of the horizontal rail and this tenon is going to expand and contract in a direction that is perpendicular to that of the stile. To many who have not lived and breathed wood principles since childhood, this is dealt with by a shrug and a raised eyebrow. It is relative, in that there are trades, and then crafts, and them artistry. The tolerances tighten with each hierarchy, and the graduations from one to another does not come overnight, nor without proper tutelage.
3) The strength of our joint between the rail and the stile is now resting solely on the properties of the tenon, which is commonly cedar. Not exactly a species exhibiting dense properties.

A natural graduation from the Blind Tenon is the Floating Tenon Joint.  Here we improve upon the more porous cedar tenon by selecting a multiple ply tenon in Russian Birch.
Advantages:
1) Eliminates the issue of the tenon breathing perpendicular to the stiles and rails.  The tenon does not breath.
2) Excellent strength and stability, with it's multiple plys.
Disadvantages:
1) Repeated slamming of an untended gate can conceivably result in a lock stile that cracks from where the Floating Tenon ends and the edge of the stile. 
2) Only a very specific species of marine ply is acceptable. 

  Carrying the above joint two steps further, we have a Full Through Tenon, secured with wedges.  Utilized by Japanese temple builders, the joint is self-sustaining in that it plays to the dimensional changes occurring from season to season.  Not only does the full tenon strengthen the gate's stile against repeated slamming when exposed to wind tunnels as well as increase the lateral integrity, but the wedges eliminate the need for glue.
Advantages:
1) The top of the joint is concealed from the falling weather.
2) The top of the joint has what we call a 'shoulder' above the tenon, preventing, by a matter of simple physics, the tenon dropping to the ravages of gravity.
3) The joint is created with dry stock between 5-9% moisture, and at it's smallest dimension.  The wedges tighten the joint to the dry conditions of the shop and once exposed to any weather--as in rain, humidity, even fog--the tenon expands and the joint grows tighter and tighter.  In the drier weather, the joint returns to the conditions in which it was created in the shop. 
4)  A glueless joint. 
5) There are temples in Japan constructed with this joint that have been standing for a thousand years.
Disadvantages:
1)  The edge of the gate's stiles can no longer be easily planed by the on-site carpenter. Planing is often required if the dimensions provided to CPW turn out to be in error and one or both of the posts or columns are in fact out of plumb.  The site carpenter must plane an edge to create the uniform clearance, and lesser experienced carpenters are going to be tempted to reach for their plastic suitcase housing a collection of nifty battery-powered tools bought at Home Depot and if he pulls out the nifty Circular Saw, we can liken the ensuing procedure to a battlefield medic performing surgery with his bayonet.

 Single and two-sided high-strength band-aids.  Colorful commodities that are also available with little actions figures

An in-progress look at Joint #6.   The first known use and still standing in near perfect condition today are two temples in Japan, built in cypress cedar in 413 A.D and 607 A.D.  Much later, and also still standing, a church in Oslo built in the 13th century. Both utilizing joint #6. 

Our methods were learned from Grandpa, furthered by Dad, and then Charles, and now Ben, who at 23 is in his 19th year of apprenticeship and recently completing a two-year intensive study at North Bennett Street's veritable school of woodworking in Boston, where for 175 years or so, they have been teaching the art of hand-cut joinery in the same building situated in the old North End. 

Although no one anticipates an assembly that will stand for 1500 years, the difference, beyond the aesthetics of a trained and practiced eye for subtle design, is a product that lasts, well . . . that lasts a few decades beyond the product of a lesser trained, less patient approach.

Below left we have a structure you've all seen before, growing off the side-wall of the residential architecture like a festered boil. In short order, the cross beam, primary joists and secondary top joists will twist and cup and warp into an insightly assembly. The joinery is a combination of metal fasteners from post-to-beam, and toe-nailing the joists.

To the right we have a CPW Pergola designed and built in the early 90's illustrating the flush joinery that provides not only a departure in aesthetics, but a far stronger assembly designed to last several lifetimes. The overhead units are a series of small panels joined and set into place with a louvre affect. There are no metal fasterners, nail, or screws anywhere within the assembly.

Below left a common carpenter's fence and adjoining arbor assembly, again illustrating a stacked, applied approach to joinery with both the fence and arbor.

To the right we have a CPW Fence, gate, and complimenting Arbor as a married assembly that provides us not only a visual confluence of the three elements, but each of them once again joined without metal fasteners.

Below left: a few common examples of lattice we've all seen far too much of.

To the right, A Prowell fence-line in San Francisco, illustrating 150-running feet of flush joinery. The horizontal members are mortised and pinned to 4" posts every 8 feet. The top cap is butterfly joined at every other post.

Because Charles has written a number of articles over the years on the art of joinery for such publications as Fine Woodworking, Fine Homebuilding, Old House Journal, This Old House, and Woodwork Magazine, among others, it seems only appropriate to carry our discussion a step further, skipping ahead to a few advanced examples in an effort to illustrate not just the sheer perplexity of this procedure, but the alluring temptation of the joint as a work of art in itself.

The below images are drawn from Japanese Joinery.  The Handbooks for Jointers and Carpenters.  By Yasuo Nakahara.  Publisher: Hartly and Marks.

Below is a look at an interlocking dovetail with stepped haunches, or shoulders. A spline, essentially, that might, to the layman, more closely resemble a Rubic's schematic but to the careful and discerning woodworker, it becomes closer to performance art.

A look at the glue-less joint, where the interlocking planes and wedges are such that the joint is self sustaining. The example here is often utilized in Japanese temples for joining the rafter tails to cross-beams. Take notice of this on your next trip to a Japanese Tea Garden. Perhaps this is what CPW uses. It's an extraordinnry joint, relying soley on the execution of the Jointer's steady hand and without the aid of glues and sticky stuff.

An assortment of variations on the traditional mortise and tenon.

As a small part of an extensive CPW interior design, the use of the traditional, yet modified, Finger Joint adds an alternative flavor to the standard Butt Joint more commonly used here.

The above finger-joint wildly popularized by Greene and Green in 1917. Brothers and architects whose greatest asset was a lifelong association with a top notch team of woodworkers who realized their designs with flawless workmanship.

An early CPW design from approximately 1985 that still draws commissions. The exposed joinery of a trestle table employing both the Exposed Wedges of the Through-Mortise & Tenon Joint, but also the Primary Vertical Wedge joining the trestle board itself.

Why is this important? Why do we concern ourselves excessivley over a piece that will never see the ravages of the elements and live it's life within the confines of a controlled temperature? What if, say, you build the table in San Francisco, where the climate is as temperate as anywhere on earth, and ship it to South Carolina, where the climate is as fluxtuaing as a Mama Bear in heat? If you aspire for a larger patronage and a scope that encompasses all climatic regions, you must, absolutely must, know your joints and their properties.

Left: Prowell oversees the early apprenticing of Ben (on the table) and his older brother Sam. These two were sooo cute at that age. All along, actually, from newborns until this very day, as young men with the social graces of an innate courtesy toward all. That's a good thing, right?

Another look at a CPW Table using the Vertical Wedge to join the trestle board.

Joinery of this nature becomes a defining feature of the work's inherent design. This same joint went on to be designed into innumerable patio and terrace tables exposed to the elements. A joint with a great deal of forgiveness.

The leg profile shows the first prototype of what later came to be known as Prowell's Ballerina Leg., elongated and maturing as a much more effeminate, even sensual profile.

The hierarchy of joinery takes us to a series of intricate CPW lamp joints, and with the CPW Stand-Up Desk on the right,a near-obssesive use of the joint as an ebony wood hinge--both featured and discussed at length in national publications.

You are expecting an essay on Gate joinery, and instead have been lead on a meandering diatribe that ends with the portrait of a craftsman who often cuts the joints to your gates standing on his head, blindfolded, and with one hand tied behind his back. And yet, hopefully, you've enjoyed yourself and the bar of your own sightedness has been raised in a manner that has served to excite you. Inspire you. For a life without inspiration is simply and utterly intolerable.