Blazing in gold, and quenching in purple,
Leaping like leopards in the sky,
Then at the feet of the old horizon
Laying her spotted face to die;
Stooping as low as the oriel window,
Touching the roof, and tinting the barn,
Kissing her bonnet to the meadow-
And the Juggler of Day is gone!
I recently acquired a 2,500 page, five inch thick, 1975 unabridged Webster’s Dictionary. But the massive heft and bulk belie its paucity of architectural information.
This dictionary has five entries for kern, but no definitions for the critical structural idea that spanned 1,000 years of architecture and responsible for every stone church in the Middle Ages and Renaissance.
The kern is the concept that enabled Dark Ages cathedrals to reach new heights, despite only stone masonry with no ability to resist tensile forces. James Ambrose, in my 1988 structural textbook, Building Structures, defines a kern as “a zone around the centroid of the section within which an eccentric force will not cause tension on the section.”
Simply put, a kern is the center third of a foundation. When stacking stone, its foundation will resist rotating, lifting a side off of the ground, or cracking in tension as long as the weight and forces of the structure above are within this center third.
As soon as forces become eccentric beyond that zone, tension happens. The foundation will want to twist in the ground and additional measures must be taken to avoid a failure. This is easily mitigated with steel today, but before the Industrial Age, builders had to design with the kern to ensure stability.
Connections are the biggest challenge of material design.
Sketch of a femur
I like to use a femur to illustrate this concept. Do you see the straight shaft of the bone? Relative to the rest, it is quite simple. Although you wouldn’t want it to happen, a femur broken in the middle can heal, maybe with assistance of pins and plates, back to 100% mobility.
Broken joints, on the other hand, are rarely fully restored. Hip replacements can be pretty successful. But the complexity of interfaces between bone, cartilage, ligaments, tendons, bursa sacs and muscles at the other end make full recovery unlikely.
Architectural materials are no different.
Sketch of column parts
A femur is much like a column. Designing a column size is relatively simple work. There are common tables to set the basic sectional dimensions capable of managing a given vertical load.
The real work in structural design is determining how the column’s base and capital are connections at its base and the beams it supports. Are they welded or bolted? Are there lateral forces being managed by those connections? How do we manage cracking and settling at the footing? Are the beams resting on top of the column or are they bolted on to its side? Are vertical columns continuing above? Countless more decisions are resolved. Just like in animal structures, failures in building structures are most likely at the connections, too. So designers spend most of their time working out connection details.
The same principle can be seen in materials. Take for example, wood. It is beautiful, but challenging to work because it is unstable. Wood warps and moves even with minor temperature or humidity changes. Much of wood design and craftsmanship involves designing around this temperamental nature.
The slab in the sketch below is a piece of wood that will move a great deal in the vertical direction. Wood is more stable along its length, but perpendicular to the grain movement can be up to a half a percent. You won’t notice this… until it cracks.
Sketch of wood joinery
Traditionally, wood movement was managed by floating a panel assembly of wood in a frame. The panel, itself a series of pieces sometimes joined by tongue-and-groove joints, floated in grooves carved into the sides of the styles and rails of the frame that held it. The subtle offsets, grooves, mortises, and tenons all do their job to avoid cracking and maintain a well-formed rectangle for the life of the piece.
In fact, the historical name for a woodworker, prior to these engineered wood products, was a joiner. The skill of the craft was artfully assembling solid wood without it coming apart.
Today, we are spoiled by engineered wood products: plywood, particle board, high density fiberboard (hardboard, such as Masonite), medium density fiberboard (MDF), oriented strand board (OSB), melamine (plastic coating), laminates (phenolic-impregnated paper), thin wood veneers, laminated timber (glue-lam, cross-laminated, laminated strand), etc. Modern glues and resins, in combination with the re-orientation of wood fibers, make it more stable.
I venture that all these engineered products have completely spoiled our sensibilities to natural materials. Before engineered wood products, wood was used only in solid form. Thus the qualitative term solid wood, although I’m not sure anybody really comprehends that term these days. Imagine the challenge of putting together cathedral paneling in solid wood with only weak animal hide glues. Outside of the rare craftsman, all the products we see and use today from big box stores, retail furnishing centers, internet merchants, and mass flat pack channels are created from engineered woods.
So, now that all of our wood products are stable, has our understanding of materials warped?
rooftop view… behind the scenes of the design process
Pre-purchase investigations and renovations always begin with a visit to the property and a tour of the existing building. The first question I always ask is to obtain any documentation and information available about the facility. But frequently, no drawings exist and little, if anything, about the building is documented.
Not a problem.
I’ve recently refined and formalized a detailed initial survey and inventory process for an existing building as a Property Condition Assessment (PCA). Having this detailed method gives comfort that we’ve turned over all the stones and looked systematically for potential pitfalls before the design process. The team looks at everything from the foundation to the roof, the architecture and all the engineered systems in between, and the site beyond.
With a couple of key engineering experts and a contractor to test various budgetary scenarios, clients end up with:
visual walk through with the team
detailed architectural survey
survey plat with known site plan information
printed and electronic CAD formats of the surveys
building code analysis
interviews of individuals with potential information about the building
municipal and authority research for recorded and outstanding problems
descriptions of all the systems
inventories of all the building equipment
summary of any physical deficiencies along a good-fair-poor scale
descriptions for remedies of poor conditions needing immediate repair
photographic summaries for the systems and findings
budgetary analysis for remedying all the discovered deficiencies
This is all documented in a formalized report, useful for purchase negotiations or evaluating the scope of additional projects within a facility.
water heater tangle
Whew! Producing all this is a lot of work, especially trying to complete it in just a week or two. It’s definitely more thorough than the average field verification route. But this methodical approach takes a building from 0 to 100 with a comprehensive document foundation for making any future explorations or decisions. And its in portable electronic formats, not scraps of paper stashed in the mechanical room.
I figured this process expansion and formalization would establish a great place for an architect and engineering team to begin a renovation, but I’ve recently been finding that a PCA is equally useful to an owner as an initial benchmark of building data, sometimes the first such record since it was built decades before.
I like it when we figure out how to solve multiple problems with a singular effort.
I always enjoy Francis D. K. “Frank” Ching’s latest sketch articles. The above is just one sketch from his latest blog post, The Principle of Contrast. Back in the day, all of us architecture students had his first work, published in 1979, Architecture: Form, Space, and Order:
It was a beautiful work in pencil, all completely written in his gorgeous hand lettering. Since then, Ching has published several more books and updated the editions a few times. They have recently been re-formatted into a single series:
Architecture: Form, Space, and Order
Architecture: Form, Space, and Order
Green Building Illustrated
Visual Dictionary of Architecture
Interior Design Illustrated
Building Structures Illustrated
Building Codes Illustrated
Introduction to Architecture
A few of his older classics are also available, but do not appear to have been re-formatted into his current series: