How To Tell Which End Of The Plank Is Crown-Up And Which End Is Roots-Down On Shou Sugi Ban Siding

This post is trivia for most people and is written with traditional tradesmen in mind.  You might need to be OCD and infatuated with wood to appreciate this. A little extra care during install can make an unpainted siding field look so much better over the long term.  Our focus is siding, but a more common reference might be the difference between random grain solid wood furniture and book-matched furniture.

This week we have two large 1×8 S3S plank siding projects going through production, one headed to Bend, Oregon, and the other to Aspen, Colorado.  Both of the builders really care about handing the keys to something magnificent to their clients, who in turn want the best. The material choices on both projects are fabulous; one is Suyaki the other Gendai, both with clear oil finish (most people want pigmented oil to color the wood to match a rendering).  One of the projects will be installed vertically and the other horizontally.

I brought it to the contractor’s attention on the vertical project that the Japanese millwork is OCD in terms of logs being fed into our cant and resaws root stock right and crown left as a rule.  A rule as in religious compliance–every stick of siding we ship is oriented the same way. The reason I’m always given in Japan is that by tradition on a vertical install it will be better feng shui if the planks are installed crown up, rootstock down.  As Americans the builder and I laughed at this idea, but honestly I believe there is something to it. What I (maybe?) have seen in Japan and North America is that boards installed crown up roots down actually mellow and oxidize more, whereas upside down the soot on yakisugi erodes off quickly and the color bleaches out.

Look at the knots. They are all pointed down. This wall was installed upside down. I’m not sure if the grade of wood was “white” (all sapwood), or if the wall bleached out more quickly due to upside-down installation.
These shiplap boards were installed left to right, rootstock up. What I’ve seen is that since upside-down the soot along the shiplap bottom edge weathers more quickly than if right-side up.

That is theoretical though.  What I can show evidence of is that it looks so much better in the long term when the grain of all the planks is matched in orientation, whether horizontally or vertically installed.  Here is an example of matched orientation on an old house I took sometime somewhere in central Japan:

Matched grain, vertically-oriented clear grade wide-plank cypress. These planks are “amado” storm covers probably left in place permanently by an elderly owner.

So how can you tell that the boards are all oriented in the same direction?  With shiplap profile it is easy to tell which side is which with our planks since the profile has a side up and a side down (all our shiplap is crown left rootstock right with the plank horizontal).  But with S3S (square edge) planks the profile doesn’t indicate which direction is which and if the installer cares then they have to judge each board one by one for direction. If you know how then it’s super easy and won’t slow you down.

There are four ways I’m aware of to tell which end is up and which is down:

Rule #1 – Overall plank grain pattern is a triangle pointed up

Since yakisugi is generally simple sawn (same as all of our siding except vertical grain) for straightness the center of the tree is always in the center of the plank, which means right and left edges of each plank are mirrored grain.  The bottom of the tree is larger diameter than further up, so there is a slight narrowing of growth rings bottom to top on the plank. This appears as a triangle pattern with the triangle point up. Kind of hard to explain in words for a tradesman so here are some pics to show this:

Good display of the triangle pattern, also knots point up and out.
Looking from the rootstock end up the tree. Note sapwood indicates the log was not laser straight so likely was growing on an incline or the tree was bending for light.
Good perspective example of narrowing growth rings towards the top of the tree. The camera is looking up towards the crown.
From a distance it is hard to tell unless you train your eyes. Note sapwood in one plank is wider towards the top, bottoms of all the planks show a triangle pattern. Knots point up and out.
Great example showing triangle pattern on an old wall section.

Rule #2 – Knots point up and out

Whether young or old, cypress branches generally point up and away from the pith.  So overwhelmingly we see this pattern:

Knots point up and out.
Standard vertical installation displaying triangle pattern and knots pointed up and out.
Fabulous example showing branches pointed up despite being older trees. These planks might have been resawn from a lower trunk section.
If you look closely at this Suyaki wall you will notice that the installers did not orient all the boards the same way. It won’t be noticeable for another 40 years or so.

Rule #3 – Growth rings are tighter above knots than below knots

This is a more advanced indicator and you have to look at several knots to judge the pattern.  Growth rings directly above branches are not as thick as those directly below branches, likely as a natural structural effect.  It’s kind of a swirl that follows a nuanced pattern. Here again pics work better than blue collar nerdspeak:

Rule #4 – There is more sapwood vs heartwood towards the crown

This is kind of a no-brainer.  Most planks will have heartwood and sapwood since cypress comes from replanted forests and our logs are all within 18~24” diameter range.  A few planks from the center will be all heartwood and maybe one from the outside of the log will be all sapwood. But generally each plank will have some of each and this makes it super easy to judge direction.

One more note is that our Suyaki and Gendai planks are much more difficult to judge than the Pika-Pika planks in these photos due to the soot layer.  It is as simple as flipping the planks over and looking at the backsides to study:

In the West we talk about random bond lines or random grain millwork.  When I carpentered in Japan my boss told me that nothing is random, it is just laid out and executed by the tradesman to appear easy on the eye.  He emphasized that it is important to view all tasks objectively and design every layout or orientation consciously and holistically. For siding that might never be re-oiled, where the grain stands out more and more over time from UV degradation, this little initial awareness by the installer can make a difference over time.  Here are a few pretty wood pics to show how matched grain can make an install age beautifully:

This is a very old wide plank yakisugi wall sawn out of large, matched logs. The planks are splined and grooves are starting to split out due to UV degradation.
It’s hard to tell from this pic but I assume the planks used for these storm windows are oriented vertically.
I love this house
This is my favorite wall in the world–not a perfect example for this post since hard to judge grain direction from an image, but I just have to throw it in. It is old growth cvg not heat-treated yakisugi.

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