Today I would like to talk about an important part of Japanese traditional roof work, the minokō. While I have made some mention of it in past postings, especially in the recently begun series on the bell tower design, I wish to dig into the matter here in more detail. As usual, I shall start my digging with the word minokō, and look more closely at the characters with which it is written in Japanese: ‘箕甲’
‘箕甲’ is composed of two kanji as you can see. The first, ‘箕’, consists of ‘其’ on the bottom, and a truncated form of ‘竹’ on the top. The lower element, ‘其’, stems from a pictograph, which looked like this:
… which is a picture of a winnow. Winnows, for those of you unfamiliar with agricultural implements, is a device used to separate the grain from the chaff, as well as remove weevils and other pests from stored grain. There are a couple of basic types of winnow, but in this case, the element ‘其’ refers to what is called a winnowing fan, a shaped basket used to toss the grain up into the air so the lighter chaff is blown away by the wind. Apparently it was a device associated to a table as well, judging by the pictograph.
Here’s a French painting from the 19th century showing a winnowing fan from that part of the world in action:
You may notice that the winnowing fan in the above photo is made from bamboo. The upper element in the character ‘箕’ is a shortened form of ‘竹’, which, surprise!, means bamboo. It means bamboo because it derives from a pictograph representing bamboo:
The second part of the word minokō is ‘甲’, the same character we encountered in a past posting, in the term for one of the eave edge build-up layers, the uragō (裏甲); ‘甲’, read kō in this case, means carapace, husk, shell and armor. Here’s the pictograph from which that kanji derives:
Thus, putting together ‘箕’ (mi) and ‘甲’ (kō) gives ‘mi–no–kō’, literally ‘the carapace of the winnower‘. Look at the shape of that above-pictured Japanese winnower basket again, and notice the shape of the basket along the transition from the rim to the basin. Now check out the minokō in the architectural sense of the term:
The minokō, described in English as a drooping verge, is a feature often found on Japanese gables and hip-gabled roofs. It comes in numerous shapes and styles. The purpose of the minokō is to transition between the edge of the barge board in the gable to the roof surface. It is an artifact of the double roof system, and unique to Japanese architecture.
In Japanese architecture, unlike the continental antecedents, there is a division in the roof between the exposed elements, like the eave and exposed boards in the gable end, and the hidden rafters which are actually producing the roof surface. When you break up the structural from the exposed components, there is of course an increase of complexity, however what opens up as well is a huge range of design possibilities.
If the roof is only single layer, and you want to curve the rafters, then the gable barge board must be curved exactly to match the roof’ profile. And since the common rafters are normally carried upon lengthwise purlins in the roof, the attachment of the verge boards, given their tall profile, is tricky. Ideally you would want to employ the purlins to carry the verge boards, or hafū, at their lower surface, just like the way the rafters are carried upon the purlins and ridge.
So, attaching the hafū boards to the purlins is one hassle in a single layer roof, especially when you want to accomplish it with joinery. And of course, the normal treatment with the gable end hafū is to place a board along their top edge which climbs with them to the peak, the nobori uragō as it may be termed. Adding more height in this area compounds the problem of fitting these wood pieces to the rest of the roof structure. The verge board assembly is in fact wanting to be higher than the rest of the surrounding roof surface. And this is what you will commonly see on Chinese gabled or hip gabled roofs – the end of the roof and ridge meet the gable edge and turn up slightly (or not so slightly a lot of the time it would appear).
By dropping the entire hafū and nobori uragō assembly down, in the double roof system, the problems of attaching the assembly to the purlins, along with the roof surface problems are solved. It means adding ‘dummy’ purlins and ridge pieces to carry the assembly in the gable, which is certainly an increase in framing complexity. These ‘dummy’ purlins and ridge, while sitting below the actual roof purlins and ridge, are not simply tacked on decoration – they do carry the weight of the verge board assembly just fine and mechanically connect to interior framing members. From the outside, looking up at the gable one can glimpse these exposed purlin and ridge pieces, and thus the structure looks as it should.
Much more important than these visual sleights of hand however, is that added bonus that comes with the double roof and the dropping of the verge board assembly down – now the shape of the hafū and nobori uragō are freed from the constriction of having to conform to the roof shape.
You can have a flat roof plane with a straight hafū, or a curved hafū. You can have the roof body in a concave curve, with a straight or curved hafū – and the hafū can be curved down to a much greater degree than the roof body if you want it to, as in this example:
The roof body can also be slightly convex (called “mukuri“), with either a flat or curved hafū in this structural arrangement. Having the double roof structural system, in summary, is incredibly versatile and opens up huge areas of architectural artistic expression.
Here’s a cluster of shrine buildings, many of which feature a minokō, even the lantern:
Lest you be thinking that the use of a minokō is confined to shrine and temple architecture, it also shows up on homes, and appears even on what some call the sine qua non of Japanese ‘traditional’ building, sukiya architecture. Look closely at these structures from Kyōto, part of the Miyako Hotel and very much in the classic sukiya idiom, and you will see the slight folds (the minokō) in the roof at the gable:
Here’s an example of a somewhat largish roof, midway through the copper shingling of the minokō:
Copper, in my opinion is by far the best roof material for roofs which have minokō as the shingles can flow so smoothly around the transition zone and allow for such a wide range of artistic possibilities. While minokō are also common on tiled roofs, they often look a little clunkier in my opinion, and the transition at the roof plane edge to minokō requires an additional tile ridge be laid along that area to keep the water out. Makes for a very heavy roof in the end:
If you return to that picture of the Japanese winnower basket, and recall that the word minokō refers to the carapace of the winnower, you may, who knows, have at first been considering the concave side, not the convex side. No need to feel astray as a result my friends, now that we’ve looked now at quite a few convex examples. You see, it so happens that architectural minokō may be concave as well, though only in copper work does this option become reasonable:
So ends our minokō diversion. I hope that I have managed to shed light on one of the lesser-known aspects of traditional Japanese architectural beauty, and to perhaps have given the reader an appreciation for all that goes into creating these sublime structures.
Thanks for coming by the Carpentry Way today.