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W O O D J O I N T SIN CLASSICAL JAPANESEARCHITECTURE

Torash ich i Su m iyosh i Gengo Matsu i



Authors' Biographies:

Torashichi Sumiyoshi

- Date of birth 1911

- Begins carp entr y apprent iceshi p in 1924

- Starts own enterpr ise in 1930

- Serves in nav y 1944- 1946

- Me mb er of "Ten ri Kyokai" , involved in

design an d constru ction of temples

- Pre par es wood shop draw ings for EishinGakuen Higashino High School (1983 -

1985)

Gengo Matsui

- Da te of bir th 1920

- Graduates in Architecture from Waseda

University 1943

- Receives Doctor of Engi neer ing 1960

- Professor of Wa se da University 1961

- Director of the Japanese Photoelastic

Association 1979

WOOD JOINTS IN CLASSICAL

JAPANESE ARCHITECTURE

© Torashichi Sumiyoshi and Gengo Ma

tsui 1989

First Published in Japan by

Kajima Institute Publishing Co., Ltd.Second printing, May 1990

English translation from the Japanese in

1991 by Ferenc Kovacs

Advisor André Gravel

Proofread and edited by Janos Nagy

Printed in Japan



W O O D J O IN T S I N C L A SS IC A L J A PA N E S E A R C H I TE C T



ii

Introduction by Yukihiro Kamiyama

Japanese architecture brings to mind stupendous Buddhist temples andshrines, plus the three- and five-story pagodas. Amongst these sacred places,one cannot help being overwhelmed by the radiance emanating from thestructures . The pur ity of the lines leaves us in awe.

Mas ter craftsmen, inspired by the beauty of the Japan ese cypress andzelkova and influenced by the Japanese culture, produced these works of art.

Behind the beauty lies the skill and knowledge of an artisan. The harmonyof the creation conceals the complexity of the assemblage. Simple elements,such as bearing blocks, all play a role in the final result.

There are many ways to join members together. Beams can be tied withropes, carved and assembled or connected with nails, screws and glue. Whenthese structures were erected, joining was an extremely elaborate technique.Master jointers were dedicated craftsmen responsible for splicing and connecting elements of a building. Many factors had to be considered. The connections had to be strong enough to transfer forces such as bending, torsion andshear, yet appearance was an important factor. A variety of techniquessometimes simple, sometimes elaborate were developed.

We can only marvel at the solutions adopted. They took into account timedependent process, such as shrinkage or slippage caused by dynamic loading.The intricacy of the internal structure of the joint is hidden by the apparentsimplicity of its appearance. Various shapes connect into each other with ease.This wisdom is the result of years of patient work; we have much to learn from

it.Master Sumiyoshi and Professor Matsui met while working on the design

an d construction of Eishin Gakuen Higashino High School (architectu re byChristopher Alexander). The school is famous for its large wooden structure,the first erected in Japan for many years.

Master Sumiyoshi contributed his experience and knowledge to the manysplices and joints available to the builders. Professor Matsui, working as anadvisor, was deeply impressed by Master Sumiyoshi's knowledge. Feeling hislifelong wisdom should not be lost, he planned this book to preserve a valuable

heritage. It is to be of interest to students of wooden architecture and engineer-



iii

ing worldwide.The purpose of this book is mentioned in the authors' comments.

Nowadays , jo in ts are mad e using metal parts. The splices and connecting jo ints have become much simpler. It is now possible to cons truct large woodenstructures using standard processes. However, the uncertain properties ofwood have brought forward the problem of weakening of the joints.

This work goes back to the fundamental of joining. It is recommended toall technicians and also to architects and engineers.

Yukihiro KamiyamaProfessor, Waseda University



iv

Authors' Comments

This book explains splices and connecting joints of traditional Japanesewooden architecture with pictures and diagrams. Although plenty of bookshave been published about splices and connecting joints, none of them haveused both pictures and diagrams as illustrations. In most cases, pictures haveonly showed one or two examples of a joint and it is difficult to comprehendthe complexity involved in joining the parts. Consequently, we decided to use

several pictures and diagrams showing the sequence of assembly which willhopefully make the descriptions easier to follow. Dimensions have also beenincluded, a feature not found in most other publications.

Our first objective is to ensure that traditional workmanship skills areaccurately transferred to the next generation. Our predecessors accumulatedthe know-how necessary to achieve complex and effective design over theyears. The intricacy of the joints enhance the character of the wood, bringingit alive. Many of these joints preserve the natural strength ratio carefully

balancing shear, bending, torsion, compression and taking shrinkage intoaccount.

Our second objective is to see whether these techniques can be utilized incontemporary architecture. This book describes the original characteristics ofthe joints. Some modifications might be required to make them effective fortoday's building technology. Bolts and modern adhesive could be used. Theauthors do not want to make such proposals; we leave it to the readers.

May, 1989Torashichi SumiyoshiGengo Matsui



vi

Contents

Introduction by Yukihiro Kamiyama

Authors' Comments

Acknowledgment

SPLICING JOINTS 1

01 Stepped dovetailed splice 202 Stepped gooseneck splice 503 Rabbeted oblique scarf splice 804 Mortised rabbeted oblique splice 1105 Blind stubbed, housed rabbeted oblique scarf splice 1506 Tenon and mortise splice 17

(1) Cross-shaped tenon and mortise splice

(2) Right angle tenon and mortise splice(3) Housed tenon and mortise splice(4) Blind tenon and mortise splice

07 Halved rabbeted oblique scarf splices 21(1) Triple-faced halved rabbeted oblique scarf splice with key(2) Miyajima splice(3) Quadruple- faced halved rabbeted oblique scarf splice

08 Housed splices 26

(1) Housed rabbeted oblique scarf splice(2) Blind tenon and mortise(3) Blind pin(4) Blind key(5) Pole tenon

09 Column splices 36(1) Four faces gooseneck splice(2) Clam-shaped splice(3) Blind splice



vii

(4) Osaka Gastle-Otemon Gate's pillar splice

CONNECTING JOINT S 4501 Half dovetailed joint 4602 Wedging joint 4803 Blind wedging joint 50

04 Housed dovetailed joint 5205 Sumiyoshi double tenon 5506 Double plug 5807 Triple plug 6208 Groundsill connectors 67

(1) Housed dovetail(2) Rabbeted tenon and mortise(3) Corner miter tenon

09 „Kyoro” system 7210 „Orioku” system 7611 Tie beam connector 8012 Hip rafter joint 83

(1) Tee-shaped girder joint(2) Gross-shaped girder joint(3) Bevelled halving

13 Corridor girder 107

MISCELLANEOUS 11301 Gable board 114

(1) Ogami with encased crossbrace(2) Ogami with surface crossbrace(3) Ogami with stub tenon and key

03 Level 12104 Batter post 122

Terminology 123



SPLICING JOINTS



2

SPLICE 01

Stepped dovetailedsplice

(Koshikake aritsugi)

This simple splice is utilized primarilyto join groundsills. The most common lum ber sections range from 105mm to 120mmsquare. The ends to be spliced are notched

at half depth. The male is shaped like thetail of a dove, narrow at the girth thenflaring out. The female is precisely hollowed

out to fit. A snug fit is a common characteristic of all joints. This joint is simply assem bled by sliding th e male into the female. No

axial shifting is required.This feature makesthis joint particularly useful on groundsills.Eventhough this splice aims to resist tensionin a structure, its effective tensile strength issmall.



SPLICE 3

Male and female The male slides into the female

Assembled spl ice



4

A tension test was carried out on anassembly of typical dimensions.

The tested splice was made of black pine with an average annual ring width of2. 5m m. Th e compressive capacity (yield

strength) of black pine is 420 kg/ cm 2 . Thefemale failed in tension by developing alongitudinal crack originating from a nookand following the grain. The ultimate tensilestrength of the splice was 480kg.

Arrangements of dial gauges

Test sample dimensions

Load-displacement curve

Before failure After failure



SPLICE 5

Stepped goosenecksplice

(Koshikake kamatsugi)

The gooseneck splice is also used ongroundsills; however, it has a higherstrength than the dovetailed splice. In practice, it is used to join larger lumber sectionsthan the preceding splice. The gooseneckwith tenon and mortise serves to splice

square section lumber between 150mm and200mm. For sections of more than 200mmoblique scarf splices are more appropriate.

Test sample dimensions. Angular dimensionsare shown on the next page.

SPLICE 02



6


Assembled spl ice



SPLICE 7

The tensile test was performed on anassembly of the same size and material asfor the dovetail splice. At ultimate strength,

two modes of failure occurred. At first the joint failed in be ar ing, crushing the hea d of

the gooseneck against the abutments of thefemale end. The second mode involved theshearing of a rib at the head of the maleend. The ultimate strength of the modeltested was 2400kg, a significant increase instrength compared to the dovetailed splice.


Before failure

1 Bearing failuremode

2 Shearing failuremode

After failure



8

SPLICE 03

Rabbeted oblique scarfsplice

(Okkake daisen tsugi)

This splice can be used to join groundsills, girders or bea ms. Th e two ends of the

jo in ts ar e identical and referred to as theupper wood and lower wood. Two mortisesare deepened through the depth of thesplice for inserting draw pins. The joint isassembled by sliding the internal face of theupper wood over the internal face of the

lower wood, keeping the surfaces of themiddle drops (surfaces „d”) in close contact. The pieces are then pressed together

and secured by pounding in two draw pins,effectively interlocking the front and backsurfaces of the join t (surfaces „a” ) . The

pins are inserted from the thicker endtoward the thinner end, in an alternatefashion. Unlike other oblique scarf splicesno axial shifting is required to assemble thissplice, making it particularly suitable forinstalling or replacing a beam between fixedsupports or a sill between anchored points.This rabbeted oblique scarf splice could bemore appropriately called „pinned rabbeted oblique scarf splice”.

For square sections between 105 mm to120 mm, the length of the splice should be 3to 4 times the width of the section.



SPLICE 9

Upper wood and lower wood The upper wood slides over the lowerwood (the draw pins are shown to display

the direction of insertion).

Completed splice. The draw pins are inserted.

The tensile test was also carried on an105 mm square section assembly made of

black pine. An even bigger st reng thincrease than that of the gooseneck splicewas obtained. The joint failed at 4000 kg by

shearing through one of the adhesion planes .

Test sample dimensions Arrangements of dial gauges



10


Before failure After fa ilure



SPLICE 11

SPLICE 04

Mortised rabbetedoblique splice

(Kanawa tsugi)

Both ends of the splice are identical;only the upper wood is displayed in thediagram. This joint is also assembled bysliding over each other the internal faces of

the upper wood and lower wood, keepingthe surfaces of the middle drops (surfaces„d”) in close con tac t.

To complete this splice, the upperwood is shifted away from the lower woodalong the longitudinal axis. Finally a singledraw pin is inserted between the middledrops, interlocking the front and back surfaces of the join t (surfaces „a ” ) . This spliceis similar to the preceding one. In this case,

the principal difference consists of having toshift away from each other the upper andlower woods to complete the splice. The

tensile test produced results identical tosplice 03.



12

For square sections between 105 mm to

120 mm, the length of the splice should be 3to 4 times the width of the section.

Upper wood and lower wood The surfaces of th e middle drops (surfaces „d”) touch

A shi ft in axial di rect ion opens a gapbetween th e middle drops of th e upperand lower woods.

The splice is completed by inserting thedraw pin.



SPLICE 13

Size of the Dimension of the test sample

Arrangement of dial gauges

Load displacement curve



14

Before failure After failure



SPLICE 15

SPLICE 05

Blind stubbed, housedrabbeted oblique scarfsplice

(Shiribasami tsugi)

The shape and mechanical propertiesof this splice are practically identical tosplice 04 . Aesthetically speaking however,this splice is said to be of a superior designthan other rabbeted oblique scarf splices;an elevation view of the splice reveals onlya clean straight line.



16

For square sections between 105 to 120mm th e length of the splice should be 3 to 4times the width of the section.

Upper wood and lower wood The surfaces of the middle drops (sur-faces „d”) touch

A sh if t in axial di rect ion opens a gapbetween the middle drops of the upperand lower wood.




SPLICE 17

SPLICE 06

Tenon and mortisesplices

(Mechiire)

(l) Cross-shaped t eno n and mortisesplic e (juji mec hii re)This splice is effective against torsion

but ca nnot resist an y tensile forces. It isoften combined with splicing plates bolted

throughout. Male and female

Assembled splice

Male Female



18

(2) Right angle ten on and mortise splice(kaneori mechiire)

Two faces of this splice reveal a cleanstraight line when assembled.

Male and female Assembled spl ice

Male Female



SPLICE 19

(3) Housed tenon and mortise splice(kakushi mechiire)Three faces of this splice reveal a clean

straight line once assembled. It is a commonmethod for splicing exposed posts.

Male and female

Assembled spl ice

Male Female



20

(4) Bl ind t eno n and mortise spl ice(hako mechiire)This beautiful splice reveals only a

clean straight line on all faces once assem bled. However, ma nu fa ct ur in g of this jo in tis technically difficult.

Male and female

Assembled spl ice

Male Female



SPLICE 21

SPLICE 07

Halved rabbeted obliquescarf splices

(Isuka tsugi)

This decorative splice is often used forfinishing, particularly on exposed ceilingmembers; it has very few structural applications. Double-faced halved rabbeted

oblique scarf splices, as shown in figure a),when applied as decorative design, aredimensioned so that the length of the in

clined plane is twice the size of the crosssection. For stronger structural use, as for

ba tt er posts for example, th e length of th e

inclined planes is made equal to the size ofthe cross section. The double-faced halvedrabbeted oblique scarf splice with key andthe single-faced halved rabbeted obliquescarf splice, as shown in figure b) an d c)respectively, are often used in buildingswhere appearance, a factor of the length ofthe splice, is not of utmost importa nce (forexample, the „residents” building of a tem

ple) . Hereafter described ar e th ree exam ples of ha lved rabbeted oblique scarf spliceswith three faces or more:

(a) Double-faced halved rabbeted obliquescarf splice

(b) Double-faced halved rabbeted obliquescarf splice with key



22

(c) Single faced rabbeted oblique sca rf splice

(1) Tr i ple- fac ed halv ed rab bet edoblique scarf splice with key

The key has no structural function. Itis designed so that the splice cannot beeasily pulled apart. As mentioned earlier,

the appearance of these joints is a directfunction of the length of the splice. However, the longer splices are also weaker.Consequently, the inclined faces of the jointare m ad e to be a max imu m of two times thesize of the cross section.



SPLICE 23

Upper wood and lower wood

Assembling t h e spl ic e The splice is completed by locking it witha key.



24

(2) Miyaj ima spli ceVery similar to the previous splice. The

difference resides in the presence of atriple-faced cone at the end of the inclined

surfaces. Very sophisticated craftsmanshipis required to manufacture this joint.


Assembling the splice The splice is completed by locking it witha key.



SPLICE 25

(3) Quadruple-faced halved rabbetedoblique scarf spliceThe simplicity of this splice hides the

complexity of manufacturing it. Meticulousattention must be devoted to finishing it.


Assembling the spl ice The splice is completed by locking it witha key.



SPLICE 08

Housed splices(Kakushi tsugi)

These splices are often used on finishing materials.(1) Ho us ed rabbe ted o bli que scarf

splice (kaku shi kanawa)

Very similar to the rabbeted obliquescarf splice except that only half of thewidth of the section is rabbeted oblique.

The other half is housed producing a cleanstraight line on two faces once assembled.This joint is useful when no significantstrength is required. The length of the spliceand inclination of the oblique surface (line1 and e) are arbitrary.



SPLICE 27

Male Female

Male and female The male slides int o th e female

The surfaces of th e middle drops (surfaces "d") touch

A shi ft in axial di rection opens a gapbetween the middle drops.


Exposed surfaces



28

(2) Bl ind teno n and mortise (hak odaimochi)Similar in shape to the previous splice

bu t wi thou t an y inclined surfaces. A key isused to lock this joint together.



SPLICE 29

Male Female


The splice is completed by inserting thekey.

Exposed surfaces after completion



30

(3) Bl ind pi n (ha ko sen)This splice also follows the model of

the rabbeted oblique scarf splice. The form

of splice 04 is carved on two perpendi cul arfaces.



SPLICE 31

Male Female

Male and female The surfaces of th e middle drops (surfaces „d”) touch.

A shi ft in axial di rect ion opens a gapbetween the middle drops.

The splice is completed by inserting twodraw pins.

Exposed surfaces after completion



32

(4) Bli nd ke y (hak o shachi )Almost identical to the previous splice

but wi thou t any inclined surfaces.

A key is used to lock the joint together.The preparation of this splice is easier thanfor the blind pin.

Male and female



SPLICE 33

Male Female

The male sl ides into the female. Same

The splice is com ple ted by inser t in g tw o Exposed surfaces after completion



34

(5) Po le te non (saotsugi)Pole tenons are used on exposed ceil

ing elements. The three faces of this splice

reveal a clean straight line once assembled.



SPLICE 35

Male Female

Male and female The male slides into the female.

Same The splice is completed by inserting twokeys.



36

SPLICE 09

Column splices(Hashira tsugi)

(1) Fou r faces goo sen eck spli ceTwo goosenecks are carved diagonally

across the section. The male and femaleslide over each other at 45° to assemble thesplice. The two goosenecks are small inrelation to the size of the section. Skillfulcraftsmanship is required while manufacturing. This splice is suitable for large columns. Hard wood, such as zelkova, is oftenused. The peculiarity of this splice is the

identical gooseneck motif found on all facesof the column.

Male Female



SPLICE 37

The male slides into the female diagonally.

Same

Same Completion



38

(2) Cla m-s hap ed splic e (kai no guc hi)This relatively long splice has a few

exclusive applications. Twice the length ofthe splice is required in assembling which isvery inconvenient for underpinning. It isusually reserved for splicing distinguished

elements such as the central column in a pa god a. Both ends exhibit a „F re nc h type”tenon and mortise pattern. Finally to stiffenthe assembly, a steel ring may slide over the

jo in t. The splice is polished with sa nd pap er .



SPLICE 39


Assembling t h e sp l ic e

Completion



40

(3) Bli nd splic e (hak o tsugi)This splice is inferior in strength to the

rabbeted oblique scarf splice because of themethod used to lock the joint. A key contributes little to the sturdiness of the assem bly co mpare d to a dr aw pin. The key holeand the longitudinal joint line are

positioned at the corner of the sectionmaking this splice very attractive on columns.



SPLICE 41

Upper wood and lower wood The upper wood slides over the lowerwood.

Same Inserting the key

Same from a different perspective The splice is completed



42

(4) Osaka Castle-Otemon Gate's pillarspliceOtemon gate is the only known exam

ple of this design. Onc e assembled, a decorative mountain skyline like pattern can beseen on the surface. An X-ray test had to becarried out to investigate the internal struc

ture of the splice. No gap exists between thetwo parts.

Male Female



SPLICE 43

Male and female (le ft: upper part of th ecolumn, right: lower part of the column)

The male is inserted into the female bysliding it upward from the center to theedge.

Same Completion



44

X-ray picture AThe bright lines are the internal parts of the

jo in t and display the outl ine of the dovetail .

X-ray picture BThe axial black lines display the grain of thewood. The horizontal lines and the mountain-shaped lines are the upper face of the maleon the inside and the seam on the outsidesurface.



CONNECTING JOINTS



46

CONNECTING JOINT 07

Half dovetailed joint(Katasage ari)

The model depicts a wall tie connecting into a corner column. The column wassplit in half lengthwise to reveal the internallocking mechanism. Wall ties are usuallycovered up, however, traditional Japanese

architecture sometimes call for exposed ties.The wedges, somewhat longer than necessary, are driven in as deep as possible toavoid rattling. First, the columns are erected, then the ties are inserted to preventhorizontal movement. Wedges are driven inafter the erection is completed. Braced wallshelp resisting horizontal earthquake loadingin Japanese wood architecture. The half

dovetail connects a single tie into a cornercolumn. The diagram below shows a tieconnecting into a column from two oppositesides.



CONNECTING JOINT 47

Arrangement of the members The brace is inserted into the slot.

The brace is inserted in its final positionopening a space for a wedge.

The joint is completed by driving in thewedge.



CONNECTING JOINT 02

Wedging joint(Wari kusabi)

This joint connects columns withgroundsills, girders, girt, etc. In the model,the column was split in half lengthwise toreveal the internal locking system. The jointis simply assembled by inserting the tenoninto the mortise. Two wedges are poundedin the tenon, splitting it open and locking itagainst the mortise.



CONNECTING JOINT 49



50

This model was also split in half.This joint is commonly used on eave

bracke ts , ha ng ing posts of lintel and whenever the tenon and mortise are better lefthidden. To assemble this joint, two wedges

are loosely driven in the tenon. The tenon isthen inserted in the mortise and driven in.The wedges hit the bottom of the mortise,opening the tenon like a fan and locking it

pe rm an en tly . Experience is impo rt ant inmanufacturing this joint. The tenon isalways cut a little bit shorter than the depthof the mortise to insure the element beingassembled is fully inside before the tenonwedges itself permanently. Some techniquesare helpful for assembling the joint success

fully. The inside of the mortise must beclean and blown free of any debris. Some

times the joint is splashed with water afterinserting the tenon into the cavity.

CONNECTING JOINT 03

Blind wedging joint(Jigoku hozo)



CONNECTING JOINT 51

D: 105 or 120



52

CONNECTING JOINT 04

Housed dovetailed joint(Okuri ari)

This joint is frequently used on hanging posts (ts uri zuk a). At first the dovetail isinserted in the larger opening of the mortise(area A) an d then shifted sideway into thenar rowe r slot (area B) which has the exact

inverted shape. Finally a wooden plug is setto ensure the joint will not easily comeapart. Sometimes the dovetail is cut in halfalong the depth of the male end. Theassembly proceeds as mentioned earlier.Th e larger open ing of the mortise (area A)is now hidden by the male. The latter form

of this joint can be used to anchor the legsof shelving units on a floor.



CONNECTING JOINT 53

Male and female The dovetail slides into the bigger end ofthe mortise.

Same The dovetail is shifted into the smallerend of the mortise.

Assembled joint The plug is not shown for clarity.



54



CONNECTING JOINT 55

CONNECTING JOINT 05

Sumiyoshi double tenon

The upper tenon is a dovetail withflaring side walls. The lower tenon is rectangular with one surface tapering up. The

joint is assembled by sliding the doub letenon upward into the mortise at the sameangle as the tapered surface of the lowertenon. Master Sumiyoshi learned of this jointfrom fellow craftsmen. An X-ray picture ofthe assembly shows some discontinuitymaking it not entirely satisfactory.

X-ray photograph showing a discontinuityafter assembly

The lower tenon appears completely whitesuggesting an imperfect fit. White gaps canalso be seen on the left and right side of thetapered tenon. A perfect fit afte r assemblyensures the integrity of a joint.



56

Male Female



CONNECTING JOINT 57

Male and female The male is inserted into the female atan angle.

Same Assembled joint



58

CONNECTING JOINT 06

Double plug

This assembly connects two beams onopposite faces of a column. The beams arespliced through the column. Larger splices(pole tenon ) produc e sturdier assemblies.The beam with the longer tenon is connected to the column first. The second

beam is inserted and shifted forward unti lthe lower tenons butt at the centre of thecolumn. The connection between the beamsand the column is completed before finishing the splice between the beams. In orderto provide the joint with enough tensileresistance, two keys and a draw pin aredriven in. One or the other would be insufficient by itself. It is important to tighten the

assembly before inserting pin and keysotherwise the components could be exposedto excessively large stress.



CONNECTING JOINT 59

Beam 1 (male) Column Beam 2 (female)

Arrangement of the members



60

Beam 1 is inser ted through th e column.

Beam 2 slides over th e pro ject ing end of th e tenon of beam 1.



CONNECTING JOINT 61

A f t e r t i g h t e n i n g t h e j o i n t , t w o keys a r e i n s e r t e d .

A draw pi n c o m p l e t e s t h e ass emb ly .



62

CONNECTING JOINT 07

Triple plug

This assembly connects three beamson three faces of a column. The two opposite beams are spliced through the column.Th e first bea m to be connecte d (beam 1,short male) is perpendicu lar to the othertwo beams. A dowel secures it to the column. The second part of the assemblage

proceeds in th e same fashion as for the prec ed ing join t. The lower part of thetenons of bea m 2 (male) and beam 3

(female) is shorter th an on the double plugdue to the presence of the ext ra beam. Avery tight joint works better. In order toachieve this, the long projecting tenon of

bea m 2 (male) is made a few millimetersshorter than the dimensions quoted in thefigure. The triple plug gives the appearanceof continuity when seen from the inside.Seen from the outside, a seam can be seenwhere the two opposite beams meet.

From left to right: beam 1 (female), beam 2 (sh ort male), column, beam 3 (male) A dowel, draw pin and two keys are at the front.



CONNECTING JOINT 63

Bea m 3 (fema le) Be am 2 (male) Bea m 1 (s ho rt male)

Column



64

Duck nest



CONNECTING JOINT 65

A r r a n g e m e n t o f t h e membe rs Bea m 1 (s ho rt male) is assem bled fi rs t.The dowel pin is inserted.

Be am 2 (male) is assem bled ne xt.

Bea m 3 (female) s l ides over th e pr oj ec ting end of t h e te no n of beam 2 (ma le) .



CONNECTING JOINT 08

Groundsill connectors(Dodai shiguchi)

(1) Housed dovetail (ari otoshi)A dovetail is carved on half of the

depth of one member. A rectangular mortise runs th roug h the dep th of the secondmember immediately behind the mortise forthe dovetail. A column with a simple tenonmay complete the assembly. A draw pin

secures the column to the groundsill. Thelength of the pole teno n on the columnequals the depth of the groundsill. Thus,even if the groundsill rots, the column willstand firm. This often happen since thegroundsill is usually made of softwood andthe column made of hardwood.

CONNECTING JOINT 67

(2) Rabb eted teno n and mortise (ko nehozo sashi)This joint is useful to assemble corner

groundsi lls. The male sill (B) has an eccentric ten on at the end . Th e female (A) has amortise cut throughout. After assembly, awedge is pounded through a slot in thetenon, locking the members together. Ifthere is enough room left at the end ofmember A (distance a — H/2), a columncan be connected over the joint using a stubtenon.

Column

Left side: housed dovetail.Right side: rabbeted tenon and mortise

Housed dovetail Eccentric rabbeted tenon and mortise



68

Arrangement of the members

Rabbeted tenon and mortise(left): After the male is assembled, a wedge is pounded in, locking th e jo in t (no column shown).Housed dovetail (right); the maleslides into the female. The columnis assembled and the joint is completed by driving in a draw pin.



CONNECTING JOINT 69

(3) Corner miter tenon (sumitome hozo

sashi)This joint also connects corner ground

sills but is more attractive than the previousone. A tongue and groove on the insideensure rigidity while a panel on the outsidegives the joint a cleaner look. The outsideseam is located at the corner making the

assembly appear to have been made out ofa single piece of wood. The tapered panel atthe end of mem ber B (male) redu ces the

dista nce (a) left at the end of mem ber A(female). For this reason, a trapezoidalstub tenon is preferred to connect a columnover the corner joint.

Groundsill (A)

Groundsill (A) Groundsill (B)



70

Arrangement of the groundsills The joint is assembled.

A wedge is pounded in. A column is set on top of the sil l.



CONNECTING JOINT 71



72

CONNECTING JOINT 09

„Kyoro” systemThis roofing system joins very special

ized elements. The eave girders run on topof the columns on the outer walls. Therafters are connected to tie beams called therainbow beams. The rainbow beams aresupported by the eave girders. The supporting point of the rainbow beams is deter

mined with a tool called the rainbow board(hikari ita). The basis for the roof supportsystem lies on the sadd le point (toge) . Th esaddle point is at the intersection of the

bo tt om edge of th e rafters and of a verticalline perpendicular to the center line of theeave girders. Often this point is locatedabove the eave girder in order to avoidweakening of the same. The rainbow beamhas a dovetail shape at the end which

connects onto the eave girder. A groove aswide as the rainbow beam is also cut intothe eave girder to give full support to the

rainbow beam. This system has to be madestrong enough to support the roofing loadand also roofers, who frequently hang ontothe tie beams during erection or use them tolift loads. The full width groove protectsagainst splitting of the tie beams. Anothergroove is sometimes cut through the top ofthe rainbow beam to receive the rafters.



CONNECTING JOINT 73

Rafter

Column

Eave girder

Covering board (mentoban) and rafter; rainbow beam, column and eave girder



74

Wall framing (column head: tenon andmortise)

The rainbow beam connects on thegirder through the kabuto dovetail

system.

A rafter is installed on the top of therainbow beam.

A covering board completes the kyorosystem.



CONNECTING JOINT 75

The pitch of the rafter is projected on the rainbow beam using the rainbow board.

The connecting point between tie beam and girder is spotted using the rainbow board.



76

CONNECTING JOINT 10

„ Orioku” system

In this case, the rafters' tie beams sitdirectly on top of the columns and the eavegirders run on top of the tie beams. Thestepped tenon of the column is notched afew millimeters shorter than shown in thediagrams to avoid having the girder acci

dentally snagged by it. The Orioku systemresults in a lower ceiling height than theKyoro. The Kyoro system is more flexible

because rafters and tie be am s do not ha veto be supported at the same location as thecolumns.

From left to right: rafter, girder, column, tie beam



CONNECTING JOINT 77

Girder

Tie beam

Column

The column is set on a groundsill. The tie beam is set onto the column(column head: stepped tenon).



78

The girder connects onto the tie beam with a cogged joint.



CONNECTING JOINT 79

Same as before The rafter s i ts on top of the eave girder.

Same as above



80

CONNECTING JOINT 1 1

Tie beam connector(Koya daimochi)

Sometimes tie beams must be splicedand tied to an internal roof beam network.The unique characteristic of this joint isthat neither the lower tie beam nor the

upper tie beam suffer a reduction in sectionat their splicing point.The diagram displays

the arrangement of such a joint with provision for a purl in post on top of theassembly. Generally purlin posts are evenlydistributed. They are not always located atthe connection of tie beams and roof beams.The dowels used to position the tie beamsover each other are usually 30 mm wide andare always drilled in vertically instead ofnormal to the internal faces of the joint.



CONNECTING JOINT 81

Tie beam (uppe r)

Ti e bea m (lowe r)

Internal roof beam

Internal roof beam



82

The lower tie sits on the internal roof beam.

The upper tie beam sits on the lower tie beam. A purlin post is added to the assembly.



CONNECTING JOINT 12

Hip rafter joint(Yosemune no sumi)

Three kinds of hip rafter joint with fivesun pitch will be int roduced (one sun is onetenth of a foot). All of these joints havecommon characteristics. The roof rafters(including corne r's eave brackets) are

normal to each other and all of them havethe same pitch.(1) Tee-shaped girder joint

Precisely manufactured tenon andmortise (goya hozo sashi) are necessary to

CONNECTING JOINT 83

make this joint . The hip rafter (sumigi) sitson top of the longer girder. An eccentric

tenon and mortise serves to assemble theeave girders.

From left to right: Corner's eave brackets,girder (A), girder (B), hip rafter

Hip rafterCorner's eave brackets

Girder (B)

Girder (A)



84

Arrangement of the girders

Girder (A) is inserted into girder (B) and a wedge is pounded in (rabbeted tenon andmortise).



CONNECTING JOINT 85

The hip rafter is set on top of the girders.

The corner ' s eave bracke ts a re ins ta l led .



86

(a) Girders layout with notches for ra ft er s (including corner eave brack ets)

Layout (1)

A carpenter square is used to layout the dimensions on site. One side of the carpenter

squ are ha s a 1:1 scale. T he other side has a scale.Figur e a) show s how to lay out the dimens ions for th e rafter sockets on th e eave girde rs.

On girder I, a line is exten ded dow n from the „toge” (point A) with the same pitch as therafte rs' (5 sun pit ch ). Th is line intersec ts girde r I on the top face an d outer face at point Ban d point C respe ctively. T wo lines, paralle l to the cen ter line of the girde r, a re layed out from

po in t B and po in t C to the inte rsec tion with gi rder II at po in t G and poin t D. Line CD isextremely important. It is called the „Kuchiwaki” line. From point D another line is layed outwith the sa me pitc h as the roof rafter's. Thi s line intersects th e end face of girde r II at pointE. Line EF is drawn across the face, parallel to the top surfaces of the girders. The planesSTUV and WXYZ represent the bottom faces of the grooves destined to receive the rafters.

The layout for the hip rafter is displayed on figure b). We have just explained how pointB an d C were cre ate d from the "to ge " (point A) on girde r I. In the same fashion, point B'and C are established on girder II. The Kuchiwaki line from point C and its counterpart onthe top surface from point B', are drawn along girder II. Line B' - intersects the inner face ofgirder I at point H (line B' H is parallel to girder' s II cente r line RQ just as line BG is parallelto girder's I center line PQ).



CONNECTING JOINT 87

(b) Hip rafter layout

(c) La yo ut for th e late ralpi tch of the top sur-face of the hip rafter

(d) Layout of the in te rsec t ionof a rafter (corner eave

bracke t ) wi th the h ip ra f te r



88

A new line, GH, is layed out on top of the intersection of the two girders. Two more po in ts , J and K ar e set on e half of t he hi p rafter wi dt h apart from th e ce nter po in t H and poin tG. The sides of the hip rafter are projected down on the top surfaces to form lines JJ' and

line KK'. On those lines, point J' and K' are extended to the intersection with the outer faceof girder II at point I. L ine IN is dra wn at one half the roof raft er's pitch (2 .5 suns pitch)on the ou ter face of girde r II, slo ping down from point I. Th e extensio n of line J J ' a nd lineK K ' give us point L an d point M, located on the oute r face of girder II. Fro m point L an dM, two vertica l lines are dr aw n dow n the face of girder II . Th e intersection of these lines withline IN produces point N and point O respectively. We now have all of the lines necessaryto cut out the groove destined to receive the hip rafter. The bottom surface of the groove isincluded within J ' K 'O N . (J'K' :width of hip rafter)

Figure c) dem ons tra tes how to layout the latera l pitch on the top surface of the hip rafter.

Th e pla ne BCD on figure c) is parallel to O 2B 1G in figure b ) . Th e latera l pitch of the to p

surface is given by the ratio of EF /B F on figure c) .

Assume AC=h

Figur e d) dem ons tra tes how to layout the cutt ing plan e for the inters ection of a roof

rafter (corne r eave brack ets includ ed) with the hip rafter. HI J on figure c) is ma de parallel

to O 1B 1G i n figure b ) . GIJ on figure c) is mad e parall el to O 2 B 2 G in figure b). The surfaces

GH J and G K N are on the side of the rafter (corner eave brackets incl ude d). T heir pitch are

GI/IJ and KN/KL respectively.



CONNECTING JOINT 89

Finally, figure e) shows the layout of the bot tom of the hip rafter where it contact s thegirder. XY Z in figure e) is made parallel to O 1 B 1G in figure b). ZYD and XYD contact theface of the girder. The pitch is FX/FD. Let the hip rafter width be W.

(e) Layo ut of th e bott om of th e hip ra ft er at the in ters ect ion with the girder



90

(2) Cross-shaped girder jointIn pract ice the girders join together in

a Tee-shaped assembly. Afterward, a

"nose" is added to the shorter girder, givingthe joint the appearance of a cross.

Girder (A)



CONNECTING JOINT 91

On top, from left to r ight: Girder B, girder nose,girder A, hip rafterO n t h e b o t t o m : r a f t e r s

Hip ra f te r



92

Girder nose

Girder

Rafter



CONNECTING JOINT 93

A r r a n g e m e n t of g i rd e rs A and B and of t h e g ird e r nose

Girder B is inserted into girder A (housed dovetai l) .



94

The girder nose slides into girder A (housed dovetail).

The hip rafter is set on top of the girders.



CONNECTING JOINT 95

The jo in t i s comp le te d by ins ta l l ing th e ra f te rs .

Layout (2)

No te : The ge ne ra l la yout disc ussed for th e Te e-sha ped gi rder jo in t will be omit te d for th enext two joints. Only new concepts need be introduced.

Th e layout of the en d of the hip rafter is displayed i n diag ram b ) . Th e pitch of the hiprafter, called nag esu mi pitc h, depe nds on the roof rafters pitch (5 sun pitch) an d is as sum ed pe rpe ndi cul ar to th e end surfaces of th e hi p rafters. The pl an PRS is pa ra ll el to O 1B 1G infigur e b) . The plan O RS is parallel to O 2 B 1 G in figure b). OQS and OPS lay within thevertical face of the hip rafter. The values required are OQ, OS and TV respectively.

Layout for cu tti ng the hip raft er's endThe surface OQS is normal to the fascia boards.



96

(3) Bevelled halving (nejigumi)The eave girders cross on top of each

other in a formation called hip corner. To ba la nc e the st re ng th along bo th axis, th egirder sections are carved out by an equalamount. Th is concept of joini ng is called bevelled ha lving. The gi rders over la p at

their intersection. The stepped tenon of thecorner column slides through the intersec

tion of the girders and extend beyond it,ready to receive the hip rafter. The hiprafter joins onto a rafter column set backfrom the corner column.



CONNECTING JOINT 97



98

G

i r d e r

A



CONNECTING JOINT 99

C o

l u m n

A n g

l e b r a c e



100

H

i p r a f t e r



CONNECTING JOINT 101

R a f t e r

C o

l u m n



102

Top: Angle brace, center from left to right: rafters, rafter column, girders A and B, hip rafterBottom: from left to right: Covering boards, columns, hip rafter post

Arrangement of the columns Assembling the eave girders




Assembling t h e ea ve g i rde rs ( t h e s t e p p e d t e n o n o f t h e c o r n e r co lumn e x t e n d s beyond t h egi rders to the top sur face of the h ip ra f te r )



104

The bevelled halving joint is completed.

The angle brace is set in place. Installing a short post to support thehip ra ft er (necessary for thi s system only)




The corner rafter is f ixed. The ra f te r co lumn i s connec ted to the

hip rafter.

The roo f ra ft er s are set . The coveri ng boards are on.



106

The eave's boards complete the structure.




CONNECTING JOINT 13

Corridor girder(Engawa no keta)

This is a more complex joint than the previous hi p corner jo in ts . The st ruct ure iscomposed of two log girders, joined in aTee-shape and of a log girder nose. Thegirder nose (B-1) gives the assembly a

ba la nc ed look. The shorte r girder (B-2)seems to form a single continuous memberwith the girder nose. To accentuate thiseffect the nose (B -l ) and the short girder(B-2) are cut out of the same piece of wood.This assemblage is extremely complex. Firstthe nose (B-l) is inserted into girder A.After the tenon has gone through, the noseis rotated at 90 degrees and pushed towardA in its final position. Afterward, the shortgirder B-2 is assembled onto girders A andB - l .

Arrangement of the log girders. Fromleft to right: girder nose (B-1), longgirder ( A) , short girder (B -2 )

The girder nose's (B-1) tenon is insertedinto girder (A) in a horizontal position.



108

The girder nose (B -1 ) is ro ta te d at 90degrees from its previous position.

After rot ation the girder nose (B-1) ispressed forward into girder (A).

The girder nose's (B-1) tenon is insertedinto girder (B-2).

Log girders with the hip rafter and column before inserting the draw pins.




The girders are instal led on top the corner column and the keys are inserted.

The hip ra ft er com ple tes t he assembly. I t is no t necessa ry to f i l l th e gap in girde r B-2 wit ha plug.



110

Top: corner column. Bo tt om from left to righ t: Girder nose B-1 , sho rt girder B - 2 , long girder A, hip raf ter

B-1 : Girder nose




B 2: Short girder (B-2)

C: Hip rafter



112

D: Corner column

A: Long girder (A)



MISCELLANEOUS



114

MISCELLANEOUS 01

Gable board

The gable board is used to cover theends of purlins and girders. The joint connecting the two sloping board is called„ogami”, which means praying with handsclapped together. Three ways of making an

(1) Ogami with encased crossbrace

„ogami” are shown. The gable boards arenot fixed vertically to the ends of the purlins. Aesthetical considerations determinethe angle at which they are fixed. The„ogami” join t is the weakest part of thegable board, consequently when exposed toloading a gap may open at the bottom. Toavoid this occurence methods 1) and 2) are

preferred.

The crossbrace is inserted onto thegable board.

Two pins lock the crossbrace in place.

Gable board

Abutme nts



MISCELLANEOUS 115

Exposed surface after completion



116

(2) Ogami with surface crossbrace

The abutm ents are inserted onto th e gable board (from top to bot tom : Abutments , gableboard, crossbrace, drawpins).

Gable board

AbutmentsCrossbrace

Abutment s



MISCELLANEOUS 117

Same as picture 1 Inserting the crossbrace

Same The drawpins secure the joint.

Exposed surface



118

(3) Ogami with stub tenon and key



MISCELLANEOUS 119



120

Exposed surface



MISCELLANEOUS 121

MISCELLANEOUS 02

Level

Traditional hand level. Longer levelsgive more accurate readings. The level is seton top of the surface to be mea sured. W ate ris poured into the middle cavity. The horizontal line is found when an equal quantityof water flows on either side down the slot.In general, the length of the level is two ken

(six feet) an d the cross section is 2 x 4sun (one sun is one ten th of a foot) . Thi shand level has been commonly used inconjugation with batter posts to set levelreferences around an area.



122

MISCELLANEOUS 03

Batter post

The batter posts are used on frames onwhich lines are taut as reference level. The

post is tap er ed to a point at one en d tomake it easy to drive into the ground. Theother end is crossbilled shaped to facilitatechecking of vertical displacements of the

posts.



Terminology

Several systems exist for designating joints. The terminology is not standardized. As poin ted out in the authors' comm ents , this book aims at describing a wide variety of splicesand joints, describing them in detail. However, no pretense is made of giving an accuratedesignation for all of the joints, nor do we try to explain the origin of the appellationsselected.

The following terminology should provide some help in understanding the technicalterms employed.

Beam (hari) : horizontal structural element which receives loading from a roof or a floorand transmits it to the columns.

Girder (keta) : horizontal str uctu ral element within the framework of the external wall pe rpend ic ul ar to the tie-beam.

Girt (dosashi) : horizontal st ruct ural element within the framework of the ex terna l wallintersecting the second floor beam perpendicularly.

Eave socket (udegi) : Bracket anchoring the eave rafters onto a beam or a girder. Whenthe eave rafters are not braced perpendicularly, the eave socket must be designed tocarry a moment (cantilever eave rafter).

Han ging post (tsurizuka) : Hanging posts are used to suspend the lintel from a beam orgirder when column height exceeds 2,7m.

Tie (nuki) : Bracing element within the in tern al framework of a wall runn ing betweencolumns.

Male-female : The positive and negative part of a splice or joint.Upper wood-lower wood : In connection with joints, the upper and lower wood refer to

two identical ends of a splice or a joint. When assembling the joint, the part whichis joined onto the end already in place is called upper wood. The other end is thelower wood.

Example: Rabbeted oblique scarf splices and oblique scarf stub tenonStub tenon (daimochi) : When the lower wood is meant to be exposed to the vertical loadfrom the upper wood over the entire section of the joint, the assembly is called stubtenon.Example: Blind stub tenon and tie stub tenon

Stepped joint (koshi kake) : When the male end of a joint is stepped to transmit a verticalload onto the female, or vice versa, the joint is said to be stepped.Example: Stepped dovetail splice and stepped gooseneck splice

Dovetail (ari) : The part of a joint shaped like the tail of a dove, narrow at the girth then

flaring out.



124

Example : Dovetailed splice, housed dovetail splice and halved dovetailTenon (hozo) : A projection at the end of the male part of a joint.

Example: True tenon and mortise, rabbeted tenon, dovetailed tenon, blind wedgedtenon

Gooseneck (kama) : Refers to the ribbed end of a long tenon.Example: Stepped gooseneck with tenon and mortise and square stepped gooseneckwith tenon and mortise

Tongue and groove/tongue (mechiire-mechihozo) : Refers t o t he joining of twoelements. A long and nar row teno n (tongue) covers the lengt h of the end surface ofthe male; an equivalent groove is carved on the end surface of the female.

Bli nd joint (hako) : Refers to an encased tenon shaped like the letter „L” or the Japanesekana „a” (ko).

Example: Blind tenon and mortise, blind stub tenon, blind pin and blind spliceCrossbilled or halved joint (isuka) : Refers to a join t where th e male a nd female are

shaped like the beak of a crossbill finch.Example: Halved rabbeted oblique scarf splice, triple-faced and quadruple-facedrabbeted oblique scarf splice, Miyajima splice

Miter joi nt (tome) : When an inclined seam is located at the intersection of two members,the seam is called miter.

Drawpin (komisen) : Two types of drawpin are used to tighten a joint. Some pins workin shear (type A) the othe r type with stand crushing pressure (type B)

Example:A) rabbeted oblique scarf splice, double-faced plug, triple-faced plugB) Mortise rabbeted oblique scarf splice, housed rabbeted oblique scarf splice, blind

pinKey (shachi) : Locking element inserted into a key hole through the sections under shear.

Example: triple-faced halved joint, Miyajima, blind stub tenon, corridor girder, etc.Wedge (kusabi) : T ape red t riangul ar element poun ded between two surfaces, driving

them apart from each other.Example: wedged through halved dovetail, blind wedging joint, wedging joint, etc.

Dowel (dabo) : Encased element inserted into a cavity passing t hro ugh two joiningsurfaces. Example: stub tenon on ties

sumiyoshi & matsui_japanese wood joints

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