types of join­ery

The join­ery in your frame not only con­nects and se­cures the tim­bers, but also plays a role in trans­fer­ring the loads and stresses of your house from one frame to an­other. All of the many types of joints are de­signed for spe­cific func­tions. Some of the mos

Timber Home Living - - Build It -

Birdsmouth. A com­plex cut made at the tail end, or bot­tom, of a rafter that al­lows the tim­ber to ex­tend over and past the wall top plate, pro­vid­ing a greater bear­ing and at­tach­ment sur­face.

Butt. One of the least com­pli­cated joints, in which mat­ing pieces are square-cut and sim­ply butted against one an­other. Be­cause this joint has lit­tle in­her­ent strength and de­pends on grav­ity or fas­ten­ers to re­main in place, it is typ­i­cally limited to in­ter­sec­tions that are not sub­ject to move­ment or strong op­pos­ing forces, such as where tim­ber posts rest atop hor­i­zon­tal beams.

Dove­tail. A com­monly used joint that in­cludes a fan-shaped tusk or tenon that drops into and in­ter­locks in a sim­i­larly shaped pocket cut. The wedge-like shape of this ex­tremely strong joint pre­vents the in­ter­locked tim­bers from shift­ing or sep­a­rat­ing from one an­other.

Lap. A joint in which the ends of two tim­bers are cut at match­ing an­gles and sim­ply over­laid, or “over­lapped,” then fas­tened to each other. Be­cause the wood grain di­rec­tion of the mat­ing pieces is par­al­lel, these joints are eas­ily con­cealed and of­ten in­vis­i­ble. Lap joints are typ­i­cally used to ex­tend, or lengthen, tim­bers in long hor­i­zon­tal runs.

Mor­tise & Tenon. A fre­quently used joint in tim­ber fram­ing, it in­cludes a male end (tenon) cut onto the end of one tim­ber that fits into a square-cut match­ing fe­male re­cep­ta­cle (mor­tise). Like many tim­ber frame joints, it is of­ten locked in place by the ad­di­tion of hard­wood dow­els, or pegs, called trun­nels (“tree nails”).

Pocket Cut. Sim­i­lar to a mor­tise, this joint re­cep­ta­cle typ­i­cally is “open” in two di­men­sions; cut into the side or top face of a tim­ber, it is de­signed to re­ceive an iden­ti­cally shaped tenon or tusk formed at the end of a mat­ing tim­ber.

Step-Lapped Rafter Seat. An im­proved type of birdsmouth and over­lap­ping joint, it typ­i­cally in­cludes com­pli­men­tary cuts in the rafter and plate to re­sist down­ward and out­ward thrust, as well as side-to-side move­ment.

Shoul­der. A ledge cut into the face of a joint; this added facet in­creases a beam’s load-car­ry­ing ca­pac­ity by trans­fer­ring down­ward force di­rectly to the post while the joint’s tenon re­sists the lat­eral load, or ten­sion.

Tongue & Fork. A spe­cial­ized joint of­ten used to con­nect the up­per ends of rafters that meet to form a peak, or gable. One tim­ber end is cut in an open U-shaped con­fig­u­ra­tion (the fork), and a sin­gle tongue formed on the in­ter­sect­ing tim­ber closely fits into the space be­tween the fork ends.

of wood needed for a tim­ber frame would take sev­eral years un­der cover, most tim­ber framers use green, or un­sea­soned, tim­ber to build their frames. Green tim­ber is eas­ier to work with tools be­cause some woods be­come very hard when dry.

Green tim­ber will shrink as it dries, and tim­ber frame builders must cal­cu­late shrink­age into a frame’s de­sign. While good join­ery de­sign is the best pre­cau­tion against ex­ces­sive shrink­age, shrink­ing tim­bers are some­times held in place by the use of draw­bor­ing. In draw­bor­ing, peg holes are drilled slightly off­set, so that the peg must take on a curve to fol­low the holes. In do­ing so, the peg acts as a spring, pulling the joint tight as it shrinks.

As the green tim­bers in your home dry and shrink, they will de­velop sur­face cracks or splits. These cracks are called checks. Checks do not af­fect the tim­ber’s per­for­mance but merely in­di­cate that the tim­ber is sea­son­ing. Most tim­ber framers use proven strate­gies to min­i­mize check­ing, such as ap­ply­ing paraf­fin to the end grain of tim­bers to slow the dry­ing process. Other com­mon strate­gies in­clude work­ing with a cer­tain cut of wood or species of wood, es­pe­cially in prom­i­nent lo­ca­tions in the frame. You can help min­i­mize the check­ing in your frame by not over­heat­ing your home dur­ing the first few win­ters you live in it and by mak­ing sure the air in your home has ad­e­quate hu­mid­ity.

US­ING RE­CY­CLED MA­TE­RI­ALS

More and more, peo­ple are sal­vaging old tim­bers from old barns, homes and in­dus­trial build­ings. Sal­vaged tim­bers that have been stand­ing for sev­eral decades or cen­turies are al­ready dry and will most likely not shrink any fur­ther. While it’s dif­fi­cult to pre­dict where a green tim­ber will check, any check­ing that has oc­curred in old tim­bers is vis­i­ble and can be hid­den in a new home. Re­cy­cled tim­bers are of­ten re-sawn to re­move any twist or warp that oc­curred as they dried.

The work in­volved in sal­vaging re­cy­cled tim­bers makes them slightly more ex­pen­sive than green tim­bers. Af­ter the old struc­ture is dis­man­tled, the tim­bers must be re-worked. First, nails are re­moved. Then the ex­te­rior weath­ered wood is skimmed and planed smooth. How­ever, if the builder wishes to re­tain the orig­i­nal hand­hewn fin­ish, the tim­bers are steam cleaned in­stead of planed. Drier wood is more dif­fi­cult to work, which also adds to the cost.

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