Build It

In truss sys­tems, engi­neer­ing and art in­ter­sect, cre­at­ing the open-con­cept de­signs that to­day’s buy­ers seek. But more im­por­tantly, they pro­vide the ba­sis for a strong, sturdy tim­ber home.

Timber Home Living - - Contents -

Su­per Struc­tures

Trusses. You lit­er­ally would not have a roof over your head with­out them. An es­sen­tial el­e­ment to any home, trusses not only sup­port your ceil­ing, they of­fer ar­chi­tec­tural in­ter­est in­side and al­low for the open ex­panse of your great room — whether your tim­ber frame is rem­i­nis­cent of a grand cathe­dral or as cozy as a cot­tage.

Un­like most mod­ern stick-built homes, tim­ber-framed trusses are fre­quently ex­posed, am­pli­fy­ing the feel­ing of space and vol­ume in­side. The tim­ber frame ceil­ing can be at the roofline rather than tied to the base of the truss’s lower beam, and in­di­vid­ual rooms can have vary­ing ceil­ing heights thanks to that flex­i­bil­ity. How­ever, the new­found ceil­ing height and ar­chi­tec­tural in­ter­est of a tim­ber truss of­ten mean an engineer is re­quired to guar­an­tee these beau­ti­ful open trusses will hold up un­der the load of the roof.

Ac­cord­ing to the Tim­ber Framers Guild, (a non-profit mem­ber­ship or­ga­ni­za­tion ded­i­cated to the art and sci­ence of tim­ber fram­ing), to de­ter­mine the span and scale of a tim­ber truss, a struc­tural engineer fol­lows these four steps: Iden­tify and quan­tify the loads of the struc­ture, ac­cord­ing to the In­ter­na­tional Res­i­den­tial Build­ing Code (in the U.S.)

Se­lect the mem­ber sizes and ma­te­ri­als for the tim­ber frame Ex­am­ine how the build­ing will be­have un­der the load

Re­fine ma­te­ri­als and mem­ber sizes to achieve ef­fec­tive per­for­mance Once de­signed and engi­neered to meet the cri­te­ria above, the trusses are

pre-cut in the tim­ber framer’s shop. They may be as­sem­bled there or on­site, depend­ing on the tim­ber framer and the site’s re­stric­tions. Mod­ern tim­ber frame trusses can be con­nected us­ing ex­posed steel plates and brack­ets or the tra­di­tional mor­tise-and-tenon method, us­ing wood pegs to se­cure the pieces to­gether in­stead of metal fas­ten­ers or nails.

There are five ba­sic mod­ern trusses: com­mon, queen post, king post, ham­mer­beam and scis­sor.

The COM­MON TRUSS is, as its name im­plies, the truss most of­ten seen in mod­ern tim­ber frames, and is both strong and af­ford­able. It’s a clean de­sign, eas­ily iden­ti­fied by the man­ner in which the lower hor­i­zon­tal beam (chord) joins the two rafters. The QUEEN POST TRUSS ex­pands on the com­mon truss with the ad­di­tion of two posts, di­vid­ing the gable. These posts are known as queen posts, and work well for draw­ing at­ten­tion to the win­dows in a great room and adding strength to the truss.

The KING POST TRUSS con­tains a sin­gle post in the cen­ter of the gable, known as the king post. This post di­vides the gable in two, and of­ten in­cludes two struts on ei­ther side. The king post truss is of­ten used in con­junc­tion with other types of trusses; its bold ap­pear­ance can serve as a fo­cal point of a home’s de­sign. The HAM­MER­BEAM TRUSS is both dra­matic and com­plex, and, with its open-air cen­ter, it re­quires the skilled eye and hand of an engineer to guar­an­tee its struc­tural in­tegrity. A big ad­van­tage of a ham­mer­beam is that since it doesn’t have a chord (the bot­tom tie beam found in the other truss styles), it can span a wide dis­tance with shorter pieces of wood. This can be a huge as­set if you are build­ing with a species in which long, straight tim­bers aren’t in plen­ti­ful sup­ply.

The SCIS­SOR TRUSS rep­re­sents a de­par­ture from the other four, of­fer­ing a unique de­sign wherein two beams run from the lower part of one rafter to the up­per part of the op­po­site rafter. The beams are notched and fit­ted to­gether to cre­ate a smooth fin­ish and strengthen the truss.

As es­sen­tial as trusses are to the struc­tural in­tegrity of your tim­ber home, they’re much more than that. They’re an artis­tic state­ment that re­flects your life­style and sets the tone for your decor. Con­sider all your op­tions care­fully be­fore choos­ing the truss that’s right for you.

Thanks to Tim­berFrameHQ for con­tribut­ing to this article and for shar­ing the de­signer’s ren­der­ings – at least one of which is bound to be found in any tim­ber frame home.

Knee braces in a post-and­beam frame pro­vide lat­eral sup­port to re­sist wind loads and pre­vent rack­ing of walls. They come in dif­fer­ent de­signs, shapes, and sizes, but their pri­mary func­tion is to pro­vide rigid­ity to the frame wher­ever any ma­jor tim­ber posts and beams may come to­gether.

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