BROCHURE # 50 DOES MY BUILDING DESIGN NEED ENGINEERING?

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1 BROCHURE # 50 DOES MY BUILDING DESIGN NEED ENGINEERING? Overview Building cnstructin has becme increasingly cmplex during the last tw decades. Buildings are larger and use new materials and cnstructin methds. Updated structural stability and safety requirements address ptential damage frm fire, earthquakes, wind, snw, and ther frces. Because f this, building design has becme increasingly cmplex. When a building f therwise cnventinal cnstructin cntains structural elements the Internatinal Residential Cde (IRC) d nt cnfrm t, these elements shall be designed in accrdance with accepted engineering practice. It may be pssible t have nly a prtin f the structure designed and calculated, hwever the extent f such design must demnstrate cmpliance f the nncnventinal elements with ther applicable cde requirements, and shall als be cmpatible with the perfrmance f the cnventinal framed system. Engineered design in accrdance with the 2012 Internatinal Building Cde (IBC) is permitted fr all buildings and structures, and parts theref, included in the scpe f the IRC. As a result, wners and builders have several design ptins: engineered design, prescriptive design, r a cmbinatin f the tw. These ptins allw bth trained prfessinals and rdinary citizens t design safe, ecnmical, and durable structures. Engineered Design With the engineered design methd, a design prfessinal registered in Washingtn State analyzes the building s design and calculates the strength f the cmpnents t ensure that it will withstand the wind, earthquake, snw, and gravity lads required by the cde. This methd is used t design buildings that: Are cmplex r f irregular shape; Are nt made frm wd, r D nt therwise meet the prescriptive requirements f the cde. Engineered designs submitted fr building permits must have the designer s structural calculatins attached t the plans. Bth the plans and the calculatins must have the designer s registratin stamp and riginal signature n them; cpies cannt be accepted. The designer must transfer any hld-dwn and shear wall nailing schedules, beam, pst, framing anchr, and ther specificatins included in the calculatins t the plan sheets. The applicant must prvide tw sets f all plans, calculatins, and specificatins when they apply fr a building permit. Prescriptive Design Prescriptive design is an alternative ckbk way t design a building t meet general cde requirements. The prescriptive methd can be used fr buildings that: Use cnventinal wd-framed cnstructin techniques; Have an rdinary shape (rectangle r cnnected rectangles); Have bearing walls n mre than 10 feet high; and Have lateral wall bracing (braced wall lines) accrding t the cde s prescriptive requirements. Unlike engineered designs, prescriptive designs can be drawn by nearly anyne with a ruler, paper, pen, basic drawing skills and a general understanding f the prescriptive design requirements described in this brchure and the Braced Wall Panels brchure. Kitsap Cunty Department f Cmmunity Develpment Phne: (360) Divisin Street, MS-36 Fax: (360) Prt Orchard, WA Frm Number: 5050B Kitsap1@c.kitsap.wa.us Revisin Date: 3/7/16 Page 1 f 6

2 Irregular Structures As mentined abve, irregular shaped buildings must be designed by a licensed design prfessinal. Accrding t the Internatinal Residential Cde, and the Internatinal Building Cde a building is cnsidered t be f irregular shape when any ne f the six cnditins listed belw are present. If yur building cntains any ne f these six cnditins, it is cnsidered an "irregular structure." In this case, an engineer r architect licensed by the state f Washingtn must prepare a lateral bracing design. Cnditin 1 When exterir braced wall panels are nt in ne plane vertically frm the fundatin t the uppermst stry in which they are required, the structure shall be cnsidered t be irregular. [See Figure (2)] Exceptin: Flrs with cantilevers r setbacks nt exceeding fur times the nminal depth f the flr jists [See Figure (2)] may supprt braced wall panels, prvided: 1. Flr jists are 2" x 10" r larger and spaced at nt mre than 16" n center. 2. The rati f the backspan t the cantilever is at least 2 t Flr jists at the ends f braced panels are dubled. 4. A cntinuus rim jist is cnnected t the ends f all cantilevered jists. The rim jist may be spliced using a metal tie nt less than 0.058" (16 galvanized gauge) and 1.5" wide fastened with six, 16d nails. The metal tie shall have a minimum yield f 33,000 psi 5. Jists at setbacks r the end f cantilevered jists shall nt carry gravity lads frm mre than a single stry having unifrm wall and rf lads, nr carry the reactins frm headers having a span f 8 feet r mre. Cnditin 2 Where a sectin f flr r rf is nt laterally supprted by braced wall lines n all edges, the structure shall be cnsidered t be irregular. [See Figure (3)]. Exceptin: Prtins f rfs r flrs that d nt supprt braced wall panels abve may extend up t 6 feet beynd a braced wall line. [See Figure (4)]. (Such as a cvered prch) Figure (2) Figure (3) Kitsap Cunty Department f Cmmunity Develpment Phne: (360) Divisin Street, MS-36 Fax: (360) Prt Orchard, WA Frm Number: 5050B Kitsap1@c.kitsap.wa.us Revisin Date: 3/7/16 Page 2 f 6

3 Figure (4) Cnditin 3 When the end f a required braced wall panel extends mre than 1 ft ver an pening in the wall belw, the structure shall be cnsidered t be irregular. This requirement is applicable t braced wall panels ffset in plane and t braced wall panels ffset ut f plane as permitted by the exceptin in item 1 abve. [See Figure (5)]. Exceptin: Braced wall panels are permitted t extend ver an pening nt mre than 8 feet in width where the header is a 4-inch by 12-inch r larger member. Cnditin 4 Where penings in flr and rf diaphragms having a maximum dimensin greater than 50 % f the distance between lines f bracing r an area greater than 25 % f the area between rthgnal pairs f braced wall lines are present, the structure shall be cnsidered t be irregular. [See Figure (8)]. Figure (8) Kitsap Cunty Department f Cmmunity Develpment Phne: (360) Divisin Street, MS-36 Fax: (360) Prt Orchard, WA Frm Number: 5050B Kitsap1@c.kitsap.wa.us Revisin Date: 12/19/13 Page 3 f 6

4 Cnditin 5 Where prtins f a flr level are vertically ffset such that the framing members n either side f the ffset cannt be lapped r tied tgether in an apprved manner, the structure shall be cnsidered t be irregular. [See Figure (6)]. Exceptin: Framing supprted directly by fundatins need nt be lapped r tied directly tgether. Figure (6) Cnditin 6 Where braced wall lines are nt perpendicular t each ther, the structure shall be cnsidered t be irregular. [See Figure (7)]. Braced Wall lines are nt perpendicular Figure (7) Braced Wall lines are nt perpendicular Kitsap Cunty Department f Cmmunity Develpment Phne: (360) Divisin Street, MS-36 Fax: (360) Prt Orchard, WA Frm Number: 5050B Kitsap1@c.kitsap.wa.us Revisin Date: 12/19/13 Page 4 f 6

5 Cnditin 7 Where abve grade stries, braced by wd wall framing, include masnry r cncrete cnstructin. Exceptin: Fireplaces, chimneys and masnry veneer 5 r less in thickness, prvided the additinal prvisins f IRC Sectin R703.7 are utilized. In seismic design categry area D 2, structures with anchred stne r masnry veneer require full engineering. See IRC Sectin R IBC Figure , Basic Cmpnents f the Lateral Bracing System Prescriptive Design If yur building design is nt f "irregular shape," it can be designed in accrdance with "prescriptive design." Prescriptive design is based n the cncept f a structural bx. One r mre structural bxes may be cmbined t create the building. Bxes may be stacked r placed side by side in the design as lng as each bx has a flr, walls and rf r ceiling, that cnnect tgether in such a way that the walls run parallel r perpendicular (90 angles) t each ther and d nt exceed 10' in height. T give the bxes adequate strength t resist the frces f wind, earthquakes, snw and ther lads, walls must have enugh slid areas withut penings (such as drs, windws, fireplaces, etc.) where braced wall panels can be built. The exterir walls, with their braced wall panels, make up the exterir braced wall lines. Interir partitins ften make up the interir braced wall lines. These braced wall lines, tgether with the ther lad-bearing walls, the fundatin, and the flr and rf diaphragms make up the essential elements f a prescriptive design. In Kitsap Cunty, a Seismic Design Categry D 2 area, all buildings using prescriptive design must satisfy all f the prescriptive design requirements listed belw. If any prtin f the building des nt satisfy all six f the fllwing prescriptive design requirements, the building must have a lateral bracing design prepared by an engineer r architect licensed by the state f Washingtn. 1. The building must have braced wall lines (walls cmprised f a series f braced wall panels) arund the perimeter, and thrugh the interir f the building at least every 25 feet, except that ne rm that des nt exceed 900 square feet, may g up t 35 feet. In n instance may a building exceed 35 feet in length withut interir braced wall lines. Kitsap Cunty Department f Cmmunity Develpment Phne: (360) Divisin Street, MS-36 Fax: (360) Prt Orchard, WA Frm Number: 5050B Kitsap1@c.kitsap.wa.us Revisin Date: 12/19/13 Page 5 f 6

6 2. Every braced wall line shall have a braced wall panel placed at the end f the braced wall line, r within 8 feet f the end if the apprpriate crner panel and/r hlddwn is used. Every braced wall line must cntain braced wall panels at least every 25' n center alng the entire wall. (Fr example, a 50-ft-lng braced wall line must cntain a braced wall panel at each end and ne in the middle.) See IRC Sectin R fr mre infrmatin. 3. Every braced wall panel shall be at least 4' wide (except the 2'8" alternate braced wall panel described in IRC ) and shall be cnstructed by ne f several methds as indicated in IRC Sectin R Bearing walls shall be cnstructed f 2 x 4 r 2 x 6 studs, nt mre than 10' in height. 5. The building must have a reinfrced, cntinuus fundatin system cmpliant with the Kitsap Cunty Prescriptive Fundatin Details (see brchure #49, Fundatin Requirements). Nte: If the fundatin des nt meet the minimum prescriptive requirements, r if the fundatin walls are mre than 9' high, frm the tp f the fting, t the tp f the wall, fundatin engineering is required. See Tables R (1) & R as adpted and amended by Kitsap Cunty in Kitsap Cunty Cde Sectin Cnclusin If yur building plans meet the prescriptive design criteria, the plans must clearly indicate all the braced wall panel lcatins and types (n exceptins). The plans must als prvide details describing hw the panels will be cnstructed, and must shw all hld-dwn lcatins (if any) n bth the flr plans and the fundatin plans. If yur building plans include a design prepared by a Washingtn State registered architect r prfessinal engineer, the plans must have the engineer's r architect's cnstructin requirements clearly indicated n the plan sheets and must have the design calculatins attached t the plan sets fr review(n exceptins). All plans designed by an engineer r architect must bear the riginal stamp and signature f the registered prfessinal wh prepared them. N phtcpies will be accepted unless specifically authrized by the design prfessinal. Kitsap Cunty Department f Cmmunity Develpment Phne: (360) Divisin Street, MS-36 Fax: (360) Prt Orchard, WA Frm Number: 5050B Kitsap1@c.kitsap.wa.us Revisin Date: 12/19/13 Page 6 f 6