CONST METH & MAT I
CONST METH & MAT I CM 313
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This 74 page Class Notes was uploaded by Ibrahim Crona on Wednesday September 9, 2015. The Class Notes belongs to CM 313 at University of Washington taught by Carrie Dossick in Fall. Since its upload, it has received 33 views. For similar materials see /class/192187/cm-313-university-of-washington in Construction Management at University of Washington.
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Date Created: 09/09/15
Intro to Wood Design 39 quotT Brought to you by Mike Drorbaugh Sr Eng Wood Specialist APA THE ENGINEERED WOOD ASSOCIATION Mike Drorbaugh is a Senior Engineered Wood Specialist in the Field Services Division at APA The Engineered Wood Association From 1972 1988 mike worked in plywood and OSB mills as a quality auditor In 1988 Mike transferred to APA s Field Services Division Over the years Mike has received specialized training in various aspects of the engineered wood products industry including production quality control design application and code issues Most recently a 10week special Inspection class designed to prepare participants for the WABO wood frame special inspectors testing and certification Mike is a frequent and popular speaker and trainer in the Western US and Canada He has conducted training sessions for Washington Association of Building Officials Oregon Building Officials Association engineering architectural and many other organizations Importance of Wood Renewab e 7 Recydable Preva ent m our hves Carbon Smk Trees generate oxygen Wood is an important natural resource and one of the few that is both recyclable and renewable It is prevalent in our lives and economy houses furniture paper railroads utility poles fuel wood etc Wood and wood products store carbon and trees use carbon dioxide thus reducing the amount of C02 in the atmosphere Plus trees produce oxygen Choices As architects designers or users of products one of your primary responsibilities will be to make choices for yourself and your clients Hopefully those choices will be informed choices that will have a positive impact on both your client and the community at large In some circles it has become fashionable to disdain or boycott the use of wood and wood products with a vague and misguided goal that it will somehow save a tree or even grander save the environment So let s take a few minutes to compare some common construction materials and their environmental impacts Rate of Material Consumption Steel Wood Cement Plastic Alum Consumption after 1955 I Baseli 39 hroughout history prior to 1955 LesterR Brown Director state of the World 1991 A World Watch Institute Report on Progress Toward a Sustainable Society ww Norton 9 Company New York London It is estimated that since 1955 we have all consumed twice as much steel and wood four times as much cement five times more plastic and seven times more aluminum than did all 0fhumaniljy before us combined AthenaTM httpwwwathenasmica M So if we have wood what is the cost to use it versus the cost of using something else The Canadian Wood Council CWC commissioned the ATHENA Sustainable Materials Institute to expand on an earlier 1999 CWC study completed by the institute which contrasted the initial environmental impact of wood steel and concrete in single family home designs This is the updated data It is a Life Cycle Assessment approach as set out in ISO 14000 series of standards Embodied Energy Wood Sheet Metal Concrete These numbers are based on assessment of difference in the categories based on comparing three 2400 square foot houses using different construction materials Neither the steel or concrete houses are fully constructed using those materials For instance the concrete house is insulated concrete form ICF construction that has a wood roof as does the steel framed house Embodied energy includes the direct and indirect energy associated with extraction 39 onsite 39 and 39 and repair activities during the first 20 years of operating the homes including all transportation energy within and between these activities stages Global W Aikmhw r 80000 60000 39 40000 20000 Wood arming Potential Sheet Metal Concrete on iuquot Air Toxicity Concrete Wood Sheet Metal Water Toxicity 4 miiu39 mm 7 y y 1 200000 800000 400000 Wood Sheet Metal Concrete an Aim w 12000 8000 4000 Solid Waste Wood Sheet Metal Concrete US Forest Conversion 100 80 60 40 20 0 Year 1600 1950 2000 Preliminary RPA Assessment Update 1992 as cited in The Great Forest Debate an Evergreen Magazine published by the Evergreen Foundation Mediord Oregon Finally should you choose to use wood products you might consider getting them from the US Canada or other places where sustainable forestry practices are well documented rather than in developing countrieseconomies In the US most of the forest land conversion has been to farms roads and cities And while it is true that the composition of many of the forests has changed Since 1950 growth has exceeded harvest and destruction by disease and fire by 15 25 every year and that trend continues Qua es OfWood OStxung amp Suff g c ones 1y Wurked shapg Warmth amp B my Undesirable Characten39sti cs ofWood ONUL perfemy straght nurpremse onze amp shape affected by mmsture efects oDecays OSuscepuble m InsectDamage Tree Composition Bark gtPROTECTIVE LAYER gtOUTSIDE IS DEAD INSIDE ALIVE Cambium gt VERY THIN gtCREATES NEW CELLS Sapwood gtSTORE NUTRIENTS amp TRANSMITS SAP gtTHICK LIVING Heartwood gtDEAD WOOD gtPROVIDES STRUCTURAL STABILITY Pith gtEARLY YEARS GROWTH gtSMALL WEAK Tree Cells oananly Hulluw Cylmdncal Cells Olmpacts the pmpemes ufwuud Primarily Hollow Cylindrical Cells TRA CHEIDS gtAxis running parallel to the tree gtT0ugh Cellulose bond by Lignin gtIMAGINE A GROUP OF STRAWS Impact on the properties of wood gtPARALLEL WITH GRAIN TUBE STRONG gtPERPENDICULAR WEAK Tree Growth OSpnngWuud earlywuud mm gmwlh Celblngerardlzss am OSummerwuud latewuud Slnwzrgmwlh ecu smaller Anddznser Springwood earlywood gtFaster growth gtCells larger and less dense Summerwood latewood gt Slower growth gtCells smaller and denser APPEARS DARKER HENCE THERINGS Construction Uses for Wood oStmdural Framing OSub uurs and RuufSheaLhmg ond ng 7 Structural amp Exposed m Structural Framing gtGENERALLY PINE FIR OR SPRUCE Sub oors and Roof decking gt GENERALLY WOOD PANELS Siding Structural amp Exposed gtSTRUCTURAL OFTEN WOOD PANELS gtEXPOSED NATURALLY DECAY RESISTANT OR TREATED CEDAR CYPRESS Finish cabinetry and Trim gtPAINTED OR LAMINATED PANELS OR SOFTWOODS gt EXPOSED FINISHED HARDWOODS Lumber Production Sawing 4 oPlam Sawmg Mammum Yield Varymg gain patta n common use 7 memg lumba 1STCUTLOG AND TRANSPO T T0 THEMILL Plain Sawing Maximum Yield Varying grain pattern gtCAUSES DRYING DISTORTIONS gtDIFFERENT SURFACE APPEARANCE gtLESS DURABILITY Most common use Framing lumber gtWHY NOT SEEN STRUCTURAL QUALITIES ACCEPTABLE ECONOMICAL Lumber Production H S awing oQuaner Sawmg ePexpmcmm Annman eusswumcmmemgmn pmm Impmved wunng lmy lass dislumnn Typical Sawing Method 21 Lumber Drying cDmn Medusa em WHY DRY WOOD gtWATER IS 30 TO 300 OF DRY WT gtSeasoned lumber 19 o or less gtHEAVY WEAKER LESS STABLE Drying Tynes Air gtCUT amp STACKED IN OPEN gtAIR DRIED CAN TAKE MONTHS Kiln gtCUT amp STACKED gtKILN DRIED A MATTER OF DAYS gtFASTER HIGHER QUALITY PROCESS Drying Effects Shrinkage gtL0n gitudinal LENGTH NEGLIGIBLE gtRADIAL MEASURABLE AMOUNT 12 BOARD 30 TO 15 2 SHRl39NKAGE 14 gtTANGENTIAL UP TO 50 gt RADIAL STRESSES INDUCED Reduced weight Increase of strength and stiffness More dimensional stable Lumber Surfacing animus Smnmh enmmmm precishm magnum 525 545 omyxzcmg lypimlly pafurmed drymg7 Purpose gt Smooth gtDimensional precision Designations 525 S45 gtFRAMING S4S gtSOME HARDWOODS S2S Performed primarily after drying gt WHY gt SHRIN AGE DURING DRYING Lumber Defects oGruWLh defects 9km at 1mm hules Demy andUr msed darrage oM anufactunng Defects 95pm at checks Cmuk haw Cup andDr ms Growth defects Knots amp knot holes gtLIMBS BRANCHES Decay andor insect damage gtMOIST CONDITIONS BORES Manufacturing Defects Splits amp checks Crook bow cup andor twist WHAT CAUSES THESE DEFECTS gtDIFFERENTIAL SHRINKAGE This is a seasoning check very common in larger timbers It may be considered a visual defect but typically is not a structural defect because checking is considered When design values are assigned to timbers Lumber Grade amp Species Graded by a smgm amp Stiffness Structural Lumber m nAppmme Flmsh Lumber Lumber said by 7 Species and Grade oEetter Grade euigqapnce 05mg url ligia39 QLElity Spe es 9mg pm Strength amp Stiffness or gt STRUCTURAL OR FRAMING LUMBER May be either machine stress rated or visually graded gtDesign values vary depending on SPECIES AND IMPERFECTIONS Appearance gt NON STRUC TURAL OR FINISH LUMBER Effect on price Grade gtHIGHER GRADE gtHIGHER ALLOWABLE STRESSES gtHIGHER PRICE gt1 amp Select Structural grades DIFFICULT TO FIND truss mfgrs buy it gt2 amp btr are MOST COMMON FOR oor joists and rafters gtStud grade most common for wall studs gtIn some applications lower grades may be allowed Appearance gtBETTER APPEARANCE gtHIGHER PRICE gtEXAMPLE 1 x 12 priced in 2001 3 1 BF 2 TWICE 2 THE PRICE OF 3 1 FIVE 5 TIMES PRICE OF 3 Considerations Affecting Strength Oanary Cunsidera uns 9Spenes 90mg Dire11un uerd Vs Gmn OOLher Facturs Lanth at TimE ufMaximumLuadlng 9Tanpemlure at Mmsmre Cundmuns 39SIZE at Shape Chamml Tmtments Species gtHARDWOODS TYP STRONGER DEN SER Grade gt LOWER IMPERFECTIONS INCREASE STRENGTH Direction of Load Vs Grain Length amp Time of Maximum Loading Duration of Load or DOL gtDEFORMATION gtWHY DESIGN CONSIDERS DEAD AND LIVE LOAD Temperature amp Moisture Conditions gtMOISTURE DECAY AND STRENGTH REDUCTION Size amp Shape gt SLENDERNESS RATIO gtAll of these design considerations are outlined in the National Design Speci cation for Wood Construction NDS published by American Wood Council or wwwawcorg Current Design Information OBulldmg cm owns Nauunal Desigq Specificahun fur Wand Cunsh uctmn Fubhshed by AmmEanud Cuunul oTradeAssumanuns oTechmcal puhlicatmns Design professionals in practice doing wood designs look to these sources for current information After this they look to textbooks and technical publications Design Selection Criteria oExpected loadstress andDr oRequired appearance oLucal availability and pnce oSelecnun Ufapprupnate Species and grade Expected loadstress or Required appearance gt LOOK IMPERFECTION S Local availability and price gtEXAMPLE TREATED PINE Vs CEDAR Selection of appropriate species and grade Lumber Pricing Factors OSpemes oGrade 4k arymg pruness OLumber Size omexmxtytu suurce transpunatmn FACTORS YOUMUSTDECIDE 0N WHYDOESSIZEAFFECT COSTBF Laminated Wood Glulam oLaminanun Pruness oWhy Laminate 7 Crale a Size nut amiable naturally Crale Slap lmpmve Quamy Lamination Process gtSELECT LUMBER GRADE gtJOINTS FINGER OR SCARF gtADHESIVES BASED ON EXPECTED MOISTURE Why Laminate Create a size not available naturally Create Shapes gtARCHES CURVES ETC Improved Quality gtPROCESS CONTROLLED gtDEFECTS REMOVED CONSIDERED gtGRAIN DIRECTION CONTROLLED USES gt CHURCHES gt LARGE RESIDENTIAL gt LODGES RESTAURANTS Glulam Concept i i Glulam is basically made from commonly available sizes of dimension lumber typically 2 x 4 2 x 6 2 x 8 etc The lumber is finger joined to make long pieces then glued together face to face to make a larger beam If lots of curvature is needed the lam stock is reduced in thickness down to 58 thicknesses Glulam comes in various appearance classifications Most beams have little curvature or camber and are used in both simple multiple and cantilever span applications As needed for either appearance or to resist high dead loads curvature can be manufactured into beams These are called haunched arches You can see they have pitch taper and considerable curvature all in one piece They also have considerable aesthetic appeal This is a closeup of the haunch portion of the beam showing that the severe curvature requires that the manufacturer use a thin lam stock probably thick Srrurtural Camp nsite Lumb imam v mu Lumber LVL Structural Composite Lumber is primarily represented by LVL shown Other products in this group include parallel strand lumber or PSL and oriented strand lumber or OSL and Laminated Strand Lumber or LSL LVL and PSL tend to be high strength compared to dimension lumber and timbers While OSL has strength and stiffness comparable to dimension lumber Structural Comp osite Lumb er pa Pavalld swam may Laminated Strand Lumber and Oriented Strand Lumber are extremely similar products They are similar to 053 in that they are made from oriented strands the primary difference is the strands are much longer 6 to 12 long It is made like 053 in a continuous process often in a continuous press PSL is made from veneer like LVL and Plywood The veneer is chopped into spaghetti and consolidated into beams in an extrusion process Structural composite lumber is primarily used as beams and headers but can be used as studs primarily for tall walls A great deal of all LVL produced is used as the chords for wood Ij oists Wood Panel Products owhy Fanelize7 Mme cummued39 pmdud Ef nant use uffurestpmducts 9lnmse labor pmmmxmy OTypes WW I Why Panelize Types gtM0re controlled product strength shrinkage etc gtEf cient use of forest products gtIncrease labor productivity gtPlyw00d made from veneer gtC0mp0site panels Combinations ofveneer and nonveneered products gtN0nveneered panels like OSB PB made from smaller particles ofwood Veneered Panels Plywood oThm layers ufveneer glued tugether oodd number uflayers oAltemanng anecan ufveneers OSXZE may a 1n OThlckness w m 14 Thin layers of veneer glued together gtVENEERS ROTARY CUT Odd number of veneers Alternating direction of veneers Face veneers parallel USES gtPrimarily for Roofs walls oors gtEXPOSEDPAIN TED SURFACES gtFORMWORK gtUsually COSTS MORE THAN OSB Plywood HDOMDO Plywood is also available With various overlays The most common overlay is resin impregnated paper that is cured to a hard smooth surface and is designated as HDO for high density overlay or MDO medium density overlay depending on the amount of resin in the paper Sometimes a high density berboard hardboard is also used as a face veneer for use as industrial panels Plyron Veneer Grades OBased an the smnnthness izmtegnty nfthe Veneers oClassi caunns A B c plugged c D oPnce Vananees i Based on the smoothness amp integrity of the veneers Classi cations A B Cplugged C D gtB and better sanded smooth Price Variances 2001 2332 Exterior AC 31 per panel 2332 Exterior BC 20 er anel MOST FORM WORK uses B grade face plywood or plywood overlaid with resin impregnated paper HDO high density overlay and MDO Medium Density Overlay FINISH AREAS MAY REQUIRE A grade faces or overlaid plywood Nonveneered Panels Onented sua Buard OSB OFamclebuard OFlberbuard no one makes waferboard anymore Oriented Strand Board OSB oAltemate gram mayan 75 layers OCEImpressed glued OStxungest cme Nunrvmeered oUses mufs Walls uurs siding l oLung strand likewuud particles INTRODUCED IN THE EARLY 80 s Now about Long strand like wood particles Alternate grain orientation 35 layers Compressed glued Strongest of the Nonveneered gtWHY IS IT THE STRONGEST gtLength and ORIENTATION 0F STANDS Generally more economical than Plywood Uses Sheathing for oors walls roofs amp siding WHY IS IT GETTING WIDESPREAD USE gt STRUCTURALLY SOUND gtECONOMICAL SUBBSTITUTE FOR PLYWOOD gtNEW GROWTH TREES Structural Panel Production US amp Canada BSF 38quot 2010 45 Plywood 155 OSB 292 Total 447 10 Plywood 1970 1975 1980 1985 1990 1995 2000 2005 2010 Numbers are in billions of square feet 38 basis One billion square feet of panels is a stack of 4 X 8 X 38 panels 168 miles tall OSB production outpaced plywood production in 1999 Particleboard amp Fiberboard oFamclebuzrd B 9Srrallvmudpamdes 39 Uses Luwmmsmrearas substrates and UDL OFiberbuard ampMDF snmmwuud ba Luwm Med density Luwastxangvh quotcs Particle board is one of the older panel products and is made from wood ber about the size of sawdust from a typical home workshop table saw It generally is bonded with a water resistant not waterproof ureaformaldehyde adhesive It is very smooth very uniform in thickness and very dense Good for oor underlayment where it won t get wet and as a substrate for wood veneers or plastic lm overlays for furniture and cabinets Fiberboard is a homogeneous panel made from cellulosic ber usually wood or cane but sometimes paper which has a density of between 10 and 31 PCF Fiberboard is used as wall sheathing has some bracing and insulation value and acoustic tiles Medium Density Fiberboard MDF has higher density from 37 to 50 PCF MDF is used with overlays or coatings primarily for furniture and moldings Panel Standards amp Grading oFSlrm andFSZrm publishedbyNahunal lnsumte ur Standards APA mg as animal cleaning 1w andsecretamt em camensw m a sundam based an enamnmmny In 1965 American Plywood Association APA now APA The Engineered Wood Association proposed a draft to National Bureau of Standards now NIST that consolidated several commercial standards for softwood plywood and became PSI which is updated every 10 yrs or so Standards based on Structural adequacy Dimensional Stability Durability of Adhesive Strucmral Ratings rmztmrm mux Euthplyvmudand osa Panel Grade Span Rating gt IN INCHES gtPERPENDICULAR TO SUPPORT gtLARGER ROOF SPAN gtSMALLER FLOOR SPAN Exposure Durability Classi cations OExtenur 7 Siding m continuous exposure oExpusurel same waterpruufgluebutluwer qualityveneers r Ennr pmtected environments Exposure Durability always on trademark gtExteri0r siding or continuous exposure but does indicate rot resistance gt Exposure 1 Same waterproof glue but veneers are not as high of quality as exterior grade for floors roof and wall sheathing It s the most common rating for structural applications gtInteri0r for protected applications where MC lt16 o Chemic al Treatment Cumbusnblllty ODecay amp Insect Combus bility gtFIRE RETARTANT TREATED gtIMPREGNATED UNDER PRESSURE gtFRT Treatment causes wood panel strength reductions Decay amp Insect gtPRESSURE IMPREGNATED gtUP TO 30 YEAR LIFE gt TYPES CREOSOTE PENTACHOROPHENOL OILY CAN T PAINT WATERBORNE SALTS GREENISH CAN IN Chromated Copper Arsenate CCA being phased out the new generation of wood preservatives e g Alkaline Copper Quat ACQ and Copper Azole are more corrosive to bright and zinc coated metal fasteners HIGH MOISTURE USES gt WHYNOT USE DECA YRESISTANT WOODS CEDAR RED W00Dl 51 Large timbers build up a char layer that insulates the underlying wood from the heat allowing wood to retain much of its strength for long periods of time in a re Unprotected steel quickly looses its structural properties in a fire There is a type of construction under the building codes called Heavy Timber construction which allows larger building heights and areas because of the good performance in re of heavy timbers Wood Polymer Composite Planks QEasym Finish ADxEdetages Henvy Wood Fasteners Nals OWuud amp Lag Screws oBuus oTuuLhed Plates oSheet Metal amp Metal Framing Dames oMachme Dnven Staples amp Nads oAdhesnes Nails iii oSharpEned metal pm Olnstallaunn Hammer nr n mechanical nal gun Ocnmmnn Nan oFimsh Nan OOLhEI types Common ltgtflat heads used mostly for structural connections Finish Nails ltgtvirtually headless finish woodwork Common Used for Framing Large Shank amp Head Bi Smaller Shank less chance for splitting wood Used Shingles Rough Casings Casing Finish Brad Finish Components Sink Head Deformed Shank Very Hard to Remove DW amp Flr Concrete Masonry amp Concrete Finish Flooring SQ Head Reduces Cracking Roofing One of Many Some Have leadRubber Washers Be very careful When specifying nails as nomenclature is uncertain and variable It s best to specify using diameter length and shank type for nails Nails 05123 7 Measuredin pennies OCEIaungs 9Enghi Flam uncuated steel 5 9Curmsunrreslslanl 39 9ReSnmel D Size Measured in pennies g Brice of 100 nails long ago gtCorresponding Lengths Same for Common amp Finish gtMost Common Light Frame Nails 16d for 2 10D AND 8D Coatings Bright Plain uncoated steel gtMOST COMMON USED NON CORROSIVE OR CONCEALED CONDITION Corrosionresistant gt EXPOSED TO WEATHER gtRUST OR STAIN LUMBER gtGALVANIZED ALUM SS ResinNinyl gtDecrease Drive amp Increase Holding gtThis nail has a smaller shaft commonly called a sinker Anchorage l Ei gtFace Perpendicular to Grain gtEnd Parallel gtToe Angle to Grain Which Has the Most Holding Power Which is most common Anchorage Machine Driven Nails amp Staples oNail Guns Staple guns 13 Oimpmved Pruducnvity oUsed in many applicatmn OFuwer actuated fasteners Canned unis APPLICATIONS gt FRAMING gt SHEATHIN G gtROOFIN G Head type gtPHILLIPS gt SLOTTED gt SQUARE HEAD gtPAN FLAT ROUND ETC Sizing Gauge amp Length gtWIRE GAUGE SAMPLES 8 amp 10 gtLENGTH IN INCHES AND FACTIONS Installation gtHAND SCREW DRIVER gt SCREW GUN OR DRILL HOLDING POWER gtTIGHTER STRONGER THAN NAILS gtCAN BE BACKED OUT amp REINSERTED Uses gt CABIN ETWORK gt SOME FRAMING APPLICATIONS gtDECKING BETTER HOLD LESS SQUEAK Lag s Crews Lag amp Drywall Screws oDrywall screws Used m attach drywall Lag Screws Large screws gtVery LARGE Screws Wrench 14 26 in 12 to 10 gtFOR HEAVIER STRUCTURAL CONNECTIONS Square or octagonal head Installed w wrench Drywall screws Used to attach drywall ltgtDrywa Screws Size 1 14 1 58 2 gtScrew Gun Fast Wood or Metal Bolts oHeavier structural cunnectmns Slzes OTypes Ma 1 A Heavier structural connections gtCOMMONLY USED W TIMBER CONSTRUCTION Sizes gt14 inch to 1 inch gtLENGTH ABOUT ANY PRACTICALLY 10 12 Types Machine gtSQUARE OR OCTAGONAL HEAD gtUSED WITH WASHER Carriage gtROUND BUTTON HEAD gt SQUARE SHANK INHIBITS TURNING Washers gtDISTRIBUTE THE COMPRESSIVE FORCE Toothed Plates he plat w numemus teem uUsea wmmum unrtmsses mm mm numbers quotmama fasmnzxs Sheet Metal Framing Devices oLxght Wm a Framing Jmst Hangers 9Frammg anth 9mg anth 9Ra er annhnr oHeavy Timber m Laminated Framing NUMEROUS TYPES AND SHAPES MOST COMMON JOIST HANGER LIGHT WOOD FRAMING ATTACHED WITH SCREWS OR NAILS HEAVY TIMBER ATTACHED WITH BOLTS LAGS Adhesives ondely usedTn Lhemanufacture ufwuud pmau mm W 7 abmeky u ON SITE gtLESS USES BECAUSE OF NEED TO CLAMP USES gt FLOOR SHEATHIN G gtBASE SOLE PLATES gtWALL PANELS not recommended for wall sheathing In some cases not allowed by code gtPANELIN G WHERE THERE IS A NEED FOR CONCEALED FASTENERS gt INCREASE STIFFNESS ELIMINATE SQUEAK Wood Manufactured Components WTrusses nWood LJosts Beams oPanel Comp onean Trusses ypes ofTrLsses rFloor ampRoof Trusses com Lmds P1tthma0 omxhng IBeams urIJoists Uses gtFLOORS amp ROOFS Sizes gtTypically 9 12 TO 24 DEEP gtLENGTH UP TO 40 FEET Composition amp cost gtTOP amp BOTTOM LUMBER OR LVL gtWEB OSB PLYWOOD gtCOST COMPARABLE TO 2x Why Use Trusses or IBeams an am sad dlmmsmnal scammy o lnstallauun mugs lam 3 3 E 1 9 U Relativ No 1DF Strength V Straight v engineered W products Pre 1i ctable Al e i Ef cient Use of Fiber 55 5r quot ti 046 less than lumber at 16quot vs Ijoist at 192quot 036 less when both are at 16quot i US Forest Service 73 Choices Finally do not take from this lecture that using steel glass concrete or any other building material is bad For certain applications they are the correct choices just as wood is the correct choice for many applications All anyone can do is the best they can to make decisions that both satisfy their client and have the least impact on everyone else and the generations to come Good uck