IRWIN Rafter Square Reference Guide
IRWIN Rafter Square Reference GuideIRWIN Rafter Square can also be used as aProtractor, Saw Guide, and Tri & Miter SquareComplete Instruction Book andRafter Length TablesL’équerre de charpente IRWIN peut égalementêtre utilisée comme rapporteur d’angle, guide descie et équerre à épaulement et à ongletGuide de référence pour l’équerrede charpente IRWIN La escuadra IRWIN para vigas también sepuede emplear como protractor, guía de sierray como tri-escuadra de inglete.Manuel d’instructions complet ettableaux des longueurs de chevrons 20118935 NorthPointe Executive DriveHuntersville, NC 28078 - U.S.A.1-800-GO-IRWINwww.irwin.comGuía de referencia IRWIN para escuadras de vigaManual de instrucciones completoy tabla de longitud de vigasC10110464www.irwin.com
IRWIN Rafter Square Reference GuideProfessional tradesmen use Rafter and Framing Squares to save time on roofconstruction projects. All of the necessary cuts for a particular rafter can be laidout with these two squares. This reference guide will provide a basic knowledge ofrafters and the rafter square to help you determine what scale and number on thesquare to use, as well as all necessary tables for reference.CONTENTSDiagrams of Rafter and Framing Squares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Types of Rafters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Using the Rafter Square . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Common Rafters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Common Rafter Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Hip and Valley Rafters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Hip Rafter Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Valley Rafter Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Jack Rafters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Jack Rafter Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Dormer Rafters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Degree Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Rafter Length Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
DIAGRAM OF RAFTER SQUAREMARK ALONGTHIS EDGEINCH SCALE234HIP AND VALLEYRAFTER SCALE( TOP CUTS )56DEG1RAFTER SEATNOTCH CUTSCRIBINGSLOTS( SPACED ¼” )P10 VA L12 TO P625715 C UTS83018103524123040154513505524603065707580SEAT CUTSCOMMON RAFTERSCALE ( TOP CUTS )COMMOONTU51011522031PCPROTRACTOR/DEGREE SCALE425345678HIINCH SCALETSFOOT[Diagram 1 – IRWIN Rafter Square]2
TYPES OF RAFTERSCommon Rafter: A rafter that runs perpendicular (90 ) from the top of the wallplate to the roof ridge; its length forms the hypotenuse or diagonal of a right (90 )triangle, with the rise and run forming the right angleValley Rafter: A rafter that runs from the top of the wall plate to the roof ridgeat the intersection of the gable extension with the main roofValley Jack Rafter: A rafter that runs from a valley rafter to the roof ridge,perpendicular to the ridgeHip Rafter: A rafter that runs diagonally from the top of the wall plate to the roofridge, forming the outside corner of the roofHip Jack Rafter: A rafter that runs from the top of the wall plate to the hip rafter,perpendicular to the wall plateCripple Jack Rafter: A rafter that runs from a hip rafter to a valley rafter,perpendicular to the roof ridgeDormer Rafter: A rafter that sits on top of the main roof without cutting into themain roof. (For example, this rafter would be used when remodeling or adding onto an existing structure.)Figures 1 and 2 on the next page show each type of rafter.3
A (DormerRafterSection)DORMERVALLEY JACKVALLEY RAFTERRIDGEFIGURE 1: Types of Rafters - 3DAll cuts on this roof can be made by using the appropriate inch rise number on the rafter square.RIDGEHIP RAFTERB (DormerRafterSection)[Fig. 1 – Types of Rafters – 3D]
5RIDGEDORMERFIGURE 2: Types of Rafters - Top LATE[Fig. 2 – Types of Rafters – Top View]
USING THE RAFTER SQUAREThe use of the Rafter Square is based on two simple building measurements:(1) the rafter run and (2) the rafter rise. These can be obtained from buildingblueprints, drawings, or actual measurements. The tables included in this referenceguide are based on these twoRISE BBTERsimple measurements.R AFRAFTE(See figure 3.)RUN BRCRafter Run: The horizontaldistance that the rafter willspan, measured in feetR AFTERARISE CRISE ARUN CRUN ARafter Rise: The verticaldistance between the highestand lowest point of the rafter,measured in feetRUN AInch Rise: The rise measuredin inches per foot runThe Inch Rise gives you thecorresponding scale numberto use on the square and iscalculated as follows. InchRise, run, and the tables inthe back of this guide are allthat you need to layout rafterlengths and cuts for common,hip, valley, and jack rafters.[Fig. 3 – Rafter Rise and Run]R AFER AR AFTR AFTERTERBRUN BR AFATERRISERUN ABRUN BFOR EVEN PITCHEDROOFS RUN A RUN BRAFTERRISERUN6
RAFTER RISE (ft) x 12RAFTER RUN (ft)The procedure for basic roof construction is as follows (See figure 4.):INCH RISE (SCALE NUMBER)1. Obtain Rafter Run: Measure or calculate the horizontal distance the rafterwill span, starting at the outside of the wall on which it rests and including anyboarding on the wall if it extends to the wall top plate.2. Obtain Roof Rise: Measure, calculate, or obtain from the blueprints thedistance in feet the ridge will be from the top of the wall.Use the following table to convert inches to feet:Convert Inches to Feet1" .08'2" .16'3" .25'4" .33'5" .42'6" .50'7" .58'8" .67'9" .75'10" .83'11" .92'3. Calculate Inch Rise: Using the table above, convert rise to feet in decimalform and calculate using the Inch Rise Formula.EXAMPLE: Run 15'; Rise 8'8" or 8.67'8.67 (ft) x 1215 (ft) 6.94 in/ft. RunYou may round off Inch Rise to the nearest inch, which can make the actual roofrise slightly higher or lower but will not matter in most cases. If the Inch Rise isprovided on a blueprint, the previous calculation is not needed.With the Inch Rise calculated, we are now ready to layout each type of rafter.7
[Fig. 4 – The Common Rafters]PLUMB CUTAWITHOUT RIDGER AFTERLENGTHRISETAILOREAVERUNSEAT NOTCHSET ON TOPPLATETAIL RUNPLUMB CUTB WITH RIDGER AFTERLENGTHRISETAILOREAVE90 RUNTAIL RUNFIGURE 4: Common Rafter8INCH RISE PER FOOT RUNRISE x 12RUNRAFTER LENGTH RUN2 RISE2(FIND IN TABLES)
COMMON RAFTERSCommon Rafter Length: Once Inch Rise and Run are calculated, use the tablesin the back of this book to find common rafter length. NOTE: For a run greater thanthat given in the tables, add any two runs that will equal the desired run, then findthe respective lengths for those two rafters and add them together.EXAMPLE: Using the 7 Inch Rise table (and our 15' run), the common rafter lengthis 17' 43 8". This is the rafter length from the top cut to the seat plumb mark.Tail or Eave Length: The tail or eave overhang must be added to the rafter length.(See figure 5 for various eave constructions.)EXAMPLE: With a tail run of 1' 8", use the same 7 Inch Rise table, under CommonRafter Length:1' Run 1' 17 8"8" Run 91 4"1' 8" Tail 1' 111 8"Common Rafter Lumber Length: To obtain the total lumber length required,an allowance for the bottom plumb cut must be added. (See figure 6.) Thisallowance can be obtained by using the tables as well.EXAMPLE: Using the 7 Inch Rise page and assuming 2 x 6 lumber (which has adepth of 51 2"), use the Rafter Depth and Bottom Allowance table to see that thecommon and jack allowance equals 33 16" inches. The total lumber length requiredfor this common rafter is:RAFTER LENGTHTAIL LENGTHBOTTOM ALLOWANCETOTAL LUMBER LENGTH9 17' 43 8" 1' 111 8" 33 16" 19' 611 16"
Common Rafter Layout1. Top Plumb Cut: If the lumber is notstraight, always put the high or crownside up. At the top of the rafter, placethe rafter square on the face of therafter as in figure 7. Pivot the layoutsquare so that the number 7 on thecommon scale lines up with the edgeof the rafter. Starting at the pivot pointalong the top edge of the square, markyour line while holding the pivot pointfirmly against the rafter and keepingthe number 7 lined up properly. Thiswill be the top plumb cut.Top plate using a 2 x 10.Best for a flat pitch roofwith 4 inch rise or less.2. Seat Notch or Birds Mouth:Using the rafter length (our example:17' 43 8"), measure down the top ofthe rafter and mark another plumbmark the same as in Step 1. This linerepresents the outside wall of yourbuilding. From this point, there are twoalternatives to marking the seat notch:Use this type of eavewhen there is verylittle overhang.a. V arying horizontal seat cutlength. As shown in figure 8a,line up the dash line at 41 4"on the square with the plumbmark and make a horizontal line,which will be perpendicular toWhen a wider eaveis wanted, 2’ or greater,some type of supportwill be needed. Tosupport center ofplywood soffit, nailup thru plywoodinto support.10[Fig. 5 – Eave Constructions]
the plumb mark. Make all seat notches the same depth and never notch morethan halfway through the rafter.b. 3 1 2" horizontal seat cut length. As shown inGTHfigure 8b, placing the pivot of the squareLENTERR AFagainst the outside of the rafter, lineup the dash line at 31 2"on theOR Hsquare with the plumbTAIL LEN GTEE AVmark and make theBOTTOMPLUMB CUTSEAT DEPTHhorizontal line.3. Tail or Bottom PlumbCut: Using the tail length(our example: 1' 113 8"),measure down the rafterfrom the seat plumb markand make the bottomplumb mark the sameas in Step 1. If the markis too close to the endof the lumber, turn thesquare over to the bottomedge of the rafter, andstill using the number 7,make the bottom plumbmark. You may wish toleave the tails long andmake the bottom plumbcuts after all the raftersare set.SEATPLUMBMARKSEAT NOTCHORBIRDS MOUTHLU MBERLENTOPPLUMBSEATGTHBOTTOM PLUMBCUT ALLOWANCE[Fig. 6 – Common Rafter Layout][Fig. 7 – Top Plumb Cut ofa Common Rafter]FIGURE 6: Common Rafter LayoutMARK ALONGTHIS EDGEDrawing shows squarein position for markingtop plumb cut of acommon rafter witha 7'' rise, or 30¼ .1234S E AT CS30C UT 245UTS753024703-V 2 165510H I P 10 116812 S556710 P C UT 50457 8O N TO 40 452 36M5M514 C O 30 3325220115105TO P 5 18AL11680D EG
5HORIZONTAL ORBOTTOM CUTS E ATC UTS80475SEATDEPTH5D EGADD FORTAIL OR EAVE390 2PLUMB MARK11 23 45 6 H IP - V17 8 ALT21012 15O P C UTS31041851524 36C 702025 3O M M O N8 10 10 3 5 TO P C 2 140 UTS 5 13452450 55 60 306570[Fig. 8a – Seat Notch Layout(varying seat cut length)]6BRING LINE ON SQUARE INLINE WITH PLUMB MARKNotch Layout(31 2" seat cut length)]1290 ADD FORTAIL OR EAVE65SEAT CUTS4ALCU IG N SSQ T LIN EATPLU UARE WE O NM B ITHMARK3PLUMBMARK3-1/2”SEAT CUTSP IV OTFIGURE 8a: Seat Notch Layout (VaryingSeat8bCut –Length)[Fig.SeatD EG807530 242 1SP C UT 5 4 3V A L TO 8 7 6H IP - 12 10 9251814 316 55 108 7 UTS20 112 10O N TO P C 30 2518 15 C O M M 45 40 354250300 5565 67012FIGURE 8b: Seat Notch Layout (3½" Seat Cut Length)5
HIP AND VALLEY RAFTERSBecause hip and valley rafters both run at a 45 angle to the common rafter, theyare treated very similarly, and the cuts and lengths apply equally to both types ofrafters. (See figure 2.)Hip-Val Length: Using the tables, obtain the hip or valley rafter length.EXAMPLE: For our example (7 inch Rise, 15' run), the hip or valley rafter lengthis 22' 113 8".[Fig. 9 – Top View of Hip Rafter Layout]RAEFTRLINTERSECTION OFHIP, RIDGE ANDRIDGE JACKENHGTTOPBEVELCUTAL M IL TI F O WA E RUS N CED ECUT TOP WALLPLATE BACK MITERALLOWANCETOP WALL PLATEMITERFASCIA13FIGURE 9: Top View of Hip Rafter Layout
BEVEL CUT[Fig. 10 - Hip Rafter Layout]LU MBERLENGTHTO PVI EWTER AFRLTHEN GSI DEVI EWLTAITOPPLUMBCUTSEAT DEPTHHORIZONTAL SEAT MARKSEAT PLUMB MARKMITERALLOWANCEIF USEDSEAT NOTCHOR BIRDS MOUTHBOTTOM PLUMB CUT ALLOWANCE FROM TABLESTail or Eave Length: Use the same procedure as that for the common rafters,taking care to use the Hip-Val column in the tables instead.FIGURE 10: Hip Rafter LayoutEXAMPLE: With a tail run of 1' 8", use the same 7 Inch Rise table, under Hip or ValRafter Length:1' Run 1' 63 8"8" Run 121 8"1' 8" Tail 2' 61 2"NOTE: If miter is desired, add the miter allowance from the tables. (See figures9 and 10.)14
Hip-Val Lumber Length: To the above determined lengths, add an allowance forthe bottom plumb cut as well as the miter allowance if used, to get the overalllumber length.EXAMPLE: Assuming a 2 x 6 again and a miter allowance using a 11 2" rafterthickness:RAFTER LENGTHTAIL LENGTHBOTTOM PLUMB ALLOWANCEMITER ALLOWANCE 22' 113 8"2' 61 2"33 16"7 8"LUMBER LENGTH 25' 915 16"NOTE: Only add miter allowance if miter is used.Hip Rafter Layout1. Top Plumb Cut: Use the square in the same manner as in Step 1 of thecommon rafter top plumb cut, except using the Hip-Val scale. Make the topplumb cut mark. (See figure 10.) Because the top plumb cut is a bevel cut andopposite rafters will have opposite bevel cuts, be sure to make the mark on theside of the rafter which will be the long side of the bevel. The bevel cut will beexplained in Step 4.2. Seat Notch: Measure the rafter length (our example: 22' 113 8") down the top ofthe rafter and make the seat plumb mark in the same manner as the top plumbmark in Step 1. Using either “Rafter Seat Cut” dashed line on the square, makethe horizontal seat mark in the same manner as with the common rafter. (Seefigures 8a and 8b.) For proper fit of the hip rafter, cut the top wall plate corneroff as shown in figure 9. This will allow the hip seat notch to set in against a fullflat corner.15
3. Tail or Bottom Plumb Cut: Measure down the top of the hip rafter from the seatplumb mark and mark the distance for the tail (our example: 2' 61 2"). Using therafter square, make the bottom plumb mark at this point. If a tail miter is used,make another plumb mark on the other side of the rafter. (See figure 10.)4. Hip Rafter Pattern Cuts: With your saw set at 45 , cut the top plumb cut,making sure the top bevels are opposite for opposite rafters. Setting the saw at45 automatically gives the plumb cut and side cut bevel. If miter is used, makethe bottom plumb cut on a 45 angle as well. If miter is not used, set the saw at90 . The seat notch is made with the saw set at 90 . (See figure 10.)Intersection of Hips on RidgeTo find the intersection points of the hip on the ridge rafter, cut the ridge rafterone foot longer at the point where the hips intersect with the ridge. Using a regularlength common rafter, set the seat notch cut over the edge of the top plate, in line[Fig. 11 – Intersection of Hips on Ridge]MARK SHOWING THE CENTERLINE OF THE TWO INTERSECTING HIPSTOP OFCOMMON RAFTERBEING USED ASA MEASURE16CUT RIDGE ABOUT 2”LONGER THAN MARK.THIS WILL ALLOW YOUTO NAIL THRU RIDGE INTOHIP, PROVIDING NO CENTERCOMMON RAFTER IS USED.IF ONE IS USED, RIDGE MUSTBE CUT AT THIS MARK.FIGURE 11: Intersection of Hips on Ridge
with the ridge. Be sure your walls are straight. Place the top end of the commonrafter even with the top of the ridge. (See figure 11.) Mark across the ridge asshown. This mark will be the center of the two intersecting hips. If a commonrafter is to be used, the ridge will be cut off at this mark and the common rafterbutted up against it. If no common rafter is used, cut the ridge about 2" longer.This will allow you to nail through the ridge into the hip.Valley Rafter Layout1. Top Plumb Cut: Using the Hip-Val scale on the square, follow the same methodwe’ve been using for the top plumb mark. Measure down the top of the rafterfrom this mark for the miter allowance (if used) obtained from the tables (ourexample: 7 8"). Make another plumb mark on both sides of the rafter. (Seefigure 13.) Be sure to use the Hip-Val scale and the length and allowance fromthe Hip-Val column in the tables.2. Seat Notch: From the first top plumb mark, measure down the valley rafterlength (Our example: 22' 113 8") and make the seat plumb mark. (See figures12 and 13.) Move down the rafter from this mark the miter allowance distanceand make another plumb mark. For the horizontal seat notch line, measure downto the seat depth on the FIRST plumb mark. Extend the horizontal line to theadded miter allowance line using the dash line on the square. (See figures 12and 13.) All seat notches must be the same depth.3. Bottom or Tail Plumb Cut: Measure down the top of the rafter from theFIRST seat plumb mark and mark the tail length (our example: 2' 61 2"). Makethe bottom plumb mark with the square. Add the miter allowance in themeasurement, if used. (See figure 13.)17
RIDGETOP PLUMBBEVEL CUTTER[Fig. 12 – Top View ofValley Rafter OWANCEIF USEDRIDGETOP WALL PLATESEAT NOTCHFASCIABEVEL CUTFIGURE 12: Top View of Valley Rafter Layout[Fig. 13 – Valley Rafter Layout]LU MBERLENGTHTO PVI EWR AFMITERALLOWGTHAN CSI DTAI LNOTE: ON VALLEY RAFTERSADD MITER ALLOWANCE TORAFTER LENGTH BEFOREMAKING SEAT CUT.LENTEREE VIEWSEAT DEPTHSEAT PLUMB MARKMITERALLOWANCEIF USEDBOTTOMPLUMB CUTALLOWANCE18SEAT NOTCHMITER PLUMB LINETOPPLUMBCUT
4. Valley Rafter Pattern Cuts: Set the saw at 45 to make the top and bottomcuts as in figure 13. Also, make the seat miter cuts with the 45 setting. Changeto 90 for the horizontal seat notch.JACK RAFTERSJack Rafter Length: The jack rafter tables are different than the other raftertables. The first column in the table lists the varying center to center spacingof jack rafters. The second column is the difference in length from one jack tothe next. (See figures 14 and 15.) This difference in length is to be added orsubtracted from the rafter length as you move from jack to jack.EXAMPLE: For a 7 Inch Rise and assuming 24" rafter spacing, the amount to addor subtract is 2' 33 4".To obtain the length of the first or longest jack, measure the distance from theedge of the last common rafter to the intersection of the hip and ridge, for a hipjack, or the valley and top plate, for a valley jack. Subtract this measurement (D)from the spacing you are using (S) to get the distance from the intersection to thefirst jack (S-D). Use the table for this distance and find the length to subtract froma common rafter length. This gives you the rafter length for the first or longestjack. (See figures 14 and 15.)EXAMPLE: Rafter spacing (S) is 24"; the distance from common rafter tointersection (D) 12"; (S-D) 12". From the 7 Inch Rise table, we have a lengthof 1' 17 8". Therefore:COMMON RAFTERSUBTRACT 17' 43 8"- 1' 17 8"FIRST JACK RAFTER LENGTH 16' 21 2"19
SEE TABLE FOR LENGTHTO ADD OR SUBTRACTS(24”)D (12”)RIDGES-D(12”)1stJACKS(24”)1’ 1-7/8”2ndJACKS(24”)3rdJACK2’ 3-¾”S(24”)thCKCOMMON[Fig. 14 – Top Viewof Hip Jack E 14: Top View of Hip Jack Rafter SpacingSSSSRIDGE[Fig. 15 – Top Viewof Valley JackRafter E
Remember to add tail length to this length. For all remaining jacks, subtract the fullspacing (S). Example: S 24" jack length subtracted 2' 33 4" from the tables.Therefore:FIRST JACK RAFTER LENGTHSUBTRACT 16' 21 2"- 2' 33 4"SECOND JACK RAFTER LENGTH 13' 103 4"Continue this process to the last jack rafter (note that this procedure is the samefor hip jacks and valley jacks). Be sure to measure jack rafter length on t
Top plate using a 2 x 10. Best for a flat pitch roof with 4 inch rise or less. FIGURE 5: Eave Constructions common Rafter Layout 1. top Plumb cut: If the lumber is not straight, always put the high or crown side up. At the top of the rafter, place the rafter square on the face of the rafter as in figure 7. Pivot the layout
Locate the jack rafter tenon onto the jack rafter fixing bolt and adjust the lower nut to align gaskets, before tightening the the top nut. Then seal the jack rafter internally to the hip. 3.1 3. INSTALLING JACK RAFTERS CRS8501A Jack rafter Sealant 4.8 x 16LG CRS8502A Hip rafter Seal jack
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JACK RAFTER will achieve a better‘pull’ when screwing into long hip rafters). Ensure bottom of rafters are tight to inside of ring beam and screw jack rafter to hip rafter with 38mm screws. Rafter should now be fitted as shown. All the main components are now in position and secure. Proceed to glaze. (
Prescriptive Rafter Span Tables: 1-1/2" LP . RAFTER SPAN Ceiling joist or rafter tie Collar tie H R H C. 5 Prescriptive Rafter Span Tables: 1-1/2" LP .
common, hip, valley and jack rafters. The instructions outlined below show the step-by-step procedure to follow for basic roof construction. STEP 1. OBTAIN RAFTER RUN: Measure or calculate the horizon- . TOP PLUMB CUT: In choosing the side of your rafter to use, put th
Colum 5: Jack Rafters Side Cut Angle column is the jack rafter side cut angle in degrees. Use your speed square to mark off this angle on top of the jack rafter to cut the cheek cut of the jack rafter. First 12" column is the length of the
truss positioned at half the span from the end wall. Loose Hip Construction 04 ITW ALPINE : TRUSSED RAFTER GUIDE Thrust battens are fixed to the truss rafters to prevent the valley frames from sliding. Hip End Construction - Standard 05 ITW ALPINE : TRUSSED RAFTER GUIDE H i p g i r d e
Am I my Brother’s Keeper? Sibling Spillover E ects: The Case of Developmental Disabilities and Externalizing Behavior Jason Fletcher, Nicole Hair, and Barbara Wolfe July 27, 2012 Abstract Using a sample of sibling pairs from the PSID-CDS, we examine the e ects of sibling health status on early educational outcomes. We nd that sibling developmental dis- ability and externalizing behavior are .
