roofframe

Rafter Design

This Rafter Design Calculator is for use with a conventional
Rafter/Ridge Board/Ceiling Joist type roof system with thrust being restrained by the ceiling joists.
Adjustments for snow load duration and repetitive member use have been made where applicable.
Table R802.5 of the IRC should be consulted. The code table R802.5.1(9) lists only 16d common nails, this calculator lists several other nail types Allowable Nail loads are published in the NDS, some examples are below.
Notice that nail strength is based on diameter and specific gravity
Single Shear, 1-1/2" thick sideboard nailed to main member with nails of given diameter.
Nail penetration at least 10 diameters into main member.
G=.67 Red oak G=.55 SYP
Mixed Maple		G=.50
Dougfir		G=.42
SPF		G=.35
Northern Species
8d box(typ gun nail).120" dia107 lbs89 lbs81 lbs69 lbs59 lbs
10d-16d box(typ gun nail).131" dia127 lbs106 lbs97 lbs82 lbs70 lbs
16d Sinker(typ hand drive nail).148" dia154 lbs128 lbs118 lbs100 lbs84 lbs
16d Common(hand drive nail).162" dia184 lbs154 lbs141 lbs120 lbs101 lbs




Live Load on roof(pounds per square foot) Select Species
Dead Load on Roof (pounds per square foot) Allowable fiberstress in Bending (PSI)(Fb):adjusted
On Center Spacing of Rafters (inches) Modulus of Elasticity (million PSI)(E,MOE)
Horizontal Span of Rafter (inches) Maximum Allowable Horizontal Shear (PSI)(Fv):adjusted
Pitch of Rafter (e.g. 6/12) Select Nail
Width of Rafter
Depth of Rafter
Fiberstress in Bending Deflection Horizontal shear
Max Moment (in-lbs) Deflection (inches) Shear (PSI)
Section Modulus Required Max 1/240 Section Area Required
Section Modulus Input (in^3) Rafter Calc
by;		 Area of Section Input (in^2)
Section Modulus Pass/Fail Deflection Pass/Fail Shear Pass/Fail
Axial Thrust at rafter to ceiling joist connection (lbs) Nails Required at Rafter to Ceiling Joist joint Total Load per Inch on Rafter(pounds)
Tension in midjoint of ceiling joists (lbs) Nails required at Ceiling Joist lap Angle of Roof from Horizontal (degrees)