Standardized Load Tables Characterizing Residential Solar Thermal and Solar Electric Installations For Residential Structures in Minnesota Jason S. Hanlon, PE, MLSE Braun Intertec Corporation September 30, 2013

Overview  Establishing Analysis/Review Criteria  Research and Analysis  Pre-Manufactured Trusses  Roof Rafters  Rafter Tables

Establishing Analysis/Review Criteria  Closely match IRC content  Consider conditions common to MN  Consider Types of Roof Mounted Solar Technologies

Establishing Analysis/Review Criteria  Closely match IRC content  Spans presented try to closely match that shown in IRC Tables  Wood Species  Roof Pitches

Establishing Analysis/Review Criteria  Closely match IRC content  Consider conditions common to MN  Wood Species --- Old Doug-Fir  Design Loading Criteria »Based on 2007 MSBC, 2006 IRC/IBC and ASCE 7-05 »Wind Load Exposure B, C, and D  Dead Weight »One Layer ½-inch OSB/Plywood or ¾-inch plank board »One layer asphalt shingles

Establishing Analysis/Review Criteria  Closely match IRC content  Consider conditions common to MN  Consider Types of Roof Mounted Solar Technologies  Photovoltaic Panels supplementing electrical services  Solar Thermal Panels supplementing heating services

Research and Analysis  Pre-Manufactured Wood Trusses  Challenges  Things to consider  Roof Rafters

Research and Analysis – Pre-Manufactured Wood Trusses  Challenges  Common design layout hard to define  Wood trusses are “efficiently” designed. »Controlling component will be the nailer plates

Research and Analysis – Pre-Manufactured Wood Trusses  What to consider  Common design throughout the industry: »Top Chord DL = 7 psf »Bottom Chord DL = 10 psf  Changes in Code prescribed Snow Load

Research and Analysis – Pre-Manufactured Wood Trusses 1998-Previous MSBC2003-Current MSBC

- Roof snow load decreased by 5 psf - Roof snow load increased by 5 psf - Roof snow load increased by 12 psf - Roof snow load increased by 2 psf Research and Analysis – Pre-Manufactured Wood Trusses Summary of Design Load Adjustments

Research and Analysis – Roof Rafters (Hand-Framed Construction)  Framing Conditions  Snow Loading  Wind Loading  Material Selfweight  Allowable Stress Design

Research and Analysis – Roof Rafters (Hand-Framed Construction)  Framing Conditions  Use of Ridge Nailer Plate (not a ridge beam)  Outward thrust is resolved at exterior wall bearing

Research and Analysis – Roof Rafters (Hand-Framed Construction)

 Framing Conditions  Use of Ridge Nailer Plate (not a ridge beam)  Outward thrust is resolved at exterior wall bearing  Allowable stress values taken from NDS (National Design Standard) for Wood Construction and Historical Douglas Fir Use Book

Research and Analysis – Roof Rafters (Hand-Framed Construction)  Framing Conditions  Snow Loading  Exposure Rating B, C and D  Design for Snow Drifting not required per IRC  Limit installation angle of panel so drifting is limited to design depth of snow »Tables presented for different lengths between PV and Solar Panels

Research and Analysis – Roof Rafters (Hand-Framed Construction) Table 1 - Maximum Allowable PV Panel Installation Angle Ground Snow Load = 50 psf, Flat Roof Snow Load = 35 psf Maximum Allowable PV Panel Installation Angle (deg) Roof Pitch PV Panel Length (in) 3:124:125:127:129:1212: Note: dash indicates that the solar panel may be installed at any angle up to 45 degrees from horizontal

Research and Analysis – Roof Rafters (Hand-Framed Construction)  Framing Conditions  Snow Loading  Wind Loading  Structures 30-ft. or less in height (average)  Not located near isolated hills or ridges or other abrupt changes in topography  Followed ASCE Slight changes in ASCE 7-10 (decrease)

Research and Analysis – Roof Rafters (Hand-Framed Construction)  Framing Conditions  Snow Loading  Wind Loading  Material Selfweight  Member DL based on wood species, size, and spacing

Research and Analysis – Roof Rafters (Hand-Framed Construction)  Framing Conditions  Snow Loading  Wind Loading  Material Selfweight  Allowable Stress Design  Shear  Bending/Compression  Deflection

Rafter Tables  Info needed to determine which table to use  Wood Species  Grade of Wood  Spacing  Ground Snow Design Requirement  Exposure Classification

Rafter Tables  Info needed to determine which table to use

Rafter Tables  Info needed to use the table  Rafter Pitch  Rafter Size  Projected Rafter Span

Rafter Tables

 Reinforced Rafter Tables  Similar Analysis approach  Uses a sistered 2x4 member of equal or greater species and grade  Installed as follows:

Rafter Tables

Questions???