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???