25 Willow St - REV ELNorthampton, MA
212 Main St.
Northampton, MA 01060
25 Willow St
Florence, MA 01062
MA License No. 56687
RE: RYTHEA, LEE
Trinity Solar | 4 Open Square Way, Suite 410 | Holyoke, MA | (413) 203-9088
December 12, 2023
Trinity Solar No.
2023-05-884186
To the Building Official:
The following information constitutes a summary of the relevant design criteria and recommendations for the support of a new photovoltaic
[PV] system on the existing roof framing components at the above-referenced location.
Criteria is as follows:
1.Existing roof framing:
Conventional roof framing at R4 is 2x6 at 16 o.c.; existing rafter span= 11' 10"; (horizontal projection)
2.Roof Loading:
• 3.0psf dead load (pounds per square foot - PV panels, mounting rails & hardware)
• 5.7psf - existing roof loads (1.7 psf - 2x6 framing, 1.5psf roof sheathing, 2.5 psf shingles)
• Ground Snow Load - 40psf - per AHJ (Authority Having Jurisdiction)
• Wind criteria - Exposure Category B, 117 mph wind
3. Existing roof modification at R4 - existing roof rafters to be "sistered" with new 2x6 rafters extending the full length of the existing
rafters and terminated before the existing rafter support connection. Non-full-length rafter sisters must "overlap" its accompanied sister a
minimum of 24" with nailing from each side in the overlap. Typical sister nailing consists of 10d nails top and bottom at 12" o.c. Within
overlap, same nailing at 6"o.c.
This installation design is in general conformance with the manufacturers’ specifications and complies with all applicable laws, codes, and
ordinances – specifically the International Building Code (2015 edition) and the International Residential Code (2015 edition), including all
Massachusetts regulations and amendments.
The spacing and fastening of the mounting brackets is a maximum of 48” o.c. between mounting brackets (staggered) and is secured using
5/16” diameter corrosive-resistant steel lag bolts. A minimum of 2½” of penetration (embedment) per lag bolt is required, which will resist all
stated loads above – including wind shear. Per NDS Section 12.1.4, clearance holes - equal to the diameter of the shank - need to be
bored into a primary framing member for the full-length of the threaded portion of the bolt to avoid splitting of the framing member.
Regards,
Ihor Bojcun, PE
Structural Engineer - Trinity Solar