HomeMy WebLinkAboutENGINEER LETTER - 21-00972 - 643 Mill Stream St - Solar Panels
9089 S 1300 W Suite 160, West Jordan, Utah 84088
Phone: 801-707-9004 Fax: 801-590-6611
Website: www.perigeecivil.com
Email: info@perigeecivil.com
November 10, 2021
Intermountain Wind and Solar
Attn: Ryan Shaw
1953 W 2425 S
Woods Cross, UT 84087
RE: 643 Mill Stream St, Rexburg, ID
Structural Evaluation for Solar Panel Installation
Dear Ryan,
This letter is regarding the residence at the above referenced address. It’s our understanding that
Intermountain Wind and Solar would like to add solar panels to the structure in the area shown in the
attached sketch.
The solar panels proposed by Intermountain Wind and Solar are less than 4 pounds per square foot
(psf). The home was constructed in 2016 with pre-manufactured trusses, and typical design loads for
roofs in residential construction of that era are 10-15 psf, with a roof live load design of 20 psf and
roof snow load of 47 psf. Based on typical materials used in residential construction for asphalt roofs,
actual dead loads are generally less than that, around 7-8 psf. This would allow for 2-3 psf to be
added. Additionally, Section 706.2 of the International Existing Building Code (IEBC) 2018 indicates
that alterations to a building which results in less than 5% of a gravity load increase may be performed
without structural evaluation of the existing structure, which would allow an additional 2 psf. Based
on the pitch of the roof and the addition of the array, the snow load can be reduced by approximately 1
psf, as shown in the attached calculations. Because of these factors, it is our opinion that the roof is
structurally adequate to support the additional dead weight of the proposed solar panels. Supports
from the array to the roof should not be spaced greater than 4’ apart, and connections between adjacent
railing rows should be staggered.
Please contact me if you have questions or need further information.
Sincerely,
Letizia Wetzel, PE
11-10-2021
Lie Solar Array
Roof snow load calculation(per ASCE 7-16)Design roof snow load =29 psf
Ground Snow, pg =47 psfRoof pitch 6 :12
Flat roof snow load, pf = 0.7 Ce Ct Is pg (Eq. 7.3-1)
Ce =0.9 (Table 7.3-.1)Ct =1.2 (Table 7-3.2; cold roof with solar panels)Is =1.0pf =35.5 psf
Sloped roof snow load, ps = Cs pf (Eq. 7.4-1)
Cs =0.8 (From Figure 7.4-1b, slippery surface)
ps =28.4 psf(1 psf reduction from design roof snow load)