HomeMy WebLinkAboutLETTER Structural Calcs Solar 262 Stanley Ave B 2020-09-231 | P a g e
FEDERAL CONSTRUCTION, INC.
3460 S FEDERAL BLVD., ENGLEWOOD, CO 80110 TEL. (720) 620 8885
email: federalconstruction@live.com FAX. (720) 502 7459
September 1, 2020
Building Official
Town of Estes Park.
Re: Application for a building permit to install photovoltaic panels on the roof at: 262 STANLEY AVE,
UNIT B, ESTES PARK, CO 80517
Dear Sir:
This letter is to certify that the roof structure of the reference building has been inspected and
deemed to be adequate without reinforcement to support the additional load of 3 psf that will be
added by the installation of the photovoltaic panels and supporting frames.
The Gable roof structure consists of per-manufactured trusses at 48” O.C. And 30 ft span. The
existing roofing material consists of asphalt shingles.
The structural study uses 2015 IBC and ASCE 7-10.
The following criteria were used:
- Ground Snow load: 66 psf (Altitude = 7600 ft) (Using linear interpolation)
- Wind Speed = Vult = 175 mph Exposure: C
- Solar system distributed weight: 3 psf design load.
Calculations are presented to certify the integrity of the panel connections under the maximum wind
uplift and live load conditions.
The panel racking connections to the roof structure are made with 5/16” Lag bolts embedded 3/4”
through the roof sheathing and 3” through the roof rafters. They are adequate to support the maximum
wind uplift load and the maximum live shear load. These Lag bolts have a pullout strength of > 750 lb
which gives a pullout safety factor in excess of 2. The racking structure, “SolarMount HD” by Unirac, can
support the maximum downward load of 153 lb/ft over a 48” maximum span. This configuration provides
adequate structural integrity with a large safety margin.
Sincerely,
Fadi Raffoul, P.E.
9-1-2020
2 | P a g e
DESIGN WIND LOAD CALCULATION
The Design wind load is calculated using method I from ASCE7 -10.
The equation for determining the Design wind load for components and cladding is:
Pnet (psf) = Kzt.I.Pnet30
Pnet (psf) = Design Wind Load
= adjustment for height and exposure category
Kst = Topographic factor at mean roof height = 1 in our case
I = Importance factor = 1 in our case
Using the following parameter:
Design wind speed Vult = 175 mph
Average roof height = 20 ft
Exposure factor = C
Roof pitch = 18.4 degrees
Effective wind area = 18 sqft (area of a single panel because of spacing between panels)
We obtain:
= 1.21
* Pnet30 = 29 psf (Down)
* Pnet30 = -49.2 psf (Uplift)
Pnet (Down force) = Pd = 35 psf
Pnet (Uplift) = Pu = -59.5 psf
9-1-2020
3 | P a g e
STRUCTURAL CALCULATIONS
Ground Snow Load = Pg = 66 psf
Roof Live Load (snow) = Ps = 0.7 Ce Ct Is Pg = .7 x 1 x 1.1 x 1 x 66 = 50.82 psf
Dead Load = 3 psf = D
Design wind load (down) = 35 psf = Pnet
Design wind load (up) = -59.5 psf = Pnet (up)
1- Total Downward Design Load Pd :
Case 1: Pd = D + PS = 3 + 50.82 = 53.82 psf
Case 2: Pd = D + 0.6 x Pnet = 3 + 0.6 x 35 = 24 psf
Case 3: Pd = D + 0.75 x PS + 0.75 x 0.6 x Pnet = 56.86 psf
Case 3 gives us the maximum value for Pd = 56.86 psf
2- Total Upward Design Load Pu:
Pu = 0.6 x D + 0.6 x Pnet (up) = 0.6 x 3 – 0.6 x 59.5 = -34 psf
• Downward design load per linear foot on racking = 153 lb/ft
We use 4 ft as our span, since our anchors should be located on a rafter (rafters are 2 ft
apart). Unirac is designed to handle up to 200lb/ft for the Heavy duty rails. (OK)
• Based on 4 ft L foot spacing we get maximum uplift of -367 lb per anchor. The anchor
used is a 5/16 in lag bolt with a minimum pullout capability of 250 lb/in penetration. Since
we are using 3 in depth with the pullout strength > 750 lb per lag bolt, this gives us: factor
of safety > 2
9-1-2020