HomeMy WebLinkAbout3626 Cassiopeia Ln - Special Inspections/Engineering - 05/12/20113bA C6—ssioPcic� L�
May 12, 2011
Namaste Solar Electric
4571 Broadway Street
Boulder, CO 80304
RE: Flush Mount Solar Photovoltaic Structural Installation
JVA Project No. 14149
JVA, Incorporated
1319 Spruce Street
Boulder, CO 80302
Ph: 303.444.1951
Fax: 303.444.1957
Toll Free: 877.444.1951
Web site:
www.jvajva.com
E-mail:
info@jvajva.com
At your request we have prepared this letter regarding the ability of the existing roof structures to resist
the superimposed dead load of the photovoltaic (PV) flush -mount systems for residential dwellings. This
letter outlines prescriptive requirements, and if fulfilled, the added dead load of the proposed PV system
will not overstress the existing structure and the flush mount modules will not add additional wind loads
to the roof framing. All other systems that do not meet the prescriptive requirements of this letter will
require design by an engineer registered in the State of Colorado.
Furthermore, this letter is only for the exclusive use between Namaste Solar and JVA. It does not apply
to any other installation by any other solar PV provider.
A project will qualify as a prescriptive installation with an acceptable supporting roof structure if all of
the following criteria are met:
1. System Type: Unirac Corporation, Solar Mount Rail with a maximum of 12" off the roof
surface. JVA understands that this installation method has been approved by a licensed engineer
in the State of Colorado. Solar modules are typically in portrait layout, if modules are in
landscape use P1000 Unistrut with a maximum span of 4'-0". In either case, each module shall
be supported by a minimum of two rails.
2. Solar Module Layout: The solar modules shall not hang below the cave of the roof system, or
extend beyond the edge of the roof, nor shall it pass the plane perpendicular to the array roof
surface at the ridge.
3. Roof Framing: The supporting roof framing must be of typical residential construction with
multiple pre-engineered wood trusses with a minimum truss chord size of 2x4 and a maximum
spacing of 24-inches or minimum rafter size of 2x6 and a maximum spacing of 48-inches. All
tied -rafter roof systems are excluded from general approval and will require site -specific
engineering.
4. Roof material: Roof material must be either single layer composition, wood or shake shingle.
Multiple layers of roof material are not covered by this letter. Concrete or tile roofs require
specific engineering.
5. Standoff Roof Brackets: Unirac Standoff Plates, Zilla Base Plates and TTI Flat Jack® are all
appropriate brackets. JVA understands that Unirac and Zilla Base plates are analyzed and sealed
by another engineer licensed in the State of Colorado. The Flat Jack® roof mount has been
evaluated by the ICC Evaluation Service under report number ESR-1999.
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BOULDER I FORT COLLINS I WINTER PARK
Flush Mount Solar Photovoltaic
Structural Installation
Page 2 of 2
6. Roof Connectors: All standoff base plates shall have two connectors and placed in the middle
third of the rafter. Standard 5/16" diameter lag screws with minimum 2" of embedment into the
primary roof framing, '/a" diameter Simpson SDS screws with 2 '/z" of embedment into primary
roof framing, or 5/16" GRK RSS Wood Screw with 2 %" of embedment into primary roof
framing are all appropriate.
7. Dead Load and Snow Load: The total dead load weight of the solar modules and racking does
not exceed 5 pounds per square foot (psf). The roof snow load does not exceed 30 psf.
8. Wind Loading: The wind loading analysis is based on 4'-0" spacing of standoff base plates and
rail spans. Therefore the 130 mph, 3 second gust, exposure C, roof zone 2; 130 mph, 3 second
gust, exposure B, roof zone 3; and 110 mph, 3 second gust, exposure C, roof zone 3 are the
maximum allowable wind loading parameters. Any wind loading parameter in excess of the
listed conditions will require site -specific engineering.
Based on the prescriptive requirements, the PV panel mounting system attaches to the existing roof with
standoff base plates spaced at a maximum of 48 inches along the length of roof joists and 48 inches
perpendicular to the joist span. As a means to help define the prescriptive criteria, enclosed with this
letter is Namaste PV Structural Requirement, No. NSE2009-075, dated August 19, 2009.
If the installation meets all of the parameters of the prescriptive requirements it is our professional
opinion that the roof framing and solar installation is appropriate. Please contact me if you have
questions or concerns.
Sincerely,
Brett A. Robinson, P.E. Reviewe y: ;� 23790
Project Manager, Mark C Cormier, P.E. ;
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