Background[edit | edit source]
Originally created by Nicholas Vandewetering of FAST.
This page is the dedicated to the literature review of Canadian Standards and Specifications on PV solar panels racking systems. Academic research, Canadian and American codes and standards, and commercial & DIY wood & metal designs have been included in this literature review.
Most ballast systems are used for roof-mounted racks. Although these systems would be built in the same manner as ground mounted systems, these builds require building permits and structural engineering stamps as they now impose an additional load on a building. Innovations have been made to help minimize the wind load and thus the weight of ballasts, but installing solar on rooftops can increase the wind load on the roof by a factor of 2 based on the tilt angle and location. Currently, there is no simplified method of assessing the feasibility of installing ballast systems on standardized structural systems for roof tops, and structural approval is done on a building-by-building basis, and can cost about CAD$900 per rooftop. Future work should be conducted to eliminate the need for case-by-case engineering approval of PV ballast systems so that newly built rooftops can automatically be built with PV, and existing standardized rooftops can implement PV such that they surpass a specific structural condition.
Literature[edit | edit source]
Innovative Ballasted Flat Roof Solar PV Racking System[edit | edit source]
https://doi.org/10.2172/1167673
Wind loads on solar panels mounted on flat roofs: Effect of geometric scale[edit | edit source]
- Negative pressures can increase by a factor of 2.
P.Eng Stamped Structural Roof Assessment - Structural Roof Load Assessment | Solar Roof Installation Permitting Service[edit | edit source]
- $900 per building approval.
City of Waterloo - Solar Panel Policy[edit | edit source]
- Permits are not required for ground mounted solar panel systems that are not connected to water or heating sources.
Municipal Climate Change Action Centre (Calgary, Alberta)[edit | edit source]
- Racking does not require a stamp if it is CSA approved. All wood is marked and graded as SPF No.2 grade, which is CSA approved. The design complies with National Research Council’s National Building Code of Canada, which refers to all CSA standards, and the National Design Specification for Wood Construction, which follows CSA O86:19 Engineering design in wood.
City of London: Building By-laws[edit | edit source]
- Searching for solar, applications for Ontario Feed-In tariffs are the only charges specified.
City of London: Permits of Approved Works Applications[edit | edit source]
- Work permit only required if excavation is required or scaffolding/cranes must be used
Norfolk County: Mounted Solar Panels on Buildings[edit | edit source]
- Building permit not required where the panel is not installed on a building.
City of Toronto: Net Zero Home Buildings[edit | edit source]
- Building permit not required for any size of ground mounted systems. Since permits are not required, plans and calculations do not need to be stamped and signed by a registered Structural engineer
US Department of Energy: Empirically Derived Strength of Residential Roof Structures for Solar Installations[edit | edit source]
- Engineering certification for the installation of solar photovoltaic (PV) modules on wood roofs is often denied because existing wood roofs do not meet structural design codes.
- This work shows that many roofs are actually sufficiently strong given the conservatism in codes, documented allowable strengths, roof structure system effects, and beam composite action produced by joist-sheathing interaction.
- Factors of safety of 2x4, 2x6, 2x8, 2x10, and 2x12 arranged in a system range from 2.1-4.6.
- TJI supported roofs saw factors of safety ranging from 2.8 to 3.0.
- Truss supported roofs saw factors of safety ranging from 3.9 to 4.4.
US Department of Energy: Structural Code Considerations for Solar Rooftop Installations[edit | edit source]
- This method of analysis neglects the composite action of the entire roof structure, yielding a conservative analysis based on a rafter or top chord of a truss. Consequently, the analysis can result in an overly conservative structural analysis.
- Testing of more than 70,000 specimens, totaling approximately 1,000,000 board feet of lumber, in bending, tension parallel to grain, and compression parallel to grain. This 10 year, $7 million dollar effort was one of the largest single research efforts ever undertaken in forest products research (Kretsmann, 2010).
- This lack of clarity has caused uncertainty in identifying factors of safety that exist within the governing codes. From the literature reviewed, it can be concluded that a numerical factor of safety does not actually exist, but rather a range or a probability of failure would better describe how allowable values are determined. Moreover, the added weight applied to a roof system due to a PV installation is not a question of encroaching on the factors of safety but rather an issue that must be analyzed as to how it affects the probability of failure.
IEEE 2nd International Conference: Structural Performance of An Existing Building Roof Subjected to Additional PV Panel Load[edit | edit source]
- Based on the analysis result, adding PV panel-loading increased elements failing. Also, the building roof has experienced additional deflection.
- The results of this study indicate that before installing PV panels over the exiting building roof, structural analysis of the roof is necessary. Accordingly, the required retrofitting measurement is to be planned. This study's finding has been one of the first attempts to thoroughly examine the roof of the existing building using finite element analysis to apply PV panel loads, using various loading scenarios.
Eng Tips: Solar Panel Structural Calculations/Sealing Drawings[edit | edit source]
Structural Engineering forum where engineers discuss their experience with solar installs on residential roofs.
- Arguments are made from truss manufacturers: "The connections are a 48" o/c and therefore load up every second truss as opposed to every truss so it's more like adding 7 PSF instead of the 3.5 psf they are claiming (assuming 24" O.C. spacing). Secondly, the lag screws are into the 1.5" dimension of the lumber therefore I also have to account for a reduction in capacity of approximately 20-30% for the top chord.'
Canadian Roofing Contractors Association: Photovoltaics in Roofing[edit | edit source]
- Extra costs to be considered: "It must be recognized that the installation of a solar array on a roof will substantially impact the cost of future roof maintenance due to the increased number of penetrations and roof top equipment components. If roof repairs are required, it may necessitate a qualified PV technician, or electrician, oversee the repair to ensure the integrity of the PV system."
- The top of the roof must be inspected for areas of ponding: On existing buildings, this means verifying the age of the roof and the remaining length of any warranties. It also means surveying the roof for stress, damage or other existing problems. Areas of ponding water, or roof edge and flashing details have to be rectified before a PV system can be installed.
Timber Frame Engineering Council: Design Guide for Timber Roof Trusses[edit | edit source]
- Standard back of the envelope analysis assumptions are made
National Research Council: Solar Ready Guidelines[edit | edit source]
Cascade: A Beginner's Guide to Trusses[edit | edit source]
- King Post Trusses span a maximum of 8'
- Quen Trusses span up to 20'
