Top Tips for Installing PV on Low-Slope Roofing

Recently we were fortunate enough to moderate a webinar via Solar Power World featuring top tips for installing solar on low-slope roofing.

Brian, our President & founder, began his career as a slate roofing contractor in the 1970’s, and his decades of experience and knowledge have made him an authoritative voice in the industry, as well as a thought leader, and the perfect person to go to when you want real answers.

Webinars are such a great way to share knowledge with the industry….as I’ve said at least a hundred times before, the more we know, the better off we all are.

In case you missed the webinar, or don’t have time to watch it, here’s a brief overview (the webinar itself gives MUCH more detailed information….and it’s only an hour long, so you should really watch it!):

What is a low-slope roof?


As defined by NRCA, the pitch of a low-slope roof is equal to or less than 3:12

Low-slope roof facts


  • Installing any roofing material on a roof with less than 3:12 pitch does not make it low-slope roofing
  • The minimum slope asphalt shingles should be installed on is typically 2:12 pitch
  • Low-slope roofs can be used on commercial roofing as well as residential
  • Low-slope roofs have a minimum ¼” rise over a 12” run (follow roofing manufacturer’s instructions
  • All low-slope roofs must allow water to drain
  • Large commercial structures will have drainage paths
  • If the roof does not drain properly, bacteria and organic growth will appear on the surface of the roof
  • This organic growth will breakdown the roofing materials prematurely
  • Roof inspections increase the life of the roof, and should be done a minimum of twice per year
  • Low-slope roofs are often patched during roof inspections
  • Roofers look for signs of wear and patch the roof prior to any problems

Important to note is that all low-slope roofs must have the ability to dry within 24 hours (humidity is an exception)

Rain-Gif-small  clock-gif-small  dry-gif-small

What are the general components of a low-slope roof assembly?


  • Roof deck: Can be Steel, Concrete or Wood
  • Optional Air or Vapor Barrier: makes the building energy efficient
  • Insulation: Can be installed as layers
  • Cover Board: Creates a hard surface over insulation, acts as fire barrier
  • Waterproof Covering: Single Ply, Built Up Roofing, Modified Bitumen, Metal Panels, Spray Polyurethane Foam

Weatherproof Covering Options

Single Ply- EPDM, TPO, PVC


  • Plastic or Rubber Based Materials
  • Various attachment methods: Adhered, ballasted or through-fastened
  • Heat welded or adhered at seams
  • Can be multiple sheets or seamless depending on manufacturer and roof size

Built-Up Roofing

built up

  • Multiple layers with Cap Sheets, or Ballast/Granules
  • Various attachment methods: Self-Adhered, Torch down, Hot Mopped, Fastened, or Ballasted
  • Asphalt, tar, or gravel-based materials
  • Low material cost

Polymer Modified Bitumen

mod bitumen

Metal Standing Seam Panel


Spray Polyurethane Foam

spray poly

 Why are low-slope roofs a good platform for solar?


  • Plentiful (many large commercial buildings)
  • Secure Locations
  • Favorable roof to wall area for good load values
  • Can accommodate large systems, good return on investment for building owners

What codes govern watertight PV installs on low-slope roofs?

ICC: International Code Council:


Building codes are performance and prescriptive requirements for building construction—including roof systems—that are established and enforced by state or local government agencies to ensure public safety, health, and welfare in commercial and industrial buildings.

  • IBC: International Building Code
  • IRC: International Residential Code
  • Both the IBC and IRC require that a flashing must be used with all mechanical attachments. This flashing must be installed per roofing manufacturers install instructions.

 Design considerations for solar on low-slope roofs

The roof must remain watertight!

design considerations

  • In most low-slope roofing, this is achieved through flashing the attachment points
  • Different low-slope roof coverings will have different flashing requirements

Wind resistance

wind walk gif

  • There are 3 zones for wind resistance analysis:
    1. Field Zone- interior- lowest wind loads
    2. Perimeter Zone- ends- middle wind loads
    3. Corner Zones- highest wind loads
  • Wind uplift could move or rip off and ruin the roof surface if the system is not engineered for the correct wind resistance

design considerations2

Fire resistance


  • Roof Systems are classified for the level of fire resistance
    • Class A- highest rated (max. spread of flames=6 ft.)
    • Class B (max. spread of flames=8ft.)
    • Class C (max. spread of flames=13 ft.)
  • The PV system must be engineered with materials to match the fire classification of the roof
  • This fire rating for PV components is governed by UL testing

Roof warranty


  • Limited Manufacturer warranties may be void if design/install/maintenance procedures are not followed
  • Flashing must match the roofing manufacturers install instructions
  • Rooftop PV cannot interfere with roof maintenance
  • Work with roofing manufacturer and the roofing contractor



  • The roof should be in good condition before installing PV – the roof should at minimum last as long as the PV system being installed
  • The removal and redesign of a PV system after only 10-15 years is a large expense
  • The return on investment of the PV system would be diminished

Evaluation prior to PV array design


Before a low-slope rooftop system is designed, the following should be evaluated:

  • Structural evaluation of the roof deck
  • Structural evaluation of the building
  • Age of the roofing materials
  • Type of roofing materials – to assure that the correct steps are taken to uphold the integrity of the roof
  • Roof drainage
  • Dirt build up
  • Roof traffic
  • Access and Safety

Low-Slope PV Mounting Options

Adhered PV- PV laminate:


  • Very low profile – aesthetic and wind load benefits
  • Lightweight
  • Used with adhered membranes with a minimum thickness of 72 mil
  • Can only be used with high temp resistant membranes and insulations as it can heat up very quickly

 Ballasted systems:


  • No roof penetrations required
  • Solar panels and racking are held in place with weight
  • Provides a quick retrofit solution
  • Can block drainage & compress insulation creating ponding water
  • Thermal expansion/contraction causes damage/wear & tear
  • Can move from HVAC vibrations
  • Creates difficulty with roof maintenance, inspection and repair

Mechanical attachments:

mech attachments

 Mechanical attachment examples:



Other flashing options for mechanical attachments:

other flashing options



Testing for low-slope products

What should you look for?


  • Rain testing
  • Mechanical load testing
  • Standing water test


Questions? Ask away – that’s what we’re here for!




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Industry leader EcoFasten Solar designs, engineers, and manufactures patented, watertight solar roof mounts. The company provides mounting solutions that are easy to install, cost-effective, rugged in fabrication, and unsurpassed in quality. Comprised of a seasoned and growing team of professionals with talent, ability, and drive, all EcoFasten Solar products are precision-designed with the installer in mind. 

(Images from: ar systems, wm roofing, horisons llc, aep span, midwest roofing kc, progreen lc, eichler vision, cda,, gold coast solar power solutions, franking machine, energie zonnepanelen, sr waterproofing)

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