Far before you bring any panels onto  the roof, you need to have decided the location and orientation of your solar panels. Here are a few tips:

  • Avoid roof valleys: snow and ice will build up there and the existence of panel corners can prevent sliding and melting.
  • Avoid peaks: panel tops should fall a foot or more below the ridge peak to minimize wind exposure from the north side.
  • Allow room all around the array of collectors -you and others will need room to install and maintain  panels. Leave at least 18 inches on the sides and the bottom to move a bout.
  • Try to center the array on the roof-it will give the roof a more balanced look.
  • Consider Structural members location: your mounts need to connect  to rafters or purlins  for support and  uplift restraint. Moving the array a few inches either way can make a ll the difference for your mounting screws.

Your options for mounting panels to the roof include: 

  • Flush mount: parallel to the roof pitch.
    How To Install A Solar Collector On Shingles Inclined Roof
  • Tilt mount: a frame or strut on the top of t he panel that tilts the panels steeper than the roof pitch.              
     How To Install A Solar Collector On Shingles Inclined Roof 
  • Free standing mount (for flat roofs only).
    How To Install A Solar Collector On Shingles Inclined Roof

 

Roof Attachments

Locating Rafters

Much of your time off the ground, you'll  be on a wood-framed roof, held  up by rafters, and covered in plywood sheathing  and  then shingles. To securely anchor panels to the  roof, you  need  to  make  sure you  are  attaching them directly into the rafters (the sheathing is too thin). Tying  your  mounts into these rafters demands care and  ingenuity, because electronic "stud finders" don't work on shingles or tiles. The common rafters used in most  roofs  are  1 1/2  inches wide. Modern stick  framing places  rafters 16 or 24 inches apart. Older  homes will have spacing that  will challenge your  imagination. You must  hit the middle of the rafter  with  your  lag or structural  screw,  otherwise the  strength of  the connection will be compromised.

Method 1: Use a wide faced hammer to strike the roof at different places. the sheathing will sound hollow, and the hammer head will bounce a bit. when you hit a rafter, you'll feel the firmness and hear the lack of reverberation. This method only approximates the location of the rafter. Finding the center line requires more careful methods.

Method 2: Use very strong permanent cylindrical magnets taped to each side of the rafter (you should be able to get into the attic). A small compass on the roof will spin when you are centered over the magnets.

Method 3: Pry up a shingle tab and use a small drill  bit (maybe 1/8 to 1/4 inch) to  probe the  roof  for  the  rafter edges. That drill bit piercing the sheathing will serve as a reference  point  on the roof to measure to the exact location of the center line of the rafter.Caulk holes afterwards.

Method 4: For  roofs  where  attic  access  is impossible, the position of  the rafter  can  be inferred from  nail or screw  depressions in the soffit fascia at  the bottom and similar clues beneath the ridge vent on  top.

Method 5: Hire a roofing specialist to provide guidance or to do  the  roof attachment and  penetration installation himself. There is nothing like years of professional experience to create a structurally sound and leak proof roof installation.

Method 6: Put the panels on a ground mount. The roof will never leak!

Connectors

We suggest using G R K's Rugged  Structural Screw and Simpson's strong drive screws. These make long-lasting connections without drilling a hole  into  the rafter first. All you need  is a portable drill  with a Torx or nut driver, and  you  can just zip  them in. You save time  by not  having  to  drill   pilot  holes  and  grab the  ratchet. The labor difference is so large  that by the  time you finish  drilling pilot holes and ratchet wrenching in just a few lag bolts, you could have finished the whole job with structural screws.

Pull Out Strength

Structural screws and lag bolts screwed  into  wood  will pull  out  if uplift  is large enough . Pull  out  strength is determined by several considerations:

  • Size and tensile strength of the screw or bolt. Consult the manufacturer's technical data.
  • Characteristics of the bolt or screw threads: fine threads will not hold as well as coarse ones.
  • The size of the "lead" pilot hole that you must drill for the lag bolt's threads (structural screws do not need  pilot  holes). Guidance on  the size of this hole varies, but a reasonable value is approximately 75% of the total fastener diameter. For a 5/16  inch  lag bolt, that  works out  to be about 7/32  inch . 
  • The final torque you place on the bolt or screw: don't over-torque it or you will strip the thread connection inside the wood.
  • The characteristics of the wood into which the bolt or screw is attached: spruce pine  fir (SPF) is one standard wood material that  designers base their analyses upon with densities ranging from  0.42 to .0.5.
  • The location of the screw or bolt in the wood  should be in the middle one third  of the cross-section.
  • The orientation of the grain of the rafter a nd the presence of any inconsistency in strength like a knot right  where  you intend to drill  the hole.

Each bolt  manufacturer offers structural ratings that you can consult for your project site and application. Structural  screws  can  handle  hundreds  of pounds of allowable uplift, depending on the screw size and  type of wood. Lag bolts can resist a bit more uplift per inch of  thread length, but  that  resistance can be compromised  by wood quality and  the  diameter of your  lead pilot  hole (too small, and  the wood will crack, too large and  the threads won't h old). A simple wood screw can't offer this kind of pull-out strength!

 How To Install A Solar Collector On Shingles Inclined Roof

Flashing (or Roof Pipe Penetration Fitting)

Flashing is a general term that describes small sheets of aluminum, galvanized steel, or copper  (and  pre-manufactured shapes like roof boots) which help roofers cover holes in the  roof and/or surround penetrations to prevent water entry  into the building.We use a lot of flashing materials which we slide under shingle tabs to reduce deformation of shingles under our panel mount brackets and  to leak-proof  the holes we have to make in the roof. Step flashing is required to waterproof shingle roofs around panels that are mounted directly on the roof sheathing. We keep a roll of copper flashing material in the truck with a pair of metal shears.

How To Install A Solar Collector On Shingles Inclined Roof How To Install A Solar Collector On Shingles Inclined Roof

Roof Attaching and Penetration

For pipe and control cable roof crossing, we suggest using one of the 2 flashing types mentioned in the previous section. An EPDM pad shall be installed under the roof shingle and between the roof and the bottom of the flashing. Caulk sealant under EPDM Pad and around the flashing.

 How To Install A Solar Collector On Shingles Inclined Roof