Array layout options

theenergyguy
theenergyguy Registered Users Posts: 12 ✭✭
in General Solar Power Topics #1
We're having a debate amoung installers here on the issue of how to properly lay out the footings and rails for a roof-mounted array....the issues are -

1) How to determine the location of roof framing. Start by tapping a hammer across the roof to locate rafter, mark it - OR - take additional step of drilling couple small holes to assure lags will hit center of rafter before marking.

2) When laying out location of standoffs (after first determining rafter locations) measure, snap lines vertical and horizontal - OR - just follow horizontal shingle lines for horizontal layout markings

3) To cross-square OR not to cross-square upper and low rails

Hopefully these descriptions are concise enough (the old picture's worth a thousand words thing)
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #2
    Re: Array layout options
    theenergyguy wrote: »
    We're having a debate amoung installers here on the issue of how to properly lay out the footings and rails for a roof-mounted array....the issues are -

    1) How to determine the location of roof framing. Start by tapping a hammer across the roof to locate rafter, mark it - OR - take additional step of drilling couple small holes to assure lags will hit center of rafter before marking.

    2) When laying out location of standoffs (after first determining rafter locations) measure, snap lines vertical and horizontal - OR - just follow horizontal shingle lines for horizontal layout markings

    3) To cross-square OR not to cross-square upper and low rails

    Hopefully these descriptions are concise enough (the old picture's worth a thousand words thing)
    A cool trick a guy I worked with came up with was simply to cut a piece of heavy gauge copper wire with two right angle bends like this: |_| The two vertical sections were cut to the same length so that when he drilled a hole in the decking and stuck the wire in the hole past the first bend and spun it until he hit a rafter with the arm he couldn't see, the arm he could see showed him where the rafter was.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Array layout options

    I do not like putting holes in a roof and then having to patch them because they're in the wrong place.

    I'd be looking at the roof structure underneath and running two-by between rafters where the array mounts are going to go. That way no matter where you drill the hole you hit solid stud material.

    Definitely make the effort to square-up the mounts, but keep an eye on the aesthetics as well; if the rectangle of the array is severely out of parallel with the roof ridge/eave and/or shingle lines it will look terrible and people don't like that. This may take considerable head scratching and possibly cardboard patterns.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #4
    Re: Array layout options

    The other option is to drill them from the inside, a couple of layout lines with a chalk line and a long pilot drill up through the rafter would work.
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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #5
    Re: Array layout options

    1st - look at roof eves, gables, skylights (usually situated between framing) etc (take off attic vents if at all possible) to figure out framing.
    2nd - pound on roof to double check exact position by sound.
    3rd - drill holes and if you miss, then use the bent copper wire to feel for framing.

    Run your array mounting along the shingle lines or whatever. Roofs are rarely all nice and square - don't get to hung up on being perfect.
    It is an asthetic thing - keep an eye to how it looks on the roof. Over measuring doesn't help much. However, do plan it all out. Use a carpenter's crayon to mark array perimeter and mountings before the first drill hole. Roofs have lots of idiosynchronies and they will foil a poor plan.
    I've just about given up trying to square the mounting rails ahead of time. Just leave some extra, position the array so it is all lined up and square with the roof edges - which often means redoing the 1st few panels. Then use a battery sawsall to cut of the extra rail ends right where you want. This is a very visible detail and almost impossible to get right until the array is down. Use rail caps to make the ends look nice.
    One of the nice features of my custom alum. angle rail system is using beam-clamps to fasten the end panels. The rail is cut off flush (or less) with the panel edge and clamped from below. You can't see anything but PV panels. Make an array look nice. Our solar reputation with that neighborhood depends on it.
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