William,
Given that blueboard (extruded polystyrene) can be safely used as an insulation layer beneath and directly supporting batteries, crushing is simply not an issue, especially with plywood to spread out point forces. Blueboard has tremendous resistance to compression, although not being an engineer I can't quantify this. I have seen a ton of industrial cells resting directly on it, fully supported with only modest dimpling.
Allan

Allan Sindelar
al...@positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
Positive Energy, Inc.
3209 Richards Lane (note new address)
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com



On 12/12/2012 4:54 AM, Jesse Dahl wrote:
Benn,

If you were to look at the roof from the side, it would look like this: 2x6 tounge and grove (laid flat and exposed inside) foam board, 3/4 plywood, shingles.  I guess I'm looking for a way to ensure my bit goes in at the right angle, perpendicular to the beams inside. 

William,  Im not sure.  I was hired by a large electrical contractor to oversee this project.  The job required NABCEP and they didn't have anyone certified. These are all things that were not thought about before hand. My hope is that the 3/4" plywood will help, blue board is very hard to crush on its face, so I can only hope it holds, if not, I don't know what they will do.....  

Jesse

Sent from my iPhone

On Dec 12, 2012, at 12:02 AM, William Miller <will...@millersolar.com> wrote:

Jesse:

How are you going to avoid crushing the foam when you tighten your fasteners?

William Miller


At 06:00 PM 12/11/2012, you wrote:
Hello,

The roof I'm currently working on is not a typical roof.  The construction is as follows:

2"x6" tongue and groove exposed inside, with 4 inches of foam (blue board) and on top of that 3/4" plywood with asphalt shingles on top of that.

I'd like to make a template to ensure that my pilot bit doesn't wander when I'm going through the blue board.  If I miss the beams inside, the hole or the lag would be exposed.
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