A structural insulated panel (SIP) roof has no embedded
lumber in the structure, and therefore nothing substantial
for attaching PV array and solar hot water mounts.
Single or double lumber splines could be put into the panels,
or I-joists at 4-foot intervals could be added. However, the
thermal bridging that they would create are at odds with the
goal of an energy-efficient building. As buildings get tighter
and more insulated, thermal bridging plays a relatively larger
role in energy loss.
One solution for mounting solar equipment to a SIP roof
is to drill completely through the roof, passing a threaded
rod through to the bottom skin and placing a large washer
under the nut. Since most SIP roofs are vaulted on the inside,
though, few homeowners would be OK with seeing the nuts
and washers on their ceilings.

Written by Patrick