We are installing roof rails on our bus so we have something to attach both our solar panels and a roof deck to. We chose to go with a Unistrut channel system, as Don says “it’s like metal lego” making it easy to put together and attach things to.
Our biggest concern when constructing our roof rails was to make sure the bolts holding the rails down could withstand the force the bus will experience when going 70 miles an hour down a highway. The last thing you need is your solar panels and rails to go flying off the bus ripping huge holes in your roof.
We drilled our holes for the bolts every 3 ft to secure down the rails, through the roof into the metal beams of the bus. Then inserted ⅜ -16 Grade 8 Zinc Plated Steel Hexagon Bolts from the inside of the bus. These bolts have a tensile strength of 150 000 psi.
We used 3 different kinds of washers for our roof rail bolts.
Outside on the bolt between the roof and the nut we used 3 kinds of washers: 1x rubber washer, 1x Grade 2 Zinc Washer (which is the same size as the rubber washer to make sure the rubber was covered as it will deteriorate slowly from sunlight if it is exposed), and 1x Grade 8 Extra Thick Zinc washer. The Grade 8 washer is obviously stronger but it was also useful because of its thickness which helped us get the bolt to sit at the desired height.
The final piece to the puzzle was a Stainless Steel lock nut . We first tried putting the sealant between the roof and the first rubber washer, but it acted like a lubricant and the rubber washer just slid out. So we only used the sealant between the top washer and nut, once it was all tightened up real good we then covered the whole exterior of the washers, nut and bolt with the sealant to ensure no water could get in!
The unistrut channel will sit on top of the nut so it is raised slightly off the roof and will follow the same washers and nuts to secure it down.
Bad luck comes in threes and we experienced this both with bus troubles and our own health issues.
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Grade 2 Zinc Washer
Fender washers have a larger outer diameter than a typical flat washer to provide a greater surface bearing. They are generally used in applications where a larger outer diameter is required for an increased bearing surface and surface load reduction. 3/8 " internal diameter.
Stainless Steel lock nut
Our hex lock nuts are very strong and are great for both indoor and outdoor use. This stainless is superior to regular steel and provides excellent rust resistance. With a nylon insert, these lock nuts greatly reduce loosening under vibrations and torque.
Incredibly versatile 100% silicone sealant that dries translucent clear. Best for sealing gaps or cracks between two surfaces; works on window, door, kitchen, bath, gutters, auto, marine and more. Indoor/outdoor; 100% waterproof. Won't yellow, shrink or crack. Mold and mildew resistant.