By adding onto my roof rack, this is how I transport 4x8 sheets without a pickup.
First, I used (2)2x4x8’s & (2)1x6x4’s and some wood screws. You may need to shorten the length of the 1x6’s depending on the width of your car. I reduced mine to 3ft 4in.
Second, I laid the 2x4’s, on the 2in side, parallel with the length of the car on the roof rack bars. I spaced the 2x4’s as wide apart as possible so that they would butt against the roof rack ‘tower’ that clamps the bars to the car’s roof rails. This will keep the 2x4’s from siding laterally along the roof rack bars.
Third, I laid a 4x8, or something large enough, on the 2x4’s to test the weight distribution on the rack so that it was balanced. Fourth, I marked on the 2x4s where I would need to notch the wood so that the 2x4’s sat down securely onto the rack bars. I also held up a 1x6 at either end to mark where I needed to screw each 1x6 to the end of the 2x4s.
Fourth, I marked on the 2x4s where I would need to notch the wood so that the 2x4’s sat down securely onto the rack bars. I also held up a 1x6 at either end to mark where I needed to screw each 1x6 to the end of the 2x4s.
Fifth, I notched the 2x4’s using a drill with a hole-saw bit and a hand saw but you could use a jig saw or whatever works for you.
Sixth, I screwed a 1x6 to each end of the two 2x4’s with the bottom of the 1x6 flush with the bottom of the 2x4’s.
Lastly, I placed the wood rack on top of my car rack to verify that the rack fit snugly.
Step 7: Important FYI's:
I would not recommend doing this if your car doesn’t already have roof rails. The forces that occur with heavy materials when you start and stop a moving vehicle can easily rip a roof rack off your car if your rack simply clamps to the cars body.
Step 8: Important FYI's:
Your car roof rails have a weight load ratio that’s recommended by the manufacturer. This can be found in the car manual. Verify what your load capacity is so that you know how much material you can carry safely. You may need to err on the side of caution and make several trips to be safe.
Step 9: Important FYI's:
When you strap your 4x8 sheets to your car you need to secure them using strong nylon straps or similar. Wrap the straps so that the 4x8’s are secure to the wood frame and the wood frame to the roof rack and the roof rack to the roof rails. If you only strap to the car roof rack and not the rails as well you could be seeing your 4x8’s and roof rack flying down the road.
Step 10: Important FYI's:
Drive slowly. I do not recommend going on the freeway. I take a non-freeway route and travel at a speed where I feel the material won’t hydroplane off the roof. So far I’ve made at least a dozen trips using this method and haven’t had any problems yet.