Hack Your Car Top Carrier: Loading Tips and Safety Smarts

Updated: Apr. 30, 2024

Getting building materials home from the lumberyard or home center is easy if you own a pickup truck or a minivan. But you can also haul items on the roof of your car or SUV if you've got a roof rack, obey the rack's weight limits and properly tie down the load.

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Upgrade a Factory Roof Rack

The roof rack that came with your car may look rugged, but most have a load rating of only 100 lbs., the equivalent of just nine 8-ft. 2×4 studs. If that’s all you plan to haul, you don’t need to modify your factory rack.

But if you plan to haul more than 100 lbs., buy a set of heavy-duty crossbars to retrofit your factory rails. Retrofit crossbars are wider than the factory units, are flat instead of curved, and carry more weight, as much as 200 lbs., depending on the vehicle. The factory roof racks on some cars have convertible crossbar/side rails. If that’s the style you have, just switch them into side rails as shown. Otherwise, remove your factory crossbars and install the new ones on the factory rails.

Install a Removable Roof Rack

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Open all four doors and locate the crossbars and rubber-cushioned feet in the recommended locations. Then swing the locking lever down to secure the clamp to the roof. Lift the front and back crossbars onto the factory side rails. Space them according to the crossbar manufacturer’s instructions. Then secure the feet to the rails using the wrench provided.

If your car doesn’t have a roof rack, you can add one without drilling any holes in your roof. Buy a set of universal crossbars and towers and a set of vehicle-specific clamps to attach it.

The best part about buying universal crossbars is that you can use them on more than one vehicle. Just buy the vehicle-specific clamps and install them in the towers. If you want to leave the crossbars on your car, buy a set of lock cylinders and install the towers to prevent theft. Otherwise, remove the crossbars to increase your gas mileage.

To install the crossbars, just locate them according to the directions that came with the clamps. Adjust the tension screw on the tower, then snap the lever down to lock in place.

How to Safely Load Your Roof Rack

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Many DIYers don’t think about how they’ll secure the load once they get the items onto the roof. So they rely on the free twine provided at checkout. Or they buy inexpensive bungee cords at the store. That’s a big mistake.

A roof rack’s load rating is based on a ‘static load’—the weight of the load when the vehicle isn’t moving. But once you hit the road, turn, encounter bumps and dips, or slow down, inertia multiplies the weight of your load by four to five times. So your tie-downs must be strong enough to keep the items from shifting or flying off. You’ll need a minimum of four 14-ft., 1,000-lb.-rated ratchet straps to get your load home safely.

Secure the load to itself

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This three-point tie-down and bundling method may seem like overkill, but it’s really the only safe way to get material home without damage or injury. Start by loading dimensional lumber onto the rack with the narrow edges resting on the crossbars. Then secure the front and back ends of each lumber bundle to prevent movement. Wrap the straps around the lumber bundle at the front and rear. Then tighten until you can’t move the middle pieces.

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Secure the load to the rack

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Hook a ratchet strap to the front bundle strap. Then wrap this strap around both crossbars and tighten. Repeat for the rear end of the bundle.

Open the rear doors and run a ratchet strap over the top of the rack and through the rear seat area of the passenger compartment. Make sure the strap is behind the driver’s headrest and tighten. This important step counteracts the ‘lift’ created by air coming off the windshield and is especially important if you have a factory roof rack that’s held in place only with small rivets.

Tips for Using Your Car Top Carrier

Plan your trips

Overloading a roof rack (even heavier-duty crossbars) is the single biggest hauling mistake DIYers make. So get your shopping list and search the home center’s website and online to find the weight of lumber and other construction materials you intend to haul on your rack. Then plan what you’ll carry on each trip, because big projects will require several trips.

Tape the lighter items

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Start the duct or nylon filament tape about 6 in. back from the end of the bundle and wrap it around to the opposite side. Repeat to cover the end of each item. Then wrap tape tightly around the entire bundle at the front and rear, making sure you cover the pieces of tape applied earlier. Then secure the bundle to the rack with ratchet straps.

Secure the overhang

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If your load extends over the hood of the car, secure it with hood loops and cinch straps. Pop the hood and drop in temporary hood straps. Or mount the straps permanently under a fender bolt. Run a rope or cinch strap through them and over and around the leading edge of the overhanging load. Snug the cinch strap just enough to prevent upward movement, but not enough to bend the hood.

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Roof rack safety tips

  • Special items require special rack attachments. Contact the rack manufacturer to buy attachments for bikes, boats and camping gear. Never jury-rig those items to a standard roof rack.
  • Roof loads change the dynamics of your vehicle, and the extra weight increases stopping distances. So stay off the highway whenever possible, drive slower, brake sooner and make wider, slower turns.
  • Pay attention to overhead clearances, especially when entering your garage.
  • Sometimes it’s just notworth it to haul it yourself. Heavy-duty crossbars, add-on racks and ratchet straps often cost more than the store charges for a delivery right to your door, especially when you add in the risk factor!
  • Never connect hooks, rope or straps to a bumper or fenderwell. A shift in weight can crack the plastic, scrape the paint or bend the body panels, costing hundreds to repair.
  • A bare roof can’t carry a load because it can’t distribute the weight out to the pillars and door frames. If you place a load on a bare roof, you’ll damage it.
  • Never haul sheet goods or mattresses. The huge surface area can create enough lift to rip the entire rack off your vehicle.