Building codes say you can put a second layer of shingles over the first layer, but it’s better to strip off the old shingles and start with a clean slate. There’s anecdotal evidence that new shingles installed over old shingles won’t last as long as a single-layered roof, most manufacturers offer the same warranty for both methods. However, if you are planning to keep the house for the long term, we suggest ripping off the old shingles so you can:
- Find out what’s been happening under that blanket of old shingles. Small leaks can cause big damage in underlying roof sheathing and framing. It’s easy to find and fix damage when you expose the roof surface.
- Replace damaged or corroded flashing and metal valleys.
- Install ice and water barrier to prevent ice dam problems.
- Have a new roof that’ll look much smoother on a flat surface than it would have on old, wavy shingles.
Special tear-off shovels have serrated edges that not only tear up the shingles but also pull out most of the old shingle nails at the same time. They have a fulcrum welded to the back of the shovel head to pry up materials. Buy or rent a couple of them if you have friends that are willing to pay you back for all the times you've helped them move.
Tearing off an old roof is a big job, but if you invest in a few specialty tools, line up a crew and a trash container, and get your ducks in a row ahead of time, the work will go much faster. You’ll most likely be required to obtain a building permit, so visit the building inspector before the job starts.
Order a trash container to hold everything you tear off (a 20-cu.-yd. unit will take care of the average 1,500-sq.-ft. roof). You’ll save tons of time if you instruct the driver to position the unit under an eave so you can dump directly into it. Be there when it’s dropped off to get it where you want it. If possible, keep the trash container for about five days. If you hustle on installing the new roof, you can throw in the new shingle wrappers and leftover shingle cut-offs, too.
Pick up felt paper, ice and water barrier and wood lath (to help felt paper stay put in the wind) so it’s on hand the day you start the tear-off. Then you’ll be able to waterproof immediately and snap the chalk lines for laying out the new shingles before the roof is cluttered with new shingle bundles. Order the shingles for delivery the day after you expect the felting to be finished. If you do that, the supplier can lift the shingles right to the roof for easy staging.
Finally, rent, borrow or buy three timesaving tools to speed up your work (Photos 1 – 3).
Figure A: Complete Roof Tear-off in 7 Steps
Position the trash container for easy loading. If you’re able to position it directly under one of the lower eaves, you’ll save extra work by dropping debris directly into it. Put old sheets of plywood under the wheels to protect your driveway.
Cover foliage near the house with reinforced plastic tarps to catch debris for easy cleanup. Lean sheets of plywood against walls to protect windows and doors, siding and electrical fixtures.
Remove the old shingles with tear-off shovels. It doesn’t matter where you start or stop. Work from the top, bottom and sides to save back muscles. Clean the roof with a push broom and remove or pound in any remaining fasteners. Besides being tripping hazards, they can work through and damage the new shingles.
Cut ice and water barrier to about 8-ft. lengths, remove the backing and adhere the sticky side to the roof sheathing along eave edges. Overlap ends at least 6 in. Code usually calls for it to project at least 2 ft. up the roof past the exterior walls, so you may need two rows on homes with wide soffits. Staple down the felt with 5/16-in. staples every few inches along lapped joints and every 6 in. or so in the open areas between rows.
Felt right over ventilation holes. Prevent accidentally stepping through the camouflaged holes by covering them with tacked-down scraps of plywood. Snap shingle layout lines and nail down lath for wind protection.
Clean up loose scraps by dragging around a trash can to transfer debris to the large container. Go over every square inch of area around the house with a magnetic broom to pick up stray fasteners (or risk putting a nail through your patio door with the lawn mower!).
Have the lumberyard deliver your shingles with a boom truck or conveyer. You’ll save hours of misery hauling thousands of pounds of shingles up ladders. Unload and distribute shingles by strategically placing them for easy reaching when you’re shingling. To cut down on rehandling bundles, figure out before delivery how many bundles of shingles each roof section needs.
Note: You can download Figure A and enlarge it in Additional Information below.
Three hardy people can tear off and felt a roof in one day, but be careful. Only tear off what you can safely protect from the weather the same day, especially if you’re working shorthanded. It always takes longer to weatherize than you think! Tear off the areas farthest from the trash container first. That way you won’t tear up the new felt paper when you haul the rest of the debris to the container.
Go over the wood surface with a fine-tooth comb after tear-off. Pound in protruding sheathing nails and remove any leftover shingle nails, then sweep and install ice and water barrier and felt.
Working Safely on a Roof
Many professional roofers don’t use safety harnesses, but they’ve got experience on their side to help keep them out of trouble. (Some are even blessed with prehensile tails.) Weekend warriors should follow these commonsense safeguards:
- Wear safety belts and ropes— especially on steeper slopes where the footing is dicey.
- Extend access ladders a few rungs above roof edges and ballast the bottom with a bundle of shingles to prevent kickouts.
- Avoid working on frosty or wet roofs.
- Be aware of overhead power lines.
- Nail down 2x4 “kickers” near well-traveled roof edges like shingle unloading points or dumping stations.