How do you lay shingles on top of shingles?
Expert Tips for Roofing Over Existing Shingles
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Remove Caps
Dave Toht
Start by removing the ridge caps. Doing it now will make it easier to keep the reroofing job clean. Use a flat pry bar or roofing shovel to pry out and remove the ridge shingles. Remove all the nails.
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Remove Obstructions
Dave Toht
Remove air vents and pipe flashings by prying out or unscrewing the fasteners holding the fixtures. If you damage shingles while doing this, repair them (see next step). Reuse a vent or flashing only if it is like new; otherwise, replace it with a new one that will fit the hole or pipe.
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Repair Broken Shingles
Dave Toht
If a shingle is torn or cracked, glue the broken piece back in place using roofing cement. If the broken piece is lost, cut a new piece to fit the existing shingle. The goal is to provide a reasonably flat surface for the new shingles to lie over, with no gaps greater than 1/2 inch.
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Sweep the Roof
Dave Toht
Using a large broom, brush away all the broken shingle pieces, twigs, and any other debris that could become trapped under the new shingles that you'll install. Keep the roof clean as you work.
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Install Flashing
Dave Toht
At the eave and the rake, install U-shaped drip-edge flashing made for reroofing jobs. Install the eave piece first, then the rake piece over it. The two pieces should meet neatly at the corners. Drive nails at high points on the underlying roof, the bottoms of the shingles.
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Install Valley Flashing
Dave Toht
If you have an open valley, install new W-shape metal or vinyl valley flashing to fit directly over the old flashing. Attach it by driving nails into the outside edges only. Do not drive nails less than 6 inches from the center of the flashing.
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Install Starter Strip
Dave Toht
Use a starter strip or cut pieces for a starter course. Rip-cut the starter strip or starter pieces so that they butt up against the second course of existing shingles and are even with the front edge of the existing roofing. Attach with nails along the top edge of the strip.
Editor's tip: If the existing roof has wavy horizontal lines, you can take out the waves by snapping a horizontal line a 1/2 inch below the shingle bottoms of one course. Install a course along the snapped line, then install succeeding courses using a guide or a snapped line.
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Cut and Install Shingles
Dave Toht
Rip-cut the shingles for the first course so they butt up against the third course of existing shingles and are even with the front edge of the starter course. Their tab slots should not line up with the tab slots of the starter course, if there are any. Nail the shingles just above the tab slots.
Editor's Tip: The thicker the new shingle, the better it will hide any imperfections in the roofing underneath. It's a good idea to use at least 40-year shingles; architectural shingles are an even better choice.
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Continue Installing Shingles
Dave Toht
Butt the succeeding courses of shingles against the bottoms of existing shingles and apply them by driving nails above the tab slots. Snap vertical control lines; there is no need to snap horizontal lines. Be sure the new tab slots do not align with the old ones.
Editor's tip: In a reroof job, the starter course (or strip) is rip-cut so it butts up against the third course of the existing shingles. Its front edge is even with the front edge of the drip edge. The rest of the shingles are full width.
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Work Around Vent
Dave Toht
Once you've installed shingles just past a plumbing vent, install the flashing piece so it will lie on top of roofing at its bottom, but be covered with roofing at its top. Depending on the width of the pipe, you may need to tear away a segment or two of the rubber boot. Apply roofing cement, slide the flashing over the pipe, and push so it lies flat on the roof.
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Install Air Vents
Dave Toht
Install air vents in a similar manner. For both plumbing-vent flashing and air vents, you'll need to cut the shingle above to go around the flashing and then install the shingle.
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Work Around Walls
Dave Toht
Where you meet a chimney or side wall, install step flashing. Apply a shingle, then a piece of flashing, then a shingle, and so on, so that each piece of flashing rests on top of the lower course and is covered by the upper course. You'll need to pry the siding outward to slip in the flashing; in some cases, you'll have to remove the siding.
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Install Counterflashing
PHOTO: Dave Toht
PHOTO: Dave Toht
Protect the step flashing with counterflashing. On a chimney, use a grinder to cut an indentation into the mortar. Cut and bend the counterflashing to fit snugly into the cut mortar and to cover at least 3 inches of the step flashing. Apply mortar with a caulking gun and set the flashing into the mortar.
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Cover Ridge
Dave Toht
Install roofing on both sides of a ridge and cut them so they butt closely together but do not overlap. Cut shingles into ridgecaps. Snap lines on either side and install the caps.
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Cut Shingles
Dave Toht
At the rake, snap a line directly above the edge of the existing shingles. Cut with a utility knife; you might want to use a straightedge. You might find it easier if you first cut from below, using the existing shingles as a cutting guide.
Installing Asphalt Shingles over an Existing Shingle Roof
Although placing new roofing over old may be allowed by some codes, &#;roofovers&#; tend to be inferior and won&#;t last as long as a roof installed over stripped sheathing. If you must do a roofover, check with your local building department first&#;codes typically require that you strip a roof if there are two or more layers or if existing shingles are curling.
Before beginning, replace or flash over old flashing as follows:
- Use aviation snips to cut away flashing around plumbing vents.
- Use a cold chisel to remove chimney counterflashing.
- Along the eaves, install a new drip-edge over the butt ends of existing shingles.
- Along the rakes, install a new J-channel drip-edge, which wraps around the old rake flashing and starter courses.
- Leave the old valley flashing in place, and install new over it.
To level out an existing asphalt-shingle roof, rip down (reduce the height of) two courses of shingles, as shown in the drawing below. Because asphalt shingles are routinely exposed 5 in., rip down the first strip (the starter course) so that it is 5 in. high. Then lay it over the original (old) first course so that the strip is flush against the butts of the original second course above. Next, rip down a second strip (second course) 10 in. high, and put it flush against the butts of the original third course. You now have a flat surface along the eaves. The third course of new shingles&#;and all subsequent shingles&#;need not be cut down, just butted to an original course above and nailed down. Use 1-1/2-in. roofing nails for roofovers&#;or whatever length is necessary to reach the sheathing.
Fine Homebuilding Recommended Products
Wirefy Crimping Tool
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Heat-Shrink Tubing
Wirefy's heat-shrink tubing is super reliable, high-quality, and great to have on hand.
Handy Heat Gun
This heat gun is great for drying joint compound, primer and paint when patching drywall and plaster walls. Plus it can soften adhesive, get a very cold small engine to start, and shrink heat-shrink tubing.
All-Weather Flashing Tape
Available in 2- to 12-in. widths, this is a good general-purpose flashing tape that sticks well to most things. It features a two-piece release paper, water-shedding layers, and good UV resistance.
Affordable IR Camera
This camera is super useful for tracking down air leaks in buildings. The one-hand pistol grip arrangement frees your other hand for steadying yourself while maneuvering tricky job sites.
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