Installing New Components Over Old Roofs

Ripping up an existing roof to install a brand new roof can be expensive. However, there are options that allow homeowners to save a little bit of money. If the existing roof is in good shape and exhibits no rot, water damage or leaks, a Monmouth County Roofing contractor may be able to lay down a brand new roof over the old one.

As with any home improvement option, there are certain advantages and disadvantages to adding a roof on top of an existing roof versus removing the old roof before installing the new one. The biggest advantage is the savings. Simply overlaying new shingles on top of old shingles can save up to 25 percent of the cost of adding a new roof. Additionally, as long as the existing roof is in good shape, an overlay avoids the mess and the labor involved in removing the existing roof.

While an overlay can be a good option for some homeowners, it should be known that there are some major drawbacks. One of the biggest cons is that adding a new layer of shingles means that homeowners or contractors can’t properly inspect the roof sheathing and underlayment. If water finds its way beneath the shingles, which happens more often than many people realize, it can get into the roof’s decking and cause damage if the underlayment has deteriorated.

Another con is that adding shingles to a roof without removing the old ones first adds weight.

Depending on their quality, a layer of shingles can weigh up to 450 pounds per 100 square feet of roofing. Most roofs are designed to hold one layer of shingles plus any snow that may fall. On homes that have roofs that were not designed to carry the weight of an extra layer of shingles, the roof decking or sheathing can actually sag.

Finally, shingles are designed to be installed on surfaces that are flat. If the old shingles are somehow misshaped, correctly laying down new shingles can be a bit of a challenge. Any defects in the old roof will be seen in the new layer. If the old layer is in good condition, a professional roofer can lay down the new shingles in a way that maintains the same step-ups. Regardless, overlaying a new roof may affect the warranty on the new shingles as most are not designed to be laid down over an existing roof.

Homeowners who are seriously interested in overlaying versus an entirely new roof may be interested in having a metal roof placed over existing shingles. While they cost more up front, they also last longer than a second layer of shingles while providing energy savings. Regardless of what type of roof is desired, homeowners should ensure that the original roof is in good condition before considering an overlay. Have a question regarding skylight installation or new gutters? Ask a roofer from Fortified Roofing of Monmouth County NJ.

Common roofer term explained by Fortified Roofing of Monmouth County NJ:


Roof decking is a layer made out of plywood, corrugated metal, OSB sheathing or other similar materials that are attached to the roof’s trusses. Not only does the decking layer provide a flat surface for the installation of shingles, it also provides a layer between the interior of the home and the elements.

Monmouth County roofer Fortified Roofing answers a question:

What can happen if I install new shingles over old shingles that have been damaged?

If the old layer of shingles have been damaged, it is likely that the structural components of the roof have been damaged as well. Adding a new layer of shingles will not keep out the elements; in fact, moisture can get under the new shingles and damage the structural components of the roof even further. Ultimately, it is likely that that both the new layer of shingles, the old layer of shingles and the structural components will need replacement.

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