If you've got an asphalt roof that needs to be replaced, generally the first question to address is whether to have the old roofing torn off or install the new roof over the existing shingles.  Check your local building code - depending on the number of roofs already installed, a tear-off may be required.  Asphalt roofing is heavy, and too many layers can result in a load your home's structure cannot safely bear. Even if your local building code permits another roof installation over the existing one, you should take into account the age of your home.  A newer home is more able to bear the weight of an additional roof; such a weight load might strain an older home.

While a tear-off is more expensive due to the additional labor as well as waste disposal, the answering that question should be based on more than economics.  Asphalt roofing is one of the most popular choices, and it's an economical product to install.  If saving money is a top priority for you, perhaps you've considered having your new roof installed on top of the old one.  While many homeowners choose this route, it can be a 'cut corners, save cash' proposition, and often cutting corners ends up costing more down the road.

If your proposed roofing contractor has given you a price based on a roof-over rather than tear-off, here are some things to consider.One of the most important aspects to consider is the condition of the roof under the shingles; this is especially important if you have an older home.  If there is any deterioration or damage to the roof decking, flashing, or any other component underneath the shingles, a new roof installed over the old one merely camouflages the problem, and it will eventually manifest itself.  There may be water damage to the plywood deck underneath; this should be repaired before a new roof is installed.  Covering over damage usually results in a new roof that has problems early, and there may be slow rot occurring underneath which you're not aware of until an expensive major repair is needed.  Other conditions which should be inspected prior to a new roof installation is the amount and type of ventilation.  Sufficient ventilation is necessary for your roof to continue to perform the way it was intended as well as to prevent the formation of ice dams.

If you are replacing your roof due to major storm damage, this is another situation where a tear-off is the best practice.  Roofs which are heavily damaged by a storm most likely have problems under the roofing itself, especially water issues.

Finally, if you install a new roof over an old one which still has time on its warranty, their may be conflicts between the warranty on the old roof and the new one.  Also, you should check the warranty for the new proposed asphalt roofing carefully to make sure there are no requirements relative to tear-off of an old roof.

The bottom line? While roofing over existing asphalt shingles may be less costly up front, in the long run it could result in substantial expense due to emergency repairs, both to the roof and your home's underlying structure and/or the interior.

Your home is probably the biggest investment you'll ever make, and your roof is its main protection.  If you're contemplating installing a new asphalt roof over the old one, we suggest you get another estimate with comparable roofing material which includes tear-off of the existing roofing.  Then you can better evaluate whether the cost savings is enough to risk further expense down the line. 

Quarve Contracting, Inc. is full-service exterior remodeling contractor, providing roofing services in the Minneapolis and St Paul metro area.