Important considerations for installing a new roof over a current one

AAR Expert Mindy Dahlquist says installing a roof over a current roof system is ideal when the roof itself is in good shape but has just reached the end of its visually appealing phase.

AAR Expert April question: When is it acceptable to install a new roof over an existing roof?

AAR Expert Mindy Dahlquist answer: Certain situations must be present for a roofing installation to occur with a new roof over an existing roof without a tear-off. This is not usually an ideal situation, although it can be a more affordable option.  

Leaving the current roof in place and installing over it can be a poor option when you have water intrusion, mold, ventilation concerns or other damages.  

Installing a roof over a current roof system is ideal when the roof itself is in good shape but has just reached the end of its visually appealing phase. Take asphalt, as an example: if the deck is still structurally sound (including the back side of the deck), ventilation is good, no major damages have occurred and granule loss isn't apparent, then the roof can be roofed over top. Shingles must be laying flat. Overlay install should not occur for an project with more than one previous layer of material (code requirement). Overlaying a roof can reduce 10-15% of cost to save on labor, disposal fees and rip-off time.  

In the roof overlay circumstances, your fastener length will become important to ensure that your fasteners are being attached into sheathing to prevent a lower pull-out strength value.