We get a lot of calls about roof top AC units. We think it is leaking in this area?!? Should we install the AC unit before we re-roof or after or during? Does the company need to use a crane to lift off from the roof? What about rusty old AC stands? And so on and so forth.
First of all, if you see that you are missing shingles underneath an AC, please do not tar the area. Tar, or mastic, is not a substitute for actual roof material. The above photo shows tar covering up where the felt paper and shingles are supposed to be installed but instead someone slathered tar to the area. This an incorrect application. When in doubt, just call us. We have free inspections.
When completely shingling a roof, we roof underneath the unit. Which means we use felt paper and shingles, not tar. For most standard sized units, we do not need to use a crane. Just labor. And we only need to raise the unit just enough to get underneath to remove the old and install the new. Now, for most people, the AC unit is usually the same age as the roof - old. A homeowner can install a new unit before re-roofing or we can certainly coordinate with your favorite AC company to do at the time of the re-roof. If the scheduling doesn't jive, we recommend that after your new shingle roof is installed, you have us come back out AFTER the AC company installs the new unit to ensure that all penetrations are sealed correctly and the roof was not damaged in any way. Most licensed AC companies are careful on new roofs, but accidents happen and we just want to make sure the roof is ready for whatever weather lies ahead. We don't like surpises any more than you do.
Also, see that wire in the upper middle part of the photo? All AC units come with wires and as AC units age, so do the wires. So, if you decide your AC unit can last a few more months and re-roofing is the first priority, please be aware that that aging wire may snap when we lift the unit to tear off and shingle underneath the unit. We obviously cannot warranty old age for a unit we are trying to be careful working around so we highly suggest that if your AC is getting up there in years, have it checked out BEFORE we roof so you don't lose air conditioning in the process.
Sometimes old AC stands are rusty due to the lovely weather elements - intense sun with times of intense rains. When changing out the AC unit, if in doubt, change it out. It is usually more cost effective to have the AC company change it out at the time of the AC unit install then having us do it at the time of the re-roof.
And in case you are wondering what we would suggest for the above photo, we would remove the shingles at the entire AC unit area and install new felt paper and shingles and tie in to the existing roof system. We would want to do it right and make sure that rain doesn't have a chance to get into the house. Comes with a warranty too. Does your tar do that?