Roof Leaks caused by Air Conditioners

Roof Leaks caused by HVAC roof mounted systems.

Damaging a roofAir Conditioners on roofs that leak can cause hundreds of dollars in repairs. The problem is finding the responsible party. I can’t tell you how many times, year in and year out, how I have been blamed for a leaky roof I installed, only to find out that someone installed a AC on the roof poorly years after I did the roof.

When it leaks, who do you call, the roofer!

AC unit on roofThe photo to the left shows how a HVAC contractor from the Sacramento area has bent , broken and stuffed his roof mount HVAC stand poorly into this roof. There is no way this roof would not leak, and it did, and who did the home owner call? Yep, you got it , me. Winner~Winner, Chicken Dinner. The shingles and underlayment needed to be repaired and during this job a broken rafter was discovered and replaced.  As you can see to the right the unit’s stand on the bottom left is extended more than the right side to make up the sag in the roof. The HVAC contractor cut a rafter and it loaded too much weight on what is called the cripple rafter which had no purlin support. { A cripple is a rafter that runs from a hip to a valley} This HVAC contractor that did this horrible job is a large company that does a lot of advertisement, but will never get a referral from me because of this type of work.

There were many issues with this installation and don’t get me wrong because for the most part HVAC contractors are great. This installation was very poor and did not get inspected by the Building Department. I have seen many maintenance issues on a Air  Conditioners that also caused leaks. I hate having to tell the customer they need to call the HVAC Contractor that work on the roof recently to come back out and fix this problem. Did you know I have seen small 1/2 holes stabbed into the elbow so the HVAC contractor can temp/test the return air, then leave that little hole. Yep those leak. I could go on and on but I think the point is made. This area of the roof is most important to get right and hiring the best to do the two jobs is critical.

AC crane lift to roofI have for years developed great working relationships with HVAC Contractors. As a roofing contractor it is good to have a few you can trust and use because things can really go well if the two know each other and work good together. The reason why is this, when the roof and HVAC are being done at the same time, both contractor that have worked together  both understand each others job responsibilities. Of course having both jobs done by the same contractor would have the best results. There are not to many contractors that cross over trades, so having the two contractors having past experience together is a good scenario. It normally goes like this.

The old HVAC removed. The roof is removed. Exposing the roof can be useful to the HVAC contractor setting the new curb or stand. Having the heavy AC unit off the roof the roofer can install the roofing easier and making a clean good looking job. The HVAC contractor then lifts the new AC and sets it on the stand and seals the unit to the plenum. Best of both worlds, if both are done at the same time. If not I advise an inspection of the both contractors to make sure this area of the roof perform well for years.


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Bob 270 posts

Since 2005 Bob has been answering questions, free of charge, here at With a strong background in residential roofing, I try to provide a practical and simple answers to the consumers questions, so it is easy to understand the issues they may have with their roof. Our answers are free so feel free to ask what you want. Use the green question box to contact myself or I have spent ten years as a union shingler, seventeen years as a California licensed roofing contractor with a general contractor endorsement and since Feb. of 2005 a roofing consultant. If I don't know the answer to your question, I will point you in the right direction.

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