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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About author

Bob 270 posts

Since 2005 Bob has been answering questions, free of charge, here at With a strong background in residential roofing and provides a practical and simple answers to hundreds of roof related questions, so it is easy to understand the issues you may have with your 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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  1. This article contains so much fruitful information which will be liked by the readers. In my opinion this is the best article in this category.
  2. C J
    July 12, 02:19 Reply
    Hello My home is a newly built construction and it's summer time witch means the ac unit is running but I noticed water leaking from the roof out of some type of drain whole from the roof of my home what could it be? The ac unit is on the side of the house but the is something blowing air in the attic What could it be causing the leak off the roof
    • Bob
      July 13, 05:18 Reply
      There could be a few problems to check. I believe you have what is called a split system HVAC. These types of HVAC units have a condensation pan and exit line to catch excessive condensation and remove it away from the living space. My home has this split system, half outside and the other half in a wall closet. My condensation line goes down into the concrete foundation to the nearest stem wall and away from leaking onto the carpet. Your split unit is outside and in the attic setting on a condensation pan and has a drain exiting somehow on the roof. This is one idea that comes to my mind. It would be a good idea to call your HVAC contractor for a check up to see why it is producing so much condensation.

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