Roof Leak From HVAC unit on commercial roof?

Can this HVAC unit be the cause of a roof leak. The roof was installed about two years ago. The leak is along the wall in the picture, water runs down the inside wall of the building. It also happens to be near an HVAC unit. It only occurs during heavy wind driven rain. A photo of the neighbors side of the wall is also included. The roofer thinks the leak is from the HVAC unit or the bare concrete block wall. Do either of these issues seem to be the likely cause.


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That open HVAC could easily be the problem, but it should leak through its own penetration. HVAC needs secured regardless. The wall leak should go all the way to the deck, if it is dry 4’ down you can blame the adjacent roof. Which way do the deck flutes run? Is the leak pinpoint or generally the whole wall? Leaks from blowing rain are 99% flashings, so the parapet details are the initial suspect. How old is the “new” roof. TPO has its own issues…

Here is a photo of the deck, hard to see but it’s a slow steady leak along 40 feet of the wall. I had my tenant check and the neighboring space has no leaks along the wall. The roof was installed Sep 2020 and it has a Mulehide NDL warrantee.

Inspect the wall flashings and T bar assembly. Should be a base anchor tie in. Make sure there is cut edge sealant on any splices. Pull some T bar and check for water cut off. If all that is tight, spray sealer the block. Be sure all your caulk is completed first.

I think Darkthirty is correct. I couldn’t see what the heck was going on with my laptop because the screen was too small. Then I had to figure out what i was looking at. Looks like they went with a deck board over an existing either PVC coated EPDM or something else. Can’t tell if you put a TPO on it or another EPDM. The buckets throw me off unless the TPO is using a bonding adhesive in the field and screw plates on the seams. Anyway, the photo on the gravel side. Darkthirty is correct. I would block fill that bare block. I’ve seen many of them leak down a 75’ wall…front to back. Your side looks like they ran the old roof up the parapet, under the cap flashing. I would check the seams of the cap flashing.
I had a one year TPO leak at an AC. I got the blame every time it rained. I went over 2 times and it was text book. The last time it leaked, me and another guy took the panels off the AC and the leak was the Electrician. Ran conduit into the AC and didn’t seal the hole, so yes, check the AC.

Both of you thanks for the replies. It is a TPO. Just wondering why the other side of the wall (neighboring tenant) wouldn’t also leak if it’s the block wall, at least they claim they have no leaks. Wondering if I address HVAC and check the cap flashing first and if that doesn’t solve it then seal the block wall. We don’t own that side of the wall so that may be an issue.


I’d inspect the parapet/field seam on your side of the wall first. No reason you can’t do a non-invasive visual inspection on their side.