# Water in hallow core or Prestress Concrete Deck



## RoofPro (Oct 29, 2008)

Guys – this is a new one for me: 

Gravel Surface BUR over a 8” Hallow Core Prestress conceted deck – 24 inch wide panels with 3 hallow cores in each pannel, vapor barrier, iso and cover board all set in hot – about 3 years old. Client has had leaks in one spot where the deck meets the wall for the life of the roof. Roofer has made several repair attempts – all to no avail. 

A worker drilled a hole in the underside of the roof deck near the leak area, and over 50 gallons of water came through the hole. They plugged the hole with a tap-con screw and pipe dope and called me. I arrived some hours latter, removed the screw and more water came out.

Hard to see how water would get to the core, and not leak at the joints in the concrete panels.

Any of you ever run into something like this?


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## cmilmoe (Jun 18, 2012)

Were all of the units thoroughly checked?

If the integrity of the roof is intact, it would make sense that a RTU could be leaking into core of the panels.

Just a possibility.


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## Pie in the Sky (Dec 21, 2011)

I would say condensation of some kind but thats way too much water. Sounds like the roof is leaking at a penetration and getting in there. I would first look and see if a pipe lines up with that void thats filling up with water. I mean the leak has to be somewhere along it, really narrows down your search area. An RTU would be a great spot too. You could always use IR to help but it may not. If you find something youll definately need to do some destructive testing. With that VR on there it really could be leaking anywhere and going in where the pipe penetrates. SOunds like a Fun one!

D


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## Grumpy (Oct 29, 2008)

Take note of the leak location inside and the direction of the void. Start at the area of the roof where the leak is being seen inside and follow a straight line directly up slope. You'll find it that way if it's coming from the roof.


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## 1985gt (Dec 21, 2010)

Welp you guys beat me to it. First I was thinking condensation until I read the whole post. There has to be a penetration along that tube. Is it possible that they sealed around the penetration on the underside thus keeping the water running in the tube? There has to be something up hill letting in water. 50 gallons hell even 5 gallons is too much for condensation.


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## RoofPro (Oct 29, 2008)

Thanks for the quick responses guys – all great points. 

The roof area in question is an addition, and the Hollow core panels span about 30 feet, where it joins the original roof deck (also hollow core). Both the addition and the original building were roofed at the same time. There are no penetrations (no pipes, curbs, drains, HVAC , etc.) in line with the core that held the water. 

Today the roofer spub back gravel starting from grave stop and extending in about 15 feet and he found a smallish fishmouth that spit water when stepped on – looked like the fishmouth extend through all the plies. Weather did not look good, so he sealed it with roof cement. We’ll come back and cut down the deck to check for wet insulation, and any sign of damage to the deck. 

The thing that still worries me is once it gets under the roof, how does the water get into the core? Only place there should be hole is at the eave where wood blocking was installed. Another possibility is that during the removal someone got a little heavy handed with the roof cutter / ax / razor back (pick your favorite implement of destruction) – but to do that kind of damage to the deck seems like a reach to me. Then again we have all seen “that guy” on the roof do some amazing things. And of course we have no reason to assume the roof leak and the hole in the deck are in the same location. 

Also given that 50 gallons came out yesterday, the void could hold a fair amount of water before the leak appears inside. The owner is renovating the space, and will probably not like the idea of removing the plug from the underside of the deck so we notice the leak ASAP. 

Fun fact – assuming the cores have a 5” diameter they could hold 4 gallons per liner foot. The 50 gallons that came out would mean the core was almost half full.


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