Low spots on a flat roof

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  #1  
Old 03-09-19, 02:34 PM
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Low spots on a flat roof

I have some areas on my flat roof that are low. When it rains it puddles there.

This new roof was installed (2 ply hot mopped) in 2015.

Recently I noticed the low spots have began to "blister" (not sure this is the correct term).





When I took a blower to it it kicked up a lot of sand and black stuff then I see some bald spots.





Called the roofing company out and they said the only way to repair this is to put more asphalt paper over the low areas, then another sheet over that but smaller, then another sheet, so basically build a pyramid to create a high spot. They will make a rectangular pyramid composed of a slightly smaller sheet for each layer.

Is this the right strategy?

The low spot shape is irregular. So if you lay a rectangular sheet down, you just raised the outside again, and so the inside spot will be lower by the same amount. I guess I don't see how this would solve the problem.

I am thinking if there is some sort of self leveling liquid that can be poured over this to level the whole thing, then another ply can be put over the whole thing to seal it off better?
 
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Old 03-09-19, 03:59 PM
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I can tell you on commercial buildings it is very common to have standing water on the flat roof. Normally it just evaporates if it doesn't drain off. I am not sure if this is really an issue. How long does the water sit?
 
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Old 03-09-19, 08:16 PM
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It sits for a few days.

Problem is we are in South Florida so the sun is hot, and for a good part of the year it rains every day. The sun bakes the standing water. Over time it eats into the roof and leak.
 
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Old 03-10-19, 04:35 AM
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The idea to lay down felt or other material with tar between layers is likely the best approach.
If you try to use some type of self leveling material there is potential for it to crack making it useless.
Layering would be a stronger longer lasting solution much like how plywood gets it strength.

Also, it may help if after the repair cures to overlay a white or silver coating over the whole roof to minimize the effect of absorbed heat on the dark surface.
 
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Old 03-13-19, 10:38 AM
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What about this? I am not a roofer so may be its a crazy idea.

Since the ponding of water has kind of traced the outline of the low spot already, if I get a few bags of fine grain playground sand, and spread that over the area, then use a piece of straight 2x4 it 2x6 to gently screed across the sand. The sand will fill in the low spot.

Then cut a piece or two rectangular felt covering the affected area, attach to the existing roofing around the edges with tar. May be add another layer over it. Fiberglass mesh around the edges, apply tar or bull over the patched area, add granules, would that work
 
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Old 03-14-19, 07:52 AM
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You're right......crazy idea.
The roofer had the right idea by layering roofing felt.

Go with that and you will not have to deal with this problem for a long time.
 
  #7  
Old 03-14-19, 01:11 PM
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I have a hard time seeing how the roofer's solution will solve the problem.

he said he will cut a rectangular piece of felt and apply over the low spot. Around the lips of the low spot, he will be building it up by say 1/16". The low spot will also raise by the same amount. He will just end up creating another ponding depression. He could add say five layers and with each layer the edge and the middle raise by the same amount. Nothing has changed. Something has to fill in the low spot so water can run off. If he stretches the felt so it doesn't dip at the low spot it will dip as soon as someone walks on the roof.
 
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