Ponding on flat roof

Hi! You all have been a wonderful help on several other projects. Now we have a roof problem. We have a gorgeous house here in Hawaii, but unfortunately it came with a flat roof (who would do that?) and when it rains here, it really rains. Tropical downpour kinda stuff. When we bought the house 12 years ago, it had a new tar paper and gravel roof (so the real estate lady said). To reduce heat in the house we covered it with that white reflective stuff, which worked great. However, the rain ponds on the roof and the next day that water gets really, really hot. The hot, ponded water has caused the white coating to curl up and peel off. There might also be other layers which have peeled, too. That makes those ponding areas not only the weakest, but the place where water is most likely to get in. Is there some product we can use to fill in those ponded places? I thought about self-leveling compounds but everything I find on them says they are for floors. I doubt if the stuff could withstand the tropical heat and weathering here in Hawaii. What can we do? Just getting a new tarpaper roof doesn't solve the problem, just delay it, because the water will still pond.
What's a good idea?

Thanks,

Tina

 

There are some "self-leveling roof products out there...in my opinion they're a waste of money and effort in most situations.

Also, keep in mind that many times a ponding flat roof which has some area "built up" in some manner just tends to spread the water out into more smaller ponds.

If your roof doesn't leak, and you're not excited about spending thousands on a new roof just yet, I'd suggest you do nothing till you ARE ready to roof it. Then ask for estimates to install a tapered insulation system prior to roofing it. A flat roofer can install it along with the roof. If done right, it will provide positive drainage of the entire roof. The insulation should help with your heat build-up as well.

None of the coatings hold up well in ponding situations. But even so, in order for the coating to stick properly, the surface needs to be thoroughly cleaned first with a mild TSP solution, and thoroughly rinsed.

 

VERY MILD....I'd prefer a mild detergent solution.(Laundry Detergent)
Just a word of warning, TSP is nothing to be taken lightly...

All phosphates, including tri-sodium phosphate (TSP), are so damaging to the environment, particularly lakes and rivers, that more than 19 states (Hawaii is one) and several counties limit the phosphorous content of any run-off to 0.5% (this is assumed to be a virtual ban). The Material Safety Data Sheet (MSDS) states; "Do not flush material into public sewer system or any water way.

Skin, eye or respiratory contact with tri-sodium phosphate is hazardous. The hazardous material identification system rates hazards as follows:

0=minimum
1=slight
2=moderate
3=high/serious
4=extreme/severe

Tri-sodium phosphate, TSP or tri-basic, is rated 3 high/serious

Powerful stuff...be careful

 

Thanks for the insights. What exactly is a "tapered insulation system?" Can it be done by DIY people? Like me?

Tina

 

Yes, but if one is going to bother with cleaning the roof, there's nothing better than mild solution of TSP to remove every single bit of junk which inteferes with a coating's ability to stick.

Very mild is simply sprinkling a few granules onto the wet roof, then working it with a garden hose/ pressure washer and a stiff broom. Then, as with ANYTHING one cleans, thoroughly rinse it off.

 

I think anyone can install the tapered insulation system IF they're "good with their hands", and/or "construction-minded.
You can find all the info you need for installing a system through the various manufacturers online...or through your roofing materials supply house.
Depending on what your roof layout is...all you need is a cordless/corded drill, some kind of pruning or "japanese"-type hand saw, a Drywall T-square, a sharp utility knife, and probably a circular saw.

The tapered insulation is usually used along with dimensional uniform boards, which together create a continous slope to the side you want to drain to. It is attached to your wood roof deck using screws and 3in. wide steel plates. Then it's roofed over.

Although it's not really complicated to do, you want to make sure you've fully educated yourself on the procedures, and of course that it meets your local building code requirements {for inspection}.