Thread: New to flat roofs

I am a newer inspector and I don't often see flat roofs around here.

I believe this is an EPDM roof at it appears to be stretched over the wall to the floor with nothing under supporting. There is no metal flashing on the top of the parapet wall. Is any part of this installation acceptable? Is a flashing required on top of the parapet wall? Any other issues here other than the obvious rubber lifting on the corner of the wall in pic3.

Thanks for the help.

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A similar but smaller roof.

How much water can a small flat roof hold?

Until the 'load weight' becomes unacceptable?? How's that calculated??

Shouldn't a roofer be able to get a 5 by 9 foot rectangle to drain???

It's EPDM and roofer saws they use it for pool linings - client didn't want any pools on the roof :-)

2 great examples of garbage work.
Aluminum or clay capping would obviously be better on the parapets.
A good roofer would build up a slope on the roof surface prior to installing the membrane. This is typically done with roofing approved insulation board.
Obviously both roofers did lousy jobs. We unfortunately don't know whether the roofer did it that way because he doesn't care or that's all he got paid for.
Either way, tear-off and replace now or wait until it starts leaking.

Originally Posted by Mike Gault

How much water can a small flat roof hold?

Until the 'load weight' becomes unacceptable?? How's that calculated??

That should be calculated by the structural engineer who designed it, and, most likely, the answer is "none".

There are very few materials which are suitable for use as pool liners, which is what you have. Almost all roofing materials require a minimum slope of 1/4" per foot.

That said, EPDM can, as I recall, be laid on a flat (as in"flat" no slope) roof, and that EPDM has been used as liners for ponds in fish farms. So the EPDM material should be okay like that, it is the structure which is the concern.

Looks like they had a flat roof, with some slope, and then put a parapet wall (albeit not a very high parapet wall) around the roof to contain the water - for what reason I do not know.

There should have been a roof drain and an emergency overflow (which could be a scupper or another roof drain), or they could have installed proper scuppers through those not-very-high-parapet walls.

Think of it this way: water is heavy, water on a roof will eventually sags the roof some, which holds more water, which is even heavier, and eventually sags the roof even more, which hold even more water, which is not heavier than it was, which sags the roof, which holds more water, which is heavier, ad infinitum ...

20 ft X 20 ft X 1 " of H2O = > 1 Ton

Originally Posted by John Kogel

20 ft X 20 ft X 1 " of H2O = > 1 Ton

1 ton = 2000 lbs

20 x 20 = 400 sf

2000 lbs / 400 sf = 5 lbs/sf

Can you stand on a roof and have anywhere near as little as 5 lbs/sf on the roof?

Originally Posted by Jerry Peck

1 ton = 2000 lbs

20 x 20 = 400 sf

2000 lbs / 400 sf = 5 lbs/sf

Can you stand on a roof and have anywhere near as little as 5 lbs/sf on the roof?

An inch of water is not much water, is what that says to me.
If the water dries up within 48 hours after a rain, it is considered to be acceptable, but poor design, nonetheless.

Originally Posted by John Kogel

If the water dries up within 48 hours after a rain, it is considered to be acceptable, ...

"it is considered to be acceptable" by whom?

Originally Posted by Jerry Peck

"it is considered to be acceptable" by whom?

Allan Carson. Take it up with him.

That trampoline taut look in pic #1 is a tear waiting to happen. I doubt there are any cant strips installed at the curbs.

Originally Posted by Jerry Peck

Looks like they had a flat roof, with some slope, and then put a parapet wall (albeit not a very high parapet wall) around the roof to contain the water - for what reason I do not know.

My guess is it's the drip edge that's creating the "parapet" and there's a bit of sag. My parents' roof has the same issue. It looks like there's a pile of organic debris which could be impeding drainage.

Originally Posted by Kristi Silber

My guess is it's the drip edge that's creating the "parapet" and there's a bit of sag. My parents' roof has the same issue. It looks like there's a pile of organic debris which could be impeding drainage.

It is possible that they used gravel stop around the edges instead of regular drip edge. Gravel stop has several configurations and 'gravel stop' heights, from quite low (almost flat) to an inch or so, and that would definitely create that condition.

Except that I was looking at the area around the plumbing vent stack - it appeared to have been built up to the same height when I looked at the photo yesterday, after looking at the photo again, I'm not so sure it is built up, possibly just patched around and the patch added thickness.

Originally Posted by Jerry Peck

There should have been a roof drain and an emergency overflow (which could be a scupper or another roof drain), or they could have installed proper scuppers through those not-very-high-parapet walls.

Have see a small roof with a 3' parapet fill with 1' to 2' of water due to a ice dam in the drain(s)---no scuppers. It finally rose to the point where it began to enter the building. After all the excitement ended---they installed scuppers! I have see the same thing in some other structures---missing scuppers until something plugs up and damage occurs. New buildings too. Something to check as the new breed of architects/engineers seem to overlook this in many structures.

Originally Posted by John Kogel

20 ft X 20 ft X 1 " of H2O = > 1 Ton

Multiply that by a foot or two and now you have some serious weights to contend with.

BTW, no small residential roof should have ponding. There's no excuse for it. A large commercial or condo building might have a few shallow ponds on it after a rain and still be acceptable. Just to clarify what we should call 'acceptable'.

I had a townhouse that had flood damage from a leaking balcony. The nice copper scupper was about 6" above the floor level. The door sill going into the house was only about 3".

Originally Posted by Rich Goeken

Have see a small roof with a 3' parapet fill with 1' to 2' of water due to a ice dam in the drain(s)---no scuppers. It finally rose to the point where it began to enter the building. After all the excitement ended---they installed scuppers! I have see the same thing in some other structures---missing scuppers until something plugs up and damage occurs. New buildings too. Something to check as the new breed of architects/engineers seem to overlook this in many structures.

That's because they failed to properly address the requirements for freeze protection of piping, which includes DWV piping. Those were roof *drains*, were they not?

Originally Posted by Jerry Peck

That's because they failed to properly address the requirements for freeze protection of piping, which includes DWV piping. Those were roof *drains*, were they not?

They were roof drains that went into the building!!! Was a bad year....

Originally Posted by Rich Goeken

They were roof drains that went into the building!!! Was a bad year....

"roof drains that went into the building"

Yeah, okay, but ... *where* "into the building" did they go? ALL (okay, basically all) roof drain go into the building through the roof drain, the drain pipe, which then goes down and out to the outdoors someplace where the discharge is intended to go ... *but not into the DWV system* of the sanitary sewer.

Originally Posted by Jerry Peck

"roof drains that went into the building"

Yeah, okay, but ... *where* "into the building" did they go? ALL (okay, basically all) roof drain go into the building through the roof drain, the drain pipe, which then goes down and out to the outdoors someplace where the discharge is intended to go ... *but not into the DWV system* of the sanitary sewer.

Not sure why you are asking as the problem was finally determined to be in the vertical pipes of the roof drain system, however I think it went to the storm drainage system.

The building was only a few years old, construction was block & brick walls, it was a very cold year and the pipes were outside the conditioned envelope. They actually froze in the walls. After they got the ice dam thawed---they did insulate the pipes and put in the scuppers. No problems after that.

Originally Posted by Rich Goeken

Not sure why you are asking as the problem was finally determined to be in the vertical pipes of the roof drain system, however I think it went to the storm drainage system.

The building was only a few years old, construction was block & brick walls, it was a very cold year and the pipes were outside the conditioned envelope. They actually froze in the walls. After they got the ice dam thawed---they did insulate the pipes and put in the scuppers. No problems after that.

That was why I was asking ... because:

Originally Posted by Jerry Peck

That's because they failed to properly address the requirements for freeze protection of piping, which includes DWV piping. Those were roof *drains*, were they not?

Originally Posted by Jerry Peck
That's because they failed to properly address the requirements for freeze protection of piping, which includes DWV piping. Those were roof *drains*, were they not?




But That's not what you asked, Jerry. No problem with the question concerning freeze protection. But you really asked...

Originally Posted by Jerry Peck

"roof drains that went into the building Yeah, okay, but ... *where* "into the building" did they go? ALL (okay, basically all) roof drain go into the building through the roof drain, the drain pipe, which then goes down and out to the outdoors someplace where the discharge is intended to go ... *but not into the DWV system* of the sanitary sewer. "

A question asking where the water went, not how the piping was protected! Note, therefore my confuston.

[QUOTE=Jerry Peck]That's because they failed to properly address the requirements for freeze protection of piping, which includes DWV piping. Those were roof *drains*, were they not?

Originally Posted by Rich Goeken

But That's not what you asked, Jerry. No problem with the question concerning freeze protection. But you really asked...

Aw, but that IS what I originally asked:

Originally Posted by Jerry Peck

[/B]roof drains that went into the building Yeah, okay, but ... *where* "into the building" did they go? ALL (okay, basically all) roof drain go into the building through the roof drain, the drain pipe, which then goes down and out to the outdoors someplace where the discharge is intended to go ... *but not into the DWV system* of the sanitary sewer.

A question asking where the water went, not how the piping was protected! Note, therefore my confuston.

The question was a two part question:
1) *where* "into the building" did they go?
2) ALL (okay, basically all) roof drain go into the building through the roof drain, the drain pipe, which then goes down and out to the outdoors someplace where the discharge is intended to go ... *but not into the DWV system* of the sanitary sewer.

Actually, the 2) part was a statement of where they usually go. The 1) part was the "*where*" part of " "into the building" did they go?"

When you said they iced up, I figured they were not protected from freezing as they are required to be.

Secondly, I was pointing out that 'they are not supposed to go to the sanitary sewer system', and kind of 'asking that' to make sure you already knew that.

[quote=Jerry Peck;206498]

Originally Posted by Jerry Peck

That's because they failed to properly address the requirements for freeze protection of piping, which includes DWV piping. Those were roof *drains*, were they not?
Aw, but that IS what I originally asked:
The question was a two part question:
1) *where* "into the building" did they go?
2) ALL (okay, basically all) roof drain go into the building through the roof drain, the drain pipe, which then goes down and out to the outdoors someplace where the discharge is intended to go ... *but not into the DWV system* of the sanitary sewer.

Actually, the 2) part was a statement of where they usually go. The 1) part was the "*where*" part of " "into the building" did they go?"

When you said they iced up, I figured they were not protected from freezing as they are required to be.

Secondly, I was pointing out that 'they are not supposed to go to the sanitary sewer system', and kind of 'asking that' to make sure you already knew that.

OK Jerry! Knew the sanitary sewer, just shortened the response. I surrender!!!

"Shouldn't a roofer be able to get a 5 by 9 foot rectangle to drain???"

Hi, All &

As to the above:

* Sure, but if the curb is only a few inches high, just let it spill-over !

So many BAD roofers just don't care...


Cheers !