Flat Roof Q:

I have a previous client that is stating that any pooling on a flat roof is a defect and the roof and decking should be replaced.

There is a slight warping of the decking with no compromise of the weather barrier [the roof isn’t leaking] nor is there any separation or curling of the Mod B. The roof is newer and was fully permitted and passed.

What are your thoughts…?

They are right in that it is a defect (bad install), but you get what you paid for.

If you are asking if it should be repaired based on a home inspection; No.
It’s not leaking. It is doing what it was intended to do. That is to keep the water outside.

Just because they didn’t replace/repair the damage below the new roof and it will not likely last as long, does not mean they get a new roof.
As far as we know, the building was priced reference to it’s age and condition.
It’s a “used car”. You don’t get new tires just because they are not balanced.

Any pooling of water should be noted in your report but but thats it.
The roof deck (below) should have been looked at…

I assume they are going after you…

E mail me and I will send you the entire packet

As of MARCH 1, 2009, the Building Code for Broward County was changed to the 2007 Florida
Building Code with High Velocity Hurricane Zone Requirements.

How deep was the pooling?

Shallow pooling under 1/2" can evaporate in less than two days is not a big concern.

Just notate it.

It was minimal at best. Roof was installed prior to the revisions of building code. Roof was not leaking…and was fully permitted and passed final.


I agree with Bob. Water should dissipate in 24 to 48 hours after a rain. If it pools longer it becomes a problem. Water weighs 8.35 lbs per gallon. If there is rotted wood or structural issue below, the water weight can cause possible collapse or further depression of roof surface.
Observe, describe the conditions.


All flat roofs have some allowable deflection designed into them. So some ponding is inevitable. Maximum design deflection on flat roofs is typically check under the maximum rain and/or snow loading accounting for plugged drains. Construction tolerances will also contribute to ponding. If the roof was designed by and architect or engineer only they can give you the maximum allowable calculated deflection. In my opinion from a home inspector’s perspective ponding just increases the potential for leaks in the ponded areas regardless of how long it takes to evaporate. I would just state" The flat roof has water ponding in areas or evidence of ponding. Although some ponding is inevitable on a flat roofs any ponded areas increases the potential for leaks."

There is actually a roofing material that is guaranteed to not leak even if ponding occurs even on a seam. It is some type of white looking material reminds me of EPDM, and also there is a liquid application that is made by a different manufacture. The guarantees are something like 15 years.
So the customer saying that ponding is required to be corrected is not necessarily true with todays advancement in roof coverings.
If needed, I can look through my reports where I asked the contractors after the repairs was made for the specs. I probably got them still laying in the pile of active reports that is a couple feet deep.

Water pooling on a roof is a deficiency in the system. It can cause leaks.
Flat roof expels water by slope ( runoff ) or by drainage. So the 0/12 roof has a slope to the drain.
suspect: reverse pitch…When the building settles all the water does not enter the drain. Pooling.
Recommend: licensed roofer re-slope the decking.
Repair: all the BUR is stripped and all nails set. Insulation that is manufactured for slope to the drain is applied. BUR roofing applied or cold membrain.
The problem is solved.

Mr.Braun that product does exist. Its works but is expensive as compared to BUR roofing.
Its effectiveness is limited. 15 years. Not a long time. The public is trained to think that 10 years is effective for roofing systems.
A well installed BUR roofing system lasts 25 to 30 years with maintenance. I have witness 40 years. I maintenance it for 25. Built in 1967 when my friends father bought it. 32 units. 4 fire walls.
Plastic cement dries out and must be replaced or re-coated on outside and inside corners and flashing and coping seams. Gravel washes down drains and must be install with a wet-coat so gravel adter to the membrane.etc.

This Company claims ponding is not an issue with the membrane.


**[/size][/FONT][FONT=Arial][size=2]Duro-Last warrants its membrane even where ponding water accumulates. Duro-Last has found no adverse effects
on its membrane because of a lack of positive drainage, however, good roofing practices incorporate the use of
positive drainage for the safety of the structure. The installing contractor is responsible to make sure roof drainage
meets local building code requirements.:slight_smile:

Tell them to buy a home without a flat deck. In my 30 years in the business I can not recall seeing one that did not have any ponding.:mrgreen:

Hello Eric, if you have the time I would appreciate a copy of the APPLICATION INFORMATION FOR RESIDENTIAL ROOFING AND RESIDENTIAL ROOFING PACKET.Thanks for your time,John

what is the best formula to determine the weight of water ponded on a flat roof ?

Q= Volume (LWH) / **7.48 *** 8.34