Message Board Thread - "Roof Survey - Large Stone Ballast"

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Roof Survey - Large Stone Ballast Dusty 6/30/2005
I recently looked a leaky flat rubber mambrane roof having large river stone ballast. The ballast is spread 2"-4" in thickness acrossed the membrane. I was on the roof about 2 hours after sundown and the roof appeared uniform in temperature. Conditions seemed right for a good scan: sunny all day, low wind and clear at night.

My question is should I have stayed on the roof longer or will the large ballast mask the moisture below?
 
Re:Roof Survey - Large Stone Ballast roofman 7/5/2005
Typically, No.

The ballast has such a large thermal mass that the wet insulation below doesn't stand a chance in altering the temp of the stone over that area enough to produce a reliable scan. If the ballast has a thin enough coverage, like a wind scoured area with say a single layer of stones, or less, you may be able to see the wet areas signature bleed through/past the stone.

As such our firm will typically tell clients that IR scans of ballasted single plys are not an option.

However, you can sometimes view the thermal inversion of a ballasted roof from an elevated position. Particularily if there is an adjacent elevated roof section. i.e. one person with the camera up high and another being directed to where the edge of the "anomaly" is, to mark it. This technique is a VERY unreliable and needs to be backed-up with core smaples from the marked areas to confirm the wet. But it has worked (and failed) on occasion.

Matt Dupuis
Structural Research Inc.
Middleton, WI
608-831-5333 Voice
608-831-6295 FAX
E-Mail mdupuis@sri-msn.com
web : www.sri-msn.com

 
Re:Roof Survey - Large Stone Ballast ron lucier 7/6/2005
I have had success in scanning ballasted roofs. The trick is to be there at the right time. The driving force is not necessarily the ambient temperature but the sky conditions. There will be very little thermal contrast with heavy cloud cover but very good contrast with a clear sky.

The attached image is from our building at 25 Esquire Rd. The roof had 4 to 6 inches of 2" and larger ballast. The wet section (one of several) is very clearly seen. As soon as I get a chance I will rescan this area as it has been fixed. The polyiso insualation was saturated according to our maintenance folks.

I also have a sequence of this section showing other wet insulation areas and many false indications indicated by excess ballast. E-mail if you need anything.

Ron Lucier
Infrared Training Center

 
Re:Roof Survey - Large Stone Ballast geologist 7/6/2005
An effective solution would be a "walk-under" roofing survey, which requires access to the underside of the roofing deck. This is a well-known procedure when inspecting metal roofing systems. See: http://www.lenphillips.com/images/FEATURES/Feature_MetalMag.pdf
 
Re:Roof Survey - Large Stone Ballast stewart 7/7/2005
We have now surveyed over 1.5 million square metres of flat roofs and always walk away from ballasted projects unless the ballast is very thin. The other comments are spot on.
 
Re:Roof Survey - Large Stone Ballast IR_Rob 1/6/2006
First thing is first, what is under that EPDM and ballast? The most imoprtant thing to know with any scan is what are you scanning. In a lot of cases it will be an EPS foam that doesn't soak up any water. So if there is a leak in the membrane it will get on the foam and eventualy find a seam between boards and settle on the deck. This makes it hard to find point of entry. Good luck.
 
Re:Roof Survey - Large Stone Ballast thermoman 1/12/2006
Agree with Stewart. It is extremely difficult to detect the actual source of leakage in heavy ballasted roof assemblies using IR.

The only effective means of determining the actual location of roof membrane leak is by means of a procedure called Electrical Field Vector Mapping (EFVM). This is a patented process from Europe and is provided by a company in Toronto (International Leak Detection) for the north american market. It has an almost 100% accuracy rating in detecting membrane leaks without removal of ballast or material over the membrane. It does not tell you how large the leak is but only that there is a discontinuity in the membrane itself. Check their web site for further information and don't waste your time trying to do this with IR.
 
Re:Roof Survey - Large Stone Ballast thermoman 1/12/2006
Sorry, International Leak Detection's web site is not up. They can be reached at leakdetection@bellnet.ca
 


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