Message Board Thread - "Scan PVC membrane on a roof"

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Scan PVC membrane on a roof Dominic A 7/11/2008
Hi guys, I did some test yesterday (night) on a PVC membrane on a roof. I realized that it reflect a lot and it is not an easy job to scan (More than I expected). The weather was almost perfect.
So, I'm asking a question: Do you guys find easily the moisture on that type of roof. PVC
I Scanned approx 15 000sq feet and I did not find anything. The roof composition is PVC membrane, polyiso (insulation), vapor barrier and steel deck.
I know that polyiso do not retain a lot of moisture so it will be more difficult to scan.

Thanks a lot
Dominic
 
Re:Scan PVC membrane on a roof ed@RBinfrared 7/22/2008
You have answered your own question. The iso will not retain moisture.
I would flood the roof and try to find water entry point(s)by shooting the underside of the steel(?) deck. Start at drip points and work backwards.
 
Re:Scan PVC membrane on a roof Dominic A 7/24/2008
ed@RBinfrared wrote:
e answered your own question. The iso will not retain moisture.
I would flood the roof and try to find water entry point(s)by shooting the underside of the steel(?) deck. Start at drip points and work backwards.
Thanks for the answer.
Maybe I di not express myself correctly (I'm french Canadian).
I saw couples of time that kind of insulation (polyiso) with moisture in it.
In case that the roof composition is: PVC, Fiberboard panel, insulation, vapor barrier, steeldeck, do the scan is possible and the reading of the pvc will be easier with the camera?

The question is: Is it possible to scan a roof with PVC membrane with "good or correct" composition (insulation) inside? Like my last exemple of roof composition. I'm asking it because the PVC has a high reflexion.

About your technique of scanning by the inside: I'm not a fan of working inside for infrared roof scan. Too much reflexion and if you have 400 000sq feet to verify, you will pass a month inside the building.

Thank you
Dom
 
Re:Scan PVC membrane on a roof Big Daddy 8/7/2008
Part of the reason nothing showed up is that PVC roof systems are usually mechanically fastened, which means that there is room for a small amount of air movement throughout the roof system possibly giving false readings. Built up and SBS systems are typically fully bonded together allowing no air movement in the system which usually shows better temperature differences.
 
Re:Scan PVC membrane on a roof IRT Surveys 8/8/2008
Big Daddy wrote:
the reason nothing showed up is that PVC roof systems are usually mechanically fastened, which means that there is room for a small amount of air movement throughout the roof system possibly giving false readings. Built up and SBS systems are typically fully bonded together allowing no air movement in the system which usually shows better temperature differences.
We have surveyed several thousand roofs over the last 7 years. PVC can be sucessfully surveyed with IR techniques -the most important factor is the temperature differential. Was the heating on when you surveyed? Were you there at night? Built up roofs are never fully bonded, torch on systems, pour and roll systems, mechanical fix or adhesive systems are all designed to allow vapour to travel below the waterproofing membrane. all systems allow the cap sheet to breath in this way. If it were fully bonded the system would blister very quickly, then crack, then fail. Regarding the survey technique - it is always better to look down upon the surface where possible, ie from a higher roof or elevated mast system.
 
Re:Scan PVC membrane on a roof Bob Berry 8/8/2008
My experience with roofs tells me that the roof build up you describe is a very difficult roof to survey and you need very good conditions to find the problems. As suggested above, a temperature differential will help. There are three main problems.

1. PVC is not a diffuse reflector like a lot of other roofing membranes, it is a mirror reflector.

2. If you are using a LWIR camera, the cold reflections from the sky are more of a problem than with a MWIR camera. The reason for this is that the peak emission is closer to the LWIR region.

3. The insulation you describe is often used with PVC roofs, and it does not really retain much moisture.

Points 1 & 2 mean that you are more likely to have problems with a LWIR camera and they will be more problematic. In the past I have used a MWIR camera and I have to say I had more success on PVC roofs and I do know that it is considered a MWIR application by many people.

Point 3, unfortunately you are stuck with this insulation and you have to work with it, but it does mean that the pattern due to thermal capacitance will be very subtle and you will have a small window of time to work with, this is the reason you need a thermal difference. This should be as much as possible for as long as possible before the survey begins.

I suggest you try it with a MWIR camera, under perfect conditions, with as large a temperature difference as possible. If possible I would also suggest you introduce a pressure difference (I know this is going to be a bit controversial), but it should increase the thermal flux in the building and while it might not be that much of a help, it will not do any harm and can ONLY help, and my experience tells me you need all the help you can get with this type of roof.
 
Re:Scan PVC membrane on a roof Doug 8/8/2008
In my present position I work with commerical rooing companies. I disagree with the statement that polyiso will not retain moisture. The top and bottom surfaces of many ISO sheets are a paper type of facer. This will ratain moisture.

Doug T.
 
Re:Scan PVC membrane on a roof Doug 8/8/2008
In my present position I work with commerical rooing companies. I disagree with the statement that polyiso will not retain moisture. The top and bottom surfaces of many ISO sheets are a paper type of facer. This will retain moisture.

Doug T.
 
Re:Scan PVC membrane on a roof Big Daddy 8/8/2008
IRT Surveys wrote:
We have surveyed several thousand roofs over the last 7 years. PVC can be sucessfully surveyed with IR techniques -the most important factor is the temperature differential. Was the heating on when you surveyed? Were you there at night? Built up roofs are never fully bonded, torch on systems, pour and roll systems, mechanical fix or adhesive systems are all designed to allow vapour to travel below the waterproofing membrane. all systems allow the cap sheet to breath in this way. If it were fully bonded the system would blister very quickly, then crack, then fail. Regarding the survey technique - it is always better to look down upon the surface where possible, ie from a higher roof or elevated mast system.
I did not say that PVC roofs could not be sucsesfully scanned. I only tried to explain the makeup of the roof system and a possible problem. IRT Surveys says that SBS and Built up roofs are never fully bonded together-absolutly wrong. As a Jouneyman roofer having installed thousands of roofs and a registered thermographer I would have to question IRT Surveys report.
 
Re:Scan PVC membrane on a roof Bob Berry 8/11/2008
Doug,

Polyiso is a closed cell structure material and as such it retains very little (if any) moisture. It comes with different facers, ie paper/paper, foil/foil, paper/foil etc. etc. If it is faced with paper, the amount of mositure it will retain is typically less that 1mm thick, the effects of an anomoly due to thermal capacitance and/or changing R value will be very slight and difficult to detect (particularly with PVC as a surface).

I would like to add, that PVC roofs are seldom bonded, and I think this is what IRT surveys was trying to imply. If they are not bonded, and foil faced polyiso has been used this becomes even MORE difficult.
 


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