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Message |
David G. Axt, CCS, CSI ,SCIP
Senior Member
Username: david_axt
Post Number: 1867
Registered: 03-2002
| | Posted on Wednesday, April 07, 2021 - 01:25 pm: |    |
What type of leak detection do you specify for low slope roofs and why?
1) Flood testing.
2) Infrared thermography.
3) Electrical capacitance/impedance testing.
4) Nuclear hydrogen detection testing.
5) Low-voltage electrical conductance testing.
6) High-voltage spark testing.
7) Electric field vector mapping.
David G. Axt, CCS, CSI, SCIP
Specifications Consultant
Axt Consulting LLC |
Edward J Dueppen, RA, CSI, CCS, LEED AP
Senior Member
Username: edueppen
Post Number: 74
Registered: 08-2013
| | Posted on Wednesday, April 07, 2021 - 02:40 pm: | |
We usually avoid roof leak testing due to the problematic nature of it. Instead we rely upon prescribed manufacturer's inspections (state when/what they need to inspect and to provide reports) and occasionally 3rd party inspectors (RRO or RRC) hired by the Owner.
When requested we will provide EFVM. We have had a few clients insist on it and a few that indicate it is not effective.
We have on occasion included flood testing when specifically requested by an institutional client. But since the ASTM standard for flood testing (ASTM D5957) specifically states it "is not intended for use on building roofing systems" we would never recommend it.
Sorry for the length and the odd formatting, but here are the notes that I keep about roof testing (I have paraphrased these from many of Ken Hercenberg and John Bunzick's postings on this forum and from presentations I have attended over the years):
• Flood: Imposes loads that may or may not be allowed for in structural design. Flooding can result in leaks and can destroy the roof system so a minor error can result in a complete tear-off. Flood testing is problematic because leaks may not show up in the limited time it is underway. In addition, with 1/4 inch slopes, it can be very difficult to create dams delineating test areas that will allow the entire roof to be tested. You usually can't put enough water on the roof (unless it's small) to test the high points because of the weight of the water.
• Infrared: Tests for differences in temperature. In some climates or weather conditions, where there is not enough heat differential, it may not work very well. While these temperature differences are often attributed to the presence of water, in some locations that may not be the case. Additionally if water has entered and migrated, the location of the water may have nothing to do with the location of the leak.
• Electronic Mapping: While this doesn't work with some forms of single-ply, most notably black EPDM, they have found this to be the most reliable but also the most expensive (short term). There are a couple of different forms of electronic mapping. EFVM is a brand name of sorts promoted by one testing agency. Still, it is pinpoint accurate in finding leaks in the field of most roof membranes. In the case of PRMA/vegetated roof systems, you can leave the wires in place and come back in the future to determine the location of damage that occurs after the overburden has been placed.
• Instead of testing, John Bunzick recommends merely having manufacturer’s field personnel on site frequently during installation.
• Electronic Leak Detection (ELD): Membrane acts as an electrical insulator between a conductive substrate and the testing equipment.
o Concrete deck is an excellent conductive/grounding substrate (according to presenter).
o ASTM D7877 is overarching standard for ELD.
The standard describes “alternative grounds” which are metal grids or conductive primers that are UL or FM approved to work as grounds for ELD.
If ELD is planned to be used, plan to provide an alternative ground if the membrane is not directly on top of conductive roof deck.
o Be aware that not every leak is detectable using ELD.
o Recommend having repair staff available during testing to make repairs and then have the repairs retested.
o Methods below:
o Electronic Field-Vector Mapping (EFVM): Wet test. Trace cable is applied over membrane and then all substrates must be wetted.
PROS:
• The only ELD system that can be used with overburden (does not rely upon direct contact of equipment and membrane (as long as trace cable is permanently installed).
• Better at pinpointing seam failures.
CONS:
• Time consuming.
• Difficult to use on vertical surfaces.
• Any metal components can cause false positives.
• Cannot be used with split slabs or pavers on pedestals.
• Repairs and retesting of repairs typically cannot be performed the same day because the surfaces must be dried before repairs can be performed.
o High Voltage ELD: Dry test.
PROS:
• Quick set up (no trace cables).
• Easy to use on vertical surfaces.
• Easy to make repairs and perform retests on the same day.
• The most effective ELD method when part of the assembly is not directly over a conductive substrate, such as when membrane is over roof insulation (but conductive substrates are still recommended directly beneath all membranes).
CONS:
• Membrane must be kept dry.
• Not as effective at pinpointing seam failures.
o Low Voltage Platform Scanning: Wet test. ASTM D8231.
PROS:
• Quick set up (no trace cables).
• Easy to use on vertical surfaces.
• Better at pinpointing seam failures.
• Can be used on black EPDM (equipment settings can distinguish between the lower conductivity of the membrane and the higher conductivity of other items).
CONS:
• Not very effective if grounding substrate is not directly below the membrane. |
David G. Axt, CCS, CSI ,SCIP
Senior Member
Username: david_axt
Post Number: 1868
Registered: 03-2002
| | Posted on Friday, April 09, 2021 - 12:49 pm: | |
Thank you Edward. This is very informative!
I am currently researching Electronic Leak Detection by Detec Systems. This system is a low voltage platform scanning wet test using ASTM D8231 and ASTM D7877.
One "Con" is a conductive primer (Detec TruGround Primer) has to be installed just below the membrane and most likely on top of the roof cover board. The primer has to be applied carefully and continuously. The primer does have to be tested to ensure it is applied properly with no breaks (open circuits). It can also be used up metal pipes/conduits and used as a ground. The primer has to be grounded at a minimum of two locations.
I would be curious to hear other's experience with Detec or other similiar ELD systems.
David G. Axt, CCS, CSI, SCIP
Specifications Consultant
Axt Consulting LLC |
Michael Chusid, RA FCSI CCS
Senior Member
Username: michael_chusid
Post Number: 598
Registered: 10-2003
| | Posted on Friday, April 09, 2021 - 02:43 pm: | |
1. Years ago, I did an earth covered roof and client was especially concerned about leaks. We had a butyl membrane loose laid on concrete deck. We used some sort of mastic between membrane and deck to segment the roof into 10 x 10 ft sections. The hope was that the mastic would dam any leaks and prevent horizontal spread of water penetrating the membrane. If they had to excavate the 24 inches of earth cover we used, they would have a better idea of where to begin. I left town and don't know how well it worked.
2. I have several published articles about lightning protection. Lightning will go where lightning wants to go when it strikes a building... but I wonder if the conductive membrane creates additional paths for the lightning to travel? Contact me if you want to discuss or copies of the articles.
Michael Chusid, RA FCSI CCS 1-818-219-4937
www.chusid.com www.buildingproduct.guru |
Edward J Dueppen, RA, CSI, CCS, LEED AP
Senior Member
Username: edueppen
Post Number: 75
Registered: 08-2013
| | Posted on Friday, April 09, 2021 - 03:15 pm: | |
Michael,
1. On your earth covered roof, that is a condition where a fully-adhered membrane would improve the situation since it would prevent leaks from migrating laterally (of course this only truly works when the membrane is in direct contact with a continuous non-absorbent substrate).
2. You raise a very interesting question regarding lightning protection! |
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