| Author |
Message |
Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP
Senior Member
Username: specman
Post Number: 843
Registered: 03-2003
| | Posted on Thursday, March 25, 2010 - 03:52 pm: |    |
I'm trying to solve what appears to be an arcane requirement for "Painted terne" that the IBC uses for valley flashing of asphalt shingles.
IBC Table 1507.2.9.2 (2006 edition) indicates that the material must have a weight of "20 pounds"--no thickness or even gage is provided. However, the weight indicated isn't compared to any specific area.
A similar situation applies to lead, listed in the same table, which indicates "2.5 pounds." But this can easily be determined since manufacturers use weight as a means of product identification, and, with a thickness of 0.42 inch and lead weighing 60 lb/sq. ft. for a 1-inch thickness (per ASTM B 749), it can be mathematically calculated that the weight is per 1 sq. ft.
However, I can't find any source (ASTM, manufacturer, etc.) that identifies terne in terms of weight, or compares weight to a given thickness.
Can anyone shed any light on this?
20 lb/sq. ft. doesn't seem likely, so is it 20 lb per square (100 sq. ft.)?
Is terne even used or manufactured anymore for flashing?
Ron Geren, AIA, CSI, CCS, CCCA, SCIP
www.specsandcodes.com |
Dale Hurttgam, NCARB, AIA,LEED AP, CSI
Senior Member
Username: dwhurttgam
Post Number: 59
Registered: 10-2005
| | Posted on Thursday, March 25, 2010 - 05:30 pm: | |
Ron - I found the following in SMACNA - 5th Edition (not sure how much this will help with the actual thickness, but it defines where the term 20# comes from):
TERNE
Terne metal consists of copper bearing steel, coated
both sides with a lead–tin alloy. Coating weights are
typically 20 (9 kg) lbs. and 40 (18 kg) lbs. The coating
weight refers to the total weight of lead–tin alloy
distributed on both sides of 112 sheets, 20 x 28 in.
(508 x 711 mm), known as a base box (436 sq. ft.
(40.50 sq m)). This translates to .047 lb./sf. (.23 kg/sq
m) and .092 lb./sf. (.45 kg/sq m) of coating.
ADVANTAGES
* Lightweight, low–expansion.
* Durable, long term permanence when
painted and maintained.
PRECAUTIONS
* Detail so that surfaces drain.
* Avoid large flat surfaces to reduce waviness.
* Solder locked flat seams.
* Use 50/50 solder, and neutralize flux after
soldering.
* Do not nailthrough metal, use cleats.
* Avoid congtact with alum, copper or acidic materials.
* Must be primed both sides prior to installation.
*Must be painted soon after installation. |
Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP
Senior Member
Username: specman
Post Number: 844
Registered: 03-2003
| | Posted on Thursday, March 25, 2010 - 06:12 pm: | |
Dale:
Thanks. I never thought to look in SMACNA.
Ron Geren, AIA, CSI, CCS, CCCA, SCIP
www.specsandcodes.com |
Steven Bruneel, AIA, CSI-CDT, LEED-AP
Senior Member
Username: redseca2
Post Number: 227
Registered: 12-2006
| | Posted on Thursday, March 25, 2010 - 06:23 pm: | |
112 sheets; Is that like a bushel of tin? |
Jeffrey Wilson CSI CCS
Senior Member
Username: wilsonconsulting
Post Number: 30
Registered: 03-2006
| | Posted on Thursday, March 25, 2010 - 08:49 pm: | |
I understand Follansbee is the sole manufacturer of terne metal. The weights listed in IBC might be out of date. Follansbee's current version of the product ("Terne II" which has the same zinc-tin-alloy coating over a steel base as it uses for "TCS II" over stainless steel) is available in weights of 0.52 psf (sheet metal weight including coating; marketed as "residential grade") and 0.61 psf ("commercial grade").
Jeff Wilson
Wilson Consulting Inc
Narberth PA |
Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP
Senior Member
Username: specman
Post Number: 845
Registered: 03-2003
| | Posted on Thursday, March 25, 2010 - 09:31 pm: | |
After looking at this further and based on the information Dale provided, the "20 pounds" indicated in the code still doesn't establish a minimum thickness.
If it could be done, I could have sheet metal the thickness of tin foil and apply the 20-lb terne coating and comply with the requirement of the IBC table.
I know I'm being facetious, since Section 1503.2.1 requires a minimum thickness for flashing of 0.019 inch (0.483 mm), regardless of metal type. However, the code confuses the issue further by stating that 26 gage galvanized sheet complies with this requirement.
Based on the multitude of sheet metal conversion charts available, 26 gage glavanized steel is 0.0217 inch (0.551 mm), which converts to a G210 coating per ASTM A 653. But looking at Table 1507.2.9.2, they list galvanized steel at 0.179 inch, which is 26 gage uncoated steel sheet. When a G90 coating is applied, the steel sheet would have a nominal thickness of 0.019 inch, which meets the code minimum--thus, the likely basis for the code requirement.
Therefore, if a terne coated product is used, is the minimum thickness based on the uncoated steel plus the coating (like galvanized steel); or, is the thickness of the base steel sheet determined by subtracting the thickness of the terne coating (which is less than G90) from the minimum thickness of 0.019 inch? I don't know. Sounds like a potential code change to me.
Ron Geren, AIA, CSI, CCS, CCCA, SCIP
www.specsandcodes.com |
John Bunzick, CCS, CCCA, LEED AP
Senior Member
Username: bunzick
Post Number: 1184
Registered: 03-2002
| | Posted on Friday, March 26, 2010 - 09:45 am: | |
Isn't it moot, since you can't actually buy Terne-coating anymore? Or are you assuming that Terne-II is acceptable? |
Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP
Senior Member
Username: specman
Post Number: 846
Registered: 03-2003
| | Posted on Friday, March 26, 2010 - 11:21 am: | |
Since the IBC doesn't define what Terne is via a reference to a standard product specification such as ASTM, then it could be anything within that category of material. So, yes, I would interpret the code to allow the TCS-II product.
Ron Geren, AIA, CSI, CCS, CCCA, SCIP
www.specsandcodes.com |
Marc C Chavez
Senior Member
Username: mchavez
Post Number: 380
Registered: 07-2002
| | Posted on Friday, March 26, 2010 - 11:23 am: | |
"To everything, Terne, Terne, Terne"
couldn't help it
Happy Friday everyone. |
John Bunzick, CCS, CCCA, LEED AP
Senior Member
Username: bunzick
Post Number: 1185
Registered: 03-2002
| | Posted on Friday, March 26, 2010 - 12:12 pm: | |
Ron, Playing the devil's advocate a bit: The code is requiring a thickness of coating for a particular alloy and substrate. If the alloy or substrate is different, why would it follow that the coating thickness should be the same? Mightn't a different alloy need a thickness to meet basic corrosion resistance? As we are all aware, this is one of the shortcomings of precscriptive code requirements--they don't keep up with the times, and inferring intent may not result in compliance in the eyes of the building inspector. |
Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP
Senior Member
Username: specman
Post Number: 847
Registered: 03-2003
| | Posted on Friday, March 26, 2010 - 12:45 pm: | |
I agree. The code is slow to adopt new materials and technologies, and even slower to weed out the archaic materials.
Flashings is one of the areas where a mix of prescriptive and performance requirements are used and, obviously, some are in conflict.
Here's what the code states for flashing in general:
"Where flashing is of metal, the metal shall be corrosion resistant with a thickness of not less than 0.019 inch (0.483 mm)(No. 26 galvanized sheet)."
The inclusion of "No. 26 galvanized sheet" at the end adds confusion and shouldn't be there at all.
Terne (without specific reference to an alloy) is only mentioned in the table regarding valley flashing for asphalt shingles. However, Table 1507.4.3(1) permits terne and terne-coated stainless steel for metal roof coverings, but requires a 40-lb coating--still with no ASTM reference.
My preference would be to require corrosion resistance through a standardized test based on an alloy having a minimum uncoated thickness. With this type of requirement the code would specify the starting point (minimum uncoated thickness) and the corrosion-resistant performance, which could have varying thicknesses.
Ron Geren, AIA, CSI, CCS, CCCA, SCIP
www.specsandcodes.com |
Ralph Liebing, RA, CSI, CDT
Senior Member
Username: rliebing
Post Number: 1163
Registered: 02-2003
| | Posted on Friday, March 26, 2010 - 01:58 pm: | |
When all else fails, try the instructions or the rep--
Follansbee rep
Territory: Washington, Oregon, Alaska, Arizona, Idaho and Montana
Contact: Tom Lally or Jim Allen
Architectural Metal Solutions, Inc.
1724 Garrett Street, Suite B
Enumclaw, WA 98022
Phone: 360-825-2404 |
John Bonar (Unregistered Guest)
Unregistered guest
| | Posted on Friday, March 26, 2010 - 04:16 pm: | |
Ron, the description that SMACNA gives for the original Terne metal is very accurate but Follansbee Steel has not manufactured that product since 1998. Follansbee Steel now manufactures TERNE II along with Klassic Kolors(pre-painted Terne II) and TCS II(Terne Coated Stainless). The original alloy was a lead/tin alloy and measured by weight 40 lbs and 20 lbs. Follansbee no longer measures the new TERNE II by weight it is measured in thickness. The "commercial grade" TERNE II would be equivalent to the old 40 lb coating but is measured as 20 microns thickness or 1 mil. The "residential grade" TERNE II would be equivalent to the old 20lb terne but is measured as 10 microns thickness or 1/2 mil. TERNE II is manufactured in only 2 gauges 30 or 28 gauge. TCS II which is a Terne coated stainless is always manufactured in the 20 microns thickness but it is manufactured in 28, 26 and 24 gauge. TCS II does not need to be painted like the TERNE II does. Both TERNE II and TCS II are still used for flashings, valleys, drip edges, built in gutters and different metal roofing styles. |
Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP
Senior Member
Username: specman
Post Number: 848
Registered: 03-2003
| | Posted on Friday, March 26, 2010 - 05:18 pm: | |
John:
Thanks for the information.
Ron Geren, AIA, CSI, CCS, CCCA, SCIP
www.specsandcodes.com |
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