Abstract

Published surveys concerning roof service life incorporate estimates from roofing professionals based on their observations and opinions. In cases where roofing products have been in service long enough for the end of life to be observed, these data have some merit, but when end-of-life empirical data are not available, accurate projections are difficult to verify. Other attempts at defining the service life relate to product warranties or lab testing. In the case of standing seam metal roofing, the variability of the materials and installation methods strongly colors the survey opinions. In steel roofing, this variability includes that of the steel thickness, the metallic coating type and thickness, the presence or absence of paint films, the types of sealants, the seam-folding details, and other construction or installation details. Related accessories and flashings of different materials and designs further confuse survey criteria and results. In the case of 55 % Al–Zn alloy-coated steel roofing systems, the prediction of service life is complicated by the fact that the product has been commercially available for under 40 years, and end of life has rarely been observed. In this paper, we combine field inspection procedures with a novel technique for securing roof samples for subsequent laboratory analysis in order to enable the prediction of roof service life for a 55 % Al–Zn alloy-coated steel roof in Denver, CO. The performance of other roof components is also quantified. A methodology is then presented that utilizes the current best practices, together with the results of this roof analysis, to predict the total roof service life of similar constructions when built using today’s practices. This work confirms previously published work that used experimental corrosion specimens to establish the long-term durability of 55 % Al–Zn alloy-coated steel. It is suggested that this work can be replicated in order to develop meaningful corrosion and material performance data for any climate in which this type of roof is constructed.

Issue Section:
Research Papers
Keywords:
55 % aluminum–zinc alloy-coated, service life, metal roofing, standing seam, atmospheric corrosion

References

1.
Cash
,
C. G.
, “
Durability of Bituminous Built-Up Roofing Membranes
,”
Durability of Building Materials and Components, ASTM STP 691, 1980
,
P. J.
 
Sereda
 and
G. G.
 
Litvan
, Eds.,
ASTM International
,
West Conshohocken, PA
, p. 741.
Crossref
Search ADS
 
2.
Cash
,
C.G.
, “
The Relative Durability of Low-Slope Roofing
,”
Proceedings of the Fourth International Symposium on Roofing Technology
, Gaithersburg, MD, Sept 17–19, 1997,
NRCA
,
Rosemont, IL
, p. 119.
3.
Schneider
,
K. G.
, and
Keenan
,
A. S.
, “
A Documented Historical Performance of Roofing Assemblies in the United States 1975–1996
,”
Proceedings of the Fourth International Symposium on Roofing Technology
, Gaithersburg, MD, Sept 17–19, 1997,
NRCA
,
Rosemont, IL
, p. 132.
4.
Hoff
,
J. L.
, “
Historical Warranty Repair Cost as a Measure of Long-Term Roof System Performance
,”
Proceedings of the Fourth International Symposium on Roofing Technology
, Gaithersburg, MD, Sept 17–19,
1997
,
NRCA
,
Rosemont, IL
, p. 125.
5.
Hoff
,
J. L.
, “
Life Cycle Assessment (LCA) and the Building Envelope: Balancing Durability and Environmental Impact
,”
Proceedings of the RCI Foundation Symposium on Building Envelope Sustainability
, Washington, D.C., April 30–May 1,
2009
,
RCI Foundation
,
Raleigh, NC
, pp. 1–14.
6.
Zoccola
,
J. C.
,
Townsend
,
H. E.
,
Borzillo
,
A. R.
, and
Horton
,
J. B.
, “
Atmospheric Corrosion Behavior of Aluminum-Zinc Alloy-Coated Steel
,”
Atmospheric Factors Affecting the Corrosion of Engineering Materials, STP
646,
1978
,
S. K.
 
Coburn
, Ed.,
ASTM International
,
Philadelphia, PA
, p. 165.
Google Scholar
Crossref
Search ADS
 
7.
Townsend
,
H. E.
, and
Borzillo
,
A. R.
, “
55% Al-Zn Alloy Coated Sheet Steel: The Versatile, Long Lasting Building Panel Steel
,”
Proceedings of the Fifth International Conference on Zinc Coated Sheet Steel
, Birmingham, UK, June 12–13,
1997
,
European General Galvanizers Association
,
Surrey, UK
.
8.
Townsend
,
H. E.
, and
Borzillo
,
A. R.
, “
Thirty-Year Atmospheric Corrosion Performance of 55% Aluminum-Zinc Alloy-Coated Sheet Steel
,”
Materials Performance
,
Vol. 35, No.
 
4
,
1996
, pp.
30
–
36
.
9.
Willis
,
D. J.
, “
Performance of 55% Al-Zn Coated Steel Sheets Used in Residential Houses in Australia
,”
Proceedings of the Fourth International Conference on Zinc and Zinc Alloy Coated Steel Sheet (GALVATECH’98)
, Chiba, Japan, September 20–23,
1998
,
The Iron and Steel Institute of Japan
,
Tokyo, Japan
, pp. 1–7.
10.
Townsend
,
H. E.
, and
Lawson
,
H. H.
, “
Twenty-One Year Results for Metallic-Coated Steel Sheet in the ASTM 1976 Atmospheric Corrosion Tests
,”
Outdoor Atmospheric Corrosion, ASTM STP
1421, 2002,
H. E.
 
Townsend
, Ed.,
ASTM International
,
West Conshohocken, PA
, p. 284.
Crossref
Search ADS
 
11.
Dutton
,
R. J.
, “
Field Performance of Low-Slope 55% Al-Zn Alloy-Coated Steel Roofing in North America After 35+ Years
,”
Proceedings of the International Zinc Aluminum Coaters Conference
, Shanghai, China, Oct 10–15,
2010
[
confidential to Zinc Aluminum Coaters Association members
].
12.
National Atmospheric Deposition Program/National Trends Network, http://nadp.sws.uiuc.edu (Last accessed June 15, 2011).
13.
Townsend
,
H. E.
, and
Zoccola
,
J. C.
, “
Atmospheric Corrosion Resistance of 55% Al-Zn Coated Sheet Steel: 13 Year Test Results
,”
Materials Performance
,
Vol. 18, No.
10
,
1979
, pp.
13
–
20
.
14.
Townsend
,
H. E.
, “
Atmospheric Corrosion Resistance of Skyward- and Groundward-Exposed Surfaces of Zinc- and 55% Al-Zn Alloy-Coated Steel Sheet
,”
Corrosion
,
Vol. 54
, No.
7
,
1998
, pp.
561
–
565
. https://doi.org/10.5006/1.3284884
Google Scholar
Crossref
Search ADS
 
15.
Haddock
,
R.
, “
Metal Roofing from A (Aluminum) to Z (Zinc) Part VII: Rooftop Equipment Mounting and Penetrations for Low-Slope Standing Seam Metal Roofs
,”
MetalMag
, May,
2008
, pp.
68
–
71
.
16.
LaQue
,
F. L.
, and
Copson
,
H. R.
,
Corrosion Resistance of Metals and Alloys
, 2nd ed.,
Reinhold Publishing Corp.
, New York,
1963
, pp.
410
–
411
.
17.
Baker
,
E. A.
, and
Lee
,
T. S.
, “
Long-Term Atmospheric Corrosion Behavior of Various Grades of Stainless Steel
,”
Degradation of Metals in the Atmosphere, ASTM STP
965, 1988,
S. W.
 
Dean
 and
T. S.
 
Lee
, Eds.,
ASTM International
,
West Conshohocken, PA
, pp.
52
–
67
.
Crossref
Search ADS
 
18.
Hunsicker
,
H.
, “
Corrosion Resistance of Aluminum and Aluminum Alloys
,”
Metals Handbook—Desk Edition
,
1985
,
H. E.
 
Boyer
 and
T. L.
 
Gall
, Eds.,
American Society for Metals
,
Metals Park, OH
, p. 6.64.
This content is only available via PDF.
All rights reserved. This material may not be reproduced or copied, in whole or in part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of ASTM International.
You do not currently have access to this content.